REFRIGERATION SYSTEM AND ACCUMULATOR

Description

TECHNICAL FIELD

The present disclosure relates to a refrigeration system and an accumulator.

BACKGROUND ART

Patent Literature 1 discloses a refrigeration system including at least two compressors and an accumulator in a refrigerant circuit in which a plurality of indoor units are connected in parallel with respect to an outdoor unit, and including oil movement pipes for moving refrigeration oil in the accumulator from the accumulator to the respective compressors and solenoid valves disposed on the oil movement pipes, respectively.

Patent Literature 2 discloses a heat source unit and a refrigeration apparatus that prevent a situation in which a gas refrigerant in a gas-liquid separator cannot be sent to an intermediate flow path when the outside-air temperature is high. In the heat source unit and the refrigeration apparatus, when a first condition is satisfied in which an medium pressure corresponding to a pressure in the intermediate flow path is greater than a predetermined value during operations of a first compressor, a second compressor, and a third compressor, a control unit executes a first operation to increase a rotation speed of the third compressor.

CITATION LIST

Patent Literature

Patent Literature 1: Japanese Patent Laid-Open No. 2002-340424

Patent Literature 2: Japanese Patent Laid-Open No. 2022-039365

SUMMARY OF INVENTION

Technical Problem

A first aspect of the present disclosure provides a refrigeration system capable of uniformly supplying oil to a plurality of compressors having different pressures.

A second aspect of the present disclosure provides a refrigeration system including a refrigeration circuit with a simple configuration, and capable of improving a refrigeration capacity.

A third aspect of the present disclosure provides an accumulator and a refrigeration system that can stably return stored refrigeration oil from suction sides of a plurality of compressors with a simpler configuration.

Solution to Problem

The refrigeration system according to the first aspect of the present disclosure includes: a refrigeration cycle circuit that connects an outdoor unit including a low-stage compressor, a high-stage compressor, an outdoor heat exchanger, an accumulator disposed between the low-stage compressor and the high-stage compressor, and an oil separator disposed on a discharge side of the high-stage compressor, an indoor unit including an indoor heat exchanger, and a refrigeration-facility unit including a refrigeration-facility heat exchanger; an oil supply circuit that supplies oil from the oil separator to the high-stage compressor through the accumulator; and an oil supply circuit that supplies oil from the accumulator to the low-stage compressor.

The present application incorporates the disclosure of Japanese Patent Application No. 2022-184007, filed on Nov. 17, 2022 in its entirety.

The refrigeration system according to the second aspect of the present disclosure includes a refrigeration circuit provided with a plurality of compressors, a heat source-side heat exchanger, a plurality of utilization-side heat exchangers, and a gas-liquid separator, the plurality of compressors include a low-stage compressor and a high-stage compressor, the plurality of utilization-side heat exchangers includes a first utilization-side heat exchanger and a second utilization-side heat exchanger having a refrigerant evaporation temperature lower than that of the first utilization-side heat exchanger, the refrigeration circuit is provided with a switching mechanism that causes the refrigerant, which is discharged from the high-stage compressor and flows through at least one of the heat source-side heat exchanger and the first utilization-side heat exchanger, to flow to the gas-liquid separator, and a throttling mechanism is provided between the heat source-side heat exchanger, the first utilization-side heat exchanger, and the gas-liquid separator.

The present application incorporates the disclosure of Japanese Patent Application No. 2023-142103, filed on Sep. 1, 2023 in its entirety.

The accumulator according to the third aspect of the present disclosure includes an accumulator body which is a container having an internal space for separating a refrigerant into gas and liquid, suction pipes which are pipes provided on suction sides of a plurality of compressors, respectively, are connected to the accumulator body, one end of the suction pipe is housed inside the accumulator body, the one end of the suction pipe is provided with a tip through which a gas refrigerant is sucked in and a suction hole located below the tip to suck refrigeration oil and refrigerant liquid stored inside the accumulator body, the accumulator body houses the other end of an oil supply pipe with one end connected to an oil separator, the oil supply pipe is provided with an opening/closing device for opening and closing the oil supply pipe, the refrigeration oil is supplied from the oil separator by opening and closing of the opening/closing device, and a quantity of the refrigeration oil is accumulated in the accumulator body such that an oil level of the refrigeration oil is located between the tip and the suction hole.

The present application incorporates the disclosure of Japanese Patent Application No. 2022-184051, filed on Nov. 17, 2022 in its entirety.

Advantageous Effects of Invention

According to the first aspect of the present disclosure, oil can be evenly supplied to the high-stage compressor or the low-stage compressor, which are different pressures. In addition, since the oil discharged to the outside of the outdoor unit returns to the accumulator, the oil accumulated in the oil separator also returns to the accumulator, and thus the oil supply circuit can be simplified. Therefore, oil can be evenly supplied to the high-stage compressor and the low-stage compressor which have different pressures, and a breakdown of the compressor due to wear can be prevented. According to the second aspect of the present disclosure, the refrigeration circuit can be provided with a simple configuration, enabling stable operation.

According to the third aspect of the present disclosure, it is possible to return stored refrigeration oil stably from the suction sides of the plurality of compressors with a simpler configuration.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a circuit diagram of a refrigeration system according to a first embodiment showing an operation during a cooling operation.

FIG. 2 is a block diagram showing a control configuration according to the first embodiment.

FIG. 3 is a circuit diagram of a refrigeration system according to the first embodiment showing an operation during a heating operation.

FIG. 4 is a circuit diagram of the refrigeration system according to the first embodiment showing a heating operation at full capacity.

FIG. 5 is a circuit diagram of the refrigeration system according to the first embodiment showing an operation when a large capacity is required in a refrigeration-facility unit and a heat quantity for heating is not required.

FIG. 6 is a flowchart showing control based on an oil level in an accumulator according to the first embodiment.

FIG. 7 is a diagram showing a refrigeration system according to a second embodiment showing an operation during a cooling operation.

FIG. 8 is a diagram showing a refrigeration circuit of a refrigeration system according to a third embodiment.

FIG. 9 is a block diagram of the refrigeration system according to the third embodiment.

FIG. 10 is a circuit diagram showing the refrigeration circuit of the refrigeration system according to the third embodiment in a heating operation.

FIG. 11 is a circuit diagram showing the refrigeration circuit of the refrigeration system according to the third embodiment in a heating operation.

FIG. 12 is a circuit diagram showing the refrigeration circuit of the refrigeration system according to the third embodiment in a heating operation.

FIG. 13 is a p-h chart showing a state of a refrigerant in the refrigeration circuit according to the third embodiment.

FIG. 14 is a flowchart showing an operation of the refrigeration system according to the third embodiment.

FIG. 15 is a circuit diagram showing a refrigeration circuit of a refrigeration system according to the third embodiment in refrigerant recovery/vacuuming work.

FIG. 16 is a circuit diagram showing a refrigeration circuit of a refrigeration system according to the third embodiment in refrigerant filling work.

FIG. 17 is a circuit diagram showing a refrigeration circuit of a refrigeration system according to the third embodiment in a regulation operation.

FIG. 18 is a diagram showing a refrigeration cycle circuit of the refrigeration system according to the first embodiment of the present disclosure in a fourth embodiment.

FIG. 19 is a block diagram of a refrigeration system according to the fourth embodiment.

FIG. 20 is a longitudinal cross-sectional view showing an accumulator according to the fourth embodiment.

FIG. 21 is a circuit diagram of refrigeration system according to the fourth embodiment showing a heating operation.

FIG. 22 is a circuit diagram of a refrigeration system according to the fourth embodiment showing a heating operation when the amount of heat exhausted from a refrigeration-facility unit is insufficient.

FIG. 23 is a circuit diagram of the refrigeration system according to the fourth embodiment showing an operation when a large capacity is required in the refrigeration-facility unit and a heat quantity for heating is not required.

FIG. 24 is a longitudinal cross-sectional view showing an accumulator according to a fifth embodiment.

FIG. 25 is a transverse cross-sectional view showing the accumulator according to the fifth embodiment.

FIG. 26 is a longitudinal cross-sectional view showing an accumulator according to a modification.

DESCRIPTION OF EMBODIMENTS

Findings on Which Present Disclosure is Based

At the time when the inventors have conceived of a refrigeration system according to a first aspect of the present disclosure, there has been a refrigeration system in which a circuit, which returns oil stored in an oil separator or an accumulator to each compressor, is provided and a throttling mechanism is provided in the circuit to supply oil to a compressor having insufficient oil.

The inventors have found a problem with such a conventional technique in which when a pressure difference occurs among a plurality of compressors, oil cannot be supplied evenly to the plurality of compressors with different pressures, and have come up with the subject matter of the present disclosure in order to solve this problem.

The present disclosure provides a refrigeration system capable of supplying oil evenly to a plurality of compressors with different pressures.

Embodiments will be described in detail below with reference to the drawings. However, unnecessarily detailed descriptions will be avoided. For example, a detailed description of a well-known matter or a redundant description of a substantially identical structure may be avoided. This is to avoid rendering a related description unduly lengthy and to thereby facilitate understanding by those skilled in the art.

The following description and the accompanying drawings are provided to allow those skilled in the art to fully understand the present disclosure, and are not intended to limit the scope of the claims.

First Embodiment

Hereinafter, a first embodiment corresponding to a first aspect of the present disclosure will be described with reference to the drawings.

1-1-1. Configuration of Refrigeration System

FIG. 1 is a diagram showing a refrigeration cycle circuit of a refrigeration system 1 according to a first embodiment.

As shown in FIG. 1, the refrigeration system 1 includes an outdoor unit 10, an indoor unit 20, and a refrigeration-facility unit 30.

The indoor unit 20 performs air conditioning on an interior of a store, for example, a convenience store or a supermarket, and the refrigeration-facility unit 30 performs cooling on an interior of a refrigerating display showcase or a freezing display showcase that serves as a cooling storage facility installed in the store.

The outdoor unit 10 includes a low-stage compressor 11 and two high-stage compressors 12 and 12. The two high-stage compressors 12 are connected in parallel to the low-stage compressor 11.

An accumulator 13 is disposed between the low-stage compressor 11 and the high-stage compressor 12.

In other words, a refrigerant discharged from the low-stage compressor 11 is separated into gas and liquid by the accumulator 13, and only the gas refrigerant is sent to the high-stage compressor 12.

An oil separator 14 is connected to a discharge side of the high-stage compressor 12. An outdoor heat exchanger 15 is connected to the oil separator 14 through a refrigerant pipe 40.

A first heating pipe 41, which is connected to the refrigerant pipe 40 between the indoor unit 20 and the accumulator 13, is connected to the refrigerant pipe 40 between the oil separator 14 and the outdoor heat exchanger 15.

In addition, a first outdoor return pipe 42, which is connected to the refrigerant pipe 40 between the refrigeration-facility unit 30 and the low-stage compressor 11, is connected to the refrigerant pipe 40 between the oil separator 14 and the outdoor heat exchanger 15.

A first switching mechanism 50 is provided between the oil separator 14 and the outdoor heat exchanger 15.

The first switching mechanism 50 includes a first cooling valve 51 that opens and closes the refrigerant pipe 40 between the oil separator 14 and the outdoor heat exchanger 15, a first heating valve 52 that is provided in a middle of the first heating pipe 41 to open and close the first heating pipe 41, and an outdoor refrigerant return valve 53 that is provided in a middle of the first outdoor return pipe 42 to open and close the first outdoor return pipe 42.

A gas-liquid separator 16 is connected to the outdoor heat exchanger 15 through the refrigerant pipe 40. A refrigeration-facility heat exchanger 31 of the refrigeration-facility unit 30 is connected to the gas-liquid separator 16 through the refrigerant pipe 40 and an inlet-side refrigeration-facility expansion mechanism 32. The refrigeration-facility heat exchanger 31 is connected to the low-stage compressor 11 through an outlet-side refrigeration-facility expansion mechanism 33.

A second cooling pipe 43, which is connected to the indoor heat exchanger 22 through an indoor expansion mechanism 21, is connected to the refrigerant pipe 40 between the outdoor heat exchanger 15 and the gas-liquid separator 16.

A second heating pipe 44, which is connected to the indoor heat exchanger 22, is connected to the refrigerant pipe 40 between the outdoor heat exchanger 15 and the gas-liquid separator 16.

A second outdoor return pipe 45, which is connected to the refrigerant pipe 40 between the refrigeration-facility heat exchanger 31 and the gas-liquid separator 16, is connected to the refrigerant pipe 40 between the outdoor heat exchanger 15 and the gas-liquid separator 16.

A second switching mechanism 54 is provided between the outdoor heat exchanger 15 and the gas-liquid separator 16. The second switching mechanism 54 includes a second cooling valve 55 that opens and closes the refrigerant pipe 40 between the outdoor heat exchanger 15 and the gas-liquid separator 16, a third cooling valve 56 that is provided in a middle of the second cooling pipe 43 to open and close the second cooling pipe 43, and a second heating valve 57 that is provided in a middle of the second heating pipe 44 to open and close the second heating pipe 44.

A refrigerant return expansion mechanism 58 is provided in a middle of the second outdoor return pipe 45 to control a flow rate of the second outdoor return pipe 45.

Check valves 59 are provided downstream of the second cooling valve 55, the third cooling valve 56, and the second heating valve 57, respectively.

The indoor heat exchanger 22 is connected to the high-stage compressor 12 through the refrigerant pipe 40, an on-off valve 23, and the accumulator 13.

In the present embodiment, a gas refrigerant return pipe 60 is provided to send a gas refrigerant from the gas-liquid separator 16 to a suction side of the accumulator 13. A gas refrigerant return expansion mechanism 61 is provided in a middle of the gas refrigerant return pipe 60.

In the present embodiment, an oil supply circuit 62 is connected to the oil separator 14 to supply oil to the high-stage compressor 12 through the accumulator 13. A high-stage motor-operated valve 63 serving as a high-stage throttling mechanism is provided in a middle of the oil supply circuit 62.

An oil supply circuit 64 is connected to the accumulator 13 to supply oil to the low-stage compressor 11. A low-stage motor-operated valve 65 serving as a low-stage throttling mechanism is provided in a middle of the oil supply circuit 64.

The accumulator 13 is provided with an oil level sensor 66 (see FIG. 2) as detection means for detecting the amount of oil in the accumulator 13.

1-1-2. Configuration of Control System of Refrigeration System

FIG. 2 is a block diagram of the refrigeration system 1, and shows a configuration of a control system of the refrigeration system 1.

As shown in FIG. 2, the outdoor unit 10 includes a control device 90 and an outdoor unit I/F 95. The control device 90 includes a control unit 91 and a storage unit 93.

The control unit 91 is a processor such as a CPU (Central Processing Unit) or an MPU (Micro Processing Unit) that operates based on a program stored in advance in the storage unit 93. The control unit 91 may be configured with a single processor or may be configured with a plurality of processors. A DSP (digital signal processor) or the like may be used as the control unit 91. Furthermore, the control circuit such as an LSI (Large Scale Integration), an ASIC (Application Specific Integrated Circuit), or an FPGA (Field-Programming Gate Array) can be used as the control unit 91.

The control unit 91 is connected to the storage unit 93, the low-stage compressor 11, and the like, and controls these units.

The control unit 91 reads the computer program stored in the storage unit 93 and operates according to the read computer program, thereby functioning as a determination unit 91a and an operation control unit 91b.

The determination unit 91a compares various temperature detection values, such as a detection value of an interior temperature Tb from an interior temperature sensor 37, with various temperature data in setting data 93a stored in the storage unit 93.

The operation control unit 91b controls various devices such as the low-stage compressor 11 and the high-stage compressor 12 in the outdoor unit 10. In addition, the operation control unit 91b transmits control signals to the indoor unit 20 and the refrigeration-facility unit 30 through the outdoor unit I/F 95 to cooperatively operate the refrigeration system 1.

The storage unit 93 includes a memory device such as a RAM (Random Access Memory) or a ROM (Read Only Memory), a fixed disk device such as a hard disk, or a portable storage device such as a flexible disk or an optical disk. In addition, the storage unit 93 stores computer programs, databases, tables, and the like used for various operations of the refrigeration system 1. These computer programs may be installed in the storage unit 93 from a computer-readable portable recording medium using a known setup program, for example. The portable recording medium may be, for example, a semiconductor storage device including a CD-ROM (compact disc read only memory), a DVD-ROM (digital versatile disc read only memory), a USB (Universal Serial Bus) memory, or an SSD (Solid State Drive). The computer programs may be installed from a predetermined server, for example.

Furthermore, the storage unit 93 may include a volatile storage region and may form a work area for the control unit 91.

The outdoor unit I/F 95 includes communication hardware such as a communication interface circuit or a connector for the outdoor unit 10 to communicate with each device via a cable according to a predetermined communication protocol. The outdoor unit I/F 95 sends data received from each device to the control device 90, and transmits data received from the control device 90 to each device.

The indoor unit 20 includes an indoor-unit control device 80 and an indoor unit I/F 85. The indoor-unit control device 80 includes an indoor-unit control unit 81 and an indoor-unit storage unit 83.

The indoor-unit control unit 81 is a processor such as a CPU or an MPU, similarly to the control unit 91.

The indoor-unit control unit 81 operates according to a computer program stored in the indoor-unit storage unit 83 to control various devices such as a blower 28 mounted in the indoor unit 20.

Similarly to the storage unit 93, the indoor-unit storage unit 83 includes a storage device such as a RAM or a ROM, and stores computer programs and the like used for various operations of the indoor unit 20.

The indoor unit I/F 85 includes communication hardware such as a communication interface circuit or a connector for the indoor unit 20 to communicate with each device. The indoor unit I/F 85 sends data received from each device to the indoor-unit control device 80, and transmits data received from the indoor-unit control device 80 to each device.

The refrigeration-facility unit 30 includes a refrigeration-facility-unit control device 70 and a refrigeration-facility unit I/F 75. The refrigeration-facility-unit control device 70 includes a refrigeration-facility-unit control unit 71 and a refrigeration-facility-unit storage unit 73.

Similarly to the control unit 91, the refrigeration-facility-unit control unit 71 is a processor such as a CPU or an MPU. The refrigeration-facility-unit control unit 71 operates according to a computer program stored in the refrigeration-facility-unit storage unit 73 to control various devices such as a blower 38 mounted in the refrigeration-facility unit 30.

Similarly to the storage unit 93, the refrigeration-facility-unit storage unit 73 includes a storage device such as a RAM or a ROM, and stores computer programs and the like used for various operations of the refrigeration-facility unit 30.

The refrigeration-facility unit I/F 75 includes communication hardware such as a communication interface circuit or a connector for the refrigeration-facility unit 30 to communicate with each device. The refrigeration-facility unit I/F 75 sends data received from each device to the refrigeration-facility-unit control device 70, and transmits data received from the refrigeration-facility-unit control device 70 to each device.

The control unit 91 acquires the oil amount detection value sent from the oil level sensor 66 of the accumulator 13.

The control unit 91 controls an opening degree of each of the high-stage motor-operated valve 63 and the low-stage motor-operated valve 65 based on the oil amount detection value of the accumulator 13.

1-2-1. Operation

Next, an operation of the present embodiment will be described.

First, a cooling operation will be described.

During a cooling operation, as shown in FIG. 1, the first cooling valve 51 is opened, and the second cooling valve 55 and the third cooling valve 56 are opened. The first heating valve 52, the second heating valve 57, the first high load valve, the outdoor return valve, and the outdoor return expansion mechanism are closed.

In this state, the low-stage compressor 11 and each of the high-stage compressors 12 are driven, whereby the refrigerant compressed by the low-stage compressor 11 is sent to each of the high-stage compressors 12, further compressed by each of the high-stage compressor 12, and discharged toward the oil separator 14.

The refrigerant passing through the oil separator 14 is sent to the outdoor heat exchanger 15 through the first cooling valve 51, and exchanges heat with outside air in the outdoor heat exchanger 15.

The refrigerant after heat exchange is sent to the gas-liquid separator 16 through the second cooling valve 55, and sent to the indoor heat exchanger 22 through the third cooling valve 56.

The refrigerant exchanges heat with indoor air in the indoor heat exchanger 22 to cool the indoor air. The refrigerant subjected to heat exchange with the indoor air is returned to each of the high-stage compressors 12 through the accumulator 13.

On the other hand, some of the refrigerant from the gas-liquid separator 16 is sent to the refrigeration-facility heat exchanger 31 through the inlet-side refrigeration-facility expansion mechanism 32, and is subjected to heat exchange in the refrigeration-facility heat exchanger 31 to cool the refrigeration-facility unit 30. The refrigerant subjected to heat exchange in the refrigeration-facility heat exchanger 31 is returned to the low-stage compressor 11 through the inlet-side refrigeration-facility expansion mechanism 32.

Next, a heating operation will be described.

FIG. 3 is a circuit diagram of the refrigeration system 1 showing a heating operation. A flow of the refrigerant is indicated by arrows in the drawing.

As shown in FIG. 3, during the heating operation, the first heating valve 52 and the second heating valve 57 are opened, and the first cooling valve 51, the second cooling valve 55, the third cooling valve 56, and the outdoor refrigerant return valve 53 are closed.

In this state, the low-stage compressor 11 and each of the high-stage compressors 12 are driven, whereby the refrigerant compressed by the low-stage compressor 11 is sent to each of the high-stage compressors 12, further compressed by each of the high-stage compressor 12, and discharged toward the oil separator 14.

The refrigerant passing through the oil separator 14 is sent to the indoor heat exchanger 22 through the first heating valve 52, and exchanges heat with indoor air in the indoor heat exchanger 22 to heat the indoor air.

The refrigerant subjected to heat exchange in the indoor heat exchanger 22 is sent to the gas-liquid separator 16 through the second heating valve 57, is then sent to the refrigeration-facility heat exchanger 31 through the inlet-side refrigeration-facility expansion mechanism 32, and is subjected to heat exchange in the refrigeration-facility heat exchanger 31 to cool the refrigeration-facility unit 30.

The refrigerant subjected to heat exchange in the refrigeration-facility heat exchanger 31 is returned to the low-stage compressor 11 through the outlet-side refrigeration-facility expansion mechanism 33.

In other words, the refrigeration system 1 of the present disclosure is configured such that during heating, the indoor heat exchanger 22 functions as a condenser and the outdoor heat exchanger 15 is not used.

Next, a heating operation at full capacity will be described.

FIG. 4 is a circuit diagram of the refrigeration system 1 showing a heating operation at full capacity. A flow of the refrigerant is indicated by arrows in the drawing.

As shown in FIG. 4, during a heating operation at full capacity, the first heating valve 52, the second heating valve 57, the high load valve, and the high load expansion mechanism are opened, and the first cooling valve 51, the second cooling valve 55, and the third cooling valve 56 are closed.

In this state, the low-stage compressor 11 and each of the high-stage compressors 12 are driven, whereby the refrigerant compressed by the low-stage compressor 11 is sent to each of the high-stage compressors 12, further compressed by each of the high-stage compressor 12, and discharged toward the oil separator 14.

The refrigerant passing through the oil separator 14 is sent to the indoor heat exchanger 22 through the first heating valve 52, and exchanges heat with indoor air in the indoor heat exchanger 22 to heat the indoor air.

The refrigerant subjected to heat exchange in the indoor heat exchanger 22 is sent to the gas-liquid separator 16 through the second heating valve 57, and is then sent to the refrigeration-facility heat exchanger 31 through the inlet-side refrigeration-facility expansion mechanism 32. The refrigerant is subjected to heat exchange in the refrigeration-facility heat exchanger 31 to cool the refrigeration-facility unit 30, and the refrigerant subjected to heat exchange in the refrigeration-facility heat exchanger 31 is returned to the low-stage compressor 11 through the outlet-side refrigeration-facility expansion mechanism 33.

On the other hand, some of the refrigerant from the gas-liquid separator 16 is sent to the outdoor heat exchanger 15 through the refrigerant return expansion mechanism 58, subjected to heat exchange in the outdoor heat exchanger 15, and then returned to the low-stage compressor 11.

Thus, exhaust heat from the refrigeration-facility heat exchanger 31 and heat pumped up by the outdoor heat exchanger 15 can be used as heat for the indoor heat exchanger 22, thereby enabling more efficiently heating.

In this case, when an outside air temperature becomes lower than an interior temperature of the refrigeration-facility unit 30, an evaporation temperature of the refrigeration-facility unit 30 should be lowered in order to pump heat from the outdoor heat exchanger 15. When the evaporation temperature of the refrigeration-facility unit 30 is lowered, the temperature will be lower than a defined temperature, a thermal cycle will be short, and a short-cycle operation will occur, which may lead to a freezing accident of a product.

In the present embodiment, therefore, the opening degree of the outlet-side refrigeration-facility expansion mechanism 33 is controlled to balance a pressure with the refrigerant sent from the outdoor heat exchanger 15, whereby it is possible to avoid the above-described inconvenience.

Next, an operation will be described in a case where a large capacity is required in the refrigeration-facility unit 30 and a heat quantity for heating is not required.

FIG. 5 is a circuit diagram of the refrigeration system 1 showing an operation when a large capacity is required in the refrigeration-facility unit 30 and a heat quantity for heating is not required. A flow of the refrigerant is indicated by arrows in the drawing.

As shown in FIG. 5, when a large capacity is required in the refrigeration-facility unit 30 and a heat quantity for heating is not required, the first cooling valve 51, the second cooling valve 55, the first heating valve 52, and the second heating valve 57 are opened, and the refrigerant return valve and the third cooling valve 56 are closed.

In this state, the low-stage compressor 11 and each of the high-stage compressors 12 are driven, whereby the refrigerant compressed by the low-stage compressor 11 is sent to each of the high-stage compressors 12, further compressed by each of the high-stage compressor 12, and discharged toward the oil separator 14.

The refrigerant passing through the oil separator 14 is sent to the outdoor heat exchanger 15 through the first cooling valve 51, and exchanges heat with outside air in the outdoor heat exchanger 15.

The refrigerant after heat exchange is sent to the gas-liquid separator 16 through the second cooling valve 55 On the other hand, the refrigerant passing through the oil separator 14 is sent to the indoor heat exchanger 22 through the first heating valve 52, exchanges heat with indoor air in the indoor heat exchanger 22 to heat the indoor air.

The refrigerant subjected to heat exchange in the indoor heat exchanger 22 interflows with the refrigerant sent from the outdoor heat exchanger 15 through the second heating valve 57, and is sent to the gas-liquid separator 16.

The refrigerant from the gas-liquid separator 16 is sent to the refrigeration-facility heat exchanger 31 through the inlet-side refrigeration-facility expansion mechanism 32. The refrigerant is subjected to heat exchange in the refrigeration-facility heat exchanger 31 to cool the refrigeration-facility unit 30, and the refrigerant subjected to heat exchange in the refrigeration-facility heat exchanger 31 is returned to the low-stage compressor 11 through the outlet-side refrigeration-facility expansion mechanism 33.

On the other hand, some of the refrigerant from the gas-liquid separator 16 is sent to the outdoor heat exchanger 15 through the refrigerant return expansion mechanism 58, and is returned to the low-stage compressor 11 after being subjected to heat exchange in the outdoor heat exchanger 15.

Thus, the outdoor heat exchanger 15 and the indoor heat exchanger 22 can be heated simultaneously by a heating operation capacity, and a heat quantity distribution thereof can be controlled. Furthermore, the outdoor heat exchanger 15 is heated, and thus frost adhering to the outdoor heat exchanger 15 can be removed.

In the present embodiment, the gas refrigerant return pipe 60 is provided to send the gas refrigerant from the gas-liquid separator 16 to the suction side of the accumulator 13. Then, the return amount of the gas refrigerant from the gas-liquid separator 16 is controlled by control of the opening degree of the gas refrigerant return expansion valve 61, whereby a differential pressure of the refrigerant sent to the indoor heat exchanger 22 can be generated.

Thus, it is possible to control the pressure by adding a specified value to the evaporation temperature of the indoor heat exchanger 22 having a high evaporation temperature. It is possible to improve efficiency of an air conditioning temperature zone, which is a weak point, using carbon dioxide (R744), a natural refrigerant with high environmental preservation characteristics.

1-2-2. Oil Level-Based Operation

Next, control based on an oil level in the accumulator 13 will be described.

FIG. 6 is a flowchart showing control based on an oil level in the accumulator 13.

First, the control unit 91 acquires an oil amount detection value from the oil level sensor 66 of the accumulator 13 (step SA1).

When it is determined that the oil level is 3 to 2 (step SA2: YES), the control unit 91 controls the opening degree of the high-stage motor-operated valve 63 to be fully closed and controls the opening degree of the low-stage motor-operated valve 65 to be large (step SA3).

When the oil level is 3 to 2, it indicates that the oil amount is sufficient, and the high-stage motor-operated valve 63 is fully closed, whereby the inflow of oil from the oil separator 14 can be prevented.

In addition, the opening degree of the low-stage motor-operated valve 65 is controlled to be large, and thus a large amount of oil can be supplied to the low-stage compressor 11.

Then, when the control unit 91 determines that the oil level in the accumulator 13 is 2 to 1 (step SA4: YES), the control unit 91 controls the opening degree of the high-stage motor-operated valve 63 to be half, and controls the opening degree of the low-stage motor-operated valve 65 to be small or fully closed (step SA5).

When the oil level is 2 to 1, the oil amount is less than that in the oil level 3, but the oil is in a secured state.

The opening degree of the high-stage motor-operated valve 63 is controlled to be half, and thus the oil from the oil separator 14 is returned to the accumulator 13. In addition, the opening degree low-stage motor-operated valve 65 is controlled to be small or fully closed, and thus it is possible to supply oil to the low-stage compressor 11 while securing the oil amount of the accumulator 13.

When the control unit 91 determines that the oil level in the accumulator 13 is 1 (step SA6: YES), the control unit 91 controls the opening degree of the high-stage motor-operated valve 63 and the low-stage motor-operated valve 65 to be fully closed (step SA7).

When the oil level is 1, there is almost no oil in the accumulator 13. Therefore, the opening degree of the high-stage motor-operated valve 63 and the low-stage motor-operated valve 65 is controlled to be fully closed, whereby an oil recovery operation of the accumulator 13 can be performed, and the oil amount in the accumulator 13 can be secured.

By the control in this manner, oil can be evenly supplied to compressors with different pressures, and a breakdown of the compressor due to wear can be prevented.

1-3. Effects

As described above, the refrigeration system of the present embodiment includes the refrigeration cycle circuit in which the outdoor unit 10 including the low-stage compressor 11, the high-stage compressor 12, the outdoor heat exchanger 15, the accumulator 13 disposed between the low-stage compressor 11 and the high-stage compressor 12, and the oil separator 14 disposed on the discharge side of the high-stage compressor 12, the indoor unit 20 including the indoor heat exchanger 22, and the refrigeration-facility unit 30 including the refrigeration-facility heat exchanger 31 are connected to each other. The refrigeration system further includes the oil supply circuit 62 that supplies the oil from the oil separator 14 to the high-stage compressor 12 through the accumulator 13, and the oil supply circuit 64 that supplies the oil from the accumulator 13 to the low-stage compressor 11.

Thus, the oil can be evenly supplied to each of the high-stage compressor 12 and the low-stage compressor 11, which have different pressures. Furthermore, since the oil discharged to the outside of the outdoor unit 10 returns to the accumulator 13, the oil accumulated in the oil separator 14 also returns to the accumulator 13, and thus the oil supply circuit 62 can be simplified. Furthermore, since the oil is supplied to the low-stage compressor 11 from the accumulator 13 set at an intermediate pressure, the oil can be easily supplied to the low-stage compressor 11 set at a low pressure. Therefore, the oil can be evenly supplied to the high-stage compressor 12 and the low-stage compressor 11, which have different pressures, and thus the breakdown of the compressors due to wear can be prevented.

In the present embodiment, the oil level sensor 66 (detection means) is provided in the accumulator 13 to detect the oil amount in the accumulator 13.

Thus, the oil amount in the accumulator 13 can be detected by the oil level sensor 66, the oil can be evenly supplied to the high-stage compressor 12 and the low-stage compressor 11 according to the oil amount in the accumulator 13, and thus the breakdown of the compressors due to wear can be prevented.

In the present embodiment, the high-stage motor-operated valve 63 (high-stage throttling mechanism) is provided in the oil supply circuit 62 that supplies the oil from the oil separator 14 to the high-stage compressor 12 through the accumulator 13.

Thus, the opening degree of the high-stage motor-operated valve 63 is controlled, and thus the oil amount supplied to the high-stage compressor 12 can be adjusted.

In the present embodiment, the low-stage motor-operated valve 65 (low-stage throttling mechanism) is provided in the oil supply circuit 64 that supplies the oil from the accumulator 13 to the low-stage compressor 11.

Thus, the opening degree of the low-stage motor-operated valve 65 is controlled, and thus the oil amount supplied to the low-stage compressor 11 can be adjusted.

In the present embodiment, the high-stage motor-operated valve 63 and the low-stage motor-operated valve 65 (motor-operated valve) are provided, and the control device 90 that controls the opening degree of the high-stage motor-operated valve 63 and the low-stage motor-operated valve 65 based on the oil amount detected by the oil level sensor 66 (detection means) that detects the oil amount in the accumulator 13, is provided.

Thus, the control device 90 controls the opening degree of the high-stage motor-operated valve 63 and the low-stage motor-operated valve 65 based on the oil amount in the accumulator 13 detected by the oil level sensor 66, and thus the oil can be supplied to each of the high-stage compressor 12 and the low-stage compressor 11, which have different pressures, with the appropriate amount. Accordingly, the oil can be evenly supplied to the high-stage compressor 12 and the low-stage compressor 11, which have different pressures, and the breakdown of the compressors due to wear can be prevented.

Second Embodiment

Next, a second embodiment of the present disclosure will be described.

2-1. Configuration of Refrigeration System

FIG. 7 is a diagram showing a refrigeration cycle circuit of a refrigeration system 1 according to a second embodiment.

The second embodiment differs from the first embodiment in the configuration of the oil supply circuit 64 that supplies oil to the low-stage compressor 11.

In the present embodiment, as shown in FIG. 7, the oil supply circuit 62 is connected to the oil separator 14 to supply oil to the high-stage compressor 12 through the accumulator 13. The high-stage motor-operated valve 63 is provided, as a high-stage throttling mechanism, in a middle of the oil supply circuit 62.

The oil supply circuit 64 is connected to the middle of the oil supply circuit 62 to supply oil to the low-stage compressor 11. The low-stage motor-operated valve 65 is provided, as a low-stage throttling mechanism, in a middle of the oil supply circuit 64.

In other words, the present embodiment has a configuration in which oil in the oil separator 14 is supplied directly to the low-stage compressor 11 without passing through the accumulator 13.

Other components are the same as those in the first embodiment, and thus the same components are denoted by the same reference numerals and will not be described.

2-2. Operation

In the present embodiment, similarly to the first embodiment, the control unit 91 also acquires an oil amount detection value from the oil level sensor 66 of the accumulator 13.

Then, when the control unit 91 determines that the oil level is 3 to 2, the control unit 91 controls the opening degree of the high-stage motor-operated valve 63 to be fully closed, and controls the opening degree of the low-stage motor-operated valve 65 to be large.

Then, when the control unit 91 determines that the oil level in the accumulator 13 is 2 to 1, the control unit 91 controls the opening degree of the high-stage motor-operated valve 63 to be half, and controls the opening degree low-stage motor-operated valve 65 to be small or fully closed When the control unit 91 determines that the oil level in the accumulator 13 is 1, the control unit 91 controls the opening degree of the high-stage motor-operated valve 63 and the low-stage motor-operated valve 65 to be fully closed.

2-3. Effects

As described above, the refrigeration system of the present embodiment includes the refrigeration cycle circuit in which the outdoor unit 10 including the low-stage compressor 11, the high-stage compressor 12, the outdoor heat exchanger 15, the accumulator 13 disposed between the low-stage compressor 11 and the high-stage compressor 12, and the oil separator 14 disposed on the discharge side of the high-stage compressor 12, the indoor unit 20 including the indoor heat exchanger 22, and the refrigeration-facility unit 30 including the refrigeration-facility heat exchanger 31 are connected to each other. The refrigeration system further includes the oil supply circuit 62 that supplies the oil from the oil separator 14 to the high-stage compressor 12 through the accumulator 13, and the oil supply circuit 64 that supplies the oil from the oil separator 14 to the low-stage compressor 11.

Thus, the oil can be evenly supplied to each of the high-stage compressor 12 and the low-stage compressor 11, which have different pressures. Furthermore, since the oil discharged to the outside of the outdoor unit 10 returns to the accumulator 13, the oil accumulated in the oil separator 14 also returns to the accumulator 13, and thus the oil supply circuit 62 can be simplified.

Furthermore, since the oil is supplied to the low-stage compressor 11 from the accumulator 13 set at an intermediate pressure, the oil can be easily supplied to the low-stage compressor 11 set at a low pressure.

In the present embodiment, the low-stage motor-operated valve 65 (low-stage throttling mechanism) is provided in the oil supply circuit 64 to supply the oil from the accumulator 13 to the low-stage compressor 11.

Thus, the opening degree of the low-stage motor-operated valve 65 is controlled, and thus the oil amount supplied to the low-stage compressor 11 can be adjusted.

Third Embodiment

Findings on Which Present Disclosure is Based

At the time when the inventors have conceived of a refrigeration system according to a second aspect of the present disclosure, there has been a refrigeration system including one refrigeration circuit that is provided with a low-stage compressor, a high-stage compressor, a plurality of utilization-side heat exchangers, and a heat source-side heat exchanger shared with these utilization-side heat exchangers, the utilization-side heat exchangers being operated in different evaporation temperature zones. Thus, the refrigeration system performs, for example, air conditioning of an air-conditioned space and cooling of the interior of the refrigeration-facility unit at the same time.

There has been known that such a refrigeration system includes a gas-liquid separator. In such a refrigeration system, the refrigerant discharged from the compressor flows into the utilization-side heat exchanger through the gas-liquid separator, thereby improving a refrigeration capacity.

In the above-described refrigeration system, the utilization-side heat exchanger is switched between a cooling operation and a heating operation. In such a refrigeration system, the inventors have found a problem that the configuration of the refrigeration circuit provided in the refrigeration system is complicated in order to flow the refrigerant, which is sent from the compressor, through the gas-liquid separator to the utilization-side heat exchanger in any of these operations, and have come to form the subject of the present disclosure to solve such a problem.

In view of the above, the present disclosure provides a refrigeration system including a refrigeration circuit with a simple configuration and capable of improving a refrigeration capacity.

Hereinafter, a third embodiment corresponding to a second aspect of the present disclosure will be described with reference to the drawings.

3-1-1. Configuration of Refrigeration System

FIG. 8 is a circuit diagram showing a refrigeration system 101 according to a third embodiment. In FIG. 8, for the convenience of description, an opening/closing device in an open state is shown in white, and an opening/closing device in a closed state and expansion mechanism are shown in black. In FIG. 8, for the convenience of description, pipes through which a refrigerant flows are shown in thick lines, and pipes through which no refrigerant flows are shown in thin lines. In subsequent circuit diagrams, opening/closing devices and pipes are shown in the same manner as in FIG. 8.

As shown in FIG. 8, the refrigeration system 101 includes an outdoor unit 110, an indoor unit 120, and a refrigeration-facility unit 130, and these units are connected to each other by refrigerant pipes to form a refrigeration circuit 102 that functions as a flow path through which a refrigerant flows.

In the present embodiment, the refrigerant used in the refrigeration circuit 102 is, for example, refrigerant carbon dioxide (R744), a natural refrigerant that is non-flammable and non-toxic.

The indoor unit 120 includes an indoor heat exchanger 122 which is a utilization-side heat exchanger. The indoor unit 120 performs air conditioning on the interior of a store, which is an air-conditioned space, based on a setting temperature set by a user in a store such as a convenience store or a supermarket.

The refrigeration-facility unit 130 includes a refrigeration-facility heat exchanger 132 which is a utilization-side heat exchanger. The refrigeration-facility unit 130 performs cooling on an interior of a refrigerating display showcase or a freezing display showcase that serves as a cooling storage facility installed in the store, based on a setting temperature set by the user.

In the refrigeration system 101, when the setting temperature of the indoor unit 120 is set, a rotational frequency of each of the compressors and an air flow rate of blowers 118 and 128 are determined based on a temperature difference between the setting temperature and a temperature in the air-conditioned space in which the indoor unit 120 is installed. Furthermore, in the refrigeration system 101, when the setting temperature of the indoor unit 120 is set, an opening degree of a throttle valve provided in the indoor unit 120 is determined such that the degree of superheat of the refrigerant at each of an inlet side and an outlet side of the indoor heat exchanger 122 becomes a specified value. Thus, the refrigeration system 101 operates such that the air-conditioned space becomes the setting temperature.

Similarly, in the refrigeration system 101, when the setting temperature of the refrigeration-facility unit 130 is set, the rotational frequency of each of the compressors and the air flow rate of blowers 118 and 138 are determined based on a temperature difference between the setting temperature and a temperature in the interior of the showcase. Furthermore, in the refrigeration system 101, when the setting temperature of the refrigeration-facility unit 130 is set, an opening degree of a throttle valve provided in the refrigeration-facility unit 130 is determined such that the degree of superheat of the refrigerant at each of an inlet side and an outlet side of the refrigeration-facility heat exchanger 132 becomes a specified value. Thus, the refrigeration system 101 operates such that the interior of the showcase becomes the setting temperature.

Hereinafter, the operation, in which the refrigeration system 101 performs the air conditioning of the air-conditioned space and the indoor cooling of the showcase, will be referred to as a first operation mode.

The outdoor unit 110 functions as a so-called heat source device. The outdoor unit 110 is formed in such a manner that a plurality of compressors, a first switching mechanism 150, an outdoor heat exchanger 115, a second switching mechanism 154, and a gas-liquid separator 116 are sequentially connected.

The outdoor heat exchanger 115 corresponds to the “heat source-side heat exchanger” in the present disclosure.

In the present embodiment, the outdoor unit 110 is provided with a mechanism in which a low-stage compressor 111 and two high-stage compressors 112 and 112 are configured as a two-stage compressor. The two high-stage compressors 112 and 112 are both connected in series to the low-stage compressor 111. The two high-stage compressors 112 and 112 are connected in parallel to each other on a downstream side of the low-stage compressor 111.

Each of the compressors is a rotary compressor in which a compression mechanism is driven by a motor, for example. Each of the high-stage compressors 112 is driven to discharge the refrigerant at a higher discharge pressure than the low-stage compressor 111.

An accumulator 113 is disposed between the low-stage compressor 111 and the high-stage compressor 112. The accumulator 113 functions as a flow divider that distributes almost evenly oil sent from an oil separator 114 to each of the high-stage compressor 112.

The oil separator 114 is connected to a discharge side of the high-stage compressor 112. The first switching mechanism 150 is connected to the oil separator 114. In other words, the first switching mechanism 150 is connected to a discharge pipe of the high-stage compressor 112 through the oil separator 114.

The first switching mechanism 150 is a mechanism that switches the refrigerant sent from the high-stage compressor 112 in the refrigeration circuit 102 to flow through any one of a plurality of flow paths.

The first switching mechanism 150 includes a pipe 140 that connects the oil separator 114 and the outdoor heat exchanger 115. A first cooling valve 151 is provided in the pipe 140. The first cooling valve 151 is located between the high-stage compressor 112 and the outdoor heat exchanger 115 on the pipe 140. The first cooling valve 151 is an opening/closing device that opens and closes the pipe 140. In the present embodiment, the first cooling valve 151 is an opening/closing device that can be switched between an open state in which a refrigerant can flow through the pipe 140 and a closed state in which a refrigerant does not flow through the pipe 140.

On the pipe 140, one end of a first heating pipe 141 is connected between the oil separator 114 and the first cooling valve 151. A first heating valve 152 is provided in the first heating pipe 141. The first heating valve 152 is an opening/closing device that opens and closes the first heating pipe 141.

The other end of the first heating pipe 141 is connected to a pipe 171 that connects the indoor heat exchanger 122 of the indoor unit 120 and a suction side of the high-stage compressor 112. Thus, the discharge side of the high-stage compressor 112 is connected to the indoor heat exchanger 122 through the first heating pipe 141.

On the pipe 171, an on-off valve 123 is provided between the point, where the other end of the first heating pipe 141 is connected, and the accumulator 113. The on-off valve 123 is an opening/closing device that opens and closes the pipe 171.

On the pipe 140, one end of a first outdoor return pipe 142 is connected between the first cooling valve 151 and the outdoor heat exchanger 115. An outdoor refrigerant return valve 153 is provided in the first outdoor return pipe 142. The outdoor refrigerant return valve 153 is an opening/closing device that opens and closes the first outdoor return pipe 142. The other end of the first outdoor return pipe 142 is connected between a refrigeration-facility heat exchanger 132 of the refrigeration-facility unit 130 and a suction side of the low-stage compressor 111.

On the pipe 172, an outlet-side refrigeration-facility pressure regulation mechanism 133 is provided between the point, where the other end of the first outdoor return pipe 142 is connected, and the refrigeration-facility heat exchanger 132. The outlet-side refrigeration-facility pressure regulation mechanism 133 is an opening/closing device that can change the opening degree from a fully closed state to a fully open state. The outlet-side refrigeration-facility pressure regulation mechanism 133 functions as a so-called throttle valve that can change the pressure of the refrigerant flowing through the pipe 172 by regulating the opening degree.

As described above, the outdoor heat exchanger 115, the indoor heat exchanger 122, the refrigeration-facility heat exchanger 132, and the low-stage compressor 111 are connected to the first switching mechanism 150.

The first switching mechanism 150 switches the flow path of the refrigerant in the refrigeration circuit 102 by opening and closing the first cooling valve 151, the first heating valve 152, and the outdoor refrigerant return valve 153, and causes the refrigerant discharged from the high-stage compressor 112 to flow into either of the outdoor heat exchanger 115 and the indoor heat exchanger 122.

For example, when the refrigeration system 101 performs a cooling operation, the refrigerant discharged from the high-stage compressor 112 flows into the outdoor heat exchanger 115.

When the refrigeration system 101 performs a heating operation, the refrigerant discharged from the high-stage compressor 112 flows into the indoor heat exchanger 122. When the refrigeration system 101 performs a heating operation and the heat quantity for heating becomes excessive, the refrigerant discharged from the high-stage compressor 112 flows into each of the outdoor heat exchanger 115 and the indoor heat exchanger 122.

As described above, the first switching mechanism 150 includes the first cooling valve 151, the first heating valve 152, and the outdoor refrigerant return valve 153.

In the present embodiment, the first cooling valve 151, the first heating valve 152, and the outdoor refrigerant return valve 153 are motor-operated on-off valves that are opened and closed by an actuator or the like.

Therefore, the first switching mechanism 150 can switch the flow path of the refrigerant in the refrigeration circuit 102 without stopping the low-stage compressor 111 and the high-stage compressor 112. In other words, the refrigeration system 101 can switch operations related to air conditioning and cooling of the interior of the showcase without stopping the low-stage compressor 111 and the high-stage compressor 112.

In the first switching mechanism 150, the first cooling valve 151, the first heating valve 152, and the outdoor refrigerant return valve 153 may be opening/closing devices capable of regulating the opening degree from a fully closed state to a fully open state.

The first switching mechanism 150 corresponds to the “other switching mechanism” in the present disclosure.

On the pipe 140, the second switching mechanism 154 is provided on an opposite side of the first switching mechanism 150 with the outdoor heat exchanger 115 sandwiched therebetween. In other words, the second switching mechanism 154 is connected to the outdoor heat exchanger 115 through the pipe 140.

The second switching mechanism 154 connects the outdoor heat exchanger 115, the indoor heat exchanger 122, the refrigeration-facility heat exchanger 132, and the gas-liquid separator 116 to one another. The second switching mechanism 154 is a mechanism that switches the refrigerant to flow through any one of a plurality of flow paths that connect the outdoor heat exchanger 115, the indoor heat exchanger 122, the refrigeration-facility heat exchanger 132, and the gas-liquid separator 116 to one another.

The second switching mechanism 154 is formed in such a manner that end portions of first to fourth pipes 173, 174, 175, and 176 are connected at connection portions A, B, C, and D in a ring shape.

A throttling mechanism 155 is disposed in the first pipe 173. A refrigerant return expansion mechanism 158 is disposed in the second pipe 174 to control the flow rate.

A check valve 159 is disposed in the third pipe 175. A check valve 159 is disposed in the fourth pipe 176. In the present embodiment, the check valve 159 is a so-called self-acting automatic valve that is opened and closed by the flow of the refrigerant.

The throttling mechanism 155 and the refrigerant return expansion mechanism 158 are flow-rate control valves capable of changing the opening degree from a fully closed state to a fully open state. The throttling mechanism 155 can change the pressure of the refrigerant flowing through the first pipe 173 by regulating the opening degree. The refrigerant return expansion mechanism 158 can change the pressure of the refrigerant flowing through the second pipe 174 by regulating the opening degree. In other words, the throttling mechanism 155 and the refrigerant return expansion mechanism 158 are so-called throttle valves.

In the third pipe 175, the check valve 159 is disposed such that the refrigerant flows only toward the connection portion C from the connection portion B. In the fourth pipe 176, the check valve 159 is disposed such that the refrigerant flows only toward the connection portion D from the connection portion C.

Each of the throttling mechanism 155, the refrigerant return expansion mechanism 158, and the check valve 159 corresponds to a “valve body” in this disclosure.

The pipe 140, in which the outdoor heat exchanger 115 is provided, is connected to the connection portion A between the throttling mechanism 155 and the refrigerant return expansion mechanism 158.

The connection portion B between the refrigerant return expansion mechanism 158 and the check valve 159 provided in the third pipe 175 is connected to a middle part of the pipe 177 connecting the gas-liquid separator 116 and the refrigeration-facility heat exchanger 132.

On the pipe 177, an inlet-side refrigeration-facility expansion mechanism 131 is provided between the point, where the connection portion B is connected, and the refrigeration-facility heat exchanger 132.

The connection portion C between the check valve 159 provided in the third pipe 175 and the check valve 159 provided in the fourth pipe 176 is connected to the indoor heat exchanger 122 through the pipe 178. In the pipe 178, an indoor expansion mechanism 121 of the indoor unit 120 is provided between one end to which the connection portion C is connected and the indoor heat exchanger 122. The indoor expansion mechanism 121 is an opening/closing device capable of changing the opening degree from a fully closed state to a fully open state.

The indoor expansion mechanism 121 functions as a so-called throttle valve that can change the pressure of the refrigerant flowing through the pipe 178 by regulating the opening degree. Each of the indoor expansion mechanism 121 and the throttling mechanism 155 corresponds to a “throttling mechanism” in this disclosure.

The connection portion D between the check valve 159 provided in the fourth pipe 176 and the throttling mechanism 155 is connected to the gas-liquid separator 116 through the pipe 179.

As described above, the gas-liquid separator 116 is connected to the outdoor heat exchanger 115, the indoor heat exchanger 122, and the refrigeration-facility heat exchanger 132 through the second switching mechanism 154. Thus, when the refrigeration system 101 performs the first operation mode, the refrigerant flows into the gas-liquid separator 116 from the pipe 179, and flows out from the pipe 177. In other words, the pipe 179 functions as an inlet-side pipe of the gas-liquid separator 116, and the pipe 177 functions as an outlet-side pipe of the gas-liquid separator 116.

The second switching mechanism 154 corresponds to a “switching mechanism” in the present disclosure.

Next, the utilization-side heat exchanger provided in the refrigeration system 101 will be described.

When the indoor unit 120 performs a cooling operation, the indoor heat exchanger 122 functions as an evaporator. In the refrigeration system 101, the rotational frequency of each of the compressors and the air flow rate of blowers 118 and 128 are determined based on a temperature difference between the setting temperature of the indoor unit 120 and a temperature in the air-conditioned space in which the indoor unit 120 is installed. Furthermore, an opening degree of the indoor expansion mechanism 121 is determined such that the degree of superheat of the refrigerant at each of an inlet side and an outlet side of the indoor heat exchanger 122 becomes a specified value. Thus, the refrigeration system 101 operates such that the air-conditioned space becomes the setting temperature. In the present embodiment, an evaporation temperature zone of the indoor heat exchanger 122 is, for example, 3° C. to 6° C.

The refrigeration-facility heat exchanger 132 functions as an evaporator. In the refrigeration system 101, the rotational frequency of each of the compressors and the air flow rate of blowers 118 and 138 are determined based on a temperature difference between the setting temperature of the refrigeration-facility unit 130 and a temperature of the interior of the showcase.

Furthermore, an opening degree of the inlet-side refrigeration-facility expansion mechanism 131 is determined such that the degree of superheat of the refrigerant at each of an inlet side and an outlet side of the refrigeration-facility heat exchanger 132 becomes a specified value. Thus, the refrigeration system 101 operates such that the interior of the showcase becomes the setting temperature.

The refrigeration-facility unit 130 of the present embodiment can select and set, as an interior temperature zone, any one temperature zone from, for example, a refrigeration temperature zone (3° C. to 6° C.), a temperature zone (3° C. 8° C.) slightly higher than the refrigeration temperature zone, a partial temperature zone (−3° C. to −1° C.), and a freezing temperature zone (−20° C. to −18° C.). For this reason, the evaporation temperature zone of the refrigeration-facility heat exchanger 132 is set lower than the interior temperature zone.

When the refrigeration-facility unit 130 is set to the refrigeration temperature zone, the evaporation temperature zone of the refrigeration-facility heat exchanger 132 is, for example, −5° C. to 0° C.

When the refrigeration-facility unit 130 is set to the partial temperature zone, the evaporation temperature zone of the refrigeration-facility heat exchanger 132 is, for example, −12° C. to −8° C.

When the refrigeration-facility unit 130 is set to the freezing temperature zone, the evaporation temperature zone of the refrigeration-facility heat exchanger 132 is, for example, −140° C. to −20° C.

In this way, the refrigeration system 101 is provided with two utilization-side heat exchangers with different evaporation temperature zones. Out of the two utilization-side heat exchangers with different evaporation temperature zones, the indoor heat exchanger 122 is connected to the inlet side of the high-stage compressor 112, and the refrigeration-facility heat exchanger 132 having a lower evaporation temperature zone than the indoor heat exchanger 122 is connected to the inlet side of the low-stage compressor 111.

The indoor heat exchanger 122 corresponds to a “first utilization-side heat exchanger” in the present disclosure, and the refrigeration-facility heat exchanger 132 corresponds to a “second utilization-side heat exchanger” in the present disclosure.

Next, the gas-liquid separator 116 will be described.

The gas-liquid separator 116 is a so-called flash tank that separates a gas-liquid two-phase refrigerant flown in into a gas refrigerant and a liquid refrigerant. In the present embodiment, when the refrigeration system 101 performs a cooling operation, the refrigerant flowing from the outdoor heat exchanger 115 flows in the gas-liquid separator 116 through the second switching mechanism 154. During the cooling operation of the refrigeration system 101, the refrigerant flowing from the second switching mechanism 154 into the gas-liquid separator 116 is depressurized by the throttling mechanism 155.

When the refrigeration system 101 performs a heating operation, the refrigerant flowing from the indoor heat exchanger 122 flows in the gas-liquid separator 116 through the second switching mechanism 154. During the heating operation of the refrigeration system 101, the refrigerant flowing from the second switching mechanism 154 into the gas-liquid separator 116 is depressurized by the indoor expansion mechanism 121.

In this way, when the refrigeration system 101 performs the first operation mode, the refrigerant flows into the gas-liquid separator 116 through the second switching mechanism 154 in a state where the pressure is regulated by the throttling mechanism 155 or the indoor expansion mechanism 121. In other words, during the first operation mode, the refrigeration system 101 is provided with the second switching mechanism 154, and thus the pressure of the refrigerant flowing into the gas-liquid separator 116 can be regulated with a simple circuit configuration.

A gas refrigerant return pipe 160 is connected to the gas-liquid separator 116, and the gas refrigerant return pipe 160 is connected to the pipe 171 and then to the accumulator 113. A gas refrigerant flow-rate control valve 161 is connected to the gas refrigerant return pipe 160. The gas refrigerant flow-rate control valve 161 is an opening/closing device capable of changing the opening degree from a fully closed state to a fully open state.

In the refrigeration system 101, flow rate of the gas refrigerant flowing through the gas refrigerant return pipe 160 is regulated by the opening degree of the gas refrigerant flow-rate control valve 161.

In the present embodiment, some of the gas refrigerant separated by the gas-liquid separator 116 are regulated in flow rate by the gas refrigerant flow-rate control valve 161, are sent to accumulator 113, and are returned to the suction side of the high-stage compressor 112.

In this way, in the gas-liquid separator 116, some of the gas refrigerant separated by the gas-liquid separator 116 are separated from the liquid refrigerant and flows out of the gas-liquid separator 116, whereby the liquid refrigerant is cooled to a saturation temperature corresponding to the pressure of the gas-liquid separator 116. In other words, the gas-liquid separator 116 in the refrigeration system 101 functions as a heat exchanger that cools the liquid refrigerant, and a refrigeration capacity of the refrigeration system 101 can be increased.

In addition, according to the refrigeration system 101, the opening degree of the gas refrigerant flow-rate control valve 161 is controlled, and the return amount of the gas refrigerant is regulated, whereby a pressure difference is generated between the front and the rear of the indoor expansion mechanism 121. In other words, it is possible to generate a differential pressure of the refrigerant between the inlet and the outlet of the indoor unit 120 in the refrigeration circuit 102 of the refrigeration system 101.

Thus, when the refrigeration system 101 performs the cooling operation in particular, the flow of the refrigerant is prevented from being stagnate. Then, in the indoor heat exchanger 122 of the refrigeration system 101 having a higher evaporation temperature of the refrigerant, it is possible to control the refrigerant flowing through the indoor heat exchanger 122 at a pressure value obtained by adding a specified pressure value to the pressure value serving as the evaporation temperature of the refrigerant.

An internal heat exchanger 164 is provided in a middle of each of the gas refrigerant return pipe 160 and the pipe 177. The internal heat exchanger 164 is a so-called economizer heat exchanger. The internal heat exchanger 164 is disposed, on the pipe 177, between the gas-liquid separator 116 and the connection portion B, and is disposed, on the gas refrigerant return pipe 160, between the gas refrigerant flow-rate control valve 161 and the accumulator 113.

The internal heat exchanger 164 houses the pipe 177 and the gas refrigerant return pipe 160 therein at the above-described position, and exchanges heat between the liquid refrigerant flowing through the pipe 177 and the gas refrigerant flowing through the gas refrigerant return pipe 160.

Therefore, in the refrigeration system 101, in the internal heat exchanger 164 the liquid refrigerant is cooled with the gas refrigerant. Then, the liquid refrigerant is more reliably brought into a supercooled state, and increases in the degree of supercooling.

Thus, even when the temperature of the liquid refrigerant in the gas-liquid separator 116 does not drop to the saturation temperature in the gas-liquid separator 116, the liquid refrigerant is cooled in the internal heat exchanger 164, and thus the temperature thereof is reduced to the saturation temperature or lower. Then, the refrigeration system 101 can secure the degree of supercooling of the liquid refrigerant, and can improve the operating efficiency.

A connection pipe 166 is provided in the refrigeration circuit 102. The connection pipe 166 connects, on the pipe 177, between the internal heat exchanger 164 and the connection portion B, and connects, on the gas refrigerant return pipe 160, between the gas refrigerant flow-rate control valve 161 and the internal heat exchanger 164. Some of the liquid refrigerant, which is subjected to heat exchange with the gas refrigerant in the internal heat exchanger 164, flows through the connection pipe 166. The liquid refrigerant flowing through the connection pipe 166 is mixed with the gas refrigerant before the heat exchange with the liquid refrigerant in the internal heat exchanger 164.

In other words, the internal heat exchanger 164 exchanges heat between the liquid refrigerant and the mixed refrigerant of the liquid refrigerant, which is cooled by heat exchange with the gas refrigerant in the internal heat exchanger 164, and the gas refrigerant.

Thus, the internal heat exchanger 164 can increase the degree of supercooling of the liquid refrigerant. Therefore, the refrigeration system 101 can improve the operating efficiency.

A liquid refrigerant flow-rate control valve 165 is provided in the connection pipe 166. The liquid refrigerant flow-rate control valve 165 is an opening/closing device capable of changing the opening degree from a fully closed state to a fully open state.

In the refrigeration system 101, the flow rate of the liquid refrigerant flowing through the connection pipe 166 is regulated by the opening degree of the liquid refrigerant flow-rate control valve 165.

Next, a service valve 190 will be described.

In the refrigeration system 101, a service valve 190 is provided in the pipe 172. On the pipe 172, the service valve 190 is provided between an outlet side of the refrigeration-facility heat exchanger 132 and the outlet-side refrigeration-facility pressure regulation mechanism 133. In the present embodiment, the service valve 190 is provided in the refrigeration-facility unit 130.

The service valve 190 includes three connection ports, for example, including pipe connection ports 192 and 194 and an external connection port 196. Each of the pipe connection ports 192 and 194 and the external connection port 196 is a valve body that can be opened and closed.

The pipe connection port 192 is connected to the pipe 172 located closer to the outlet-side refrigeration-facility pressure regulation mechanism 133. The pipe connection port 194 is connected to the pipe 172 located on the outlet side of the refrigeration-facility heat exchanger 132. In the present embodiment, the pipe connection ports 192 and 194 are normally opened.

The external connection port 196 is provided to allow the pipe 172 to be communicable with the outside, and is formed to allow connection of an external device. In the present embodiment, for example, a manifold gauge, a refrigerant recovery device 150, a vacuuming unit 152, and a refrigerant filling unit 154 are connected (see FIGS. 15 and 16). The external connection port 196 is closed when no external device is connected. The external connection port 196 may be manually opened and closed by a worker.

In the refrigeration system 101, since the service valve 190 is provided between the outlet side of the refrigeration-facility heat exchanger 132 and the outlet-side refrigeration-facility pressure regulation mechanism 133, connection ports for external devices can be provided without significantly changing the layout structure of the refrigeration circuit 102. In addition, since the service valve 190 is provided at a location close to the connection point between the outdoor unit 110 and the refrigeration-facility unit 130, the refrigeration system 101 can improve workability when the external device is connected to the refrigeration system 101.

The service valve 190 corresponds to a “connection port” in the present disclosure.

3-1-2. Configuration Related to Control of Refrigeration System

FIG. 9 is a block diagram of the refrigeration system 101.

As shown in FIGS. 8 and 9, the refrigeration system 101 is provided with a plurality of refrigerant pressure sensors 180. The refrigerant pressure sensors 180 are provided at predetermined locations of the refrigeration circuit 102 including the outdoor unit 110, the indoor unit 120, and the refrigeration-facility unit 130. The refrigerant pressure sensors 180 detect the pressure of the refrigerant flowing through those locations.

As shown in FIG. 8, the refrigerant pressure sensor 180 is provided, on the pipe 177, between the gas-liquid separator 116 and the internal heat exchanger 164. The refrigerant pressure sensor 180 is provided, on the gas refrigerant return pipe 160, between the gas refrigerant flow-rate control valve 161 and the accumulator 113.

Furthermore, the refrigerant pressure sensor 180 is provided, on the pipe 171, between the connection point of the pipe 171 and the first heating pipe 141, and the indoor heat exchanger 122. Furthermore, the refrigerant pressure sensor 180 is provided, on the pipe 172, between the outlet-side refrigeration-facility pressure regulation mechanism 133 and the suction side of the low-stage compressor 111.

The refrigerant pressure sensor 180 is provided on the refrigerant pipe that connects the discharge side of the high-stage compressor 112 and the oil separator 114.

As shown in FIGS. 8 and 9, the refrigeration system 101 is provided with a plurality of refrigerant temperature sensors 182. The refrigerant temperature sensors 182 are provided at predetermined locations of the refrigeration circuit 102 including the outdoor unit 110, the indoor unit 120, and the refrigeration-facility unit 130. The refrigerant temperature sensors 182 detect the temperature of the refrigerant flowing through these locations.

As shown in FIG. 8, the refrigerant temperature sensors 182 are provided on the refrigerant pipe located on the suction side and the refrigerant pipe located on the discharge side in each of the high-stage compressors 112. In addition, the refrigerant temperature sensor 182 is provided, on the pipe 172 located on the suction side of the low-stage compressor 111, between the outlet-side refrigeration-facility pressure regulation mechanism 133 and the suction side of the low-stage compressor 111.

Furthermore, the refrigerant temperature sensors 182 are provided on the refrigerant pipes connected to the inlet side and the outlet side of each of the indoor heat exchanger 122 and the refrigeration-facility heat exchanger 132.

As shown in FIG. 9, the refrigeration system 101 includes a space temperature sensor 127. The space temperature sensor 127 is disposed in the air-conditioned space of the indoor unit 120, and detects the temperature of the air-conditioned space.

The refrigeration system 101 includes an interior temperature sensor 137. The interior temperature sensor 137 is disposed inside a refrigerating display showcase or a freezing display showcase provided in the refrigeration-facility unit 130, and detects the interior temperature.

The blowers 118, 128, and 138 are provided in the outdoor unit 110, the indoor unit 120, and the refrigeration-facility unit 130, respectively. The blowers 118, 128, and 138 flow air to the outdoor heat exchanger 115, the indoor heat exchanger 122, and the refrigeration-facility heat exchanger 132, respectively, and facilitate heat exchange between the refrigerant and the air flowing through each of the outdoor heat exchanger 115, the indoor heat exchanger 122, and the refrigeration-facility heat exchanger 132.

The outdoor unit 110 includes an outdoor-unit communication portion 206 that communicates with the indoor unit 120 through a control wiring. The outdoor-unit communication portion 206 is configured with communication hardware, for example, a connector and a communication circuit that conform to a predetermined communication standard.

The outdoor unit 110 includes a control device 200. An outdoor unit I/F 205 is configured with communication hardware, for example, a connector and a communication circuit that conform to a predetermined communication standard. The outdoor unit I/F 205 communicates with the low-stage compressor 111, the high-stage compressor 112, the blower 118, the refrigerant pressure sensor 180, the refrigerant temperature sensor 182, and the outdoor-unit communication portion 206. The outdoor unit I/F 205 communicates with the first cooling valve 151, the first heating valve 152, the outdoor refrigerant return valve 153, the throttling mechanism 155, the refrigerant return expansion mechanism 158, the on-off valve 123, the gas refrigerant flow-rate control valve 161, the liquid refrigerant flow-rate control valve 165, and the service valve 190.

Furthermore, the outdoor unit I/F 205 communicates with an indoor unit I/F 215, a space temperature sensor 127, and a refrigeration-facility unit I/F 225.

The outdoor unit 110 includes the control device 200. The control device 200 includes a control unit 201 and a storage unit 203.

The control unit 201 is a processor such as a CPU (Central Processing Unit) or an MPU (Micro Processing Unit) that operates based on a program stored in advance in the storage unit 203. The control unit 201 may be configured with a single processor or may be configured with a plurality of processors. A DSP (digital signal processor) or the like may be used as the control unit 201. Furthermore, the control circuit such as an LSI (Large Scale Integration), an ASIC (Application Specific Integrated Circuit), or an FPGA (Field-Programming Gate Array) can be used as the control unit 201.

The control unit 201 is capable of receiving various signals from each of portions provided in the outdoor unit 110, the indoor unit 120, and the refrigeration-facility unit 130 through the outdoor unit I/F 205.

The control unit 201 is connected, through the outdoor unit I/F 205, to each portion of the outdoor unit 110, for example, the storage unit 203 or the low-stage compressor 111, the indoor unit 120, and the refrigeration-facility unit 130 in a wired or wireless manner, and controls each portion.

The control unit 201 reads the computer program stored in the storage unit 203 and operates according to the read computer program, thereby functioning as an operation control unit 201a and a determination unit 201b.

The operation control unit 201a controls various devices such as each of the low-stage compressor 111, the high-stage compressor 112, and the opening/closing device provided in the outdoor unit 110. In addition, the operation control unit 201a transmits control signals to the indoor unit 120 and the refrigeration-facility unit 130 through the outdoor unit I/F 205 to cooperatively operate the refrigeration system 101.

The operation control unit 201a can change the rotation speed of the compression mechanism provided in each of the compressors, and can also change the discharge pressure of the refrigerant.

The operation control unit 201a can regulate the opening degree of the gas refrigerant flow-rate control valve 161, the throttling mechanism 155, the indoor expansion mechanism 121, the inlet-side refrigeration-facility expansion mechanism 131, the outlet-side refrigeration-facility pressure regulation mechanism 133, and the refrigerant return expansion mechanism 158. The operation control unit 201a can switch the opening/closing devices provided in each of the first switching mechanism 150 and the second switching mechanism 154, and the on-off valve 123 to either an open state or a closed state.

The determination unit 201b compares detection values of the refrigerant pressure sensors 180 or detection values of the refrigerant temperature sensors 182 with data such as a reference temperature or a reference pressure value included in setting data 103a stored in the storage unit 203.

The operation control unit 201a controls each unit of the refrigeration system 101 based on the determination from the determination unit 201b.

The storage unit 203 includes a memory device such as a RAM (Random Access Memory) or a ROM (Read Only Memory), a fixed disk device such as a hard disk, or a portable storage device such as a flexible disk or an optical disk. In addition, the storage unit 203 stores computer programs, databases, tables, and the like used for various operations of the refrigeration system 101.

These computer programs may be installed in the storage unit 203 from a computer-readable portable recording medium using a known setup program, for example. The portable recording medium may be, for example, a semiconductor storage device including a CD-ROM (compact disc read only memory), a DVD-ROM (digital versatile disc read only memory), a USB (Universal Serial Bus) memory, or an SSD (Solid State Drive). The computer programs may be installed from a predetermined server, for example.

Furthermore, the storage unit 203 may include a volatile storage region and may form a work area for the control unit 201.

The storage unit 203 stores the setting data 203a. The setting data 203a includes data on the setting temperature of the indoor unit 120 and data on the setting temperature of the refrigeration-facility unit 130.

The setting data 203a includes data, for example, the rotation speed that is a specified value for each compressor and a reference pressure value that is a specified value indicating a differential pressure at a predetermined location in the refrigeration circuit 102.

The setting data 203a includes data related to the first operation mode. Specifically, the setting data 203a includes information on the opening/closing or the opening degree of each of the valve bodies provided in the refrigeration circuit 102 when the first operation mode is performed. The control unit 201 controls each of the units in the refrigeration circuit 102 according to the data related to the first operation mode. Thus, the refrigeration system 101 performs the first operation mode.

The setting data 203a includes a second operation mode. The second operation mode is an operation mode of the refrigeration system 101 that is performed in conjunction with the operation of an external device connected to the external connection port 196. The setting data 203a includes information on the opening/closing or the opening degree of each of the valve bodies provided in the refrigeration circuit 102 when the second operation mode is performed. The control unit 201 controls each of the units in the refrigeration circuit 102 according to the data related to the second operation mode. Thus, the refrigeration system 101 performs the second operation mode.

In the present embodiment, the setting data 203a includes, as the second operation mode, three operation modes of a refrigerant recovery/vacuuming mode, a refrigerant charging mode, and a regulation operation mode.

The outdoor unit I/F 205 includes communication hardware such as a communication interface circuit or a connector for the outdoor unit 110 to communicate with each device according to a predetermined communication protocol via a cable and the like. The outdoor unit I/F 205 sends data received from each device to the control device 200, and transmits data received from the control device 200 to each device.

The control device 200 includes an operation panel 232. Operating elements are provided on the operation panel 232. When the operating elements are operated, the control device 200 transmits a signal to the outdoor unit 110 to switch the operation mode of the refrigeration system 101 from the first operation mode to the second operation mode. In the present embodiment, according to the operation of the operation panel 232, the control device 200 switches to any one of three second operation modes of the refrigerant recovery/vacuuming mode, the refrigerant charging mode, and the regulation operation mode, and executes the switched mode.

The control device 200 is provided with a display panel 234. The display panel 234 performs a predetermined screen display according to the signal transmitted from the outdoor unit 110. In the present embodiment, the display panel 234 can display, for example, an operating status when the first operation mode or the second operation mode is executed, or the presence or absence of malfunction in each unit of the refrigeration system 101, and notify a worker of the operating status or the malfunction.

The control device 200 corresponds to a “control unit” in the present disclosure. The operation panel 232 corresponds to an “operation unit” in the present disclosure. The display panel 234 corresponds to a “display unit” in the present disclosure.

The indoor unit 120 includes an indoor-unit control device 210 and the indoor unit I/F 215. The indoor-unit control device 210 includes an indoor-unit control unit 211 and an indoor-unit storage unit 213.

Similarly to the control unit 201, the indoor-unit control unit 211 is a processor such as a CPU or an MPU. The indoor-unit control unit 211 operates according to a computer program stored in the indoor-unit storage unit 213 to control various devices such as the blower 128 mounted in the indoor unit 120. In addition, the indoor-unit control unit 211 receives signals output from various sensors such as the space temperature sensor 127 mounted in the indoor unit 120.

Similarly to the storage unit 203, the indoor-unit storage unit 213 includes a storage device such as a RAM or a ROM, and stores computer programs and the like used for various operations of the indoor unit 120.

The indoor unit I/F 215 includes communication hardware such as a communication interface circuit or a connector for the indoor unit 120 to communicate with each device. The indoor unit I/F 215 sends data received from the space temperature sensor 127 and each device to the indoor-unit control device 210, and transmits data received from the indoor-unit control device 210 to each device.

The refrigeration-facility unit 130 includes a refrigeration-facility-unit control device 220 and a refrigeration-facility unit I/F 225. The refrigeration-facility-unit control device 220 includes a refrigeration-facility-unit control unit 221 and a refrigeration-facility-unit storage unit 223.

Similarly to the control unit 201, the refrigeration-facility-unit control unit 221 is a processor such as a CPU or an MPU. The refrigeration-facility-unit control unit 221 operates according to a computer program stored in the refrigeration-facility-unit storage unit 223 to control various devices such as the blower 138 mounted in the refrigeration-facility unit 130. In addition, the refrigeration-facility-unit control unit 221 receives signals output from various sensors such as the interior temperature sensor 137 mounted in the refrigeration-facility unit 130.

Similarly to the storage unit 203, the refrigeration-facility-unit storage unit 223 includes a storage device such as a RAM or a ROM, and stores computer programs and the like used for various operations of the refrigeration-facility unit 130.

The refrigeration-facility unit I/F 225 includes communication hardware such as a communication interface circuit or a connector for the refrigeration-facility unit 130 to communicate with each device. The refrigeration-facility unit I/F 225 sends data received from the interior temperature sensor 137 and each device to the refrigeration-facility-unit control device 220, and transmits data received from the refrigeration-facility-unit control device 220 to each device.

The operation control unit 201a and the determination unit 201b may be provided not only in the control unit 201 but also in the indoor-unit control unit 211 or the refrigeration-facility-unit control unit 221. For example, the operation control unit 201a and the determination unit 201b may be provided in a processor provided in another location of the refrigeration system 101. For example, the operation control unit 201a and the determination unit 201b may be provided in a processor provided in a server device or the like provided outside the refrigeration system 101. Such a server device may be capable of controlling each unit of the refrigeration system 101 via a network constituted of, for example, a public line network, a dedicated line, other communication lines, and various communication facilities.

3-2. Operation of Refrigeration System

Next, an operation of the present embodiment will be described.

3-2-1. Cooling Operation

First, an operation of the refrigeration system 101 during a cooling operation will be described.

During the cooling operation, as shown in FIG. 8, the outdoor heat exchanger 115 is used as a gas cooler or a radiator, and the indoor heat exchanger 122 and the refrigeration-facility heat exchanger 132 are used as evaporators.

During the cooling operation, the control device 200 opens the first cooling valve 151 and closes the first heating valve 152 and the outdoor refrigerant return valve 153 in the first switching mechanism 150. In addition, the control device 200 opens the throttling mechanism 155 and closes the refrigerant return expansion mechanism 158 in the second switching mechanism 154.

In this state, the low-stage compressor 111 and each of the high-stage compressors 112 are driven, whereby the refrigerant compressed by the low-stage compressor 111 is sent to each of the high-stage compressors 112, further compressed by each of the high-stage compressor 112, and discharged toward the oil separator 114.

The refrigerant passing through the oil separator 114 is sent to the outdoor heat exchanger 115 through the first cooling valve 151 of the first switching mechanism 150, and exchanges heat with outside air in the outdoor heat exchanger 115.

The refrigerant after heat exchange is sent from the connection portion A of the second switching mechanism 154 through the throttling mechanism 155 to the gas-liquid separator 116. The liquid refrigerant separated in the gas-liquid separator 116 reaches the connection portion B of the second switching mechanism 154 after passing through the pipe 177 and being subjected to heat exchange with the gas refrigerant in the internal heat exchanger 164. One refrigerant branched at the connection portion B passes through the pipe 178 and is sent to the indoor heat exchanger 122 through the check valve 159 provided in the pipe 175 and the indoor expansion mechanism 121 of the indoor unit 120.

In the indoor heat exchanger 122, the refrigerant exchanges heat with the indoor air to cool the indoor air. The refrigerant subjected to heat exchange with the indoor air passes through the pipe 171, and is returned to the suction side of each of the high-stage compressors 112 through the on-off valve 123 and the accumulator 113.

The other refrigerant branched at the connection portion B is sent to the refrigeration-facility heat exchanger 132 through the inlet-side refrigeration-facility expansion mechanism 131 of the refrigeration-facility unit 130, and is subjected to heat exchange in the refrigeration-facility heat exchanger 132 to cool the refrigeration-facility unit 130. The refrigerant subjected to heat exchange in the refrigeration-facility heat exchanger 132 is returned to the low-stage compressor 111 through the outlet-side refrigeration-facility pressure regulation mechanism 133.

In the cooling operation of the above-described refrigeration system 101, the refrigerant discharged from the high-stage compressor 112 and radiating heat while maintaining the pressure at a high pressure in the outdoor heat exchanger 115 is reduced in pressure by the throttling mechanism 155 to become an intermediate pressure, and is sent to the gas-liquid separator 116.

3-2-2. Heating Operation

Next, an operation of the refrigeration system 101 during a heating operation will be described.

FIG. 10 is a circuit diagram of the refrigeration system 101 showing a heating operation. In FIG. 10, a flow of the refrigerant is indicated by arrows in the drawing, and the refrigerant pipes through which the refrigerant flows are indicated by thick lines.

In the refrigeration system 101, the heating operation is performed, using the indoor heat exchanger 122 as a gas cooler or a radiator and the refrigeration-facility heat exchanger 132 as an evaporator.

As shown in FIG. 10, during the heating operation, the control device 200 opens the first heating valve 152 and closes the first cooling valve 151 and the outdoor refrigerant return valve 153 in the first switching mechanism 150. In addition, the control device 200 closes the throttling mechanism 155 and the refrigerant return expansion mechanism 158 in the second switching mechanism 154.

In this state, the low-stage compressor 111 and each of the high-stage compressors 112 are driven, whereby the refrigerant compressed by the low-stage compressor 111 is sent to each of the high-stage compressors 112, further compressed by each of the high-stage compressor 112, and discharged toward the oil separator 114.

The refrigerant passing through the oil separator 114 is sent to the indoor heat exchanger 122 through the first heating valve 152 of the first switching mechanism 150, and exchanges heat with indoor air in the indoor heat exchanger 122 to heat the indoor air.

The refrigerant subjected to heat exchange in the indoor heat exchanger 122 passes through the indoor expansion mechanism 121, reaches the connection portion C of the second switching mechanism 154, and is sent to the gas-liquid separator 116 through the check valve 159 and the throttling mechanism 155 provided in the pipe 176. The refrigerant separated in the gas-liquid separator 116 passes through the pipe 177, reaches the connection portion B of the second switching mechanism 154, and is sent to the refrigeration-facility heat exchanger 132 through the inlet-side refrigeration-facility expansion mechanism 131. The refrigerant exchange heat in the refrigeration-facility heat exchanger 132, and cools the refrigeration-facility unit 130.

The refrigerant subjected to heat exchange in the refrigeration-facility heat exchanger 132 passes through the pipe 172 and is returned to the suction side of the low-stage compressor 111 through the outlet-side refrigeration-facility pressure regulation mechanism 133. In the refrigeration system 101 of the present disclosure, during the heating operation, the indoor heat exchanger 122 functions as a gas cooler or a radiator, and the outdoor heat exchanger 115 is not used. In other words, the refrigeration system 101 can perform heat exchange in the refrigeration-facility heat exchanger 132 using the refrigerant whose heat is radiated in the indoor heat exchanger 122, and thus can be operated without using the outdoor heat exchanger 115.

In the refrigeration system 101 of the present disclosure, during the heating operation, since the liquid refrigerant flows only through the refrigeration-facility unit 130, the opening degree of the gas refrigerant flow-rate control valve 161 is smaller compared to during cooling operation.

3-2-3. Heating Operation When Amount of Heat Exhausted From Refrigeration-Facility Unit is Insufficient

Next, an operation will be described in a case where a heating operation is performed when the amount of heat exhausted from the refrigeration-facility unit 130 is insufficient.

FIG. 11 is a circuit diagram of the refrigeration system 101 showing a heating operation when the amount of heat exhausted from the refrigeration-facility unit 130 is insufficient.

As shown in FIG. 11, during a heating operation at full capacity, the control device 200 opens the first heating valve 152, the outdoor refrigerant return valve 153, and the refrigerant return expansion mechanism 158, and closes the first cooling valve 151 and the throttling mechanism 155.

In this state, the low-stage compressor 111 and each of the high-stage compressors 112 are driven, whereby the refrigerant compressed by the low-stage compressor 111 is sent to each of the high-stage compressors 112, further compressed by each of the high-stage compressor 112, and discharged toward the oil separator 114.

The refrigerant passing through the oil separator 114 is sent to the indoor heat exchanger 122 through the first heating valve 152, and exchanges heat with indoor air in the indoor heat exchanger 122 to heat the indoor air.

The refrigerant subjected to heat exchange in the indoor heat exchanger 122 is sent to the gas-liquid separator 116 through the check valve 159 provided in the pipe 176, and then sent to the refrigeration-facility heat exchanger 132 through the inlet-side refrigeration-facility expansion mechanism 131. The refrigerant, which cools the refrigeration-facility unit 130, and is subjected to heat exchange in the refrigeration-facility heat exchanger 132 is regulated through the outlet-side refrigeration-facility pressure regulation mechanism 133 to have the same pressure as that of the refrigerant which is sent from the first outdoor return pipe 142, and is returned to the low-stage compressor 111. This is an operation when the outside air temperature is lower than the interior temperature of the refrigeration-facility unit 130.

On the other hand, some of the refrigerant from the gas-liquid separator 116 are sent to the outdoor heat exchanger 115 through the refrigerant return expansion mechanism 158, and are returned to the low-stage compressor 111 after heat exchange in the outdoor heat exchanger 115.

Thus, exhaust heat from the refrigeration-facility heat exchanger 132 and heat pumped up by the outdoor heat exchanger 115 can be used as heat for the indoor heat exchanger 122, thereby increasing the heating capacity when the amount of heat exhausted from the refrigeration-facility unit 130 is insufficient.

Conventionally, when the outside air temperature is lower than the interior temperature of the refrigeration-facility unit 130, it is necessary to lower the evaporation temperature of the refrigeration-facility unit 130 in order to pump heat from the outdoor heat exchanger 115. However, when the evaporation temperature of the refrigeration-facility unit 130 is lowered, there is a concern that the temperature will be lower than the setting temperature of the refrigeration-facility unit 130.

Therefore, according to the present embodiment, the opening degree of the outlet-side refrigeration-facility pressure regulation mechanism 133 is controlled, whereby it is possible to achieve the balance of the pressure with the refrigerant sent from the outdoor heat exchanger 115, and to prevent a drop in the evaporation temperature of the refrigeration-facility unit 130.

3-2-4. Heating Operation When Large Capacity is Required in Refrigeration-Facility Unit but Heat Quantity for Heating is Not Required

Next, an operation will be described in a case where a large capacity is required in the refrigeration-facility unit 130 but a heat quantity for heating is not required.

FIG. 12 is a circuit diagram of the refrigeration system 101 showing an operation when a large capacity is required in the refrigeration-facility unit 130 but a heat quantity for heating is not required.

As shown in FIG. 12, when a large capacity is required in the refrigeration-facility unit 130 but a heat quantity for heating is not required, the control device 200 opens the first cooling valve 151, the throttling mechanism 155, the first heating valve 152, and the check valve 159 provided in the pipe 176, and closes the refrigerant return valve and the check valve 159 provided in the pipe 175.

In this state, the low-stage compressor 111 and each of the high-stage compressors 112 are driven, whereby the refrigerant compressed by the low-stage compressor 111 is sent to each of the high-stage compressors 112, further compressed by each of the high-stage compressor 112, and discharged toward the oil separator 114.

The refrigerant passing through the oil separator 114 is sent to the outdoor heat exchanger 115 through the first cooling valve 151, and exchanges heat with outside air in the outdoor heat exchanger 115.

The refrigerant after heat exchange is sent to the gas-liquid separator 116 through the throttling mechanism 155.

The refrigerant passing through the oil separator 114 is sent to the indoor heat exchanger 122 through the first heating valve 152, exchanges heat with indoor air in the indoor heat exchanger 122 to heat the indoor air.

The refrigerant subjected to heat exchange in the indoor heat exchanger 122 interflows with the refrigerant sent from the outdoor heat exchanger 115 through the check valve 159 provided in the pipe 176, and is sent to the gas-liquid separator 116.

The refrigerant from the gas-liquid separator 116 is sent to the refrigeration-facility heat exchanger 132 through the inlet-side refrigeration-facility expansion mechanism 131. The refrigerant, which cools the refrigeration-facility unit 130, and is subjected to heat exchange in the refrigeration-facility heat exchanger 132 is returned to the low-stage compressor 111 through the outlet-side refrigeration-facility pressure regulation mechanism 133.

On the other hand, some of the refrigerant from the gas-liquid separator 116 is sent to the outdoor heat exchanger 115 through the refrigerant return expansion mechanism 158, and is returned to the low-stage compressor 111 after being subjected to heat exchange in the outdoor heat exchanger 115.

Thus, during the heating operation, the exhaust heat from the refrigeration-facility unit 130 can be radiated by the outdoor heat exchanger 115 and the indoor heat exchanger 122, whereby the cooling capacity of the refrigeration-facility unit 130 can be increased, and frost adhering to the outdoor heat exchanger 115 can be removed.

In this way, when the refrigeration system 101 perform the heating operation, the use state of the outdoor heat exchanger 115 can be switched to any one of a state of not being used, a state of being used as an evaporator, and a state of being used as a condenser, depending on the load on the indoor unit 120 and the refrigeration-facility unit 130. Therefore, the refrigeration system 101 can perform a stable heating operation depending on the load on the indoor unit 120 and the refrigeration-facility unit 130.

3-2-5. State of Refrigerant in Refrigeration Circuit

FIG. 13 is a p-h chart showing a state of the refrigerant in the refrigeration circuit 102. In FIG. 11, a vertical axis p represents a pressure (MPa), and a horizontal axis h represents enthalpy (KJ/kg).

Here, a refrigerant of the refrigeration system 101 during the cooling operation will be described.

On the suction side of the low-stage compressor 111, the state of the refrigerant is located at point Pl in FIG. 13. The refrigerant is a refrigerant evaporated in the refrigeration-facility heat exchanger 132, and a gas refrigerant at point P1. For the convenience of description, a pressure at point Pl is referred to as a low pressure.

When a low-pressure refrigerant is sucked into the low-stage compressor 111 and adiabatically compressed, the state of the refrigerant is located at point P2 in FIG. 13. Hereinafter, for the convenience of description, a pressure at point P2 is referred to as an intermediated pressure. In the present embodiment, a differential pressure between the low pressure and the intermediate pressure is, for example, 1.0 MPa.

Such a refrigerant is mixed with the refrigerant evaporated in the indoor heat exchanger 122 and the gas refrigerant flowing through the gas refrigerant return pipe 160. The mixed refrigerants are lowered in temperature while being maintained at an intermediate pressure, and becomes a state at point P3 in FIG. 13.

When the refrigerant in the state at point P3 is adiabatically compressed, such a refrigerant is in a state at point P4 in FIG. 13. Hereinafter, for the convenience of description, a pressure at point P4 is referred to as a high pressure.

When such a refrigerant is discharged from the high-stage compressor 112, the refrigerant radiates heat while being maintained at a high pressure in the outdoor heat exchanger 115. Therefore, the refrigerant is in a state at point P5 in FIG. 13.

The refrigerant in the state at point P5 is depressurized by the throttling mechanism 155, and is in a state at point P6 in FIG. 13. At point P6, the refrigerant has a pressure value higher than the intermediate pressure. Hereinafter, for the convenience of description, the pressure at point P2 is referred to as a medium pressure. In the present embodiment, a differential pressure between the intermediate pressure and the medium pressure and the intermediate pressure is, for example, 0.5 MPa.

As described above, even when the refrigeration system 101 performs either the cooling operation or the heating operation, the low-pressure liquid refrigerant depressurized by the throttling mechanism 155 or the indoor expansion mechanism 121 flows into the gas-liquid separator 116. Thus, when the refrigeration system 101 performs the first operation mode, the pressure of the refrigerant entering the gas-liquid separator 116 can be regulated.

The refrigerant in the state at point P6 is separated into a liquid refrigerant and a gas refrigerant by the gas-liquid separator 116. Out of these refrigerants, the gas refrigerant is discharged from the gas-liquid separator 116 through the gas refrigerant return pipe 160.

As the gas refrigerant is separated from discharged from the gas-liquid separator 116, the liquid refrigerant is cooled to a state at point P7 on a saturated liquid line, as shown in FIG. 13.

As described above, the gas refrigerant return pipe 160 is connected to the suction side of the high-stage compressor 112. In other words, the gas refrigerant is sucked by the high-stage compressor 112 and discharged from the gas-liquid separator 116. Thus, in the refrigeration system 101, the liquid refrigerant stored in the gas-liquid separator 116 is cooled to the state at point P7 on the saturated liquid line.

The refrigeration system 101 includes one low-stage compressor 111 and two high-stage compressors 112. In other words, in the refrigeration system 101, the capacity of the high-stage compressor 112 is larger than that of the low-stage compressor 111. The gas refrigerant is sucked by these high-stage compressors 112, and thus the refrigeration system 101 can cool the liquid refrigerant in the gas-liquid separator 116 to the state at point P7 on the saturated liquid line even when the outside air of the air-conditioned space or the refrigeration-facility unit 130 is high, for example, in summer.

In this way, the refrigeration system 101 can perform the first operation mode even when the ambient temperature of the utilization-side heat exchanger is high.

The liquid refrigerant exchanges heat with the gas refrigerant in the internal heat exchanger 164, and is in a state at point P8 in FIG. 13. At point P8, the liquid refrigerant is in a supercooled state. The gas refrigerant, which exchanges heat with the liquid refrigerant in the internal heat exchanger 164, is in a state at point P11 in FIG. 13.

The liquid refrigerant flowing out from the internal heat exchanger 164 branches off at the connection portion B and flows to the indoor unit 120 and the refrigeration-facility unit 130. The liquid refrigerant flowing to the indoor unit 120 is depressurized to an intermediate pressure by the indoor expansion mechanism 121, and is in a state at point P9 in FIG. 13. Thereafter, the liquid refrigerant flowing to the indoor unit 120 evaporates in the indoor heat exchanger 122, and is in the state at point P3 in FIG. 13. The refrigerant flows out from the indoor unit 120, and is sent to the suction side of the high-stage compressor 112. Similarly, the gas refrigerant flowing out from the internal heat exchanger 164 is also sent to the suction side of the high-stage compressor 112.

The liquid refrigerant flowing into the refrigeration-facility unit 130 is depressurized to an intermediate pressure by the inlet-side refrigeration-facility expansion mechanism 131, and is in a state at point P10 in FIG. 13. Thereafter, the liquid refrigerant flowing into the refrigeration-facility unit 130 evaporates in the refrigeration-facility heat exchanger 132, and is in the state at point Pl in FIG. 13. The refrigerant flows out from the refrigeration-facility unit 130 and is sent to the suction side of the low-stage compressor 111.

As shown in FIG. 13, the refrigeration system 101 of the present embodiment is a system including the refrigeration circuit 102 to perform a two-stage compression, two-stage expansion cycle.

As described above, in the refrigeration system 101, the opening degree of the gas refrigerant flow-rate control valve 161 is controlled, and the return amount of the gas refrigerant is regulated, whereby the inlet side of the indoor heat exchanger 122 becomes an intermediate pressure, and the outlet side of the indoor heat exchanger 122 becomes a middle pressure. In other words, it is possible to generate a differential pressure of the refrigerant between the inlet and the outlet of the indoor expansion mechanism 121 in the refrigeration circuit 102 of the refrigeration system 101.

Thus, in the indoor heat exchanger 122 of the refrigeration system 101 having a higher evaporation temperature of the refrigerant, it is possible to control the refrigerant flowing through the indoor heat exchanger 122 at a pressure value obtained by adding a specified pressure value to the pressure value serving as the evaporation temperature of the refrigerant.

Thus, in the refrigeration system 101, it is possible to improve efficiency of an air conditioning temperature zone using carbon dioxide (R744), a natural refrigerant with high environmental preservation characteristics, and to improve the efficiency of the entire refrigeration system.

As described above, the refrigeration system 101 can be stably perform the state change of the refrigerant shown in FIG. 13 by regulating the pressure of the refrigerant using the throttling mechanism 155, the indoor expansion mechanism 121, and the gas refrigerant flow-rate control valve 161, and regulating the temperature of the refrigerant using the gas-liquid separator 116. Therefore, the refrigeration system 101 can perform a stable operation by regulating the pressure and temperature of the refrigerant according to the load on the indoor unit 120 and the refrigeration-facility unit 130 caused by the outside air temperature or the like.

Furthermore, in the refrigeration system 101, the liquid refrigerant and the gas refrigerant separated in the gas-liquid separator 116 exchange heat with each other in the internal heat exchanger 164. Thus, the liquid refrigerant sent to the indoor unit 120 and the refrigeration-facility unit 130 is supercooled. For this reason, even when the temperature of the refrigerant fluctuates due to external heat radiation or heat capacity of the gas-liquid separator 116, or fluctuation in an operating load of the refrigeration system 101, the liquid refrigerant is prevented from rising to a temperature at which flash gas is generated, for example. Then, the refrigeration system 101 can stably evaporate the refrigerant in the indoor heat exchanger 122 and the refrigeration-facility heat exchanger 132.

Additionally, in the refrigeration system 101, some of the liquid refrigerant, which exchanges heat with the gas refrigerant in the internal heat exchanger 164, is mixed with the gas refrigerant before heat exchange with the liquid refrigerant, through the connection pipe 166. Thus, in the internal heat exchanger 164, the liquid refrigerant exchanges heat with the mixed refrigerant of the liquid refrigerant, which is cooled by heat exchange with the gas refrigerant in the internal heat exchanger 164, and the gas refrigerant. Therefore, the internal heat exchanger 164 can increase the degree of supercooling of the liquid refrigerant, and the refrigeration system 101 can improve the operating efficiency.

3-2-6. Operation of Refrigeration System During Cooling Operation

FIG. 14 is a flowchart showing an operation of the refrigeration system 101.

Next, an operation related to pressure control of the refrigeration system 101 during the cooling operation will be described.

As shown in FIG. 14, the determination unit 201b acquires a detection value of the refrigerant pressure sensor 180 provided on the discharge side of the indoor heat exchanger 122 and a detection value of the refrigerant pressure sensor 180 provided on the discharge side of the refrigeration-facility heat exchanger 132. The determination unit 201b calculates a differential pressure between an intermediate pressure and a low pressure from these acquired detection values. The determination unit 201b compares the calculated value with data of a reference pressure value involved in the setting data 203a stored in the storage unit 203 (step SB1).

When the calculated value is greater than the reference pressure value involved in the setting data 203a stored in the storage unit 203 (step SB1: YES), the determination unit 201b acquires a detection value of the refrigerant pressure sensor 180 provided in the pipe 177 through which the liquid refrigerant discharged from the gas-liquid separator 116 flows. The determination unit 201b calculates a differential pressure between the intermediate pressure and the medium pressure, from such a detection value and the detection value of the refrigerant pressure sensor 180 provided on the discharge side of the indoor heat exchanger 122. Then, the determination unit 201b compares the calculated value with the data of the reference pressure value involved in the setting data 203a stored in the storage unit 203 (step SB2).

When the calculated value is greater than the reference pressure value involved in the setting data 203a stored in the storage unit 203 (step SB2: YES), the operation control unit 201a drives each of the compressors and the blowers 118, 128, and 138 to become the setting temperature of the indoor unit 120 (step SB3).

In step SB1, when the calculated value of the differential pressure between the intermediate pressure and the low pressure is equal to or smaller than the reference pressure value in the setting data 203a stored in the storage unit 203 (step SB1: NO), the operation control unit 201a regulates the opening degree of the gas refrigerant flow-rate control valve 161 and the throttling mechanism 155 to increase the intermediate pressure (step SB4).

In the refrigeration system 101, the intermediate pressure increases when the opening degree of the throttling mechanism 155 increases or the opening degree of the gas refrigerant flow-rate control valve 161 decreases.

Thereafter, the determination unit 201b acquires the detection value of refrigerant pressure sensor 180 provided on the discharge side of the indoor heat exchanger 122 and the detection value of the refrigerant pressure sensor 180 provided on the discharge side of the refrigeration-facility heat exchanger 132. The determination unit 201b calculates the differential pressure between the intermediate pressure and the low pressure from these acquired detection values, and compares the calculated value and the data of the reference pressure value involved in the setting data 203a stored in the storage unit 203 (step SB5).

When the calculated value of the differential pressure between the intermediate pressure and the low pressure is equal to or smaller than the reference pressure value involved in the setting data 203a stored in the storage unit 203 (step SB5: NO), the operation control unit 201a performs step SB4 again.

When both the calculated values of the differential pressure between the intermediate pressure and the low pressure are greater than the reference pressure value involved in the setting data 203a stored in the storage unit 203 (step SB1: YES), the determination unit 201b performs step SB2.

Thus, in the refrigeration system 101, a differential pressure of a predetermined value or more is generated at the low-stage compressor 111, and the suction side and the discharge side of each of the high-stage compressors 112. Therefore, in the refrigeration system 101, the occurrence of poor compression in the low-stage compressor 111 and each of the high-stage compressors 112 is prevented.

As described above, the refrigeration system 101 of the present embodiment is provided with the internal heat exchanger 164 that exchanges heat between the liquid refrigerant flowing from the gas-liquid separator 116 to the indoor heat exchanger 122 and the refrigeration-facility heat exchanger 132 and the gas refrigerant discharged from the gas-liquid separator 116.

Furthermore, the gas refrigerant discharged from the gas-liquid separator 116 is mixed with some of the liquid refrigerant that exchanges heat with the gas refrigerant discharged from the gas-liquid separator 116 in the internal heat exchanger 164, through the connection pipe 166. Thus, in the refrigeration system 101, the liquid refrigerant becomes a lower temperature, leading in improving the refrigeration capacity of the indoor unit 120 through which the liquid refrigerant flows.

When the setting temperature of the indoor unit 120 is higher than the temperature of the liquid refrigerant by a predetermined value or greater, the refrigeration system 101 reduces the opening degree of the indoor expansion mechanism 121 to restrict the flow rate of the liquid refrigerant flowing to the indoor unit 120. Thus, in the refrigeration system 101, the medium pressure, which is the pressure of the refrigerant flowing out from the indoor heat exchanger 122, in other words, the refrigerant sucked into each of the high-stage compressor 112, decreases.

In step SB2, when the calculated value of the differential pressure between the intermediate pressure and the medium pressure is smaller than the reference pressure value involved in setting data 203a stored in the storage unit 203 (step SB2: NO), the operation control unit 201a reduces the rotational frequency of the high-stage compressor 112 (step SB6).

Next, the determination unit 201b determines whether the reduced rotational frequency of the high-stage compressor 112 is greater than a specified value involved in the setting data 203a stored in the storage unit 203 (step SB7).

When the rotational frequency is greater than the specified value (step SB7: YES), the determination unit 201b again acquires a detection value of the refrigerant pressure sensor 180 provided in the pipe 177 through which the liquid refrigerant discharged from the gas-liquid separator 116 flows. The determination unit 201b calculates a differential pressure between the intermediate pressure and the medium pressure, from the acquired detection value and the detection value of the refrigerant pressure sensor 180 provided on the discharge side of the indoor heat exchanger 122. The determination unit 201b compares the calculated value with the data of the reference pressure value involved in the setting data 203a stored in the storage unit 203 (step SB8).

When the calculated value is greater than the reference pressure value involved in the setting data 203a stored in the storage unit 203 (step SB8: YES), the operation control unit 201a drives each of the compressors and the blowers 118, 128, and 138 to become the setting temperature of the indoor unit 120 (step SB3).

when the calculated value of the differential pressure between the intermediate pressure and the medium pressure is equal to or smaller than the reference pressure value involved in setting data 203a stored in the storage unit 203 (step SB8: NO), the operation control unit 201a again reduces the rotational frequency of the high-stage compressor 112 (step SB6).

In step SB7, when the rotational frequency of the high-stage compressor 112 is lower than the specified value (step SB7: YES), the operation control unit 201a reduces the opening degree of the liquid refrigerant flow-rate control valve 165 (step SB9). Thereafter, the operation control unit 201a drives each of the compressors and the blowers 118, 128, and 138 to become the setting temperature of the indoor unit 120 (step SB3).

As described above, the refrigeration system 101 can control the rotational frequency of the high-stage compressor 112 to maintain the differential pressure between the intermediate pressure and the low pressure at a predetermined value or less. Accordingly, the refrigeration system 101 can improve the refrigeration efficiency of the indoor unit 120 while preventing the input to the high-stage compressor 112. Therefore, the refrigeration system 101 can improve the efficiency of the cooling operation while saving energy.

When the rotational frequency becomes smaller than the specified value, the refrigeration system 101 reduces the opening degree of the liquid refrigerant flow-rate control valve 165. Thus, the refrigeration system 101 reduces the flow rate at which the liquid refrigerant subjected to heat exchange with the gas refrigerant discharged from the gas-liquid separator 116 in the internal heat exchanger 164 is mixed with the gas refrigerant discharged from the gas-liquid separator 116. Therefore, the flow rate of the liquid refrigerant sent to the indoor unit 120 is reduced, and the decrease in the medium pressure is prevented. Furthermore, the refrigeration system 101 prevents the driving of each of the high-stage compressors 112 from being stopped.

In the above-described cooling operation of the refrigeration system 101, the refrigerant discharged from the high-stage compressor 112 and radiating heat while maintaining its pressure at a high pressure in the outdoor heat exchanger 115 is depressurized to the medium pressure by the throttling mechanism 155, and is sent to the gas-liquid separator 116.

On the other hand, during the heating operation of the refrigeration system 101, the refrigerant discharged from the high-stage compressor 112 radiates heat while maintaining its pressure at a high pressure in the indoor heat exchanger 122. The refrigerant is depressurized to the medium pressure by the indoor expansion mechanism 121, and is sent to the gas-liquid separator 116.

In the heating operation of the refrigeration system 101 when the amount of heat exhausted from the refrigeration-facility unit 130 is insufficient, the refrigerant discharged from the high-stage compressor 112 and radiating heat while maintaining its pressure at a high pressure in the outdoor heat exchanger 115 is depressurized to the medium pressure by the throttling mechanism 155, and is sent to the gas-liquid separator 116. Similarly, the refrigerant discharged from the high-stage compressor 112 and radiating heat while maintaining its pressure at a high pressure in the indoor heat exchanger 122 is depressurized to the medium pressure by the indoor expansion mechanism 121, and is sent to the gas-liquid separator 116.

In the heating operation of the refrigeration system 101 when a large capacity is required in the refrigeration-facility unit 130 but a heat quantity for heating is not required, the refrigerant discharged from the high-stage compressor 112 and radiating heat while maintaining its pressure at a high pressure in the indoor heat exchanger 122 is depressurized to the medium pressure by the indoor expansion mechanism 121, and is sent to the gas-liquid separator 116. In addition, some of the liquid refrigerant flowing out from the gas-liquid separator 116 is depressurized to the low pressure from the medium pressure by the refrigerant return expansion mechanism 158, and is sent to the outdoor heat exchanger 115.

As described above, the refrigeration system 101 includes the first switching mechanism 150. Thus, the refrigeration system 101 can switch between the cooling operation and the heating operation. In addition, during the heating operation, the refrigeration system 101 includes the first switching mechanism 150, so that the outdoor heat exchanger 115 can be switched between a state of not being used as a condenser and a state of being used as a condenser depending on the surplus or deficiency of the heat quantity.

As described above, the refrigeration system 101 includes the second switching mechanism 154. Thus, in both cases where the indoor heat exchanger 122 functions as an evaporator and where the indoor heat exchanger 122 functions as a condenser, the refrigeration system 101 can send out the refrigerant, which is sent out from each of the high-stage compressors 112, to the heat exchanger functioning as an evaporator through the gas-liquid separator 116. Therefore, the refrigeration system 101 can increase the refrigeration capacity.

Specifically, when the indoor unit 120 performs the cooling operation, the refrigerant discharged from each of the high-stage compressors 112 flows into the gas-liquid separator 116 by the second switching mechanism 154, and then flows into the indoor heat exchanger 122 and the refrigeration-facility heat exchanger 132.

When the indoor unit 120 performs the heating operation, the refrigerant sent out from each of the high-stage compressors 112 flows into the gas-liquid separator 116 by the second switching mechanism 154, and then flows into the refrigeration-facility heat exchanger 132 or the outdoor heat exchanger 115 depending on the surplus or deficiency of the heat quantity for heating.

Furthermore, the refrigeration system 101 includes the first switching mechanism 150 and the second switching mechanism 154, and can switch, during the heating operation, the outdoor heat exchanger 115 among a state of not being used, a state of being used as a condenser, and a state of being used as a evaporator depending on the surplus or deficiency of the heat amount. Thus, during the heating operation, the refrigeration system 101 switches the state of the outdoor heat exchanger, so that cooling exhaust heat from the refrigeration-facility heat exchanger 132 can be used to adjust surplus or deficiency of the heat quantity for heating of the indoor unit 120.

In this way, the refrigeration system 101 includes the first switching mechanism 150 and the second switching mechanism 154, thereby capable of increasing the refrigeration capacity and adjusting the surplus or deficiency of the heat quantity for heating while preventing an increase in the number of valve bodies and opening/closing devices to be controlled. In other words, the refrigeration system 101 can increase the refrigeration capacity and adjust the surplus or deficiency of the heat quantity for heating using the refrigeration circuit 102 with a simple configuration.

3-2-7. Operation Related to Refrigerant Recovery

FIG. 15 is a circuit diagram showing a refrigeration circuit 102 of the refrigeration system 101 during refrigerant recovery/vacuuming work.

Next, the operation related to refrigerant recovery will be described.

A shown in FIG. 15, when a worker performs refrigerant recovery/vacuuming work on the refrigeration system 101, first, a refrigerant recovery device 150 or a vacuuming unit 152 is connected to the external connection port 196 of the service valve 190 through the connection pipe 156. The external connection port 196 is released by the worker after the connection pipe 156 is connected.

Next, the worker operates the operation panel 232 to select the refrigerant recovery/vacuuming mode. Thus, a predetermined signal is transmitted to the control device 200 from the operation panel 232. Upon receiving the signal, the control unit 201 controls all of the opening/closing devices provided in the refrigeration system 101 to be fully open. When all of the opening/closing devices are fully open, the control device 200 display, on the display panel 234, a screen indicating that the refrigeration system 101 performs the refrigerant recovery/vacuuming mode. Thereafter, the worker drives the refrigerant recovery device 150 or the vacuuming unit 152 to recover the refrigerant in the refrigeration circuit 102.

3-2-8. Operation Related to Refrigerant Filling

FIG. 16 is a circuit diagram showing a refrigeration circuit 102 of the refrigeration system 101 during refrigerant filling work.

Next, the operation related to refrigerant filling will be described.

As shown in FIG. 16, when a worker performs refrigerant filling work on the refrigeration system 101, first, a refrigerant filling unit 154 is connected to the external connection port 196 of the service valve 190 through the connection pipe 156. The external connection port 196 is released by the worker after the connection pipe 156 is connected.

Next, the worker operates the operation panel 232 to select the refrigerant filling mode. Thus, a predetermined signal is transmitted to the control device 200 from the operation panel 232. Upon receiving the signal, the control unit 201 controls each of the first cooling valve 151, the first heating valve 152, the outdoor refrigerant return valve 153, the on-off valve 123, the throttling mechanism 155, the refrigerant return expansion mechanism 158, the gas refrigerant flow-rate control valve 161, the liquid refrigerant flow-rate control valve 165, the indoor expansion mechanism 121, and the outlet-side refrigeration-facility pressure regulation mechanism 133 to be fully closed. Upon receiving the signal, the control unit 201 controls each of the check valves 159, which are provided in the pipes 175 and 176, and the inlet-side refrigeration-facility expansion mechanism 131 to be open. When such control of these opening/closing devices is completed, the control device 200 causes the display panel 234 to display a screen indicating that the refrigeration system 101 performs the refrigerant filling mode. Thereafter, the worker drives the refrigerant filling unit 154 to send out the refrigerant to the refrigeration circuit 102.

Thus, the refrigerant is stored in the refrigeration-facility heat exchanger 132 and the gas-liquid separator 116 in the refrigeration circuit 102.

FIG. 17 is a circuit diagram showing a refrigeration circuit 102 of the refrigeration system 101 during a regulation operation.

When the refrigeration system 101 performs a cooling operation after the refrigerant filling work, the external connection port 196 is closed by the worker as shown in FIG. 17.

Next, the worker operates the operation panel 232 to select the regulation operation mode. Thus, a predetermined signal is transmitted from the operation panel 232 to the control device 200. Upon receiving the signal, the control unit 201 controls each of the first heating valve 152, the outdoor refrigerant return valve 153, the refrigerant return expansion mechanism 158, the check valve 159 provided in the pipe 176, and the outlet-side refrigeration-facility pressure regulation mechanism 133 to be fully closed. Upon receiving the signal, the control unit 201 controls each of the first cooling valve 151, the on-off valve 123, the throttling mechanism 155, the check valve 159 provided in the pipe 176, the gas refrigerant flow-rate control valve 161, the liquid refrigerant flow-rate control valve 165, the indoor expansion mechanism 121, and the inlet-side refrigeration-facility expansion mechanism 131 to be fully open. When the control of these opening/closing devices is completed, the control device 200 causes the display panel 234 to display a screen indicating that the refrigeration system 101 performs the regulation operation mode. Thereafter, the worker drives each of the high-stage compressors 112 and the indoor unit 120 in a state of stopping the refrigeration-facility unit 130 and the low-stage compressor 111. Thus, the refrigerant is sent out to the outdoor heat exchanger 115 and the indoor heat exchanger 122 in the refrigeration circuit 102. In this case, the indoor expansion mechanism 121 opens such that the medium-pressure refrigerant flowing in from the gas-liquid separator 116 becomes a low-pressure refrigerant. Therefore, a high-pressure refrigerant, an intermediate-pressure refrigerant, and a medium-pressure refrigerant are generated in the refrigeration system 101.

3-3. Effects

As described above, according to the present embodiment, the refrigeration system 101 includes the refrigeration circuit 102 that connects the outdoor unit 110 including the plurality of compressors, the outdoor heat exchanger 115, and the gas-liquid separator 116, the indoor unit 120 including the indoor heat exchanger 122, and the refrigeration-facility unit 130 including the refrigeration-facility heat exchanger 132.

The plurality of compressors are configured by the low-stage compressor 111 and the high-stage compressor 112, the indoor heat exchanger 122 having a high refrigerant evaporation temperature is connected to the high-stage compressor 112, and the refrigeration-facility heat exchanger 132 having a low refrigerant evaporation temperature is connected to the low-stage compressor 111.

The refrigeration circuit 102 includes the second switching mechanism 154 that causes the refrigerant discharged from the high-stage compressor 112 and flowing through at least either of the outdoor heat exchanger 115 or the indoor heat exchanger 122 to flow into the gas-liquid separator 116. The throttling mechanism 155 is provided between the outdoor heat exchanger 115 and the gas-liquid separator 116 to regulate the pressure of the refrigerant, and the indoor expansion mechanism 121 is provided between the indoor heat exchanger 122 and the gas-liquid separator 116.

Thus, the refrigeration system 101 can be formed with the refrigeration circuit 102 with a simple configuration, and can send the refrigerant to the evaporator through the gas-liquid separator 116 in both the case of performing the cooling operation and the case of performing the heating operation. Therefore, the refrigeration system 101 can improve the refrigeration capacity with a simple circuit configuration.

As in the present embodiment, the second switching mechanism 154 includes the pipes 173 to 176 that connect the outdoor heat exchanger 115, the indoor heat exchanger 122, the refrigeration-facility heat exchanger 132, and the gas-liquid separator 116 to one another. Each of the pipes 173 to 176 may be provided with the throttling mechanism 155 that regulates the flow of the refrigerant, the refrigerant return expansion mechanism 158, and the check valve 159.

Thus, in the refrigeration system 101, the refrigerant subjected to heat exchange by the gas-liquid separator 116 can be sent to any one of the outdoor heat exchanger 115, the indoor heat exchanger 122, and the refrigeration-facility heat exchanger 132 depending on the operation of the indoor unit 120 and the refrigeration-facility unit 130. Therefore, the refrigeration system 101 can increase the refrigeration capacity of the indoor unit 120 and the refrigeration-facility unit 130.

As in the present embodiment, the second switching mechanism 154 may include the check valve 159 and the throttling mechanism 155, as valve bodies.

Thus, in the refrigeration system 101, the refrigerant subjected to heat exchange by the gas-liquid separator 116 can be sent to any one of the outdoor heat exchanger 115, the indoor heat exchanger 122, and the refrigeration-facility heat exchanger 132 depending on the operation of the indoor unit 120 and the refrigeration-facility unit 130. Therefore, the refrigeration system 101 can increase the refrigeration capacity of the indoor unit 120 and the refrigeration-facility unit 130.

As in the present embodiment, the first switching mechanism 150 may be a mechanism that switches among any one of a flow path in which the refrigerant discharged from the high-stage compressor 112 flows to the outdoor heat exchanger 115, a flow path in which the refrigerant discharged from the high-stage compressor 112 flows to the indoor heat exchanger 122, and a flow path in which the refrigerant discharged from the high-stage compressor 112 flows to both the outdoor heat exchanger 115 and the indoor heat exchanger 122.

Thus, the refrigeration system 101 can include the refrigeration circuit 102 with simpler configuration. In addition, the refrigeration system 101 can switch the operation without stopping the compressor.

As in the present embodiment, the first switching mechanism 150 may be provided with the first cooling valve 151 located between the discharge side of the high-stage compressor 112 and the outdoor heat exchanger 115 and the outdoor refrigerant return valve 153 located downstream of the first cooling valve 151 and between the discharge side of the high-stage compressor 112 and the suction side of the low-stage compressor 111.

Thus, the refrigeration system 101 can switch among any one of a flow path in which the refrigerant discharged from the high-stage compressor 112 flows to the outdoor heat exchanger 115, a flow path in which the refrigerant discharged from the high-stage compressor 112 flows to the indoor heat exchanger 122, a flow path in which the refrigerant discharged from the high-stage compressor 112 flows to both the outdoor heat exchanger 115 and the indoor heat exchanger 122. Therefore, the refrigeration system 101 can include the refrigeration circuit 102 with a simpler configuration.

As in the present embodiment, the refrigeration system 101 includes the control device 200 that controls each of the units of the refrigeration circuit 102. The control device 200 includes the operation panel 232 that can be operated by the worker. The control device 200 includes, as operation modes of the refrigeration circuit 102, the first operation mode in which the refrigerant flowing through the indoor heat exchanger 122 and the refrigeration-facility heat exchanger 132 is regulated at a predetermined temperature and the second operation mode in which the operation is performed according to the operation of the external device connected to the refrigeration circuit 102. The control device 200 may switch between the first operation mode and the second operation mode according to the operation on the operation panel 232.

Thus, the refrigeration system 101 can switch between the first operation mode and the second operation mode according to the operation on the operation panel 232. Therefore, in the refrigeration system 101, the worker can easily switch between the operation modes.

As in the present embodiment, the control device 200 may include a plurality of second operation modes, and may switch between the second operation modes according to the operation on the operation panel 232.

Thus, in the refrigeration system 101, the worker can perform the work related to the refrigerant recovery/vacuuming and the refrigerant filling according to the operation on the operation panel 232. Therefore, in the refrigeration system 101, the worker can easily perform the work related to the refrigerant recovery/vacuuming and the refrigerant filling.

As in the present embodiment, the control device 200 may include a display panel 234 that displays a status of the refrigeration circuit 102 in each of the operation modes.

Thus, in the refrigeration system 101, the worker can perform the work related to the refrigerant recovery/vacuuming and the refrigerant filling according to the operation on the control device 200 while checking the status of the refrigeration system 101. Therefore, in the refrigeration system 101, the worker can easily perform the work related to the refrigerant recovery/vacuuming and the refrigerant filling.

As in the present embodiment, the service valve 190, to which the external device can be connected, may be provided between the refrigeration-facility heat exchanger 132 and the suction side of the low-stage compressor 111.

Thus, in the refrigeration system 101, the service valve 190 is provided at a location close to the connection point between the outdoor unit 110 and the refrigeration-facility unit 130. Therefore, the refrigeration system 101 can improve workability when the external device is connected to the refrigeration system 101.

Other Embodiments

As described above, the first and second embodiments have been described as examples of techniques disclosed in the present application. However, the techniques of the present disclosure are not limited thereto, and are also applicable to embodiments where changes, replacements, additions, omissions, etc., are appropriately made. In addition, it is also possible to combine the components described in the first and second embodiments to create new embodiments.

Hereinafter, other embodiments will be described as examples.

The connection pipe 166 is provided in the refrigeration system 101 in the embodiments described above, but the connection pipe 166 may not be provided.

In the above-described embodiments, the outlet-side refrigeration-facility pressure regulation mechanism 133 and the service valve 190 are provided in the refrigeration-facility unit 130. However, the present invention is not limited thereto, and the outlet-side refrigeration-facility pressure regulation mechanism 133 and the service valve 190 may be provided in the outdoor unit 110. For example, the outlet-side refrigeration-facility pressure regulation mechanism 133 and the service valve 190 may be provided in the pipe 172 between the outdoor unit 110 and the refrigeration-facility unit 130.

In the above-described embodiments, the refrigeration system 101 includes one indoor heat exchanger 122 and one refrigeration-facility heat exchanger 132. However, the present invention is not limited thereto, and the refrigeration system 101 may include another refrigeration-facility heat exchanger 132 instead of the indoor heat exchanger 122. In other words, the refrigeration system 101 may include a plurality of refrigeration-facility units 130 without including the indoor unit 120.

In this case, the plurality of refrigeration-facility heat exchangers 132 have different evaporation temperature zones. Out of the plurality of refrigeration-facility heat exchangers 132, the refrigeration-facility heat exchanger 132 having a higher evaporation temperature zone is connected to the inlet side of the high-stage compressor 112, and the refrigeration-facility heat exchanger 132 having a lower evaporation temperature zone is connected to the inlet side of the low-stage compressor 111.

For example, when the refrigeration system 101 includes the refrigeration-facility unit 130 set to the freezing temperature zone and the refrigeration-facility unit 130 set to the refrigeration temperature zone, the refrigeration-facility heat exchanger 132 in the refrigeration-facility unit 130 set to the refrigeration temperature zone is connected to the inlet side of the high-stage compressor 112. On the other hand, the refrigeration-facility heat exchanger 132 in the refrigeration-facility unit 130 set to the freezing temperature zone is connected to the inlet side of the low-stage compressor 111.

In the above-described embodiments, a plurality of utilization-side heat exchangers connected to the inlet side of the high-stage compressor 112 may be provided in parallel in the pipes 178 and 171. Similarly, a plurality of utilization-side heat exchangers connected to the inlet side of the low-stage compressor 111 may be provided in parallel in the pipes 177 and 172.

Furthermore, for example, a plurality of indoor heat exchangers 122 may be provided in parallel to each other in the pipes 178 and 171. In this case, the indoor expansion mechanism 121 may be provided on the inlet side of each of the indoor heat exchangers 122. In this case, the refrigeration system 101 includes a plurality of indoor units 120. In this case, one or a plurality of indoor heat exchanger 122 and one or a plurality of refrigeration-facility heat exchanger 132 may be provided in parallel in the pipes 178 and 171.

A plurality of refrigeration-facility heat exchangers 132 may be provided in parallel to each other in the pipes 177 and 172. In this case, an inlet-side refrigeration-facility expansion mechanism 131 may be provided on the inlet side of each of the refrigeration-facility heat exchangers 132. In this case, at least one of the refrigeration-facility heat exchangers 132 provided in parallel in the pipes 177 and 172 may have an evaporation temperature zone different from that of the other refrigeration-facility heat exchangers 132.

The control device 200 may include a touch panel having integrally the functions of the operation panel 232 and the display panel 234.

Furthermore, for example, the control device 200 may be provided in either the indoor unit 120 or the refrigeration-facility unit 130. For example, either the operation panel 232 or the display panel 234 may be provided integrally in any one of the outdoor unit 110, the indoor unit 120, and the refrigeration-facility unit 130.

Furthermore, for example, the control device 200 may be provided integrally in an operation terminal such as a remote control provided in the indoor unit 120 or the refrigeration-facility unit 130. The remote control is a terminal that controls setting temperature of the indoor unit 120 or the refrigeration-facility unit 130 or starts up the indoor unit 120 or the refrigeration-facility unit 130.

Furthermore, for example, the control device 200 may be a communication terminal such as a smartphone or a tablet in which apps or programs are installed to transmit a predetermined signal to the outdoor unit 110 or each unit of the refrigeration system 101. In this case, the control device 200 may be capable of communicating with the outdoor unit 110 and each unit of the refrigeration system 101 via a network constituted of a public line network, a dedicated line, other communication lines, and various communication facilities. Specific aspects of such a network are not limited. The communication network may include at least one of a wireless communication circuit and a wired communication circuit.

Furthermore, for example, the control device 200 may be a server device in which apps or programs are installed to transmit a predetermined signal to the outdoor unit 110 or each unit of the refrigeration system 101. The server device may be capable of communicating with the outdoor unit 110 and each unit of the refrigeration system 101 via the above-described network.

Each unit shown in FIG. 9 is an example and not particularly limited to a specific implementation. Thus, hardware individually corresponding to each component does not necessarily need to be implemented, and functions of each component may be achieved by one processor executing a computer program. Some functions achieved by software in the above-described embodiments may be achieved by hardware, or some functions achieved by hardware may be achieved by software. Specific detailed components of other units of the outdoor unit 110, the indoor unit 120, and the refrigeration-facility unit 130 are optionally changeable without departing from the spirit of the present invention.

Step units of the operation shown in FIG. 12 are divisions according to main processing contents to facilitate understanding of operation of each unit of the refrigeration system 101, and the operation is not limited by a division scheme of processing units and their names. The division into a larger number of step units may be made in accordance with processing contents. The division may be made such that one step unit includes a larger number of processes. Moreover, orders of steps may be interchanged as appropriate without interference with the spirit of the present invention.

Note that the above-described embodiments are intended to illustrate the technology of the present disclosure, and thus various modifications, substitutions, additions, omissions, and the like can be made within the claims or equivalents thereof.

Findings on Which Present Disclosure is Based

At the time when the inventors have conceived of a refrigeration system according to a third aspect of the present disclosure, there has been a technology to provide a refrigeration apparatus capable of preventing refrigeration oil from concentrating in a specific compressor and ensuring stable oil level control. The refrigeration apparatus includes at least two compressors and an accumulator in a refrigeration cycle circuit where a plurality of indoor units are connected in parallel with respect to an outdoor unit. The refrigeration apparatus is provided with oil movement pipes for moving refrigeration oil in the accumulator from the accumulator to the respective compressors and solenoid valves disposed on the oil movement pipes.

However, in such a refrigeration apparatus, since a solenoid valve is provided for each of the pipes connected to the accumulator, there is a concern that costs will increase. In addition, depending on the configuration of the compressor and the refrigeration cycle circuit, there is a concern that the solenoid valve is not provided.

For example, in the refrigeration system including a plurality of compressors for compressing the sucked refrigerant in multiple stages, there is a technique in which an oil separator is connected to a discharge side of each of the compressors, and the refrigeration oil discharged together with the refrigerant from the compressors is returned from an oil equalization pipe of each of the compressors.

However, in such a refrigeration system, when the compressor is, for example, an internal high-pressure compressor, there is a concern that a sufficient pressure difference cannot be obtained between the inside of the compressor and the discharge side, making it impossible to return the refrigeration oil.

For example, in the refrigeration system including a plurality of compressors for compressing the sucked refrigerant in multiple stages, there is a technique in which a sensor such as a float switch is attached to each of the plurality of compressors to detect an oil level and oil supply is controlled.

However, in such a refrigeration system, since a sensor is individually attached to each of the compressors, there is a concern that costs will increase. In addition, the refrigeration system needs to use a compressor to which a sensor can be attached, which may reduce the freedom of design and development.

The inventors have found the above-described problems in the refrigeration system, and have come up with the subject matter of the present disclosure in order to solve these problems.

In view of the above, the present disclosure provides an accumulator and a refrigeration system that can stably return stored refrigeration oil from the suction sides of the plurality of compressors with a simpler configuration.

Embodiments will be described in detail below with reference to the drawings. However, unnecessarily detailed descriptions will be avoided. For example, a detailed description of a well-known matter or a redundant description of a substantially identical structure may be avoided. This is to avoid rendering the following description unduly lengthy and to thereby facilitate understanding by those skilled in the art.

The following description and the accompanying drawings are provided to allow those skilled in the art to fully understand the present disclosure, and are not intended to limit the scope of the claims.

Fourth Embodiment

Hereinafter, a fourth embodiment corresponding to a third aspect of the present disclosure will be described with reference to the drawings.

4-1-1. Configuration of Refrigeration System

FIG. 18 is a diagram showing a refrigeration cycle circuit of a refrigeration system 301 according to a fourth embodiment. FIG. 18 shows an operation of the refrigeration system 301 during a cooling operation.

As shown in FIG. 18, the refrigeration system 301 includes a heat source unit 310, an indoor unit 320, and a refrigeration-facility unit 330.

The indoor unit 320 performs air conditioning on a space within a store, for example, a convenience store or a supermarket, and the refrigeration-facility unit 330 performs cooling on an interior of a refrigerating display showcase or a freezing display showcase that serves as a cooling storage facility installed in the store.

The heat source unit 310 includes a low-stage compressor 311 and two high-stage compressors 312 and 312. The two high-stage compressors 312 are connected in parallel to the low-stage compressor 311. In the present embodiment, the two high-stage compressors 312 are internal high-pressure compressors.

An accumulator 313 is disposed between the low-stage compressor 311 and the high-stage compressor 312.

In other words, a refrigerant discharged from the low-stage compressor 311 is separated into gas and liquid by the accumulator 313, and only the gas refrigerant is sent to the high-stage compressor 312.

An oil separator 314 is connected to a discharge side of the high-stage compressor 312. An outdoor heat exchanger 315 is connected to the oil separator 314 through a refrigerant pipe 340. The outdoor heat exchanger 315 corresponds to a so-called heat source-side heat exchanger.

A first heating pipe 341, which is connected to the refrigerant pipe 340 between the indoor unit 320 and the accumulator 313, is connected to the refrigerant pipe 340 between the oil separator 314 and the outdoor heat exchanger 315.

In addition, a first outdoor return pipe 342, which is connected to the refrigerant pipe 340 between the refrigeration-facility unit 330 and the low-stage compressor 311, is connected to the refrigerant pipe 340 between the oil separator 314 and the outdoor heat exchanger 315.

A first switching mechanism 350 is provided between the oil separator 314 and the outdoor heat exchanger 315. The first switching mechanism 350 includes a first cooling valve 351 that opens and closes the refrigerant pipe 340 between the oil separator 314 and the outdoor heat exchanger 315, a first heating valve 352 that is provided in a middle of the first heating pipe 341 to open and close the first heating pipe 341, and an outdoor refrigerant return valve 353 that is provided in a middle of the first outdoor return pipe 342 to open and close the first outdoor return pipe 342.

A gas-liquid separator 316 is connected to the outdoor heat exchanger 315 through the refrigerant pipe 340. A refrigeration-facility heat exchanger 331 of the refrigeration-facility unit 330 is connected to the gas-liquid separator 316 through the refrigerant pipe 340 and an inlet-side refrigeration-facility expansion mechanism 332. The refrigeration-facility heat exchanger 331 is connected to the low-stage compressor 311 through an outlet-side refrigeration-facility pressure adjustment mechanism 333.

A second cooling pipe 343, which is connected to the indoor heat exchanger 322 through an indoor expansion mechanism 321, is connected to the refrigerant pipe 340 between the outdoor heat exchanger 315 and the gas-liquid separator 316.

A second heating pipe 344, which is connected to the indoor heat exchanger 322, is connected to the refrigerant pipe 340 between the outdoor heat exchanger 315 and the gas-liquid separator 316.

A second outdoor return pipe 345, which is connected to the refrigerant pipe 340 between the refrigeration-facility heat exchanger 331 and the gas-liquid separator 316, is connected to the refrigerant pipe 340 between the outdoor heat exchanger 315 and the gas-liquid separator 316.

A second switching mechanism 354 is provided between the outdoor heat exchanger 315 and the gas-liquid separator 316. The second switching mechanism 354 includes a second cooling valve 355 that opens and closes the refrigerant pipe 340 between the outdoor heat exchanger 315 and the gas-liquid separator 316, a third cooling valve 356 that is provided in a middle of the second cooling pipe 343 to open and close the second cooling pipe 343, and a second heating valve 357 that is provided in a middle of the second heating pipe 344 to open and close the second heating pipe 344.

A refrigerant return expansion mechanism 358 is provided in a middle of the second outdoor return pipe 345 to control a flow rate of the second outdoor return pipe 345.

Check valves 359 are provided downstream of the second cooling valve 355, the third cooling valve 356, and the second heating valve 357, respectively.

The indoor heat exchanger 322 is connected to the high-stage compressor 312 through the refrigerant pipe 340, an on-off valve 323, and the accumulator 313.

In the present embodiment, a gas refrigerant return pipe 360 is provided to send a gas refrigerant from the gas-liquid separator 316 to a suction side of the accumulator 313. A gas refrigerant flow-rate control valve 361 is provided in a middle of the gas refrigerant return pipe 360.

The heat source unit 310 according to the present embodiment functions as a so-called outdoor unit. For example, when the heat source unit 310 includes a housing, each component and each device of the heat source unit 310 may not be integrally housed in the housing.

In the present embodiment, the indoor heat exchanger 322 and the refrigeration-facility heat exchanger 331 function as a so-called utilization-side heat exchanger. In other words, the indoor unit 320 and the refrigeration-facility unit 330 function as utilization-side heat exchanger unit 309 with respect to the heat source unit 310 (FIG. 19).

FIG. 19 is a block diagram of the refrigeration system 301.

As shown in FIG. 19, the blowers 318, 328, and 338 are provided in the heat source unit 310, the indoor unit 320, and the refrigeration-facility unit 330, respectively. The blowers 318, 328, and 338 flow air to the outdoor heat exchanger 315, the indoor heat exchanger 322, and the refrigeration-facility heat exchanger 331, respectively, and facilitate heat exchange between the refrigerant and the air flowing through each of the outdoor heat exchanger 315, the indoor heat exchanger 322, and the refrigeration-facility heat exchanger 331.

The heat source unit 310 includes a control device 390 and a heat source unit I/F 395. The control device 390 includes a control unit 391 and a storage unit 393.

The control unit 391 is a processor such as a CPU (Central Processing Unit) or an MPU (Micro Processing Unit) that operates based on a program stored in advance in the storage unit 393. The control unit 391 may be configured with a single processor or may be configured with a plurality of processors. A DSP (digital signal processor) or the like may be used as the control unit 391. Furthermore, the control circuit such as an LSI (Large Scale Integration), an ASIC (Application Specific Integrated Circuit), or an FPGA (Field-Programming Gate Array) can be used as the control unit 391.

The control unit 391 is connected to the storage unit 393 and the low-stage compressor 311, and controls these units.

The control unit 391 reads the computer program stored in the storage unit 393 and operates according to the read computer program, thereby functioning as a determination unit 391a and an operation control unit 391b.

The determination unit 391a compares a detection value of the sensor provided in each unit of the refrigeration system 301 with various data in setting data 393a stored in the storage unit 393.

The operation control unit 391b controls various devices such as the low-stage compressor 311 and the high-stage compressor 312 in the heat source unit 310.

In addition, the operation control unit 391b transmits control signals to the indoor unit 320 and the refrigeration-facility unit 330 through the heat source unit I/F 395 to cooperatively operate the refrigeration system 301.

The storage unit 393 includes a memory device such as a RAM (Random Access Memory) or a ROM (Read Only Memory), a fixed disk device such as a hard disk, or a portable storage device such as a flexible disk or an optical disk. In addition, the storage unit 393 stores computer programs, databases, tables, and the like used for various operations of the refrigeration system 301. These computer programs may be installed in the storage unit 393 from a computer-readable portable recording medium using a known setup program, for example. The portable recording medium may be, for example, a semiconductor storage device including a CD-ROM (compact disc read only memory), a DVD-ROM (digital versatile disc read only memory), a USB (Universal Serial Bus) memory, or an SSD (Solid State Drive). The computer programs may be installed from a predetermined server, for example.

Furthermore, the storage unit 393 may include a volatile storage region and may form a work area for the control unit 391.

The storage unit 393 stores setting data 393a. The setting data 393a includes data of setting value related to the amount of refrigeration oil stored in the accumulator 313. A control upper-limit temperature T1 is higher than a setting temperature T5.

The heat source unit I/F 395 includes communication hardware such as a communication interface circuit or a connector for the heat source unit 310 to communicate with each device via a cable according to a predetermined communication protocol. The outdoor unit I/F 395 sends data received from each device to the control device 390, and transmits data received from the control device 390 to each device.

The indoor unit 320 includes an indoor-unit control device 380 and an indoor unit I/F 385. The indoor-unit control device 380 includes an indoor-unit control unit 381 and an indoor-unit storage unit 383.

The indoor-unit control unit 381 is a processor such as a CPU or an MPU, similarly to the control unit 391. The indoor-unit control unit 381 operates according to a computer program stored in the indoor-unit storage unit 383 to control various devices such as a blower 328 mounted in the indoor unit 320. In addition, the indoor-unit control unit 381 receives output signals from various sensors mounted on the indoor unit 320.

Similarly to the storage unit 393, the indoor-unit storage unit 383 includes a storage device such as a RAM or a ROM, and stores computer programs and the like used for various operations of the indoor unit 320.

The indoor unit I/F 385 includes communication hardware such as a communication interface circuit or a connector for the indoor unit 320 to communicate with each device. The indoor unit I/F 385 sends data received from each device to the indoor-unit control device 380, and transmits data received from the indoor-unit control device 380 to each device.

The refrigeration-facility unit 330 includes a refrigeration-facility-unit control device 370 and a refrigeration-facility unit I/F 375. The refrigeration-facility-unit control device 370 includes a refrigeration-facility-unit control unit 371 and a refrigeration-facility-unit storage unit 373.

Similarly to the control unit 391, the refrigeration-facility-unit control unit 371 is a processor such as a CPU or an MPU. The refrigeration-facility-unit control unit 371 operates according to a computer program stored in the refrigeration-facility-unit storage unit 373 to control various devices such as a blower 338 mounted in the refrigeration-facility unit 330. In addition, the refrigeration-facility-unit control unit 371 receives output signals from various sensors mounted on the refrigeration-facility unit 330.

Similarly to the storage unit 393, the refrigeration-facility-unit storage unit 373 includes a storage device such as a RAM or a ROM, and stores computer programs and the like used for various operations of the refrigeration-facility unit 330.

The refrigeration-facility unit I/F 375 includes communication hardware such as a communication interface circuit or a connector for the refrigeration-facility unit 330 to communicate with each device. The refrigeration-facility unit I/F 375 sends data received from each device to the refrigeration-facility-unit control device 370, and transmits data received from the refrigeration-facility-unit control device 370 to each device.

4-1-1. Configuration of Accumulator

FIG. 20 is a longitudinal cross-sectional view showing an accumulator 313. FIG. 20 shows a cross section taken along a line passing through a center of the accumulator 313 in a plan view and cutting along in an up-down direction of the accumulator 313. In FIG. 20, for the convenience of description, an oil level W is indicated by a two-dot chain line.

As shown in FIG. 20, the accumulator 313 includes an accumulator body 400.

The accumulator body 400 is a container formed as a vertically elongated hollow body including an internal space S. The accumulator body 400 is disposed such that a longitudinal direction thereof extends in the up-down direction.

A side surface 401 extending in the up-down direction of wall surfaces of the accumulator body 400 is formed in a cylindrical shape surrounding the entire periphery of sides of the internal space S.

A top surface 403 of the accumulator body 400 is formed in an upwardly convex spherical shape. Similarly, a bottom surface 405 of the accumulator body 400 is formed in an downwardly convex spherical shape. The top surface 403 is continuous with an upper end of the side surface 401, and the bottom surface 405 is continuous with a lower end of the side surface 401.

As shown in FIGS. 18 and 20, a plurality of pipes that function as flow paths for the refrigerant or the refrigeration oil is connected to the accumulator 313.

Specifically, a discharge pipe 362 having one end connected to the discharge side of the low-stage compressor 311 is connected to the accumulator 313. The discharge pipe 362 penetrates the wall surface of the accumulator body 400, and the other end 420 of the discharge pipe 362 is disposed in the internal space S. The discharge pipe 362 penetrates the top surface 403. The other end 420 entering the internal space S extends downward and is then bent upward, so that the entire end is formed in a J-shape. Thus, a tip 421 of the other end 420 is disposed toward the top surface 403.

The tip 421 is spaced at a predetermined distance from the top surface 403. The distance is set according to the discharge amount of the low-stage compressor 311, that is, the flow velocity of the gas refrigerant and the discharge amount of the high-stage compressor 312.

The refrigerant and the refrigeration oil is discharged into the internal space S from the discharge pipe 362. In the accumulator 313, the refrigeration oil and the liquid refrigerant are separated from the gas refrigerant inside the accumulator body 400.

Thus, the refrigeration oil and the liquid refrigerant are stored on the bottom surface 405 side of the accumulator body 400.

The refrigerant and the refrigeration oil discharged from the discharge pipe 362 collides toward the top surface 403. Vaporous refrigeration oil in the refrigeration oil is liquefied by collision with the top surface 403, flows along the top surface 403 and the side surface 401, and is stored in a lower part of the internal space S. Liquidous refrigeration oil on the refrigeration oil is collected by collision with the top surface 403, flows along the top surface 403 and the side surface 401, and is stored in a lower part of the internal space S.

Thus, the accumulator 313 can efficiently store the refrigeration oil on the bottom surface 405 side of the accumulator 313. Therefore, the accumulator 313 can maintain the amount of refrigeration oil stored in the accumulator 313 at a predetermined amount.

A pair of suction pipes 364 includes one end 422 disposed in the internal space S to be connected to the accumulator 313. Each of the suction pipes 364 includes the other end connected to the suction side of each of the high-stage compressors 312. Each of the suction pipes 364 has the same entire length in the longitudinal direction.

Each of the suction pipes 364 penetrates the wall surface of the accumulator body 400, and one end 422 of each of the suction pipes 364 is disposed in the internal space S. The suction pipes 364 penetrate the top surface 403. Each of the one ends 422 entering the internal space S extends to a position close to the bottom surface 405 side, and is then bent upward, so that the entire end is formed in a J-shape. Thus, a tip 423 of the one end 422 is disposed toward the top surface 403. Each of the one ends 422 is located lower than the other end 420.

Each of the tips 423 is spaced at a predetermined distance from the top surface 403. The distance is set according to the discharge amount of the low-stage compressor 311, that is, the flow velocity of the gas refrigerant and the discharge amount of the high-stage compressor 312.

In the internal space S, each of the one ends 422 is formed to have substantially the same number of times of bending and a bend R.

A bent portion 424 is located at the lowest end of each of the other ends 422. The bent portion 424 is disposed at a position spaced at a predetermined distance from the bottom surface 405 side.

The bent portion 424 is provided with a suction hole 425 which is a through hole. The suction holes 425, which are provided in the suction pipes 364, respectively, are formed to have substantially the same dimension.

As described above, the internal space S stores the refrigerant discharged from the discharge pipe 362 and the refrigeration oil. In the accumulator 313, the gas refrigerant separated from the refrigeration oil and the liquid refrigerant inside the accumulator body 400 enters from the tip 423 of the one end 422. Thus, the gas refrigerant separated in the accumulator 313 is sucked into each of the high-stage compressors 312 through each of the suction pipes 364.

The refrigeration oil is stored on the bottom surface 405 side of the accumulator body 400. Since an oil level W of the refrigeration oil is located above each of the bent portions 424, the refrigeration oil enters each of the one ends 422 from each of the suction holes 425.

Along with the gas refrigerant entering from the tip 423, the refrigeration oil entering the one end 422 is sucked into each of the high-stage compressors 312 through each of the suction pipes 364. Specifically, the refrigeration oil stored in the accumulator body 400 enters each of the ends 422 from each of the suction holes 425 due to the flow of the gas refrigerant entering from the tip 423. Then, the refrigeration oil entering each of the ends 422 is sent out, by the flow of the gas refrigerant, to the suction side of each of the high-stage compressors 312 through each of the suction pipes 364.

Thus, even when the high-stage compressors 312 are internal high-pressure compressors, the refrigeration system 301 can send the refrigeration oil stored in the accumulator 313 to each of the high-stage compressors 312.

As described above, the suction pipes 364 have the same entire length in the longitudinal direction. Furthermore, each of the one ends 422 is formed to have substantially the same number of times of bending and a bend R. Thus, the gas refrigerant sucked into each of the suction pipes 364 flows through each of the suction pipes 364 at substantially the same flow velocity, and is sucked into each of the high-stage compressors 312.

For this reason, the refrigeration system 301 can evenly send the refrigeration oil stored in the accumulator 313 together with the gas refrigerant to each of the high-stage compressors 312. In other words, the accumulator 313 can distribute the refrigerant oil to each of the high-stage compressors 312 in substantially the same supply amount.

An oil supply pipe 366 having one end connected to the oil separator 314 is connected to the accumulator 313. The oil supply pipe 366 penetrates the wall surface of the accumulator body 400, and the other end 426 of the oil supply pipe 366 is disposed in the internal space S. The oil supply pipe 366 penetrates the top surface 403. The other end 426 entering the internal space S extends downward and is then bent upward, so that the entire end is formed in a J-shape. Thus, a tip 427 of the other end 426 is disposed toward the top surface 403.

The refrigeration oil discharged from the oil supply pipe 366 collides toward the top surface 403. The refrigeration oil is collected by collision with the top surface 403, flows along the top surface 403 and the side surface 401, and is stored in a lower part of the internal space S.

An oil supply motor-operated valve 369 is provided in the oil supply pipe 366. The oil supply motor-operated valve 369 is opened and closed by driving of a motor to open and close the oil supply pipe 366. The amount of refrigeration oil discharged from the oil supply pipe 366 is regulated by opening and closing of the oil supply motor-operated valve 369. The opening and closing of the oil supply motor-operated valve 369 is controlled by the operation control unit 391b.

The oil supply motor-operated valve 369 is provided in the oil supply pipe 366 at a position located outside the accumulator body 400.

The oil supply motor-operated valve 369 corresponds to an “opening/closing device” in the present disclosure.

An oil level sensor 430 is provided in the internal space S of the accumulator body 400. The oil level sensor 430 is a sensor that detects a height position of the oil level W of the refrigeration oil relative to the bottom surface 405 in the up-down direction inside the accumulator body 400. The oil level sensor 430 transmits a detection value to the control device 390 via a signal line or the like.

In the control device 390, when the detection value is received, the determination unit 391a compares the detection value of the sensor provided in each unit of the refrigeration system 301 with the setting value involved in the setting data 393a stored in the storage unit 393. In the present embodiment, the setting value is a value that the height position of the oil level W of the refrigeration oil becomes equal to or higher than the height position of the suction hole 425 and equal to or lower than the height position of the one end 422.

Based on the determination result of the determination unit 391a, the operation control unit 391b opens and closes the oil supply motor-operated valve 369 such that the height position of the oil level W of the refrigeration oil becomes equal to or higher than the height position of the suction hole 425 and equal to or lower than the height position of the one end 422.

Thus, it is possible to manage the amount of refrigeration oil stored in the accumulator 313 and returned to the plurality of high-stage compressors 312 with one oil level sensor 430. Therefore, the accumulator 313 can always store the refrigeration oil at a storage amount of which the height position of the oil level W becomes equal to or higher than the height position of the suction hole 425 and equal to or lower than the height position of the one end 422. Then, in the accumulator 313, a predetermined amount of refrigeration oil can be stably returned to the plurality of high-stage compressors 312.

In the refrigeration system 301, there is no need to attach a sensor relating to the amount of refrigeration oil to each of the plurality of high-stage compressors 312, and thus the manufacturing costs can be reduced.

Metal powder and sludge may be mixed into the refrigerant and the refrigeration oil discharged from the discharge pipe 362 and the oil supply pipe 366.

As described above, the bent portion 424 and the suction hole 425 are disposed at positions spaced at a predetermined distance from the bottom surface 405 side. The bottom surface 405 is formed in a downwardly convex spherical shape.

Thus, contaminants such as metal powder and sludge are retained below the bent portion 424 and are prevented from entering the suction hole 425. Therefore, the contaminants are prevented from being sent to the plurality of high-stage compressors 312.

4-2. Operation

Next, an operation of the present embodiment will be described.

First, a cooling operation will be described.

When the refrigeration system 301 performs a cooling operation, as shown in FIG. 18, the first cooling valve 351 is opened, and the second cooling valve 355 and the third cooling valve 356 are opened. The first heating valve 352, the second heating valve 357, the first high load valve, the outdoor return valve, and the outdoor return expansion mechanism are closed.

In this state, the low-stage compressor 311 and each of the high-stage compressors 312 are driven, whereby the refrigerant compressed by the low-stage compressor 311 is sent to each of the high-stage compressors 312, further compressed by each of the high-stage compressor 312, and discharged toward the oil separator 314.

The refrigerant passing through the oil separator 314 is sent to the outdoor heat exchanger 315 through the first cooling valve 351, and exchanges heat with outside air in the outdoor heat exchanger 315.

The refrigerant after heat exchange is sent to the gas-liquid separator 316 through the second cooling valve 355, and sent to the indoor heat exchanger 322 through the third cooling valve 356.

The refrigerant exchanges heat with indoor air in the indoor heat exchanger 322 to cool the indoor air. The refrigerant subjected to heat exchange with the indoor air is returned to each of the high-stage compressors 312 through the accumulator 313.

On the other hand, some of the refrigerant from the gas-liquid separator 316 is sent to the refrigeration-facility heat exchanger 331 through the inlet-side refrigeration-facility expansion mechanism 332, and is subjected to heat exchange in the refrigeration-facility heat exchanger 331 to cool the refrigeration-facility unit 330. The refrigerant subjected to heat exchange in the refrigeration-facility heat exchanger 331 is returned to the low-stage compressor 311 through the inlet-side refrigeration-facility expansion mechanism 332.

Next, a heating operation will be described.

FIG. 21 is a circuit diagram of the refrigeration system 301 showing a heating operation. A flow of the refrigerant is indicated by arrows in the drawing.

As shown in FIG. 21, during the heating operation, the first heating valve 352 and the second heating valve 357 are opened, and the first cooling valve 351, the second cooling valve 355, the third cooling valve 356, and the outdoor refrigerant return valve 353 are closed.

In this state, the low-stage compressor 311 and each of the high-stage compressors 312 are driven, whereby the refrigerant compressed by the low-stage compressor 311 is sent to each of the high-stage compressors 312, further compressed by each of the high-stage compressor 312, and discharged toward the oil separator 314.

The refrigerant passing through the oil separator 314 is sent to the indoor heat exchanger 322 through the first heating valve 352, and exchanges heat with indoor air in the indoor heat exchanger 322 to heat the indoor air.

The refrigerant subjected to heat exchange in the indoor heat exchanger 322 is sent to the gas-liquid separator 316 through the second heating valve 357, is then sent to the refrigeration-facility heat exchanger 331 through the inlet-side refrigeration-facility expansion mechanism 332, and is subjected to heat exchange in the refrigeration-facility heat exchanger 331 to cool the refrigeration-facility unit 330.

The refrigerant subjected to heat exchange in the refrigeration-facility heat exchanger 331 is returned to the low-stage compressor 311 through the outlet-side refrigeration-facility pressure adjustment mechanism 333. In other words, the refrigeration system 301 of the present disclosure is configured such that during heating, the indoor heat exchanger 322 functions as a gas cooler or a radiator, and the outdoor heat exchanger 315 is not used.

Next, an operation of the refrigeration system 301 will be described in a case where a heating operation is performed when the amount of heat exhausted from the refrigeration-facility unit 330 is insufficient.

FIG. 22 is a circuit diagram of the refrigeration system 301 showing a heating operation when the amount of heat exhausted from the refrigeration-facility unit 330 is insufficient. A flow of the refrigerant is indicated by arrows in the drawing.

As shown in FIG. 22, during a heating operation at full capacity, the first heating valve 352, the second heating valve 357, and the high load valve and high load expansion mechanism are opened, and the first cooling valve 351, the second cooling valve 355, and the third cooling valve 356 are closed.

In this state, the low-stage compressor 311 and each of the high-stage compressors 312 are driven, whereby the refrigerant compressed by the low-stage compressor 311 is sent to each of the high-stage compressors 312, further compressed by each of the high-stage compressor 312, and discharged toward the oil separator 314.

The refrigerant passing through the oil separator 314 is sent to the indoor heat exchanger 322 through the first heating valve 352, and exchanges heat with indoor air in the indoor heat exchanger 322 to heat the indoor air.

The refrigerant subjected to heat exchange in the indoor heat exchanger 322 is sent to the gas-liquid separator 316 through the second heating valve 357, and then sent to the refrigeration-facility heat exchanger 331 through the inlet-side refrigeration-facility expansion mechanism 332. The refrigerant, which cools the refrigeration-facility unit 330, and the refrigerant subjected to heat exchange in the refrigeration-facility heat exchanger 331 is adjusted through the outlet-side refrigeration-facility pressure adjustment mechanism 333 to have the same pressure as that of the refrigerant which is sent from the first outdoor return pipe 342, and is returned to the low-stage compressor 311. In the heating operation of the refrigeration system 301, the operation is performed when the outside air temperature is lower than the temperature inside the refrigeration-facility unit 330.

On the other hand, some of the refrigerant from the gas-liquid separator 316 are sent to the outdoor heat exchanger 315 through the refrigerant return expansion mechanism 358, and is returned to the low-stage compressor 311 after heat exchange in the outdoor heat exchanger 315.

Thus, exhaust heat from the refrigeration-facility heat exchanger 331 and heat pumped up by the outdoor heat exchanger 315 can be used as heat for the indoor heat exchanger 322, thereby increasing the heating capacity when the amount of heat exhausted from the refrigeration-facility unit 330 is insufficient.

In this case, when an outside air temperature becomes lower than an interior temperature of the refrigeration-facility unit 330, the refrigeration system 301 cannot pump heat from the outdoor heat exchanger 315 unless an evaporation temperature of the refrigeration-facility unit 330 is lowered. On the other hand, in the refrigeration system 301, when the evaporation temperature of the refrigeration-facility unit 330 is lowered, it will become lower than a specified temperature, a thermal cycle will be short, and a short-cycle operation will occur, which may lead to a freezing accident of a product.

In the present embodiment, therefore, the opening degree of the outlet-side refrigeration-facility pressure adjustment mechanism 333 is controlled to balance a pressure with the refrigerant sent from the outdoor heat exchanger 315, whereby it is possible to avoid the above-described inconvenience.

Next, an operation will be described in a case where a large capacity is required in the refrigeration-facility unit 330 but a heat quantity for heating is not required.

FIG. 23 is a circuit diagram of the refrigeration system 301 showing an operation when a large capacity is required in the refrigeration-facility unit 330 but a heat quantity for heating is not required. A flow of the refrigerant is indicated by arrows in the drawing.

As shown in FIG. 23, when a large capacity is required in the refrigeration-facility unit 30 but a heat quantity for heating is not required, the first cooling valve 351, the second cooling valve 355, the first heating valve 352, and the second heating valve 357 are opened, and the refrigerant return valve and the third cooling valve 356 are closed.

In this state, the low-stage compressor 311 and each of the high-stage compressors 312 are driven, whereby the refrigerant compressed by the low-stage compressor 311 is sent to each of the high-stage compressors 312, further compressed by each of the high-stage compressor 312, and discharged toward the oil separator 314.

The refrigerant passing through the oil separator 314 is sent to the outdoor heat exchanger 315 through the first cooling valve 351, and exchanges heat with outside air in the outdoor heat exchanger 315.

The refrigerant after heat exchange is sent to the gas-liquid separator 316 through the second cooling valve 355.

On the other hand, the refrigerant passing through the oil separator 314 is sent to the indoor heat exchanger 322 through the first heating valve 352, exchanges heat with indoor air in the indoor heat exchanger 322 to heat the indoor air.

The refrigerant subjected to heat exchange in the indoor heat exchanger 322 interflows with the refrigerant sent from the outdoor heat exchanger 315 through the second heating valve 357, and is sent to the gas-liquid separator 316.

The refrigerant from the gas-liquid separator 316 is sent to the refrigeration-facility heat exchanger 331 through the inlet-side refrigeration-facility expansion mechanism 332. The refrigerant, which cools the refrigeration-facility unit 330, and the refrigerant subjected to heat exchange in the refrigeration-facility heat exchanger 331 is returned to the low-stage compressor 311 through the outlet-side refrigeration-facility pressure adjustment mechanism 333.

On the other hand, some of the refrigerant from the gas-liquid separator 316 is sent to the outdoor heat exchanger 315 through the refrigerant return expansion mechanism 358, and is returned to the low-stage compressor 311 after being subjected to heat exchange in the outdoor heat exchanger 315.

Thus, during the heating operation, the exhaust heat from the refrigeration-facility unit 330 can be radiated by the outdoor heat exchanger 315 and the indoor heat exchanger 322, whereby the cooling capacity of the refrigeration-facility unit 330 can be increased, and frost adhering to the outdoor heat exchanger 315 can be removed.

In the present embodiment, the gas refrigerant return pipe 360 is provided to send the gas refrigerant from the gas-liquid separator 316 to the suction side of the accumulator 313. Then, in the refrigeration system 301, the return amount of the gas refrigerant from the gas-liquid separator 316 is controlled by control of the opening degree of the gas refrigerant flow-rate control valve 361, whereby a differential pressure of the refrigerant sent to the indoor heat exchanger 322 can be generated.

Thus, the refrigeration system 301 can control the pressure by adding a specified value to the evaporation temperature of the indoor heat exchanger 322 having a high evaporation temperature. Therefore, in the refrigeration system 301, it is possible to improve efficiency of an air conditioning temperature zone, which is a weak point, using carbon dioxide (R744), a natural refrigerant with high environmental preservation characteristics, and to improve the efficiency of the refrigeration system as a whole.

As described above, the accumulator 313 stores a predetermined amount of the refrigeration oil sent out from the low-stage compressor 311 and the refrigeration oil sent out from the oil separator 314. Then, in the refrigeration system 301, the refrigeration oil is evenly sent out to each of the high-stage compressors 312 through each of the suction pipes 364, together with the gas refrigerant. Specifically, the refrigeration oil stored in the accumulator 313 is sucked into each of the suction holes 425 by the flow of the gas refrigerant, which flows from the accumulator 313 to the tip 423, out of the refrigerant flowing with the operation of the refrigeration system 301. Then, the refrigeration oil sucked into each of the suction holes 425 is sucked into the suction side of each of the high-stage compressors 312 through each of the suction pipes 364, by the flow of the gas refrigerant flowing through the suction pipes 364.

Thus, the refrigeration system 301 can stably supply the refrigeration oil to each of the high-stage compressors 312. In the refrigeration system 301, it is not necessary to provide a refrigeration oil separator such as an oil separator individually for each of the high-stage compressors 312, and the manufacturing costs can be reduced.

Each of the suction pipes 364 has the same entire length in the longitudinal direction. Each of the one ends 422 is formed to have substantially the same number of times of bending and a bend R. Furthermore, the suction holes 425, which are provided in the suction pipes 364, respectively, are formed to have substantially the same dimension.

Thus, the gas refrigerant sucked into each of the suction pipes 364 flows through each of the suction pipes 364 at substantially the same flow velocity, and is sucked into each of the high-stage compressors 312.

Therefore, in the refrigeration system 301, the refrigeration oil stored in the accumulator 313 can be sent with the equivalent amount to each of the high-stage compressors 312, together with the gas refrigerant, and the refrigeration oil can be evenly distributed to each of the high-stage compressors 312.

4-3. Effects

As described above, according to the present embodiment, the refrigeration system 301 includes the accumulator 313 to which the pipes provided in the low-stage compressor 311 and the plurality of high-stage compressors 312, respectively, are connected. The accumulator 313 includes the accumulator body 400, the one end 422 of the suction pipe 364 is housed inside the accumulator body 400. The one end 422 is provided with the suction hole 425, which sucks the refrigeration oil and the refrigerant liquid stored inside the accumulator body 400, below the tip 423 of the one end 422. The other end 426 of the oil supply pipe 366 is housed inside the accumulator body 400, and the oil supply pipe 366 is provided with the oil supply motor-operated valve 369 that opens and closes the oil supply pipe 366. Then, the accumulator body 400 is supplied with the refrigeration oil from the oil separator 314 by opening and closing of the oil supply motor-operated valve 369. Thus, the accumulator body 400 stores the refrigeration oil in an amount such that the oil level W is located between the tip 423 and the suction hole 425 in the height direction of the accumulator 313.

Thus, the accumulator 313 stores the refrigeration oil sent out to each of the high-stage compressors 312 at a predetermined amount. Therefore, the refrigeration system 301 can stably send the refrigeration oil to each of the high-stage compressors 312 from the accumulator 313.

As in the present embodiment, each of the suction pipes 364 has the same length, and the one end 422 of each of the suction pipes 364 has the same shape. Then, upper ends of the suction pipes 364 are spaced apart from the bottom surface 405 of the accumulator body 400 and are disposed at the same height, and the refrigeration oil is supplied with the equivalent amount to each of the high-stage compressors 312 through each of the suction pipes 364.

Thus, in the accumulator 313, the equivalent amount of gas refrigerant is sucked into each of the suction pipes 364, and the flow velocity of the gas refrigerant is constant. In the accumulator 313, the equivalent amount of refrigeration oil is sucked into each of the suction pipes 364 together with the gas refrigerant.

Therefore, the refrigeration system 301 can evenly distribute the refrigeration oil to each of the high-stage compressors 312.

As in the present embodiment, the oil level sensor 430 is provided in the accumulator body 400 to detect the position of the oil level W, and the other end 426 of the oil supply pipe 366 is housed inside the accumulator body 400. The oil supply motor-operated valve 369 is provided in the oil supply pipe 366 to open and close the oil supply pipe 366. In the refrigeration system 301, the oil supply motor-operated valve 369 may be opened and closed based on the detection result of the oil level sensor 430, and thus the refrigeration oil may be supplied to the inside of the accumulator body 400 from the oil separator 314 through the oil supply pipe 366.

Thus, in the refrigeration system 301, it is possible to manage the amount of refrigeration oil stored in the accumulator 313 and returned to the plurality of high-stage compressors 312 with one oil level sensor 430. Therefore, the refrigeration system 301 can maintain the amount of refrigeration oil returned to the plurality of high-stage compressors 312 at a predetermined amount. In the refrigeration system 301, there is no need to attach a sensor relating to the amount of refrigeration oil to each of the plurality of high-stage compressors 312, and thus the manufacturing costs can be reduced.

As in the present embodiment, the accumulator 313 may be configured such that the refrigerant and the refrigeration oil discharged from the discharge pipe 362 collides toward the top surface 403.

Thus, the accumulator 313 can efficiently store the refrigeration oil on the bottom surface 405 side of the accumulator 313. Therefore, the accumulator 313 can maintain the amount of refrigeration oil stored in the accumulator 313 at a predetermined amount.

As in the present embodiment, the bent portion 424 and the suction hole 425 may be disposed at positions spaced at a predetermined distance from the bottom surface 405 side. The bottom surface 405 may be formed in a downwardly convex spherical shape.

Thus, contaminants such as metal powder and sludge are retained below the bent portion 424 and are prevented from entering the suction hole 425. Therefore, the refrigeration system 301 prevents the contaminants from being sent to the plurality of high-stage compressors 312.

Fifth Embodiment

Hereinafter, a fifth embodiment will be described with reference to FIG. 24.

FIG. 24 is a longitudinal cross-sectional view showing an accumulator 413 according to a fifth embodiment. FIG. 24 shows a cross section taken along a line passing through a center of the accumulator 413 in a plan view and cutting along in an up-down direction of the accumulator 413. In FIG. 24, for the convenience of description, an oil level W is indicated by a two-dot chain line. In FIG. 24, the same components as those in FIG. 20 are denoted by the same reference numerals and will not be described.

The refrigeration system 301 according to the second embodiment differs from the refrigeration system 301 according to the first embodiment at least in that the accumulator 413 is used instead of the accumulator 13.

Hereinafter, the accumulator 413 will be described, but the same components similar to those of the accumulator 13 will not be described.

As shown in FIG. 24, the accumulator 413 includes an accumulator body 500.

A top surface 503 and a bottom surface 505 of the accumulator body 500 are formed as flat surfaces in a direction intersecting a longitudinal direction of the accumulator body 200.

In the accumulator 413, the other end 420 of a discharge pipe 362 is disposed in an internal space S such that a tip 421 faces a side surface 401. Similarly, the other end 426 of an oil supply pipe 366 is disposed such that a tip 427 faces the side surface 401.

In the present embodiment, the other end 420 of the discharge pipe 362 extends downwards and is then bent toward the side surface 401, so that the entire end is formed in an L-shape and disposed in the internal space S. Similarly, the other end 426 of an oil supply pipe 366 extends downwards and is then bent into an L-shape toward the side surface 401, so that the entire end is formed in the L-shape and disposed in the internal space S. Thus, an opening provided at each of the tips 421 and 427 is disposed to face the side surface 401.

In addition, the other end 420 and the other end 426 may be formed in another shape without being limited to the L-shape, as long as the tip 421 and the tip 427 face the side surface 401.

FIG. 25 is a transverse cross-sectional view of the accumulator 413 showing a flow of refrigeration oil. FIG. 25 shows a transverse cross-sectional view perpendicular to the longitudinal direction of the accumulator 413 and at a position intersecting the discharge pipe 362. For the convenience of description, the suction pipe 364 and the oil level sensor 430 are not shown in FIG. 25.

As shown in FIG. 25, a refrigerant and refrigeration oil discharged from the tip 421 of the discharge pipe 362 collide toward the side surface 401. Vaporous refrigeration oil in the refrigeration oil is liquefied by collision with the side surface 401, flows along the side surface 401, and is stored in a lower part of the internal space S. Similarly, the refrigeration oil discharged from a tip 427 of an oil supply pipe 366 is liquefied by collision with the side surface 401, flows along the side surface 401, and is stored in a lower part of the internal space S.

Thus, the accumulator 413 can efficiently store the refrigeration oil on the bottom surface 405 side of the accumulator 413. Therefore, the accumulator 413 can maintain the amount of refrigeration oil stored in the accumulator 413 at a predetermined amount.

Other Embodiments

As described above, the first embodiment to the fifth embodiment have been described as examples of techniques disclosed in the present application. However, the techniques of the present disclosure are not limited thereto, and are also applicable to embodiments where changes, replacements, additions, omissions, etc., are appropriately made. In addition, it is also possible to combine the components described in the first embodiment to create new embodiments.

Hereinafter, other embodiments will be described as examples.

FIG. 26 is a longitudinal cross-sectional view showing an accumulator 513 according to a modification of the present disclosure. FIG. 26 shows a cross section taken along a line passing through a center of the accumulator 513 in a plan view and cutting along in an up-down direction of the accumulator 513. In FIG. 26, for the convenience of description, an oil level W is indicated by a two-dot chain line. In FIG. 26, the same components as those in FIG. 20 are denoted by the same reference numerals and will not be described.

In the fourth and fifth embodiments, the discharge pipe 362, the suction pipe 364, and the oil supply pipe 366 penetrating the top surface 403 or 503 have been described. However, the present invention is not limited thereto, and the discharge pipe 362, the suction pipe 364, and the oil supply pipe 366 may be connected to the accumulator 513 by penetrating the side surface 401, as shown in FIG. 26, for example. In this case, the discharge pipe 362, the suction pipe 364, and the oil supply pipe 366 are bent toward the top surface 403 in the internal space S.

Note that the above-described embodiments are intended to illustrate the technology of the present disclosure, and thus various modifications, substitutions, additions, omissions, and the like can be made within the claims or equivalents thereof.

Supplementary Note

The following techniques are disclosed according to the above-described embodiments.

(Technique 1) A refrigeration system including: a refrigeration cycle circuit that connects an outdoor unit including a low-stage compressor, a high-stage compressor, an outdoor heat exchanger, an accumulator disposed between the low-stage compressor and the high-stage compressor, and an oil separator disposed on a discharge side of the high-stage compressor, an indoor unit including an indoor heat exchanger, and a refrigeration-facility unit including a refrigeration-facility heat exchanger; an oil supply circuit that supplies oil from the oil separator to the high-stage compressor through the accumulator; and an oil supply circuit that supplies oil from the accumulator to the low-stage compressor.

According to the above described configuration, oil can be respectively supplied to the high-stage compressor or the low-stage compressor, which have different pressures. In addition, since the oil discharged to the outside of the outdoor unit returns to the accumulator, the oil accumulated in the oil separator also returns to the accumulator, and thus the oil supply circuit can be simplified. Furthermore, since oil is supplied to the low-stage compressor from the accumulator being in a medium pressure state, the oil can be easily supplied to low-stage compressor being in a low pressure state.

Therefore, oil can be evenly supplied to the high-stage compressor and the low-stage compressor which have different pressures, and a breakdown of the compressor due to wear can be prevented.

(Technique 2) A refrigeration system including: a refrigeration cycle circuit that connects an outdoor unit including a low-stage compressor, a high-stage compressor, an outdoor heat exchanger, an accumulator disposed between the low-stage compressor and the high-stage compressor, and an oil separator disposed on a discharge side of the high-stage compressor, an indoor unit including an indoor heat exchanger, and a refrigeration-facility unit including a refrigeration-facility heat exchanger; a high-stage oil supply circuit that supplies oil from the oil separator to the high-stage compressor through the accumulator; and a low-stage side oil supply circuit that supplies oil from the oil separator to the low-stage compressor.

According to the above-described configuration, oil can be respectively supplied to the high-stage compressor or the low-stage compressor, which have different pressures. In addition, since the oil discharged to the outside of the outdoor unit returns to the accumulator, the oil accumulated in the oil separator also returns to the accumulator, and thus the oil supply circuit can be simplified. Furthermore, since oil is supplied to the low-stage compressor from the accumulator being in a medium pressure state, the oil can be easily supplied to low-stage compressor being in a low pressure state.

(Technique 3) The refrigeration system according to Technique 1 or 2, in which the accumulator is provided with a detection means for detecting an amount of oil in the accumulator.

According to the above-described configuration, the oil amount in the accumulator can be detected by the detection means, the oil can be evenly supplied to the high-stage compressor and the low-stage compressor according to the oil amount in the accumulator, and thus the breakdown of the compressors due to wear can be prevented.

(Technique 4) The refrigeration system according to Technique 1 or 2, in which a high-stage throttling mechanism is provided in the oil supply circuit that supplies the oil from the oil separator to the high-stage compressor through the accumulator.

According to the above-described configuration, the opening degree of the high-stage throttling mechanism is controlled, and thus the oil amount supplied to the high-stage compressor can be adjusted.

(Technique 5) The refrigeration system according to Technique 1, in which a low-stage throttling mechanism is provided in the oil supply circuit that supplies the oil from the accumulator to the low-stage compressor.

According to the above-described configuration, the opening degree of the low-stage throttling mechanism is controlled, and thus the oil amount supplied to the low-stage compressor can be adjusted.

(Technique 6) The refrigeration system according to Technique 2, in which a low-stage throttling mechanism is provided in the low-stage side oil supply circuit that supplies the oil from the oil separator to the low-stage compressor.

According to the above-described configuration, the opening degree of the low-stage throttling mechanism is controlled, and thus the oil amount supplied to the low-stage compressor can be adjusted.

(Technique 7) The refrigeration system according to Technique 3, in which a high-stage throttling mechanism provided in the oil supply circuit that supplies the oil to the high-stage compressor through the accumulator and a low-stage throttling mechanism provided in the oil supply circuit that supplies the oil from the accumulator to the low-stage compressor are configured by a motor-operated valve, and the refrigeration system comprises a control device that controls an opening degree of the motor-operated valve based on the amount of oil detected by the detection means for detecting the amount of oil in the accumulator.

According to the above-described configuration, the control device controls the opening degree of the high-stage motor-operated valve and the low-stage motor-operated valve based on the oil amount in the accumulator detected by the detection means, and thus the oil can be respectively supplied to the high-stage compressor or the low-stage compressor, which have different pressures, with the appropriate amount. Accordingly, the oil can be evenly supplied to the high-stage compressor 12 and the low-stage compressor, which have different pressures, and the breakdown of the compressors due to wear can be prevented.

(Technique 8) A refrigeration system including a refrigeration circuit including a plurality of compressors, a heat source-side heat exchanger, a plurality of utilization-side heat exchangers, and a gas-liquid separator, the plurality of compressors include a low-stage compressor, and a high-stage compressor, the plurality of utilization-side heat exchangers include a first utilization-side heat exchanger, and a second utilization-side heat exchanger having a refrigerant evaporation temperature lower than that of the first utilization-side heat exchanger, the refrigeration circuit is provided with a switching mechanism that causes a refrigerant, which is discharged from the high-stage compressor and flows through at least one of the heat source-side heat exchanger and the first utilization-side heat exchanger, to flow to the gas-liquid separator, and throttling mechanisms are provided between the heat source-side heat exchanger and the gas-liquid separator and between the first utilization-side heat exchanger and the gas-liquid separator to regulate a pressure of the refrigerant.

Thus, the refrigeration system can be formed with the refrigeration circuit with a simple configuration, and can send the refrigerant to the heat exchanger functioning as an evaporator through the gas-liquid separator in both the case of performing the cooling operation and the case of performing the heating operation. Therefore, the refrigeration system can improve the refrigeration capacity with a simple circuit configuration.

(Technique 9) The refrigeration system according to Technique 8, in which the switching mechanism includes pipes that connect the heat source-side heat exchanger, the first utilization-side heat exchanger, the second utilization-side heat exchanger, and the gas-liquid separator to one another, and a valve body is provided in each of the pipes to regulate a flow of the refrigerant.

Thus, in the refrigeration system, the refrigerant subjected to heat exchange by the gas-liquid separator can be sent to any one of the heat source-side heat exchanger, the first utilization-side heat exchanger, and the second utilization-side heat exchanger. Therefore, the refrigeration system can increase the refrigeration capacity.

(Technique 10) The refrigeration system according to Technique 9, in which the switching mechanism includes, as the valve body, a check valve, and the throttling mechanism.

Thus, in the refrigeration system, the refrigerant subjected to heat exchange by the gas-liquid separator can be sent to any one of the utilization-side heat exchanger, the first utilization-side heat exchanger, and the second utilization-side heat exchanger. Therefore, the refrigeration system can increase the refrigeration capacity.

(Technique 11) The refrigeration system according to any one of Techniques 8 to 10, in which the refrigeration circuit includes another switching mechanism that switches to any one of: a flow path in which the refrigerant discharged from the high-stage compressor flows to the heat source-side heat exchanger, a flow path in which the refrigerant discharged from the high-stage compressor flows to the first utilization-side heat exchanger, and a flow path in which the refrigerant discharged from the high-stage compressor flows to both the heat source-side heat exchanger and the first utilization-side heat exchanger.

Thus, the refrigeration system can include the refrigeration circuit with simpler configuration. In addition, the refrigeration system can switch the operation without stopping the compressor.

(Technique 12) The refrigeration system according to Technique 11, in which the another switching mechanism includes a first cooling valve that is a valve body located between a discharge side of the high-stage compressor and the heat source-side heat exchanger, and an outdoor refrigerant return valve that is a valve body located downstream of the first cooling valve and between the discharge side of the high-stage compressor and a suction side of the low-stage compressor.

Thus, the refrigeration system can switch between any one of a flow path in which the refrigerant discharged from the high-stage compressor flows to the heat source-side heat exchanger, a flow path in which the refrigerant discharged from the high-stage compressor flows to the first utilization-side heat exchanger, a flow path in which the refrigerant discharged from the high-stage compressor flows to both the outdoor heat exchanger and the first utilization-side heat exchanger. Therefore, the refrigeration system can include the refrigeration circuit with a simpler configuration.

(Technique 13) The refrigeration system according to any one of Techniques 8 to 12, in which the refrigeration system further includes a control unit that controls each component of the refrigeration circuit, the control unit includes an operation portion that can be operated by a worker, the control unit includes, as operation modes of the refrigeration circuit, a first operation mode in which a refrigerant flowing through the first utilization-side heat exchanger and the second utilization-side heat exchanger is regulated at a predetermined temperature, and a second operation mode in which an operation is performed according to an operation of an external device connected to the refrigeration circuit, and the control unit switches between the first operation mode and the second operation mode according to an operation on the operation portion.

Thus, the refrigeration system can switch between the first operation mode and the second operation mode according to the operation on the operation portion. Therefore, in the refrigeration system, the worker can easily switch between the operation modes.

(Technique 14) The refrigeration system according to Technique 13, in which the control unit includes a plurality of second operation modes, and switches between the second operation modes according to the operation on the operation portion.

Thus, in the refrigeration system, the worker can perform the work related to the refrigerant recovery/vacuuming and the refrigerant filling according to the operation on the operation portion. Therefore, in the refrigeration system, the worker can easily perform the work related to the refrigerant recovery/vacuuming and the refrigerant filling.

(Technique 15) The refrigeration system according to Technique 13 or 14, in which the control unit includes a display portion that displays a status of the refrigeration circuit in each of the operation modes.

Thus, in the refrigeration system, the worker can perform the work related to the refrigerant recovery/vacuuming and the refrigerant filling according to the operation on the control unit while checking the status of the refrigeration system. Therefore, in the refrigeration system, the worker can easily perform the work related to the refrigerant recovery/vacuuming and the refrigerant filling.

(Technique 16) The refrigeration system according to any one of Techniques 8 to 15, in which a connection port is provided between the second utilization-side heat exchanger and a suction side of the low-stage compressor to be connectable to an external device.

Thus, the refrigeration system can improve workability when the external device is connected to the refrigeration system.

(Technique 17) An accumulator in which suction pipes serving as pipes provided on suction sides of a plurality of compressors, respectively, are all connected to an accumulator body which is a container having an internal space for separating a refrigerant into gas and liquid, in which, one end of each of the suction pipes is housed inside the accumulator body, the one end of each of the suction pipes is provided with a tip through which a gas refrigerant is sucked in and a suction hole located below the tip to suck refrigeration oil and refrigerant liquid stored inside the accumulator body, the other end of an oil supply pipe with one end connected to an oil separator is housed inside the accumulator body, the oil supply pipe is provided with an opening/closing device that opens and closes the oil supply pipe, the refrigeration oil is supplied from the oil separator by opening and closing of the opening/closing device, and thus the refrigeration oil is stored in the accumulator body in an amount such that an oil level of the refrigeration oil is located between the tip and the suction hole, and the refrigeration oil sucked from each of the suction holes is supplied to each of the compressors through each of the suction pipes.

According to the above-described configuration, the accumulator stores the refrigeration oil sent out to each of the compressors at a predetermined amount. Therefore, each of the compressors can be stably supplied with the refrigeration oil from the accumulator.

(Technique 18) The accumulator according to Technique 17, in which each of the plurality of suction pipes has the same length, the end of each of the plurality of suction pipes has the same shape, the tip of each of the plurality of suction pipes is spaced apart from a bottom surface of the accumulator body and is disposed at the same height, and the refrigeration oil sucked from each of the suction holes is supplied with an equivalent amount to each of the compressors through each of the suction pipes.

According to the above-described configuration, in the accumulator, the equivalent amount of gas refrigerant is sucked into each of the suction pipes, and the flow velocity of the gas refrigerant is constant. In the accumulator, the equivalent amount of refrigeration oil is sucked into each of the suction pipes together with the gas refrigerant.

Therefore, the refrigeration can be evenly supplied to each of the compressors from the accumulator.

(Technique 19) The accumulator according to Technique 17 or 18, in which an oil level sensor is provided in the accumulator body to detect a position of the oil level, and the opening/closing device is opened and closed based on a detection result of the oil level sensor, and the refrigeration oil is supplied to an inside of the accumulator body from the oil separator through the oil supply pipe.

According to the above-described configuration, in the accumulator, it is possible to manage the amount of refrigeration oil stored in the accumulator and returned to the plurality of compressors with one oil level sensor. Therefore, the accumulator can maintain the amount of refrigeration oil returned to the plurality of compressors at a predetermined amount. In addition, there is no need to attach a sensor relating to the amount of refrigeration oil to each of the plurality of compressors, and thus the manufacturing costs can be reduced.

(Technique 20) The accumulator according to Technique 19, in which at least one of the pipes is a discharge pipe connected to a discharge side of each of the compressors, and supplies the refrigeration oil and the refrigerant to the inside of the accumulator body, and an end of the discharge pipe and the other end of the oil supply pipe are disposed spaced apart from a wall surface at a distance that allows the refrigeration oil and the refrigerant supplied from the discharge pipe and the oil supply pipe to collide with the wall surface of the accumulator body and to be liquified.

According to the above-described configuration, the accumulator can efficiently store the refrigeration oil on the bottom surface side of the accumulator.

Therefore, the accumulator can maintain the amount of refrigeration oil stored in the accumulator at a predetermined amount.

(Technique 21) The accumulator according to any one of Techniques 17 to 20, in which the suction hole is provided at a position spaced apart from the bottom surface of the accumulator body.

According to the above-described configuration, contaminants such as metal powder and sludge are retained below the suction hole in the accumulator body and are prevented from entering the suction hole. Therefore, the accumulator prevents the contaminants from being sent to the plurality of compressors.

(Technique 22) A refrigeration system including: the accumulator according to any one of Techniques 17 or 21; and a refrigeration cycle circuit that connects a heat source unit including the compressor and the heat source-side heat exchanger, and a utilization-side heat exchanger unit including a utilization-side heat exchanger.

According to the above-described configuration, the refrigeration system obtains the same effect as that of the above-described accumulator.

INDUSTRIAL APPLICABILITY

A first aspect of the present disclosure can be suitably used as a refrigeration system capable of supplying oil evenly to a plurality of compressors with different pressures.

A second aspect of the present disclosure can be suitably used as a refrigeration system capable of improving efficiency of an air conditioning temperature zone using a natural refrigerant, and improving the efficiency of the entire system.

A third aspect of the present disclosure is applicable to a refrigeration system. Specifically, the present disclosure is applicable to a commercial refrigeration system including an outdoor unit, an indoor unit, and a refrigeration-facility unit.

REFERENCE SIGNS LIST

• • 1 refrigeration system
  • 10 outdoor unit
  • 11 low-stage compressor
  • 12 high-stage compressor
  • 13 accumulator
  • 14 oil separator
  • 15 outdoor heat exchanger
  • 16 gas-liquid separator
  • 20 indoor unit
  • 21 indoor expansion mechanism
  • 22 indoor heat exchanger
  • 23 on-off valve
  • 30 refrigeration-facility unit
  • 31 refrigeration-facility heat exchanger
  • 32 inlet-side refrigeration-facility expansion mechanism
  • 33 outlet-side refrigeration-facility expansion mechanism
  • 40 refrigerant pipe
  • 41 first heating pipe
  • 42 first outdoor return pipe
  • 43 second cooling pipe
  • 44 second heating pipe
  • 45 second outdoor return pipe
  • 50 first switching mechanism
  • 51 first cooling valve
  • 52 first heating valve
  • 53 outdoor refrigerant return valve
  • 54 second switching mechanism
  • 55 second cooling valve
  • 56 third cooling valve
  • 57 second heating valve
  • 58 refrigerant return expansion mechanism
  • 59 check valve
  • 60 gas refrigerant return pipe
  • 61 gas refrigerant return expansion mechanism
  • 62 oil supply circuit
  • 63 high-stage motor-operated valve
  • 64 oil supply circuit
  • 65 low-stage motor-operated valve
  • 66 oil level sensor
  • 70 refrigeration-facility-unit control device
  • 71 refrigeration-facility-unit control unit
  • 80 indoor-unit control device
  • 81 indoor-unit control unit
  • 90 control device
  • 91 control unit
  • 101 refrigeration system
  • 102 refrigeration circuit
  • 110 outdoor unit
  • 111 low-stage compressor
  • 112 high-stage compressor
  • 113 accumulator
  • 114 oil separator
  • 115 outdoor heat exchanger (heat source-side heat exchanger)
  • 116 gas-liquid separator
  • 118, 128, 138 blower
  • 120 indoor unit
  • 121 indoor expansion mechanism
  • 122 indoor heat exchanger (first utilization-side heat exchanger)
  • 123 on-off valve
  • 127 space temperature sensor
  • 130 refrigeration-facility unit
  • 131 inlet-side refrigeration-facility expansion mechanism
  • 132 refrigeration-facility heat exchanger (second utilization-side heat exchanger)
  • 133 outlet-side refrigeration-facility pressure regulation mechanism
  • 137 interior temperature sensor
  • 140 pipe
  • 141 first heating pipe
  • 142 first outdoor return pipe
  • 150 first switching mechanism (another switching mechanism)
  • 151 first cooling valve
  • 152 first heating valve
  • 153 outdoor refrigerant return valve
  • 154 second switching mechanism (switching mechanism)
  • 155 throttling mechanism
  • 158 refrigerant return expansion mechanism
  • 159 check valve
  • 160 gas refrigerant return pipe
  • 161 gas refrigerant flow-rate control valve
  • 164 internal heat exchanger
  • 165 liquid refrigerant flow-rate control valve
  • 166 connection pipe
  • 171 pipe
  • 172 pipe
  • 173 first pipe
  • 174 second pipe
  • 175 third pipe
  • 176 fourth pipe
  • 177 pipe
  • 178 pipe
  • 179 pipe
  • 180 refrigerant pressure sensor
  • 182 refrigerant temperature sensor
  • 190 service valve
  • 192 pipe connection port
  • 194 pipe connection port
  • 196 external connection port
  • 200 control device
  • 201 control unit
  • 201a operation control unit
  • 201b determination unit
  • 203 storage unit
  • 203a setting data
  • 205 outdoor unit I/F
  • 206 outdoor-unit communication portion
  • 210 indoor-unit control device
  • 211 indoor-unit control unit
  • 213 indoor-unit storage unit
  • 215 indoor unit I/F
  • 220 refrigeration-facility-unit control device
  • 221 refrigeration-facility-unit control unit
  • 223 refrigeration-facility-unit storage unit
  • 225 refrigeration-facility unit I/F
  • 232 operation panel
  • 234 display panel
  • 250 refrigerant recovery device
  • 252 vacuuming unit
  • 254 refrigerant filling unit
  • 256 connection pipe
  • A, B, C, D connection portion
  • 301 refrigeration system
  • 310 outdoor unit
  • 311 low-stage compressor
  • 312 high-stage compressor
  • 313, 413, 513 accumulator
  • 314 oil separator
  • 315, 322, 331 heat exchanger
  • 362 discharge pipe
  • 364 suction pipe
  • 366 oil supply pipe
  • 369 oil supply motor-operated valve (opening/closing device)
  • 400, 500 accumulator body
  • 420,422, 426 end
  • 421, 423, 427 tip
  • 424 bent portion
  • 425 suction hole
  • 430 oil level sensor
  • W oil level