TEMPERATURE ADJUSTMENT SYSTEM

Description

CROSS-REFERENCE TO RELATED APPLICATION

The present application claims priority to International Application No. PCT/JP2023/020310, filed May 31, 2023, the entire contents of which are incorporated herein by reference.

FIELD

The present disclosure relates to a temperature adjustment system.

BACKGROUND

A heat pump air conditioner may include a refrigerant circuit using a flammable HC refrigerant, a water circulation circuit including an indoor heat exchanger, and a plate-type heat exchanger that exchanges heat between the refrigerant circuit and the water circulation circuit. In such a heat pump air conditioner, when the heat pump air conditioner is used under an environment where an outdoor temperature satisfies a specific condition, there is a risk that the plate-type heat exchanger could freeze and break down.

Patent Literature 1 (JP 2001-201107 A) discloses a heat pump device that drains water in a plate-type heat exchanger and a water circulation circuit by manually opening a water draining unit installed in the water circulation circuit when there is a possibility that the plate-type heat exchanger freezes.

SUMMARY

A temperature adjustment system according to a first aspect is a temperature adjustment system that sends temperature-adjusted water to a first water pipe that is a utilization-side water pipe, and includes a first unit. The first unit includes a refrigerant circuit through which a refrigerant that is highly flammable is circulatable, a second water pipe, and a first heat exchanger. The second water pipe is a heat source-side water pipe connected to the first water pipe. The first heat exchanger exchanges heat between the water and the refrigerant. The first unit further includes an automatic on-off valve that automatically releases the water in the first heat exchanger at a low temperature.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic configuration diagram of a temperature adjustment system.

FIG. 2 is a block diagram of a control unit.

FIG. 3 is a perspective view of a first unit as viewed from a bottom surface (lower side).

FIG. 4 is a flowchart showing an operation of the control unit.

FIG. 5 is a flowchart showing an operation of the control unit according to Modification D.

DETAILED DESCRIPTION

First Embodiment

(1) Overall Configuration

FIG. 1 is a schematic configuration diagram of a temperature adjustment system 1 according to an embodiment. The temperature adjustment system 1 is a refrigeration cycle device that sends temperature-adjusted water to a first water pipe 201 that is a utilization-side water pipe. The temperature adjustment system 1 includes a first unit 400 and a control unit 300. The first unit 400 includes a refrigerant circuit 100, a second water pipe 202 that is a heat source-side water pipe connected to the first water pipe 201, an automatic on-off valve 230, and a casing 410. A water circuit 200 is configured by connecting the first water pipe 201 and the second water pipe 202 via connection portions 200a and 200b. The casing 410 accommodates the refrigerant circuit 100, the second water pipe 202, and a first heat exchanger 120.

The temperature adjustment system 1 performs a cooling operation and a heating operation. Specifically, the temperature adjustment system 1 causes a refrigerant charged in the refrigerant circuit 100 to perform a refrigeration cycle, heats or cools the water charged in the water circuit 200, and executes the cooling operation and the heating operation of an air conditioning target space on a utilization side by using the water.

(2) Detailed Configuration

(2-1) Refrigerant Circuit

The refrigerant circuit 100 includes a compressor 110, the first heat exchanger 120, a second heat exchanger 130, a switching mechanism 140, and an expansion mechanism 150. Each part of the refrigerant circuit 100 is connected by a pipe. The refrigerant circuit 100 is filled with a highly flammable refrigerant. The highly flammable refrigerant is a refrigerant having high flammability classified as high flammability (A3) in ISO817. In the present embodiment, the refrigerant is R290 (propane).

(2-1-1) Compressor

The compressor 110 compresses a low-pressure refrigerant in the refrigeration cycle to a high pressure by using a compression mechanism. The compressor 110 includes a suction portion 110a and a discharge portion 110b.

The suction portion 110a sucks a low-pressure refrigerant from the refrigerant circuit 100 and supplies the refrigerant to the compression mechanism. The discharge portion 110b discharges the refrigerant compressed to a high pressure by the compression mechanism to the refrigerant circuit 100. A compression capacity of the compressor 110 is controlled by the control unit 300.

(2-1-2) First Heat Exchanger

The first heat exchanger 120 exchanges heat between the refrigerant charged in the refrigerant circuit 100 and the water charged in the water circuit 200. The first heat exchanger 120 includes a refrigerant flow path 121 and a water flow path 122.

The refrigerant flowing through the refrigerant circuit 100 passes through the refrigerant flow path 121. The refrigerant flow path 121 includes a first end 121a and a second end 121b. The first end 121a and the second end 121b function as an inlet for the refrigerant to the refrigerant flow path 121 and an outlet for the refrigerant from the refrigerant flow path 121.

Water flowing through the water circuit 200 passes through the water flow path 122. The refrigerant flow path 121 has a first end 122a and a second end 122b. The first end 122a functions as an outlet for water from the water flow path 122. The second end 122b functions as an inlet for water to the water flow path 122. In the water flow path 122, a first temperature sensor 123 that detects a temperature of water flowing through the first end 122a and a second temperature sensor 124 that detects a temperature of water flowing through the second end 122b are disposed. The first temperature sensor 123 and the second temperature sensor 124 are, for example, thermistors.

In an implementation, the first heat exchanger 120 is a plate-like heat exchanger.

(2-1-3) Second Heat Exchanger

The second heat exchanger 130 exchanges heat between the refrigerant charged in the refrigerant circuit 100 and air at the installation location of the second heat exchanger 130. The second heat exchanger 130 has a first end 130a and a second end 130b. The first end 130a and the second end 130b function as an inlet for the refrigerant to the second heat exchanger 130 and an outlet for the refrigerant from the second heat exchanger 130. A third temperature sensor 131 that detects the temperature of outside air that has passed through second heat exchanger 130 is disposed in the second heat exchanger 130. The third temperature sensor 131 is, for example, a thermistor.

The second heat exchanger 130 is installed outside the air conditioning target space such as outdoors. In an implementation, the second heat exchanger 130 is a microchannel-like heat exchanger.

(2-1-4) Switching Mechanism

The switching mechanism 140 switches a refrigerant flow direction in the refrigerant circuit 100 between two states. The switching mechanism 140 is a four-way switching valve. The switching mechanism 140 includes a first port P1, a second port P2, a third port P3, and a fourth port P4.

The first port P1 is connected to the discharge portion 110b of the compressor 110. The second port P2 is connected to the second end 130b of the second heat exchanger 130. The third port P3 is connected to the suction portion 110a of the compressor 110. The fourth port P4 is connected to the second end 121b of the refrigerant flow path 121 of the first heat exchanger 120.

The switching mechanism 140 is switched between a first state (state indicated by a solid line in FIG. 1) and a second state (state indicated by a broken line in FIG. 1). In the first state, the switching mechanism 140 causes the first port P1 and the second port P2 to communicate with each other, and causes the third port P3 and the fourth port P4 to communicate with each other. In the second state, the switching mechanism 140 causes the first port P1 and the fourth port P4 to communicate with each other, and causes the second port P2 and the third port P3 to communicate with each other. The state of the switching mechanism 140 is controlled between the first state and the second state by the control unit 300.

(2-1-5) Expansion Mechanism

The expansion mechanism 150 decompresses the refrigerant flowing between the first end 130a of the second heat exchanger 130 and the first end 121a of the refrigerant flow path 121 of the first heat exchanger 120 to a low pressure. One end of the expansion mechanism 150 is connected to the first end 130a of the second heat exchanger 130, and the other end is connected to the first end 121a of the refrigerant flow path 121 of the first heat exchanger 120.

In an implementation, the expansion mechanism 150 is an electric expansion valve. The opening degree of the expansion mechanism 150 is controlled by the control unit 300.

(2-2) Water Circuit

The water circuit 200 includes a pump 210, a third heat exchanger 220, and the automatic on-off valve 230. The water circuit 200 is filled with water that is a heating medium. The water circuit 200 includes the first water pipe 201 that is a utilization-side water pipe, and the second water pipe 202 that is a heat-source-side water pipe connected to the first water pipe 201. The first water pipe 201 and the second water pipe 202 are connected via the connection portions 200a and 200b. Each part of the water circuit 200 is connected by a pipe.

(2-2-1) Pump

The pump 210 circulates water filled in the water circuit 200 in the water circuit 200. The pump 210 includes a suction portion 210a and a discharge portion 210b.

The pump 210 applies a predetermined pressure to the water in the water circuit 200 sucked from the suction portion 210a, and discharges the water from the discharge portion 210b to the water circuit 200 again.

The suction portion 210a is connected to a second end 220b (described below) of the third heat exchanger 220. The discharge portion 210b is connected to the connection portion 200b. The pump 210 is controlled by the control unit 300.

(2-2-2) Third Heat Exchanger

The third heat exchanger 220 is installed in the air conditioning target space and exchanges heat between the water filled in the water circuit 200 and air at the installation location of the third heat exchanger 220. The third heat exchanger 220 has a first end 220a and a second end 220b. The first end 220a functions as an inlet for water flowing into the third heat exchanger 220. The second end 220b functions as an outlet for water flowing out of the third heat exchanger 220. The first end 220a is connected to the connection portion 200a. The second end 220b is connected to the suction portion 210a of the pump 210.

(2-2-3) Automatic On-Off Valve

The automatic on-off valve 230 is provided on a water pipe 203 branched from the water circuit 200 downstream of the first end 122a in the water circuit 200. The automatic on-off valve 230 is disposed inside the casing 410.

The automatic on-off valve 230 is a mechanical on-off valve whose opening degree changes in accordance with the temperature of the water flowing through the first heat exchanger 120, and automatically releases the water in the first heat exchanger 120 at a low temperature. The temperature of the water flowing through the first heat exchanger 120 is the temperature of the water flowing through the second water pipe 202 at the position where the automatic on-off valve 230 is disposed. Here, since the first end 122a and the automatic on-off valve 230 are connected by a short pipe, a temperature difference hardly occurs. Therefore, the temperature of the water flowing through the first heat exchanger 120 is also the temperature of the water flowing out of the first end 122a functioning as the outlet for the water from the water flow path 122.

The automatic on-off valve 230 automatically opens when the temperature of the water flowing through the first heat exchanger 120 falls below a first threshold value, and automatically closes when the temperature of the water flowing through the first heat exchanger 120 exceeds a second threshold value higher than the first threshold value. In the present embodiment, the first threshold value is 4° C., and the second threshold value is 5° C. In this case, the automatic on-off valve 230 starts to open when the temperature of the water flowing through the first heat exchanger 120 is 4° C., and is fully opened when the temperature is lower than 3° C. When the temperature of the water flowing through the first heat exchanger 120 exceeds 5° C., the automatic on-off valve 230 is fully closed.

(2-3) Casing

FIG. 3 is a perspective view of the first unit 400 as viewed from a bottom surface (lower side). In the following description, the “upper side”, “lower side”, “left side”, “right side”, “front side”, and “rear side” respectively denote directions indicated in FIG. 3 unless otherwise specified. These directions indicate directions in a state where the first unit 400 is attached and normally used. In the present embodiment, an up-down direction is a vertical direction.

The first unit 400 includes the casing 410 having a substantially rectangular parallelepiped box shape. The casing 410 accommodates the refrigerant circuit 100, the second water pipe 202, and the first heat exchanger 120. The automatic on-off valve 230 is disposed inside the casing 410.

The casing 410 includes a bottom plate 420 which is a horizontally long substantially rectangular plate-shaped member constituting a bottom surface (lower) of the casing 410. The bottom plate 420 is provided with an opening 430 communicating with the outside of the casing 410. The water released from the automatic on-off valve 230 is configured to be drained to the outside of the casing 410 through the opening 430. Drain water generated in the second heat exchanger 130 is also drained to the outside of the casing 410 through the opening 430. In other words, the opening 430 of the bottom plate 420 serves as a drain port for the water released from the automatic on-off valve 230 and a drain port for the drain water generated in the second heat exchanger 130.

(2-4) Control Unit

FIG. 2 is a block diagram of the control unit 300. The control unit 300 is electrically connected to the compressor 110, the switching mechanism 140, the expansion mechanism 150, the pump 210, the first temperature sensor 123, the second temperature sensor 124, and the third temperature sensor 131 so as to be able to transmit and receive signals. The control unit 300 is configured to acquire information such as an operating state of each device and a measurement value of each sensor. The control unit 300 is configured to control each device of the refrigerant circuit 100 on the basis of the acquired information to cause the refrigerant circuit 100 to perform the refrigeration cycle and implement the cooling operation and the heating operation of the air conditioning target space.

The control unit 300 is implemented by a computer, e.g., the control unit 300 may be a control computer. The control unit 300 includes a control calculation device and a storage device. A processor such as a CPU or a GPU can be used for the control calculation device. The control calculation device reads a program stored in the storage device and performs predetermined calculation processing in accordance with the program. Furthermore, the control calculation device can write calculation results in the storage device and read information stored in the storage device in accordance with the program.

(3) Overall Operation

The control unit 300 is configured to control each device in the cooling operation, the heating operation, and a reverse cycle defrost operation as described below.

(3-1) Cooling Operation

When execution of the cooling operation is instructed to the temperature adjustment system 1, the control unit 300 is configured to cause the compressor 110 and the pump 210 to start operation, to set the switching mechanism 140 to the first state, and to control the opening degree of the expansion mechanism 150.

(3-1-1) Refrigerant Circuit

When the compressor 110 starts the operation, a low-pressure gas refrigerant in the refrigeration cycle is sucked from the suction portion 110a, compressed to a high pressure in the refrigeration cycle, and then discharged from the discharge portion 110b as the gas refrigerant. The high-pressure gas refrigerant that has flowed out of the discharge portion 110b passes through the switching mechanism 140 through the first port P1 and the second port P2 in that order, and flows into the second heat exchanger 130 from the second end 130b. The high-pressure gas refrigerant that has flowed into the second heat exchanger 130 exchanges heat with the air at the installation location of the second heat exchanger 130 to be condensed, and becomes a high-pressure liquid refrigerant to flow out from the first end 130a. In other words, the second heat exchanger 130 functions as a radiator.

The high-pressure liquid refrigerant that has flowed out of the second heat exchanger 130 passes through the expansion mechanism 150, and flows into the refrigerant flow path 121 of the first heat exchanger 120 from the first end 121a. The refrigerant that has passed through the expansion mechanism 150 is decompressed to a low pressure and becomes a refrigerant of a gas-liquid two-phase state.

The low-pressure refrigerant that has flowed into the refrigerant flow path 121 exchanges heat with the water flowing through the water flow path 122 and evaporates, becomes a low-pressure gas refrigerant, and flows out of the second end 121b. In other words, the refrigerant flow path 121 of the first heat exchanger 120 functions as an evaporator.

The low-pressure gas refrigerant that has flowed out of the first heat exchanger 120 passes through the switching mechanism 140 through the fourth port P4 and the third port P3 in that order, and is again sucked into the compressor 110 from the suction portion 110a.

(3-1-2) Water Circuit

When the pump 210 starts the operation, the water filled in the water circuit 200 is sucked from the suction portion 210a and then discharged from the discharge portion 210b.

The water that has flowed out of the discharge portion 210b flows into the water flow path 122 of the first heat exchanger 120 from the second end 122b. The water that has flowed into the water flow path 122 exchanges heat (is cooled) with the low-pressure refrigerant flowing through the refrigerant flow path 121, and flows out of the first end 122a.

The water that has flowed out of the first heat exchanger 120 flows into the third heat exchanger 220 from the first end 220a. The water that has flowed into the third heat exchanger 220 exchanges heat with the air at the installation location of the third heat exchanger 220. Accordingly, the air in the air conditioning target space is cooled.

The water that has exchanged heat with the air at the installation location of the third heat exchanger 220 flows out from the second end 220b and then is sucked again from the suction portion 210a into the pump 210.

(3-2) Heating Operation

When execution of the heating operation is instructed to the temperature adjustment system 1, the control unit 300 is configured to cause the compressor 110 and the pump 210 to start operation, to set the switching mechanism 140 to the second state, and to control the opening degree of the expansion mechanism 150.

(3-2-1) Refrigerant Circuit

When the compressor 110 starts the operation, a low-pressure gas refrigerant in the refrigeration cycle is sucked from the suction portion 110a, compressed to a high pressure in the refrigeration cycle, and then discharged from the discharge portion 110b as the gas refrigerant. The high-pressure gas refrigerant that has flowed out of the discharge portion 110b passes through the switching mechanism 140 through the first port P1 and the fourth port P4 in that order, and flows into the refrigerant flow path 121 of the first heat exchanger 120 from the second end 121b. The high-pressure gas refrigerant that has flowed into the first heat exchanger 120 exchanges heat with the water flowing through the water flow path 122 to be condensed, becomes a high-pressure liquid refrigerant, and flows out of the first end 121a. In other words, the refrigerant flow path 121 of the first heat exchanger 120 functions as a radiator.

The high-pressure liquid refrigerant that has flowed out of the first heat exchanger 120 flows into the second heat exchanger 130 from the first end 130a through the expansion mechanism 150. The refrigerant that has passed through the expansion mechanism 150 is decompressed to a low pressure and becomes a refrigerant of a gas-liquid two-phase state.

The low-pressure refrigerant that has flowed into the second heat exchanger 130 evaporates by mutual heat exchange with the air at the installation location of the second heat exchanger 130, becomes a low-pressure gas refrigerant, and flows out of the second end 130b. In other words, the second heat exchanger 130 functions as an evaporator.

The low-pressure gas refrigerant that has flowed out of the second heat exchanger 130 passes through the switching mechanism 140 through the second port P2 and the third port P3 in that order, and is again sucked into the compressor 110 from the suction portion 110a.

(3-2-2) Water Circuit

When the pump 210 starts the operation, the refrigerant filled in the water circuit 200 is sucked from the suction portion 210a and then discharged from the discharge portion 210b.

The water that has flowed out of the discharge portion 210b flows into the water flow path 122 of the first heat exchanger 120 from the second end 122b. The water that has flowed into the water flow path 122 exchanges heat (is heated) with the high-pressure refrigerant flowing through the refrigerant flow path 121, and flows out of the first end 122a.

The water that has flowed out of the first heat exchanger 120 flows into the third heat exchanger 220 from the first end 220a. The water that has flowed into the third heat exchanger 220 exchanges heat with the air at the installation location of the third heat exchanger 220. Accordingly, the air in the air conditioning target space is heated.

The water that has exchanged heat with the air at the installation location of the third heat exchanger 220 flows out from the second end 220b and then is sucked again from the suction portion 210a into the pump 210.

(3-3) Reverse Cycle Defrost Operation

The reverse cycle defrost operation is an operation for removing frost adhering to the second heat exchanger 130. The flow of the reverse cycle defrost operation by the control unit 300 will be described with reference to FIG. 4.

(3-3-1) Start of Reverse Cycle Defrost Operation

The control unit 300 is configured to acquire the temperature detected by the third temperature sensor 131 at predetermined intervals during the heating operation (step S11). When the acquired temperature is less than a predetermined value, the control unit 300 is configured to determine that frost has been formed on the second heat exchanger 130 (step S12).

When determining that frost has been forming on the second heat exchanger 130, the control unit 300 is configured to stop the operation of the compressor 110 to stop the heating operation (step S13). The control unit 300 is configured to lower output of the pump 210 or to stop the operation of the pump 210.

When determining in step S12 that frost has not been formed on the second heat exchanger 130, the control unit 300 is configured to return to step S11 and to acquire the temperature detected by the third temperature sensor 131 at predetermined intervals.

When determining in step S12 that frost has been formed on the second heat exchanger 130, the control unit 300 is configured to switch a refrigerant flow direction in the refrigerant circuit 100 to the same direction as in the cooling operation and to start the reverse cycle defrost operation (step S14). In other words, the control unit 300 is configured to start the operation of the compressor 110, to set the switching mechanism 140 to the first state, and to control the opening degree of the expansion mechanism 150. In addition, the control unit 300 is configured to control the operation of the pump 210.

When the compressor 110 starts the operation, a low-pressure gas refrigerant in the refrigeration cycle is sucked from the suction portion 110a, compressed to a high pressure in the refrigeration cycle, and then discharged from the discharge portion 110b as the gas refrigerant in the refrigerant circuit 100. The high-pressure gas refrigerant that has flowed out of the discharge portion 110b passes through the switching mechanism 140 through the first port P1 and the second port P2 in that order, and flows into the second heat exchanger 130 from the second end 130b. The high-pressure refrigerant that has flowed into the second heat exchanger 130 supplies heat to the second heat exchanger 130. As a result, the frost adhering to the second heat exchanger 130 melts, and the second heat exchanger 130 is defrosted.

The high-pressure refrigerant that has flowed out of the second heat exchanger 130 passes through the expansion mechanism 150, and flows into the refrigerant flow path 121 of the first heat exchanger 120 from the first end 121a. The refrigerant that has passed through the expansion mechanism 150 is decompressed to a low pressure and becomes a refrigerant of a gas-liquid two-phase state. The low-pressure refrigerant that has flowed into the refrigerant flow path 121 exchanges heat with the water flowing through the water flow path 122, becomes a low-pressure gas refrigerant, and flows out of the second end 121b.

The low-pressure gas refrigerant that has flowed out of the first heat exchanger 120 passes through the switching mechanism 140 through the fourth port P4 and the third port P3 in that order, and is again sucked into the compressor 110 from the suction portion 110a.

In the water circuit 200, the water filled in the water circuit 200 flows into the water flow path 122 of the first heat exchanger 120 from the second end 122b. The water that has flowed into the water flow path 122 exchanges heat (is cooled) with the low-pressure refrigerant flowing through the refrigerant flow path 121, and flows out of the first end 122a. Accordingly, the water in the water flow path 122 is cooled.

(3-3-2) Stop of Reverse Cycle Defrost Operation

When the temperature of the water flowing through the water flow path 122 is excessively lowered by the reverse cycle defrost operation, there is a possibility that the first heat exchanger 120 could freeze.

Therefore, the control unit 300 is configured to acquire the temperatures detected by the first temperature sensor 123 and the second temperature sensor 124 at predetermined intervals during the reverse cycle defrost operation (step S15). In a case where any of the detected temperatures falls below a third threshold value, the control unit 300 is configured to determine that there is a possibility that the first heat exchanger 120 could freeze if the reverse cycle defrost operation (step S16) were continued. In the present embodiment, the third threshold value is 6° C.

When determining that there is a possibility that the first heat exchanger 120 could freeze, the control unit 300 is configured to stop the reverse cycle defrost operation and to restart the heating operation (steps S17 and S18). In other words, after stopping the operation of the compressor 110 and stopping the reverse cycle defrost operation, the control unit 300 is configured to start the operations of the compressor 110 and the pump 210, to set the switching mechanism 140 to the second state, and to control the opening degree of the expansion mechanism 150.

When determining in step S16 that there is no possibility that the first heat exchanger 120 could freeze, the control unit 300 is configured to return to step S15 and to acquire temperatures detected by the first temperature sensor 123 and the second temperature sensor 124 at predetermined intervals.

Here, as described above, the automatic on-off valve 230 starts to open when the temperature of the water flowing through the first heat exchanger 120 is 4° C., and is fully opened when the temperature is lower than 3° C. When the temperature of the water flowing through the first heat exchanger 120 exceeds 5° C., the automatic on-off valve 230 is fully closed. The temperature of the water flowing through the first heat exchanger 120 is the temperature of the water flowing out of the first end 122a functioning as an outlet for the water from the water flow path 122, and is the temperature of the water flowing through the second water pipe 202 at the position where the automatic on-off valve 230 is disposed. When the temperature detected by the first temperature sensor 123 or the second temperature sensor 124 falls below 6° C., the control unit 300 is configured to stop the reverse cycle defrost operation. During the reverse cycle defrost operation, the temperature of the water flowing out of the first end 122a is substantially the same as the temperature detected by the first temperature sensor 123, and is lower than the temperature detected by the second temperature sensor 124.

Therefore, the control unit 300 is configured to stop the reverse cycle defrost operation before the automatic on-off valve 230 starts to open due to a decrease in the temperature of the water flowing through the water flow path 122. As a result, the water filled in the water circuit 200 can be prevented from being released from the automatic on-off valve 230.

When the heating operation is restarted, as described above, the high-pressure gas refrigerant that has flowed out of the discharge portion 110b flows into the refrigerant flow path 121 of the first heat exchanger 120 from the second end 121b. The water that has flowed into the water flow path 122 exchanges heat (is heated) with the high-pressure refrigerant flowing through the refrigerant flow path 121, and flows out of the first end 122a. Accordingly, the water in the water flow path 122 is heated.

Therefore, since the temperature of the water flowing through the water flow path 122 rises, the water filled in the water circuit 200 can be prevented from being released from the automatic on-off valve 230.

(4) Characteristics

(4-1)

The temperature adjustment system 1 according to the present embodiment is a temperature adjustment system 1 that sends temperature-adjusted water to the first water pipe 201 that is a utilization-side water pipe. The temperature adjustment system 1 includes the first unit 400. The first unit 400 includes the refrigerant circuit 100 through which a highly flammable refrigerant circulates, the second water pipe 202, and the first heat exchanger 120. The second water pipe 202 is a heat source-side water pipe connected to the first water pipe 201. The first heat exchanger 120 exchanges heat between the water and the refrigerant. The first unit 400 further includes the automatic on-off valve 230 that automatically releases water in the first heat exchanger 120 at a low temperature.

In this temperature adjustment system 1, when there is a possibility that the first heat exchanger 120 could freeze, the water in the first heat exchanger 120 is automatically released. It is therefore possible to suppress a situation in which the water is not released when there is a possibility that the first heat exchanger 120 could freeze. As a result, failure of the first heat exchanger 120 due to freezing can be suppressed. Therefore, leakage of the highly flammable refrigerant due to failure of the first heat exchanger 120 and circulation of the leaking highly flammable refrigerant through the utilization-side first water pipe 201 can be suppressed.

(4-2)

In the temperature adjustment system 1 according to the present embodiment, the automatic on-off valve 230 automatically opens when the temperature of the water flowing through the first heat exchanger 120 falls below a first threshold value, and automatically closes when the temperature of the water flowing through the first heat exchanger 120 exceeds the second threshold value higher than the first threshold value.

In this temperature adjustment system 1, since the automatic on-off valve 230 senses a water temperature and automatically opens and closes, it is possible to suppress a situation in which water is not released when there is a possibility that the first heat exchanger 120 could freeze. As a result, failure of the first heat exchanger 120 due to freezing can be suppressed. Therefore, leakage of the highly flammable refrigerant due to failure of the first heat exchanger 120 and circulation of the leaking highly flammable refrigerant through the utilization-side first water pipe 201 can be suppressed.

(4-3)

In the temperature adjustment system 1 according to the present embodiment, the automatic on-off valve 230 is a mechanical on-off valve whose opening degree changes in accordance with the temperature of the water flowing through the first heat exchanger 120.

In this temperature adjustment system 1, there is no need for special control, and cost can be suppressed.

(4-4)

In the temperature adjustment system 1 according to the present embodiment, the first unit 400 further includes the casing 410 that accommodates the refrigerant circuit 100, the second water pipe 202, and the first heat exchanger 120. The automatic on-off valve 230 is disposed in the casing 410.

In the temperature adjustment system 1, the automatic on-off valve 230 can be prevented from being directly exposed to snow, wind, and rain. As a result, it is possible to suppress erroneous opening and closing of the automatic on-off valve 230 and freezing of the automatic on-off valve 230 due to environmental conditions outside the automatic on-off valve 230.

(4-5)

In the temperature adjustment system 1 according to the present embodiment, the first unit 400 further includes the second heat exchanger 130 that exchanges heat between the refrigerant and the outdoor air. The temperature adjustment system 1 further includes the control unit 300. The control unit 300 is configured to control the reverse cycle defrost operation of melting frost adhering to the second heat exchanger 130. The control unit 300 is configured to stop the reverse cycle defrost operation when the temperature of the water flowing through the first heat exchanger 120 falls below the third threshold value during the reverse cycle defrost operation.

In the temperature adjustment system 1, the reverse cycle defrost operation is stopped on the basis of a detected water temperature. Accordingly, freezing of the first heat exchanger 120 and opening of the automatic on-off valve 230 during the reverse cycle defrost operation can be suppressed.

(4-6)

In the temperature adjustment system 1 according to the present embodiment, the casing 410 includes the bottom plate 420. The bottom plate 420 has the opening 430 communicating with the outside of the casing 410. The water in the first heat exchanger 120 released from the automatic on-off valve 230 is drained to the outside of the casing 410 through the opening 430. The temperature adjustment system 1 can prevent the water from accumulating in the casing 410.

(4-7)

In the temperature adjustment system 1 according to the present embodiment, the first unit 400 further includes the second heat exchanger 130 that exchanges heat between the refrigerant and the outdoor air. The drain water from the second heat exchanger 130 is discharged from the opening 430 to the outside of the casing 410.

In the temperature adjustment system 1, the opening 430 of the bottom plate 420 serves as a drain port for the water in the first heat exchanger 120 and a drain port for the drain water from the second heat exchanger 130. As a result, since the number of the openings 430 can be suppressed, the strength of the bottom plate 420 can be maintained.

(5) Modifications

The specific configuration of the embodiment of the present invention can be changed without departing from the gist of the present invention. Modifications applicable to the embodiment of the present invention will be described.

(5-1) Modification A

In the present embodiment, the automatic on-off valve 230 is provided on a water pipe 203 branched from the water circuit 200 downstream of the first end 122a in the water circuit 200. However, the automatic on-off valve 230 may be provided upstream of the second end 122b in the water circuit 200.

In that case, the temperature of the water flowing through the first heat exchanger 120 is the temperature of the water flowing in from the second end 122b functioning as an inlet for the water into the water flow path 122, and is the temperature of the water flowing through the second water pipe 202 at the position where the automatic on-off valve 230 is disposed.

In the configuration according to the present modification, in a case where there is a possibility that the first heat exchanger 120 could freeze, the water filled in the water circuit 200 is released from the automatic on-off valve 230 before flowing into the first heat exchanger 120. Accordingly, it is possible to suppress failure of the first heat exchanger 120 due to freezing, leakage of a highly flammable refrigerant due to failure of the first heat exchanger 120, and circulation of the leaking highly flammable refrigerant through the utilization-side first water pipe 201.

(5-2) Modification B

In the present embodiment, the control unit 300 is configured to acquire the temperatures detected by the first temperature sensor 123 and the second temperature sensor 124 at predetermined intervals during the reverse cycle defrost operation. However, the control unit 300 may acquire only the temperature detected by first temperature sensor 123.

In this temperature adjustment system 1, freezing of the first heat exchanger 120 and opening of the automatic on-off valve 230 during the reverse cycle defrost operation can be suppressed.

(5-3) Modification C

In the present embodiment, the control unit 300 determines that frost is formed on the second heat exchanger 130 when the temperature detected by the third temperature sensor 131 is less than the predetermined value. However, a method of detecting frosting may include other suitable methods. The control unit 300 may be configured to detect frost formation on the second heat exchanger 130 by using, for example, the temperature of the refrigerant flowing through the second heat exchanger 130 and the temperature of the air passing through the second heat exchanger 130.

(5-4) Modification D

In the present embodiment, the control unit 300 is configured to detect frost formation on the second heat exchanger 130 during the heating operation. However, the control unit 300 may detect frost formation on the second heat exchanger 130 while the operation of temperature adjustment system 1 is stopped.

FIG. 5 is a diagram illustrating a flow of the reverse cycle defrost operation by the control unit 300 in a case where the reverse cycle defrost operation is performed while the operation is stopped.

The control unit 300 is configured to acquire the temperature detected by the third temperature sensor 131 at predetermined intervals while the operation is stopped (step S21). When the acquired temperature is less than a predetermined value, the control unit 300 is configured to determine that frost has been formed on the second heat exchanger 130 (step S22).

When determining that frost has not been formed on the second heat exchanger 130, the control unit 300 is configured to return to step S21 and to acquire the temperature detected by the third temperature sensor 131 at predetermined intervals.

When determining in step S22 that frost has been formed on the second heat exchanger 130, the control unit 300 is configured to switch a refrigerant flow direction in the refrigerant circuit 100 to the same direction as in the cooling operation and starts the reverse cycle defrost operation (step S23). In other words, the control unit 300 is configured to start the operations of the compressor 110 and the pump 210, to set the switching mechanism 140 to the first state, and to control the opening degree of the expansion mechanism 150.

The control unit 300 is configured to acquire the temperatures detected by the first temperature sensor 123 and the second temperature sensor 124 at predetermined intervals during the reverse cycle defrost operation (step S24). In a case where any of the detected temperatures falls below the third threshold value, the control unit 300 is configured to determine that there is a possibility that the first heat exchanger 120 freezes by continuing the reverse cycle defrost operation (step S25).

When determining that there is a possibility that the first heat exchanger 120 could freeze, the control unit 300 is configured to stop the operation of the compressor 110 and to stop the reverse cycle defrost operation (step S26).

When determining in step S25 that there is no possibility that the first heat exchanger could freeze, the control unit 300 is configured to return to step S24 and acquires temperatures detected by the first temperature sensor 123 and the second temperature sensor at predetermined intervals.

After stopping the reverse cycle defrost operation, the control unit 300 may continue the operation of the pump 210 for a predetermined period. By suppressing accumulation of the water in the water flow path 122 of the first heat exchanger 120, freezing of first heat exchanger can be suppressed.

In the configuration according to the present modification, the control unit 300 is configured to stop the reverse cycle defrost operation before the automatic on-off valve 230 starts to open due to a decrease in the temperature of the water flowing through the water flow path 122. As a result, the water filled in the water circuit 200 can be prevented from being released from the automatic on-off valve 230.

Other Embodiments

While the embodiment of the present disclosure has been described above, it will be understood that various changes in forms and details can be made without departing from the gist and scope of the present disclosure recited in the claims.

REFERENCE SIGNS LIST

• • 1 temperature adjustment system
  • 100 refrigerant circuit
  • 110 compressor
  • 120 first heat exchanger
  • 121 refrigerant flow path
  • 122 water flow path
  • 130 second heat exchanger
  • 140 switching mechanism
  • 150 expansion mechanism
  • 200 water circuit
  • 201 first water pipe
  • 202 second water pipe
  • 210 pump
  • 220 third heat exchanger
  • 230 automatic on-off valve
  • 300 control unit
  • 400 first unit
  • 410 casing
  • 420 bottom plate
  • 430 opening

CITATION LIST

Patent Literature

Patent Literature 1: JP 2001-201107 A