REFRIGERATION CYCLE APPARATUS

Description

TECHNICAL FIELD

The present disclosure relates to a refrigeration cycle apparatus.

BACKGROUND ART

Many thermal appliances, such as air conditioners for business purposes, having a refrigerant circuit of a large scale may comprise an oil return path in order to reduce a quantity of oil in the refrigerant circuit. Japanese Patent No. 3874980 (PTL 1) discloses an air conditioner having an oil return path. The oil return path has one end connected to an oil separator and has the other end connected to a refrigerant pipe extending from an evaporator to a compressor.

CITATION LIST

Patent Literature

• • PTL 1: Japanese Patent No. 3874980

SUMMARY OF INVENTION

Technical Problem

The configuration disclosed in Japanese Patent No. 3874980 has a possibility that refrigerant may flow to the oil return path when the oil separator has a small quantity of oil therein. When the refrigerant flows into the oil return path, refrigerant which does not contribute to capacity circulates through the compressor and the oil return path. As a result, the compressor's work increases and the refrigeration cycle apparatus has a reduced coefficient of performance (COP) disadvantageously.

The present disclosure has been made to describe an embodiment to solve such a problem as described above, and contemplates a refrigeration cycle apparatus capable of appropriately returning refrigerator oil to a compressor while avoiding a reduced COP.

Solution to Problem

The present disclosure relates to a refrigeration cycle apparatus. The refrigeration cycle apparatus comprises a compressor, an oil separator, a first heat exchanger, an expansion valve, and a second heat exchanger. The compressor, the oil separator, the first heat exchanger, the expansion valve, and the second heat exchanger constitute a refrigerant circuit through which refrigerant circulates. The refrigeration cycle apparatus further comprises an oil return path configured to return refrigerator oil from the oil separator to an inlet of the compressor, a flow rate adjustment mechanism disposed at the oil return path, and an oil quantity sensing device configured to detect a quantity of refrigerator oil stored in the oil separator. The flow rate adjustment mechanism is configured to operate in response to an output of the oil quantity sensing device to control a flow rate of a fluid passing through the oil return path.

Advantageous Effects of Invention

The presently disclosed refrigeration cycle apparatus can reduce a flow rate of a fluid passing through an oil return path when there is a possibility that refrigerant may be introduced into the oil return path, and the refrigeration cycle apparatus can thus appropriately return refrigerator oil to the compressor while avoiding a reduced COP.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram showing a configuration of a refrigeration cycle apparatus according to a first embodiment.

FIG. 2 is a flowchart for illustrating how a flow rate adjustment mechanism is controlled according to the first embodiment.

FIG. 3 is a diagram showing a configuration of a refrigeration cycle apparatus according to a second embodiment.

FIG. 4 is a diagram showing a configuration of a refrigeration cycle apparatus according to a third embodiment.

FIG. 5 is a diagram representing how refrigerator oil changes in temperature when the refrigerator oil flows through an oil sensing path 17B.

FIG. 6 is a diagram representing how refrigerant changes in temperature when the refrigerant flows through oil sensing path 17B.

FIG. 7 is a diagram showing a configuration of a refrigeration cycle apparatus according to a fourth embodiment.

FIG. 8 is a diagram showing a configuration of a refrigeration cycle apparatus according to a fifth embodiment.

FIG. 9 is a diagram showing a configuration of a refrigeration cycle apparatus according to a sixth embodiment.

FIG. 10 is a diagram showing a configuration of a refrigeration cycle apparatus according to a seventh embodiment.

FIG. 11 is a flowchart for illustrating how a flow rate adjustment mechanism is controlled according to an eighth embodiment.

DESCRIPTION OF EMBODIMENTS

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. Hereinafter, while a plurality of embodiments will be described, it is planned from the beginning of the application to appropriately combine the configurations described in the embodiments. In the drawings, identical or equivalent components are identically denoted and will not be described repeatedly.

First Embodiment

FIG. 1 is a diagram showing a configuration of a refrigeration cycle apparatus according to a first embodiment. A refrigeration cycle apparatus 1001 comprises a compressor 10, an oil separator 11, a heat exchanger 13, an expansion valve 14, a heat exchanger 15, and a controller 600. Compressor 10, oil separator 11, heat exchanger 13, expansion valve 14, and heat exchanger 15 constitute a refrigerant circuit C1 through which refrigerant circulates. For a cooling operation, heat exchanger 13 acts as a condenser and heat exchanger 15 acts as an evaporator.

Refrigeration cycle apparatus 1001 further comprises an oil return path RP configured to return refrigerator oil from an oil discharge outlet of oil separator 11 to an inlet of compressor 10, a flow rate adjustment mechanism 16 disposed at oil return path RP, an oil quantity sensing device 17 configured to detect a quantity of oil stored in oil separator 11, and controller 600 configured to control flow rate adjustment mechanism 16 in response to an output of oil quantity sensing device 17. The refrigerator oil is returned to the inlet of compressor 10 through oil return path RP. Flow rate adjustment mechanism 16 operates in response to a command received from controller 600 to control a flow rate of a fluid (refrigerator oil and refrigerant) passing through oil return path RP.

Although not shown, a liquid receiver may be provided between heat exchanger 13 and expansion valve 14. Furthermore, although not shown, heat exchangers 13 and 15 are each provided with a fan.

Controller 600 comprises a CPU (central processing unit) 601, a memory 602 (ROM (read only memory) and RAM (random access memory)), an input/output buffer (not shown), and the like. CPU 601 loads a program that is stored in the ROM into the RAM or the like and executes the program. The program stored in the ROM is a program in which a processing procedure for controller 600 is described. Controller 600 controls each device in the refrigeration cycle apparatus in accordance with these programs. This control is not limited to processing by software and may also be processed by dedicated hardware (or electronic circuitry).

Note that controller 600 may be distributed to an indoor unit and an outdoor unit and connected through communication.

FIG. 2 is a flowchart for illustrating how the flow rate adjustment mechanism is controlled according to the first embodiment. In step S1, controller 600 determines whether oil separator 11 has a reduced quantity of refrigerator oil based on an output of oil quantity sensing device 17. When oil separator 11 has an insufficient quantity of refrigerator oil therein, there is a possibility that refrigerant may flow through oil return path RP. Refrigerant that flows through oil return path RP, bypasses heat exchanger 13, expansion valve 14, and heat exchanger 15 of refrigerant circuit C1, and returns to compressor 10, is hereinafter referred to as bypassed refrigerant.

When the oil separator has a reduced quantity of oil (YES in S1), controller 600 controls flow rate adjustment mechanism 16 to reduce a flow rate of a fluid flowing through oil return path RP in step S2.

In contrast, when the oil separator does not have a reduced quantity of oil (NO in S1), controller 600 controls flow rate adjustment mechanism 16 to increase the flow rate of the fluid flowing through oil return path RP in step S3.

In this way, flow rate adjustment mechanism 16 can be controlled to hold some quantity of refrigerator oil in oil separator 11 to reduce a quantity of bypassed refrigerant flowing through oil return path RP when the oil separator has a reduced quantity of oil. This can prevent refrigerant which does not contribute to a cooling capacity from circulating through compressor 10 and oil return path RP, and thus prevent an increased work of compressor 10 and hence a reduced COP.

Second Embodiment

In a second embodiment will be described a first specific example of oil quantity sensing device 17 described in the first embodiment. FIG. 3 is a diagram showing a configuration of a refrigeration cycle apparatus according to the second embodiment. In a refrigeration cycle apparatus 1002 shown in FIG. 3, oil quantity sensing device 17 comprises an oil level sensor 17A configured to sense a level of a surface of oil in oil separator 11. Remainder of refrigeration cycle apparatus 1002 is similar in configuration to that of refrigeration cycle apparatus 1001 shown in FIG. 1, and accordingly, will not be described repeatedly. Note that controller 600 is not shown in the following figures.

Oil level sensor 17A can for example be a float-type sensor, a capacitance sensor, a self-heating sensor, or the like.

The float-type sensor has a mechanism in which a float floating on the surface of oil in oil separator 11 moves up and down, and the float-type sensor senses an oil level depending on the position of the float.

The capacitance sensor comprises a plate capacitor. As a dielectric constant between electrodes changes in response to immersion in oil, the capacitor also changes in capacitance. By detecting a change in capacitance, whether the refrigerator oil has a larger quantity than a reference value can be detected.

The self-heating sensor has a resistive element that electrically conducts and generates heat. When the resistive element is immersed in oil, the resistive element changes in temperature and hence in resistance value. By detecting that the resistance value changes, whether the refrigerator oil has a larger quantity than the reference value can be detected.

Thus using an oil level sensor as the oil quantity sensing device to control the flow rate adjustment mechanism can reduce a quantity of bypassed refrigerant flowing through oil return path RP when the oil separator has a reduced quantity of oil. This can prevent refrigerant which does not contribute to a cooling capacity from circulating through compressor 10 and oil return path RP, and thus prevent an increased work of compressor 10 and hence a reduced COP.

Third Embodiment

In a third embodiment will be described a second specific example of oil quantity sensing device 17 described in the first embodiment. FIG. 4 is a diagram showing a configuration of a refrigeration cycle apparatus according to the third embodiment. In a refrigeration cycle apparatus 1003 shown in FIG. 4, oil quantity sensing device 17 comprises an oil sensing path 17B, a solenoid valve 17C, a cooling device 17D, and a temperature sensor 17E. Remainder of refrigeration cycle apparatus 1003 is similar in configuration to that of refrigeration cycle apparatus 1001 shown in FIG. 1, and accordingly, will not be described repeatedly.

Cooling device 17D comprises an internal heat exchanger 171. Internal heat exchanger 171 is configured so that a gaseous refrigerant of low temperature and low pressure having passed through heat exchanger 15 and a fluid (refrigerator oil and/or gaseous refrigerant) passing through oil sensing path 17B exchange heat.

Oil sensing path 17B has a suction inlet P3 set at oil separator 11 at a predetermined level. Suction inlet P3 is higher in level than an oil discharge outlet P4 of oil separator 11 and lower in level than a gas flow inlet P1 and a gas discharge outlet P2.

Along oil sensing path 17B are disposed solenoid valve 17C, internal heat exchanger 171, and temperature sensor 17E in this order. Oil sensing path 17B joins the oil return path at a junction point P5 upstream of flow rate adjustment mechanism 16.

FIG. 5 is a diagram representing how refrigerator oil changes in temperature when the refrigerator oil flows through oil sensing path 17B. FIG. 6 is a diagram representing how refrigerant changes in temperature when the refrigerant flows through oil sensing path 17B.

As shown in FIG. 5, when the oil level is higher than the level of suction inlet P3, oil sensing path 17B has refrigerator oil flowing therethrough. When the refrigerator oil is cooled by internal heat exchanger 171, the refrigerator oil has a temperature decreasing from a temperature T1 to a temperature T2 equal to or lower than the saturated gas temperature. In contrast, as shown in FIG. 6, when the oil level is lower than the level of suction inlet P3, oil sensing path 17B has refrigerant flowing therethrough. When the refrigerant is cooled by internal heat exchanger 171, the refrigerant only has a temperature decreasing to the saturated gas temperature T3. When internal heat exchanger 171 is appropriately designed, the difference in temperature indicated in FIGS. 5 and 6 can be caused.

Accordingly, when the oil level is sensed, solenoid valve 17C is opened and temperature sensor 17E measures temperature. When the temperature measured with temperature sensor 17E is lower than the saturated gas temperature converted from the pressure sensed with a high-pressure sensor (not shown), it can be sensed that the oil level is lower than the level of suction inlet P3.

As described above, when the oil quantity sensing device detects an oil level based on how a fluid flowing through oil sensing path 17B changes in temperature when the fluid is cooled, and the flow rate adjustment mechanism is controlled, a quantity of bypassed refrigerant flowing through oil return path RP when the oil separator has a reduced quantity of oil can be reduced. This can prevent refrigerant which does not contribute to a cooling capacity from circulating through compressor 10 and oil return path RP, and thus prevent an increased work of compressor 10 and hence a reduced COP.

Fourth Embodiment

In a fourth embodiment will be described a third specific example of oil quantity sensing device 17 described in the first embodiment. FIG. 7 is a diagram showing a configuration of a refrigeration cycle apparatus according to the fourth embodiment. A refrigeration cycle apparatus 1004 shown in FIG. 7 further comprises a bypass flow path BP, a heat exchanger 19, and an expansion valve 20 in addition to the configuration of refrigeration cycle apparatus 1001 shown in FIG. 1.

Heat exchanger 19 has a first flow path and a second flow path and is configured to exchange heat between refrigerant flowing through the flow paths. The first flow path of heat exchanger 19 passes refrigerant having passed through heat exchanger 13. Bypass flow path BP branches from a branching point between an outlet of the first flow path of heat exchanger 19 and expansion valve 14 and joins refrigerant circuit C1 in a vicinity of the inlet of compressor 10.

Furthermore, oil quantity sensing device 17 comprises oil sensing path 17B, solenoid valve 17C, cooling device 17D, and temperature sensor 17E. Remainder of refrigeration cycle apparatus 1004 is similar in configuration to that of refrigeration cycle apparatus 1001 shown in FIG. 1, and accordingly, will not be described repeatedly.

Cooling device 17D in the fourth embodiment comprises an internal heat exchanger 172. Internal heat exchanger 172 is configured so that refrigerant in bypass flow path BP after passing through heat exchanger 19 and a fluid (refrigerator oil and/or gaseous refrigerant) passing through oil sensing path 17B exchange heat.

Oil sensing path 17B has suction inlet P3 set at oil separator 11 at a predetermined level. Suction inlet P3 is higher in level than oil discharge outlet P4 of oil separator 11 and lower in level than gas flow inlet P1 and gas discharge outlet P2.

Along oil sensing path 17B are disposed solenoid valve 17C, internal heat exchanger 172, and temperature sensor 17E in this order. Oil sensing path 17B joins the oil return path at junction point P5 upstream of flow rate adjustment mechanism 16.

In the fourth embodiment as well, designing internal heat exchanger 172 so as to cause the difference in temperature represented in FIGS. 5 and 6 allows an oil level to be detected.

As well as the third embodiment, the fourth embodiment can also prevent an increased work of compressor 10 and hence a reduced COP. Further, expansion valve 20 can be used to control a flow rate of refrigerant flowing through bypass flow path BP, so that a quantity of heat exchanged in heat exchanger 172 can be adjusted to any value, and even when a refrigeration cycle is changed in state, it can be handled across a wide range, and this facilitates designing heat exchanger 172.

Fifth Embodiment

In a fifth embodiment, a first specific example of the flow rate adjustment mechanism described in the first embodiment will be described. FIG. 8 is a diagram showing a configuration of a refrigeration cycle apparatus according to the fifth embodiment. A refrigeration cycle apparatus 1005 shown in FIG. 8 comprises a linear expansion valve (LEV) 16A as flow rate adjustment mechanism 16. Remainder of refrigeration cycle apparatus 1005 is similar in configuration to that of refrigeration cycle apparatus 1001 shown in FIG. 1, and accordingly, will not be described repeatedly.

Using linear expansion valve 16A allows controller 600 to operate in response to an output of oil quantity sensing device 17 to increase/decrease a flow rate of a fluid (refrigerant and refrigerator oil) passing through oil return path RP.

In the fifth embodiment, oil quantity sensing device 17 can be of any of the configurations described in the second to fourth embodiments. Furthermore, controller 600 can apply the control described in the first embodiment to control a flow rate.

Sixth Embodiment

In a sixth embodiment, a second specific example of the flow rate adjustment mechanism described in the first embodiment will be described. FIG. 9 is a diagram showing a configuration of a refrigeration cycle apparatus according to the sixth embodiment. In a refrigeration cycle apparatus 1006 shown in FIG. 9, flow rate adjustment mechanism 16 comprises a solenoid valve 16B and a capillary tube 16C disposed at oil return path RP in series. Remainder of refrigeration cycle apparatus 1006 is similar in configuration to that of refrigeration cycle apparatus 1001 shown in FIG. 1, and accordingly, will not be described repeatedly.

As described above, oil return path RP is provided with capillary tube 16C and solenoid valve 16B, and solenoid valve 16B is controlled to be opened when a flow rate is increased, and solenoid valve 16B is controlled to be closed when a flow rate is decreased. Thus, controller 600 can adjust a flow rate of the refrigerant and refrigerator oil passing through oil return path RP.

In the sixth embodiment, oil quantity sensing device 17 can be of any of the configurations described in the second to fourth embodiments. Furthermore, controller 600 can apply the control described in the first embodiment to control a flow rate.

When oil return path RP is provided with an LEV, as described in the fifth embodiment, it is preferable to use a component different from expansion valve 14. Oil return path RP passes refrigerator oil and refrigerant of high temperature discharged from compressor 10, and accordingly, the LEV is required to be significantly heat resistant. Therefore, the LEV disposed at oil return path RP, as used in FIG. 8, will be of a special specification and may be an expensive component. In contrast, a capillary tube and a solenoid valve are simple in structure and also significantly heat resistant, and this allows common components to be also used for the oil return path, and the flow rate adjustment mechanism to be configured inexpensively.

Seventh Embodiment

In a seventh embodiment, a third specific example of the flow rate adjustment mechanism described in the first embodiment will be described. FIG. 10 is a diagram showing a configuration of a refrigeration cycle apparatus according to the seventh embodiment. In a refrigeration cycle apparatus 1007 shown in FIG. 10, oil return path RP branches into a flow path RP1 and a flow path RP2 at a branching point BP1 and subsequently has the flow paths joined together at a junction point MP1. Flow rate adjustment mechanism 16 comprises solenoid valve 16B and capillary tube 16C disposed at flow path RP1 in series, and a capillary tube 16D disposed at flow path RP2.

In the seventh embodiment, oil quantity sensing device 17 can be of any of the configurations described in the second to fourth embodiments. Furthermore, controller 600 can apply the control described in the first embodiment to control a flow rate.

As shown in FIG. 10, oil return path RP is branched into flow paths RP1 and RP2 in parallel, and the flow paths are provided with capillary tubes 16C and 16D, respectively, and one flow path RP1 is provided with solenoid valve 16B. Controller 600 can adjust a flow rate by opening solenoid valve 16B when the flow rate is to be increased and closing solenoid valve 16B when the flow rate is to be decreased.

In the configuration shown in FIG. 9, when a flow rate is decreased, the flow rate is zeroed, whereas in the configuration shown in FIG. 10, even when a flow rate is decreased, a determined quantity of refrigerator oil can be returned to compressor 10.

Eighth Embodiment

In the first embodiment, while the refrigeration cycle apparatus is in operation, a quantity of refrigerant flowing through oil return path RP is constantly monitored, and flow rate adjustment mechanism 16 controls a flow rate. Flow rate adjustment mechanism 16 also has a movable part, and accordingly, it is advantageous in terms of the longevity of the apparatus that the movable part is moved less frequently.

Accordingly, in an eighth embodiment, the control illustrated in FIG. 2 is applied only in a situation where refrigerant easily flows into oil return path RP.

FIG. 11 is a flowchart for describing how a flow rate adjustment mechanism is controlled according to the eighth embodiment. In step S11, controller 600 determines whether a condition for determining whether to apply flow rate adjustment control is established.

For example, controller 600 determines that the condition of step S11 is established when compressor 10 has an operating frequency lower than a reference frequency. The reference frequency can be a frequency that is half the upper limit of the operating frequency of the compressor, for example.

When compressor 10 has a low operating frequency, compressor 10 discharges refrigerator oil in a reduced quantity. Oil separator 11 has a reduced quantity of refrigerator oil therein, and refrigerant easily returns to oil return path RP. In contrast, when oil separator 11 has a large quantity of refrigerator oil therein, oil return path RP mainly passes refrigerator oil, and the COP is unlikely to decrease due to the presence of the oil return path. Therefore, whether to apply the flow rate adjustment control is determined based on the compressor's operating frequency, as described above.

Note that the condition for applying the flow rate adjustment control is not limited thereto. For example, controller 600 may determine that the condition in step S11 for applying the flow rate adjustment control is established when a difference in pressure between the inlet and outlet of compressor 10 is smaller than a reference threshold value. In that case, the reference threshold value can be half of a maximum value of the difference in pressure.

For a given diameter of a fluid passage restriction unit of the flow rate adjustment mechanism, a larger differential pressure increases a quantity of fluid passing through oil return path RP and thus helps refrigerant to return. Accordingly, whether to apply the flow rate adjustment control may be determined based on the magnitude of the differential pressure, as described above.

When the condition for applying the flow rate adjustment control is not established (NO in S11), controller 600 fixes a flow rate of flow rate adjustment mechanism 16 to a standard value in step S15. This allows flow rate adjustment mechanism 16 to have a movable part moved less frequently, which is advantageous for the product in longevity.

When the condition for applying the flow rate adjustment control is established (YES in S11), controller 600 proceeds to step S12 to determine, based on an output of oil quantity sensing device 17, whether oil separator 11 has a reduced quantity of refrigerator oil therein. When oil separator 11 has an insufficient quantity of refrigerator oil therein, there is a possibility that refrigerant may flow through oil return path RP.

When the oil separator has a reduced quantity of refrigerator oil therein (YES in S12), controller 600 controls flow rate adjustment mechanism 16 to reduce a flow rate of a fluid flowing through oil return path RP in step S13.

In contrast, when the oil separator does not have a reduced quantity of refrigerator oil therein (NO in S12), controller 600 controls flow rate adjustment mechanism 16 to increase the flow rate of the fluid flowing through oil return path RP in step S14.

Thus controlling flow rate adjustment mechanism 16 to hold some quantity of refrigerator oil in oil separator 11 can reduce a quantity of bypassed refrigerant flowing through oil return path RP when the oil separator has a reduced quantity of refrigerator oil therein. This can prevent refrigerant which does not contribute to a cooling capacity from circulating through compressor 10 and oil return path RP, and thus prevent an increased work of compressor 10 and hence a reduced COP.

In the eighth embodiment, oil quantity sensing device 17 can be of any of the configurations described in the second to fourth embodiments. Furthermore, flow rate adjustment mechanism 16 can be of any of the configurations described in the fifth to seventh embodiments.

The eighth embodiment can achieve an effect similar to those of the first to seventh embodiments and also extend flow rate adjustment mechanism 16 in longevity to be longer than the first to seventh embodiments do.

SUMMARY

Hereinafter, reference will be made to the drawings again to summarize the embodiments.

• • (1) A refrigeration cycle apparatus 1001 shown in FIG. 1 of the present disclosure comprises a compressor 10, an oil separator 11, a heat exchanger 13, an expansion valve 14, and a heat exchanger 15. Compressor 10, oil separator 11, heat exchanger 13, expansion valve 14, and heat exchanger 15 constitute a refrigerant circuit C1 through which refrigerant circulates. Refrigeration cycle apparatus 1001 further comprises an oil return path RP configured to return refrigerator oil from oil separator 11 to the inlet of compressor 10, a flow rate adjustment mechanism 16 disposed at oil return path RP, and an oil quantity sensing device 17 configured to detect a quantity of refrigerator oil stored in oil separator 11. Flow rate adjustment mechanism 16 is configured to operate in response to an output of oil quantity sensing device 17 to control a flow rate of a fluid passing through oil return path RP.
  • (2) In clause 1, as shown in FIG. 3, oil quantity sensing device 17 comprises an oil level sensor 17A configured to detect a level of a surface of oil in the oil separator.
  • (3) In clause 1, as shown in FIG. 4, oil quantity sensing device 17 comprises an oil sensing path 17B that is connected to oil separator 11 at a suction inlet P3 higher in level than an oil discharge outlet P4 at which oil return path RP has one end connected to oil separator 11, and that is connected to oil return path RP at a junction point P5 provided at oil return path RP, a cooling device 17D configured to cool a fluid passing through oil sensing path 17B, and a temperature sensor 17E configured to detect a temperature of a portion of oil sensing path 17B after passing through cooling device 17D.
  • (4) In clause 3, as shown in FIG. 4, cooling device 17D comprises a heat exchanger 171 configured to exchange heat between refrigerant directed in refrigerant circuit C1 from heat exchanger 15 toward compressor 10 and the fluid passing through oil sensing path 17B.
  • (5) In clause 3, as shown in FIG. 7, refrigeration cycle apparatus 1004 further comprises a bypass flow path BP configured to branch a portion of refrigerant flowing in refrigerant circuit C1 from heat exchanger 13 toward expansion valve 14 and return the portion to compressor 10. Cooling device 17D comprises a heat exchanger 172 configured to exchange heat between refrigerant passing through bypass flow path BP and the fluid passing through oil sensing path 17B.
  • (6) In any one of clauses 1 to 5, as shown in FIG. 8, flow rate adjustment mechanism 16 comprises a linear expansion valve 16A.
  • (7) In any one of clauses 1 to 5, as shown in FIG. 9, flow rate adjustment mechanism 16 comprises a solenoid valve 16B and a capillary tube 16C disposed at oil return path RP in series.
  • (8) In any one of clauses 1 to 5, as shown in FIG. 10, oil return path RP branches into a flow path RP1 and a flow path RP2 at a branching point BP1, and the flow paths RP1 and RP2 are subsequently joined together at a junction point MP. Flow rate adjustment mechanism 16 comprises solenoid valve 16B and capillary tube 16C disposed at flow path RP1 in series, and a capillary tube 16D disposed at flow path RP2.
  • (9) In any one of clauses 1 to 8, refrigeration cycle apparatus 1001 further comprises a controller 600 configured to control compressor 10 and flow rate adjustment mechanism 16. As shown in FIG. 11, controller 600 is configured to apply a first control (S15) or a second control (S12 to S14) while compressor 10 is in operation. Controller 600 is configured to fix a flow rate of flow rate adjustment mechanism 16 in the first control, Controller 600 is configured to control a flow rate of flow rate adjustment mechanism 16 in response to the output of oil quantity sensing device 17 in the second control.
  • (10) In clause 9, as shown in FIG. 11, controller 600 is configured to apply the first control (S15) when compressor 10 has an operating frequency higher than a threshold value, and apply the second control (S12 to S14) when the compressor has an operating frequency lower than the threshold value.
  • (11) In clause 9, as shown in FIG. 11, controller 600 is configured to apply the first control (S15) when a difference in pressure between the inlet and outlet of compressor 10 is smaller than a threshold value, and apply the second control (S12 to S14) when the difference in pressure is larger than the threshold value.

It should be understood that the embodiments disclosed herein are illustrative and non-restrictive in any respect. The scope of the present disclosure is defined by the terms of the claims rather than by the foregoing description of the embodiments, and is intended to encompass any modification equivalent in meaning and scope to the terms of the claims.

REFERENCE SIGNS LIST

10 compressor, 11 oil separator, 13, 15, 19, 171, 172 heat exchanger, 14, 20 expansion valve, 16 flow rate adjustment mechanism, 16A linear expansion valve, 16B, 17C solenoid valve, 16C, 16D capillary tube, 17 oil quantity sensing device, 17A oil level sensor, 17B oil sensing path, 17D cooling device, 17E temperature sensor, 600 controller, 601 CPU, 602 memory, 1001-1007 refrigeration cycle apparatus, BP bypass flow path, BP1 branching point, C1 refrigerant circuit, MP, MP1, P5 junction point, P1 gas flow inlet, P2 gas discharge outlet, P3 suction inlet, P4 oil discharge outlet, RP oil return path, RP1, RP2 flow path.