Refrigeration device

Abstract

The present disclosure provides a refrigeration device capable of enhancing efficiency.　A refrigeration device according to the present disclosure comprises a refrigeration circuit in which a compressor, a heat source-side heat exchanger, a gas-liquid separator, and a use-side heat exchanger are connected. The refrigeration device has: a liquid pump that feeds a liquid refrigerant from the gas-liquid separator to a cooling-side heat exchanger, among the heat source-side heat exchanger and the use-side heat exchanger; and a check valve that is provided in parallel with the liquid pump and prevents backflow of the refrigerant toward the gas-liquid separator. The refrigerant that has passed through the cooling-side heat exchanger branches into an intake-side pipe connected to the intake side of the compressor and a return pipe connected to the gas-liquid separator. The intake-side pipe and the return pipe are each provided with a switching valve.

Description

Refrigeration equipment

[0001] The present disclosure relates to refrigeration devices.

[0002] Patent Document 1 discloses a refrigeration system that uses carbon dioxide as a refrigerant and enables highly efficient operation. This refrigeration system includes a pressure-reducing tank provided downstream of a gas cooler, an auxiliary circuit that draws the refrigerant from the pressure-reducing tank into an intermediate pressure section of a throttling / compression means, and a main circuit that exchanges heat between the refrigerant flowing out of the pressure-reducing tank and the refrigerant throttled in the auxiliary circuit and then flows to the main throttling means.

[0003] Patent Document 2 discloses a refrigeration cycle device that uses an ejector to achieve high efficiency. This refrigeration cycle device includes an ejector that receives refrigerant discharged from a compressor and passed through an outdoor heat exchanger and discharges the refrigerant into a gas-liquid separator, and an internal heat exchanger that uses a portion of the liquid refrigerant in the gas-liquid separator that is sucked into the ejector to cool the refrigerant flowing from the gas-liquid separator to the indoor heat exchanger.

[0004] Patent Document 3 discloses a refrigeration cycle device that achieves high efficiency by using an expansion mechanism and a sub-refrigerant circuit independent from a main refrigerant circuit. This refrigeration cycle device has a main expansion mechanism that expands refrigerant flowing toward a main user-side heat exchanger and recovers power, and a sub-user-side heat exchanger that further cools the refrigerant after power recovery before flowing it to the user-side heat exchanger.

[0005] Patent No. 6292480

[0006] Patent No. 5213986

[0007] Patent No. 7193706

[0008] The present disclosure provides a refrigeration device that can achieve high efficiency.

[0009] This specification includes the entire content of Japanese Patent Application No. 2024-061397, filed on April 5, 2024. A refrigeration device according to a first aspect of the present disclosure includes a refrigeration circuit connecting a compressor, a heat source heat exchanger, a gas-liquid separator, and a user-side heat exchanger, and includes a liquid pump that sends liquid refrigerant from the gas-liquid separator to a cooling-side heat exchanger between the heat source-side heat exchanger and the user-side heat exchanger, and a check valve that is arranged in parallel with the liquid pump and prevents backflow of refrigerant toward the gas-liquid separator. The refrigerant that has passed through the cooling-side heat exchanger branches off and flows into a suction-side pipe connected to the suction side of the compressor and a return pipe connected to the gas-liquid separator, and the suction-side pipe and the return pipe are each provided with an on-off valve. This specification includes the entire content of Japanese Patent Application No. 2024-061396, filed on April 5, 2024. A refrigeration system according to a second aspect of the present disclosure includes a refrigeration circuit connecting a compressor, a heat source-side heat exchanger, a gas-liquid separator, and a user-side heat exchanger, and further includes a liquid pump that sends liquid refrigerant from the gas-liquid separator to a cooling-side heat exchanger of the heat source-side heat exchanger and the user-side heat exchanger, and a path that sends the liquid refrigerant from the gas-liquid separator to a downstream side of the liquid pump without passing through the liquid pump. This specification includes the entire contents of Japanese Patent Application No. 2024-061398, filed on April 5, 2024. A refrigeration device in a third aspect of the present disclosure includes a refrigeration circuit connecting a compressor, a heat source side heat exchanger, a gas-liquid separator, and a user side heat exchanger, and includes a liquid pump that sends liquid refrigerant from the gas-liquid separator to a cooling side heat exchanger of the heat source side heat exchanger and the user side heat exchanger, a check valve that is provided in parallel with the liquid pump and prevents backflow of refrigerant toward the gas-liquid separator, and an ejector into which refrigerant that has flowed through a gas cooler of the heat source side heat exchanger or the user side heat exchanger flows and which sends the inflowing refrigerant to the gas-liquid separator, and a suction port of the ejector is connected to a suction pipe provided on the outlet side of the cooling side heat exchanger.a cooling suction pipe branching from the main pipe and connected to a suction port of the ejector; a cooling throttle valve decompressing the refrigerant in the cooling suction pipe; and a heat exchanger cooling the refrigerant flowing from the ejector to the gas-liquid separator. This specification includes the entire contents of Japanese Patent Application No. 2024-061399, filed on April 5, 2024. a cooling throttle valve that adjusts the flow rate of the cooling pipe; and a subcooling heat exchanger that cools the refrigerant in the main pipe with refrigerant that has been decompressed by the cooling throttle valve.

[0010] In a refrigeration apparatus according to a first aspect of the present disclosure, when the cooling load of the cooling-side heat exchanger is not high, the refrigerant in the cooling-side heat exchanger can be returned to the gas-liquid separator through the return pipe by operating the liquid pump or natural circulation via the check valve, thereby reducing the workload of the compressor. When the cooling load of the cooling-side heat exchanger is high, the refrigerant flowing to the cooling-side heat exchanger through the check valve can be compressed by the compressor. This improves the efficiency of the refrigeration apparatus. In a refrigeration apparatus according to a second aspect of the present disclosure, the liquid refrigerant in the gas-liquid separator can be sent to the cooling-side heat exchanger without using a compressor, thereby reducing the workload of the compressor compressing the gas refrigerant. Furthermore, the liquid refrigerant can easily circulate between the gas-liquid separator and the cooling-side heat exchanger through the path even after the liquid pump is stopped. This improves the efficiency of the refrigeration apparatus. In a refrigeration apparatus according to a third aspect of the present disclosure, the suction force of the ejector can be used to easily return the refrigerant in the cooling-side heat exchanger to the gas-liquid separator. Furthermore, the refrigeration apparatus according to a fourth aspect of the present disclosure can increase the flow rate of the cooling suction pipe by using the suction force of the ejector, enabling cooling by the heat exchanger, and liquefying the refrigerant flowing into the gas-liquid separator. This allows for high efficiency of the refrigeration apparatus. The refrigeration apparatus according to a fifth aspect of the present disclosure can reduce the pressure of the refrigerant entering the gas-liquid separator while recovering power using an expansion mechanism, and can subcool the refrigerant flowing into the cooling-side heat exchanger using a subcooling heat exchanger, thereby improving refrigeration capacity. This allows for high efficiency of the refrigeration apparatus.

[0011] 1 is a diagram showing a refrigeration circuit of a refrigeration device according to embodiment 1; FIG. 2 is a diagram showing a refrigeration circuit during medium-load cooling operation; FIG. 3 is a diagram showing a refrigeration circuit during air-cooled cooling operation; FIG. 4 is a diagram showing a refrigeration circuit during high-load cooling operation; FIG. 5 is a diagram showing a refrigeration circuit during heating operation; FIG. 6 is a diagram showing a refrigeration circuit of a refrigeration device according to embodiment 2; FIG. 7 is a diagram showing a refrigeration circuit during medium-load cooling operation; FIG. 8 is a diagram showing a refrigeration circuit during air-cooled cooling operation;

[0012] (Knowledge, etc., that Forms the Basis of the Present Disclosure) At the time the inventors conceived the present disclosure, there was a technology in the field of refrigeration equipment that uses carbon dioxide, a type of natural refrigerant, as a refrigerant. Carbon dioxide has a low global warming potential, is non-flammable, and is non-toxic, making its use expected to expand as a refrigerant with a low environmental impact. Because carbon dioxide's critical temperature is within the operating temperature range, it was previously considered to have issues with efficiency. However, in low-temperature equipment operating at temperatures around −45°C to −5°C, the high suction density of the compressor can be utilized, and refrigeration units using carbon dioxide as a refrigerant have been put into practical use with performance similar to that of units using chlorofluorocarbons. However, when using carbon dioxide as a refrigerant, it is difficult to take advantage of the high suction density, particularly in equipment operating in the air-conditioning temperature range. The inventors discovered a problem: it is difficult to achieve high efficiency when using carbon dioxide as a refrigerant, and technological development to further improve efficiency is required. To solve this problem, the present disclosure constitutes the subject matter of the present disclosure. Therefore, the present disclosure provides a refrigeration unit that can achieve high efficiency.

[0013] Hereinafter, embodiments will be described in detail with reference to the drawings. However, more detailed description than necessary may be omitted. For example, detailed description of already well-known matters or redundant description of substantially identical configurations may be omitted. This is to avoid unnecessary redundancy in the following description and to facilitate understanding by those skilled in the art. Note that the accompanying drawings and the following description are provided to enable those skilled in the art to fully understand the present disclosure, and are not intended to limit the subject matter described in the claims.

[0014] (Embodiment 1) Hereinafter, embodiment 1 will be described with reference to the drawings. [1-1. Configuration] [1-1-1. Overall Configuration] Fig. 1 is a diagram showing a refrigeration circuit 2 of a refrigeration device 1 according to embodiment 1. In the drawing, open on-off valves and throttle valves are shown in white, and closed on-off valves and throttle valves are shown in white. Also in the drawing, wiring through which refrigerant flows is shown in thick lines, and pipes through which refrigerant does not flow are shown in thin lines.

[0015] The refrigeration system 1 is a device having a refrigeration circuit 2 that transfers heat through a refrigeration cycle. The refrigeration system 1 of this embodiment is an air conditioner installed in buildings such as commercial buildings, office buildings, and hotels. The refrigeration system 1 has an outdoor unit 10 and an indoor unit 20. The refrigeration circuit 2 is formed as a circuit through which a refrigerant circulates by connecting the outdoor unit 10 and the indoor unit 20. In this embodiment, the refrigeration circuit 2 uses carbon dioxide (R744), a natural refrigerant that is non-flammable, non-toxic, and has a small environmental impact.

[0016] The outdoor unit 10 is a device that is mainly installed outdoors. In this embodiment, the outdoor unit 10 is installed on the roof of a building. The outdoor unit 10 has a heat source-side heat exchanger 14 that exchanges heat between the refrigerant inside and the outside air.

[0017] The indoor units 20 are devices that are mainly installed in spaces to be conditioned, such as the interior of a building. The number of indoor units 20 installed in the refrigeration system 1 is not particularly limited as long as it is one or more, but FIG. 1 shows one indoor unit 20 installed on each of the upper and lower floors of the building. Hereinafter, when distinguishing between the indoor units 20, the indoor unit 20 installed on the upper floor will be referred to as indoor unit 20H, and the indoor unit 20 installed on the lower floor will be referred to as indoor unit 20L. That is, in this embodiment, the outdoor unit 10 is located higher than the indoor unit 20H, and the indoor unit 20H is located higher than the indoor unit 20L.

[0018] Each indoor unit 20 has a user-side heat exchanger 21 and a user-side throttle valve 22. The user-side heat exchanger 21 is a heat exchanger that exchanges heat between the refrigerant inside it and the air in the space to be conditioned. The user-side throttle valve 22 is a valve that adjusts the flow rate of refrigerant flowing into the user-side heat exchanger 21. The indoor unit 20 conditions the air in the space to be conditioned by heating or cooling the air in the space to be conditioned with the user-side heat exchanger 21. In this embodiment, of the components of the refrigeration circuit 2, the devices and apparatuses other than the user-side heat exchanger 21, the user-side throttle valve 22, and the piping connecting the outdoor unit 10 and the indoor unit 20 are provided in the outdoor unit 10.

[0019] [1-1-2. Configuration of the Refrigeration Circuit] The refrigeration circuit 2 has a low-stage compressor 11 and a high-stage compressor 12. The low-stage compressor 11 and the high-stage compressor 12 correspond to the "compressor" in this disclosure. The low-stage compressor 11 and the high-stage compressor 12 are connected in series, allowing for two-stage compression. The low-stage compressor 11 compresses the refrigerant and discharges it to the suction side of the high-stage compressor 12. The high-stage compressor 12 compresses the refrigerant on the suction side and discharges it toward the oil separator. The oil separator 13 returns the oil in the refrigerant to the compressors 11 and 12. The discharge side of the high-stage compressor 12 is connected to the first switching mechanism 51 via the oil separator 13.

[0020] The first switching mechanism 51 is a mechanism for switching the refrigerant flow path, and includes a first cooling valve 53, a first heating valve 54, a second cooling valve 55, and a heating throttle valve 56, which are connected in a circular arrangement.

[0021] The discharge side of the high-stage compressor 12 is connected between the first cooling valve 53 and the first heating valve 54 of the first switching mechanism 51 via the oil separator 13. In the first switching mechanism 51, the high-temperature side of the heat source-side heat exchanger 14 is connected between the first cooling valve 53 and the second heating valve 56. The high-temperature side of the user-side heat exchanger 21 is connected between the first heating valve 54 and the second cooling valve 55.

[0022] The first switching mechanism 51 switches the destination of the refrigerant discharged from the high-stage compressor 12 between the heat source-side heat exchanger 14 and the user-side heat exchanger 21 by opening either the first cooling valve 53 or the first heating valve 54. Of the heat exchangers 14 and 21, the one that is the destination of the refrigerant discharged from the high-stage compressor 12 functions as a gas cooler. In this specification, a gas cooler refers to a heat exchanger that dissipates heat into the gas refrigerant therein. That is, during cooling operation of the refrigeration device 1, the heat source-side heat exchanger 14 serves as a gas cooler, and during heating operation, the user-side heat exchanger 21 serves as a gas cooler.

[0023] The low-temperature side of the heat source-side heat exchanger 14 is connected to the second switching mechanism 52. The low-temperature side of the user-side heat exchanger 21 is connected to the second switching mechanism 52 via the user-side throttle valve 22. That is, regardless of which of the heat exchangers 14, 21 functions as a gas cooler, the refrigerant that has passed through the gas cooler flows into the second switching mechanism 52.

[0024] The second switching mechanism 52 is a mechanism for switching the refrigerant flow path, and includes a third cooling valve 57, a third heating valve 58, a fourth cooling valve 59, and a heating throttle valve 60, which are connected in a circular arrangement in this order.

[0025] The low-temperature side of the heat source-side heat exchanger 14 is connected between the third cooling valve 57 and the heating throttle valve 60 of the second switching mechanism 52. The low-temperature side of the user-side heat exchanger 21 is connected between the third heating valve 58 and the fourth cooling valve 59 via the user-side throttle valve 22. In addition, in the second switching mechanism 52, the inlet of the gas-liquid separator 17 is connected between the third cooling valve 57 and the third heating valve 58 via the high-pressure receiver 15 and the throttle valve 16.

[0026] The second switching mechanism 52 opens either the third cooling valve 57 or the third heating valve 58, whichever is located between the gas cooler and the high-pressure receiver 15. As a result, the second switching mechanism 52 allows the refrigerant that has passed through the gas cooler to flow into the gas-liquid separator 17, regardless of which of the heat exchangers 14, 21 is functioning as the gas cooler. In this embodiment, the second switching mechanism 52 has check valves 61, 62 that prevent the refrigerant from flowing back from the high-pressure receiver 15 toward the gas cooler. The check valve 61 is provided between the high-pressure receiver 15 and the third cooling valve 57. The check valve 62 is provided between the high-pressure receiver 15 and the third heating valve.

[0027] Whether the second switching mechanism 52 opens the third cooling valve 57 or the third heating valve 58 is determined by which of the heat exchangers 14, 21 the first switching mechanism 51 selects as a gas cooler. That is, the first switching mechanism 51 and the second switching mechanism 52 are controlled to operate in conjunction with each other. Hereinafter, the first switching mechanism 51 and the second switching mechanism 52 will be collectively referred to as the flow path switching mechanism 50.

[0028] As described above, the high-pressure receiver 15 is provided between the second switching mechanism 52 and the inlet of the gas-liquid separator 17. The high-pressure receiver 15 is a so-called receiver tank. The high-pressure receiver 15 temporarily stores the refrigerant cooled by the gas cooler and allows the liquid refrigerant in the stored refrigerant to flow to the throttle valve 16.

[0029] The throttle valve 16 is provided upstream of the inlet of the gas-liquid separator 17. The throttle valve 16 reduces the pressure of the liquid refrigerant sent from the high-pressure receiver 15, and causes the liquid refrigerant to flow into the gas-liquid separator 17 after being mixed with gas and liquid.

[0030] The gas-liquid separator 17 is a device that separates the refrigerant that flows in into the gas-liquid separator 17 into gas refrigerant and liquid refrigerant. The gas-liquid separator 17 flows the separated gas refrigerant into a gas vent pipe 30. The gas vent pipe 30 is a pipe that connects the gas-liquid separator 17 to the suction sides of the compressors 11 and 12. The gas vent pipe 30 has a bifurcated low-stage branch pipe 31 and a high-stage branch pipe 32. The low-stage branch pipe 31 is connected to the suction side of the low-stage compressor 11 via a low-stage throttle valve 33. The high-stage branch pipe 32 is connected to the suction side of the high-stage compressor 12 via a high-stage throttle valve 34.

[0031] A liquid pump 40 is provided at the liquid side outlet of the gas-liquid separator 17. When driven, the liquid pump 40 sends the liquid refrigerant from the gas-liquid separator 17 toward the second switching mechanism 52. The liquid pump 40 is, for example, a centrifugal pump, an axial flow pump, or a mixed flow pump.

[0032] A main pipe 41 is connected to the downstream side of liquid pump 40. Main pipe 41 is a pipe that connects the outlet of liquid pump 40 and second switching mechanism 52. In other words, main pipe 41 allows the liquid refrigerant from gas-liquid separator 17, which has been sent to liquid pump 40, to flow to second switching mechanism 52.

[0033] The refrigeration circuit 2 is also provided with a path 42 that is parallel to the liquid pump 40. The path 42 is a path that allows the liquid refrigerant from the gas-liquid separator 17 to flow to the main pipe 41 downstream of the liquid pump 40 without passing through the liquid pump 40. The path 42 connects the main pipe 41 to a liquid side outlet of the gas-liquid separator 17 that is different from the liquid side outlet to which the liquid pump is connected.

[0034] A check valve 43 is provided in the path 42 to prevent the refrigerant from flowing back toward the gas-liquid separator 17. That is, the check valve 43 is provided in parallel with the liquid pump 40.

[0035] A cooling pipe 44 branches off from the main pipe 41. The cooling pipe 44 connects the main pipe 41 and the gas vent pipe 30. Specifically, the cooling pipe 44 branches off from the main pipe 41 at a portion upstream of the junction of the main pipe 41 with the downstream side of the check valve 43. The cooling pipe 44 is provided with a cooling throttle valve 45 that reduces the pressure of the refrigerant.

[0036] A subcooling heat exchanger 46 is provided downstream of the liquid pump 40, which exchanges heat between the liquid refrigerant in the main pipe 41 and the refrigerant in the cooling pipe 44 after passing through the cooling throttle valve 45. The refrigerant in the cooling pipe 44 is cooled by passing through the cooling throttle valve 45, and therefore, in the subcooling heat exchanger 46, the refrigerant in the main pipe 41 is cooled by the refrigerant in the cooling pipe 44. Specifically, the subcooling heat exchanger 46 cools the refrigerant in the main pipe 41 downstream of the junction with the path 42. That is, the subcooling heat exchanger 46 can cool both the refrigerant sent to the liquid pump 40 and the refrigerant that has passed through the path 42.

[0037] The refrigerant in the main pipe 41 downstream of the subcooling heat exchanger 46 is cooled by an external cooling device 47. The external cooling device 47 cools the refrigerant in the main pipe 41 by a refrigeration cycle that uses refrigerant separated from the refrigerant in the refrigeration circuit 2.

[0038] The external cooling device 47 only needs to have the minimum amount of equipment required to establish a refrigeration cycle and cool the refrigerant in the main pipe 41. Therefore, the configuration of the external cooling device 47 can be simplified more easily than the configuration of the refrigeration circuit 2, and refrigerant leakage from the external cooling device 47 is less likely to occur. Furthermore, since the external cooling device 47 can easily be configured to operate with a smaller amount of refrigerant than the refrigeration circuit 2, even if refrigerant leaks from the external cooling device 47, the amount of leakage can easily be reduced. In other words, the external cooling device 47 can easily be configured to reduce the risk of refrigerant leakage.

[0039] For this reason, a refrigerant that is more flammable, toxic, and has a greater environmental impact in the event of leakage than carbon dioxide but has higher energy efficiency than carbon dioxide can be used in the refrigeration cycle of external cooling device 47. In the present embodiment, external cooling device 47 can appropriately perform leakage management even when using a refrigerant that has higher energy efficiency in the refrigeration cycle than carbon dioxide, such as an HFC (hydrofluorocarbon) refrigerant, an HFO (hydrofluoroolefin) refrigerant, or a mixed refrigerant containing these.

[0040] The main pipe 41 is connected to the second switching mechanism 52 between the fourth cooling valve 59 and the heating throttle valve 60 downstream of the external cooling device 47 .

[0041] The second switching mechanism 52 switches the destination of the liquid refrigerant in the main pipe 41 between the heat source-side heat exchanger 14 and the user-side heat exchanger 21 by opening either the fourth cooling valve 59 or the heating throttle valve 60. At this time, the heat exchanger into which the liquid refrigerant in the main pipe 41 flows functions as a cooling-side heat exchanger. In this specification, a cooling-side heat exchanger refers to a heat exchanger that absorbs heat with the refrigerant therein. That is, during cooling operation of the refrigeration system 1, the user-side heat exchanger 21 serves as the cooling-side heat exchanger, and during heating operation, the heat source-side heat exchanger 14 serves as the cooling-side heat exchanger. In this embodiment, the second switching mechanism 52 has a check valve 63 that prevents backflow from the user-side throttle valve 22 toward the main pipe 41. The check valve 63 is provided in the second switching mechanism 52 between the fourth cooling valve 59 and the user-side throttle valve 22.

[0042] As described above, the high-temperature sides of the heat exchangers 14, 21 are each connected to the first switching mechanism 51, and therefore the refrigerant that has passed through the cooling-side heat exchanger flows into the first switching mechanism 51. In the first switching mechanism 51, the suction-side pipe 18, which is a pipe connected to the suction side of the low-stage compressor 11, is connected between the second cooling valve 55 and the second heating valve 56. The return pipe 70 is connected between the second cooling valve 55 and the second heating valve 56. The return pipe 70 is connected to the first switching mechanism 51 in parallel with the suction-side pipe 18.

[0043] The first switching mechanism 51 opens either the second cooling valve 55 or the second heating valve 56, whichever is located between the cooling-side heat exchanger and the suction-side pipe 18. Therefore, the first switching mechanism 51 allows the refrigerant from the cooling-side heat exchanger to flow through the suction-side pipe 18 and the return pipe 70, regardless of which of the heat exchangers 14 and 21 functions as the cooling-side heat exchanger.

[0044] The suction side pipe 18 is provided with a suction side on-off valve 19. More specifically, the suction side on-off valve 19 is located in the suction side pipe 18 upstream of the junction of the low-stage branch pipe 31 and the suction side pipe 18.

[0045] The return pipe 70 is a pipe that returns the refrigerant from the first switching mechanism 51 to the gas-liquid separator 17. A return-side on-off valve 71 is provided in the return pipe 70. A check valve 72 that prevents backflow of the refrigerant from the gas-liquid separator 17 side toward the first switching mechanism 51 is also provided in the return pipe 70. The suction-side on-off valve 19 and the return-side on-off valve 71 correspond to the "on-off valve" in this disclosure.

[0046] An oil separator 73 is provided in the return pipe 70. The oil separator 73 separates oil mixed in the refrigerant in the return pipe 70 and returns the oil to the suction sides of the compressors 11 and 12. In this embodiment, the oil separator 73 returns the oil in the return pipe 70 to the gas vent pipes 30 located on the suction sides of the compressors 11.

[0047] A heat exchanger 74 is also provided in the return pipe 70. The heat exchanger 74 is a heat exchanger that cools the refrigerant in the return pipe 70 with outside air. That is, the heat exchanger 74 can liquefy the gas component of the refrigerant in the return pipe 70 that has evaporated in the cooling-side heat exchanger.

[0048] The refrigeration system 1 has a blower 74a that blows outside air to the heat exchanger 74. The refrigeration system 1 also has a water supply means 74b that supplies water to lower the temperature of the intake air of the heat exchanger 74 by using the latent heat of evaporation. Therefore, the heat exchanger 74 can cool the refrigerant in the return pipe 70 even when the outside air temperature is about 5°C higher than the refrigerant in the return pipe 70.

[0049] Similarly, the refrigeration system 1 has a blower 14a that blows outside air to the heat source-side heat exchanger 14. The refrigeration system 1 also has water supply means 14b that supplies water to lower the temperature of the intake air of the heat source-side heat exchanger 14 by using latent heat of evaporation. The water supply means 14b supplies water to lower the temperature of the intake air of the heat source-side heat exchanger 14 by using latent heat of evaporation when the heat source-side heat exchanger 14 functions as a gas cooler. This improves the efficiency of heat exchange when the heat source-side heat exchanger 14 functions as a gas cooler.

[0050] The water supply means 14b, 74b may be, for example, a device that sprays water directly onto the heat exchangers 14, 74. Alternatively, the water supply means 14b, 74b may be, for example, a so-called indirect water sprinkler device that supplies water to a breathable filter provided on the outside air intake side of the heat exchangers 14, 74 and uses the latent heat of evaporation of water adhering to the filter to lower the temperature of the intake air of the heat exchangers 14, 74. Alternatively, the water supply means 14b, 74b may be any other device, mechanism, etc. that can lower the temperature of the intake air of the heat exchangers 14, 74 by utilizing the latent heat of evaporation of water.

[0051] [1-1-3. Configuration of the Control Device] As shown in FIG. 1 , the refrigeration device 1 is provided with a control unit 90. The control unit 90 is a device that controls each part of the refrigeration device 1. The control unit 90 has a processor such as a CPU (Central Processing Unit) and an MPU (Micro-Processing Unit), and a storage medium such as a hard disk, a flash memory, and an optical disk. The control unit 90 controls each part of the refrigeration device 1 by loading a program from the storage medium into the processor and executing the program by the processor. The control unit 90 may also have wired logic such as an ASIC (Application Specific Integrated Circuit) instead of a processor and a storage medium. The control unit 90 may also have a combination of a processor, a storage medium, and wired logic.

[0052] The control unit 90 also includes communication hardware that complies with wireless or wired communication standards, such as a connector, a communication circuit, etc. The control unit 90 communicates with each part of the refrigeration device 1 via this communication hardware.

[0053] The control unit 90 individually controls the on / off and rotation speed of each compressor 11, 12 and liquid pump 40. The control unit 90 switches the open and closed states of each valve 19, 53 to 60, 71, which are on-off valves. The control unit 90 also switches the open and closed states of each throttle valve 16, 22, 33, 34, 45, 60, which are throttle valves with adjustable opening degrees, and adjusts their opening degrees. The control unit 90 switches the on / off states of each air blower 14a, 74a and controls the air blowing volume. The control unit 90 controls whether or not water is supplied by the water supply means 14b, 74b, and the amount of water supplied.

[0054] [1-2. Operation] The operation of the refrigeration system 1 configured as above will be described below. The refrigeration system 1 easily improves the APF (Annual Performance Factor) by switching the refrigerant flow path to increase energy efficiency depending on the cooling load. First, the operation during cooling operation when the cooling load is low or medium, i.e., when the cooling load is medium or less, will be described.

[0055] [1-2-1. Operation during cooling operation under medium load or less] Fig. 2 is a diagram showing the refrigeration circuit 2 during medium load cooling operation. Note that Fig. 1 shows the refrigeration circuit 2 during low load cooling operation. As shown in Figs. 1 and 2, during cooling operation under medium load or less, the control unit 90 opens the cooling valves 53, 55, 57, and 59. The control unit 90 also closes the heating valves 54, 56, and 58 and the heating throttle valve 60. As a result, the heat source side heat exchanger 14 functions as a gas cooler, and the user side heat exchanger 21 functions as a cooling side heat exchanger.

[0056] Furthermore, the control unit 90 closes the suction-side on-off valve 19 and opens the return-side on-off valve 71. As a result, each of the compressors 11, 12 no longer directly draws in the refrigerant that has passed through the use-side heat exchanger 21, which is a cooling-side heat exchanger, but instead draws in the gas refrigerant separated in the gas-liquid separator 17 via the gas vent pipe 30.

[0057] 1 , the control unit 90 opens the high-stage throttle valve 34 and closes the low-stage throttle valve 33, and then drives only the high-stage compressor 12 of the compressors 11 and 12. As a result, the gas refrigerant separated in the gas-liquid separator 17 is compressed in a single stage by the high-stage compressor 12 and discharged as high-temperature gas refrigerant.

[0058] On the other hand, when the cooling load is medium, the control unit 90 closes the high-stage throttle valve 34 and opens the low-stage throttle valve 33 as shown in Fig. 2, and then drives both of the compressors 11 and 12. As a result, the gas refrigerant separated in the gas-liquid separator 17 is compressed in two stages by the two compressors 11 and 12, and is discharged from the high-stage compressor 12 as high-temperature gas refrigerant.

[0059] Whether the cooling load is low or medium, the refrigerant discharged from the high-stage compressor 12 flows into the first switching mechanism 51 via the oil separator 13, passes through the first cooling valve 53, and flows into the heat source side heat exchanger 14.

[0060] In the heat source-side heat exchanger 14, the high-temperature gas refrigerant dissipates heat to the outside air and is cooled. During cooling operation, the control unit 90 activates the water supply means 14b to promote cooling of the refrigerant. After dissipating heat in the heat source-side heat exchanger 14, the refrigerant flows into the second switching mechanism 52 and then flows into the high-pressure receiver 15 via the third cooling valve 57.

[0061] Of the refrigerant that has flowed into the high-pressure receiver 15, the liquid refrigerant is reduced in pressure by the throttle valve 16 to become a medium-temperature gas-liquid mixture, and then flows into the gas-liquid separator 17. The refrigerant that has flowed into the gas-liquid separator 17 is separated into gas refrigerant and liquid refrigerant, and the separated gas refrigerant is sucked back into each of the compressors 11, 12 via the gas vent pipe 30.

[0062] In this way, when the cooling load is medium or less, the gas refrigerant in the gas-liquid separator 17 is compressed by each compressor 11, 12, dissipates heat in the heat source side heat exchanger 14, and returns to the gas-liquid separator 17 again without passing through the user side heat exchanger 21, where it is separated into gas refrigerant and liquid refrigerant. In other words, each compressor 11, 12 performs the work of liquefying the gas refrigerant in the gas-liquid separator 17 and returning it to the gas-liquid separator 17 again. On the other hand, the compressors 11, 12 do not perform the work of sending the liquid refrigerant from the gas-liquid separator 17 to the user side heat exchanger 21.

[0063] A liquid pump 40 is used to send the liquid refrigerant to the use-side heat exchanger 21. The control unit 90 drives the liquid pump 40 to send the liquid refrigerant stored in the gas-liquid separator 17 to the use-side heat exchanger 21. Driving the liquid pump 40 causes the liquid refrigerant in the gas-liquid separator 17 to flow into the main pipe 41. Note that a check valve 43 prevents the refrigerant sent to the liquid pump 40 from flowing back toward the gas-liquid separator 17.

[0064] The control unit 90 uses the subcooling heat exchanger 46 and the external cooling device 47 to cool the refrigerant in the main pipe 41 to a predetermined target temperature. At this time, the control unit 90 cools the refrigerant in the main pipe 41 by using the external cooling device 47 preferentially over the subcooling heat exchanger 46. That is, when the refrigerant in the main pipe 41 can be cooled to the target temperature by the external cooling device 47 alone, the control unit 90 closes the cooling throttle valve 45 and does not perform cooling by the subcooling heat exchanger 46. On the other hand, when the refrigerant in the main pipe 41 cannot be subcooled to the target temperature by the external cooling device 47 alone, the control unit 90 opens the cooling throttle valve 45 and performs cooling by the subcooling heat exchanger 46.

[0065] The liquid refrigerant that has passed through the main pipe 41 flows into the second switching mechanism 52, passes through the fourth cooling valve 59 and the check valve 63, flows into each indoor unit 20, and flows through the use-side throttle valve 22 into the use-side heat exchanger 21. In the use-side heat exchanger 21, the liquid refrigerant absorbs heat from the air in the space to be conditioned, and some of it becomes gas refrigerant, cooling the air in the space to be conditioned. This cools the space to be conditioned.

[0066] The refrigerant that has passed through the use-side heat exchanger 21 flows into the first switching mechanism 51, and reaches the suction-side pipe 18 and the return pipe 70 via the second cooling valve 55. As described above, when the cooling load is medium or less, the suction-side on-off valve 19 is closed and the return-side on-off valve 71 is open. Therefore, the refrigerant that has passed through the first switching mechanism 51 is not sucked into the compressors 11 and 12, and returns to the gas-liquid separator 17 via the return pipe 70.

[0067] The refrigerant passing through the return pipe 70 is cooled by the heat exchanger 74. When the cooling load is medium or less, the control unit 90 operates the water supply means 74b to facilitate liquefaction of the refrigerant in the return pipe 70. The refrigerant that has passed through the heat exchanger 74 is returned to the gas-liquid separator 17.

[0068] In this way, when the cooling load is medium or less, the liquid refrigerant in the gas-liquid separator 17 is sent by the liquid pump 40 to the user-side heat exchanger 21 to cool the space to be conditioned, and returns to the gas-liquid separator 17 through a closed cycle without passing through each compressor 11, 12. In other words, the refrigeration circuit 2 is configured to be able to independently store the liquid refrigerant in the gas-liquid separator 17 by driving the compressors 11, 12, and send the liquid refrigerant from the gas-liquid separator 17 toward the user-side heat exchanger 21 by driving the liquid pump 40.

[0069] When refrigerant containing gas refrigerant returns from the return pipe 70 to the gas-liquid separator 17 due to insufficient cooling in the heat exchanger 74, the gas refrigerant increases and the liquid refrigerant decreases in the gas-liquid separator 17 when the conditioned space is cooled by the operation of the liquid pump 40. The control unit 90 drives the compressors 11 and 12 by an amount sufficient to compensate for the decrease in the liquid refrigerant in the gas-liquid separator 17.

[0070] In order to achieve the above-described operation, when the cooling load is low, the control unit 90 controls each part of the refrigeration device 1 so that the pressure in each part of the refrigeration circuit 2 satisfies the following inequality (A): P1<P5≦P9<P8≦P0<P7 (A) where, as shown in FIG. 1 , in inequality (A), P0 represents the pressure on the outlet side of the liquid pump 40, P1 represents the suction pressure of the high-stage compressor 12, P5 represents the pressure inside the gas-liquid separator 17, P7 represents the pressure in the piping on the inlet side of the indoor unit 20L on the low floor, P8 represents the pressure in the piping on the inlet side of the indoor unit 20H on the high floor, and P9 represents the pressure in the piping on the outlet side of the indoor units 20L and 20H. Note that P7 represents the pressure in the piping located at the same height as the indoor unit 20L, and P8 represents the pressure in the piping located at the same height as the indoor unit 20H.

[0071] When the cooling load is medium or less, as described above, the liquid pump 40 operates to return the liquid refrigerant in the gas-liquid separator 17 to the gas-liquid separator 17 through a closed cycle that does not pass through the compressors 11 and 12. In this closed cycle, even if the liquid pump 40 is stopped after the liquid pump 40 operates, natural circulation of the refrigerant may occur between the gas-liquid separator 17 and the user-side heat exchanger 21.

[0072] When natural circulation is occurring, the liquid refrigerant in the gas-liquid separator 17 flows into the main pipe 41 via the path 42, instead of into the stopped liquid pump 40, which has a high resistance. After flowing into the main pipe 41, the liquid refrigerant flows through the same closed cycle as when the liquid pump 40 is driven, into the user-side heat exchanger 21 and the return pipe 70, and returns to the gas-liquid separator 17. By utilizing natural circulation, the control unit 90 can continue cooling operation by simply driving the liquid pump 40 when natural circulation is to be generated or when natural circulation is attenuated due to flow path resistance, making it easier to further improve energy efficiency.

[0073] In this embodiment, the refrigeration system 1 is installed under conditions that particularly facilitate natural circulation. Specifically, because the outdoor unit 10 equipped with the gas-liquid separator 17 is located higher than the indoor units 20L, 20H, the difference in elevation between the gas-liquid separator 17 and each of the indoor units 20L, 20H facilitates refrigerant circulation between the gas-liquid separator 17 and each of the indoor units 20L, 20H. Furthermore, as described above, a portion of the liquid refrigerant evaporates due to heat absorption in the user-side heat exchangers 21. Therefore, the lighter refrigerant that has partially evaporated in the user-side heat exchangers 21 is easily returned to the gas-liquid separator 17 by being pushed out by the heavier liquid refrigerant flowing from the gas-liquid separator 17 toward the user-side heat exchangers 21 of each of the indoor units 20L, 20H.

[0074] Furthermore, since the liquid refrigerant in the gas-liquid separator 17 returns to the gas-liquid separator 17 through a closed cycle that does not pass through the compressors 11 and 12, the oil that has flowed into the gas-liquid separator 17 cannot return to the compressors 11 and 12 during the closed cycle. In contrast, in this embodiment, the oil that has flowed into the gas-liquid separator 17 is returned to the compressors 11 and 12 by an oil separator 73 that returns the oil in the refrigerant in the return pipe 70 to the gas vent pipe 30 outside the closed cycle.

[0075] [1-2-2. Operation During Air-Cooling Cooling Operation] Figure 3 is a diagram showing the refrigeration circuit 2 during air-cooling cooling operation. When the cooling load is medium or less, the liquid refrigerant in the gas-liquid separator 17 does not decrease under the condition that the refrigerant evaporated in the user-side heat exchanger 21 is entirely returned to liquid refrigerant through the heat exchanger 74 of the return pipe 70. In such a case, air-cooling cooling operation is possible, in which the refrigerant is liquefied using only the heat exchanger 74 without operating the compressors 11 and 12. For example, air-cooling cooling operation is easy to perform in an environment with low outdoor temperatures, such as when the refrigeration device 1 is operated to prevent the room temperature from rising due to the exhaust heat of equipment installed in the conditioned space.

[0076] When performing air-cooling operation, the control unit 90 stops the compressors 11 and 12 from a cooling operation state of medium load or less, and closes the throttle valve 16, the low-stage side throttle valve 33, the high-stage side throttle valve 34, and the cooling throttle valve 45. As a result, the suction side and discharge side of the compressors 11 and 12 are no longer in communication with the gas-liquid separator 17. Furthermore, the refrigerant in the main pipe 41 no longer passes through the cooling pipe 44, and the refrigerant in the main pipe 41 is not cooled by the subcooling heat exchanger 46.

[0077] During air-cooling operation, the control unit 90 drives the liquid pump 40 to cause the liquid refrigerant in the gas-liquid separator 17 to flow through the use-side heat exchanger 21 and return pipe 70 via a closed cycle similar to that in the case where the cooling load is medium or less, and then return the liquid refrigerant to the gas-liquid separator 17. Also, as in the case where the cooling load is medium or less, the control unit 90 stops the liquid pump 40 when natural circulation of the refrigerant occurs in the closed cycle, and drives the liquid pump 40 only when natural circulation is generated or when the natural circulation is attenuated.

[0078] In this way, during air-cooling operation, the compressors 11 and 12, which consume particularly large amounts of energy, are not driven, so the energy required for air-cooling operation can be significantly reduced. The more situations in which air-cooling operation can be performed throughout the year, the easier it is to improve the APF of the refrigeration system 1.

[0079] [1-2-3. Operation During High-Load Cooling Operation] Figure 4 shows the refrigeration circuit 2 during high-load cooling operation. During operation when the cooling load is medium or less, subcooled liquid refrigerant flows through the user-side heat exchanger 21, which tends to increase heat leakage when the ambient temperature is high and the cooling load is high. Because such heat leakage occurs significantly in the gas-liquid separator 17, the refrigerant temperature drop in the gas-liquid separator 17 is suppressed, and the liquid refrigerant is cooled by the subcooling heat exchanger 46 and the external cooling device 47, thereby increasing the subcooling effect and enhancing the refrigeration effect. Furthermore, when the cooling load is high, the refrigeration system 1 switches to superheat control, which creates a temperature difference between the inlet and outlet of the user-side heat exchanger 21 (the cooling-side heat exchanger), thereby utilizing the latent heat of evaporation to cool the air in the conditioned space.

[0080] As in the case of a medium load or less, the control unit 90 opens the cooling valves 53, 55, 57, and 59 and closes the heating valves 54, 56, and 58 and the heating throttle valve 60. Unlike the case of a medium load or less, the control unit 90 also opens the suction side on-off valve 19 and closes the return side on-off valve 71. As a result, the refrigerant that has passed through the use side heat exchanger 21, which is a cooling side heat exchanger, is compressed in two stages in the compressors 11 and 12 without returning to the gas-liquid separator 17 via the return pipe 70.

[0081] The refrigerant compressed in the two stages by the compressors 11, 12 flows into the gas-liquid separator 17 through the same path as in the case of a medium load or less. In addition, the control unit 90 closes the low-stage throttle valve 33 and opens the high-stage throttle valve 34. As a result, the gas refrigerant separated in the gas-liquid separator 17 is sucked into the high-stage compressor 12 through the gas vent pipe 30, and the temperature of the refrigerant discharged from the high-stage compressor 12 is reduced.

[0082] When the cooling load is high, the suction-side on-off valve 19 is open, and the main pipe 41 and path 42 communicate with the suction sides of the compressors 11 and 12. Therefore, the control unit 90 stops the liquid pump 40, and causes the liquid refrigerant separated in the gas-liquid separator 17 to flow into the main pipe 41 via path 42 by circulation caused by the operation of the compressors 11 and 12. The liquid refrigerant in the main pipe 41 follows the same path as in the case of a medium load or lower, and flows into each indoor unit 20 while being cooled by the subcooling heat exchanger 46 and the external cooling device 47.

[0083] The refrigerant that flows into each indoor unit 20 is decompressed by the use-side throttle valve 22 and absorbs heat and evaporates in the use-side heat exchanger 21. The refrigerant that passes through the use-side heat exchanger 21 passes through the second cooling valve 55 and the suction-side on-off valve 19 of the first switching mechanism 51 and the suction-side piping 18, and is compressed in two stages in the compressors 11 and 12. The control unit 90 controls the opening of the use-side throttle valve 22 so that the refrigerant that flows into the use-side heat exchanger 21 reaches a specified degree of superheat, thereby preventing liquid compression in the compressors 11 and 12. Furthermore, when the cooling load is high, the refrigerant does not pass through the return piping 70, so the control unit 90 stops the water supply means 74b.

[0084] That is, when the cooling load is high, as in a normal two-stage compression cycle, the compressors 11 and 12 not only perform the work of liquefying the refrigerant and storing it in the gas-liquid separator 17, but also perform the work of circulating the liquid refrigerant in the gas-liquid separator 17 to the user-side heat exchanger 21.

[0085] [1-2-4. Operation during heating operation] Figure 5 is a diagram showing the refrigeration circuit 2 during heating operation. The refrigeration device 1 is configured to be able to perform heating operation in addition to cooling operation according to the cooling load. During heating operation, the control unit 90 opens the heating valves 54, 56, and 58 and the heating throttle valve 60 of the flow path switching mechanism 50 and closes the cooling valves 53, 55, 57, and 59. As a result, the heat source side heat exchanger 14 functions as a cooling side heat exchanger, and the user side heat exchanger 21 functions as a gas cooler.

[0086] The control unit 90 also opens the suction-side on-off valve 19 and closes the return-side on-off valve 71. As a result, the refrigerant that has passed through the heat-source-side heat exchanger 14, which is a cooling-side heat exchanger, is compressed in two stages by the compressors 11 and 12 and flows into the first switching mechanism 51 via the oil separator 13.

[0087] The refrigerant that has flowed into the first switching mechanism 51 flows into each indoor unit 20 via the first heating valve 54, and is cooled by dissipating heat to the air in the space to be conditioned in the utilization-side heat exchanger 21. This heats the space to be conditioned.

[0088] The refrigerant that has passed through the user-side heat exchanger 21 passes through the user-side throttle valve 22, the third heating valve 58 of the second switching mechanism 52, and the check valve 62, and flows into the high-pressure receiver 15. The liquid refrigerant that has flowed into the high-pressure receiver 15 is decompressed by the throttle valve 16, becoming a low-temperature gas-liquid mixture, and flows into the gas-liquid separator 17.

[0089] During heating operation, the control unit 90 closes the low-stage throttle valve 33 and opens the high-stage throttle valve 34. As a result, the gas refrigerant separated in the gas-liquid separator 17 is sucked into the high-stage compressor 12 via the gas vent pipe 30, causing the pressure in the gas-liquid separator 17 to reach a specified value and lowering the temperature of the refrigerant discharged from the high-stage compressor 12.

[0090] During heating operation, the suction-side on-off valve 19 is open, so the main pipe 41 and the path 42 are connected to the suction sides of the compressors 11 and 12. Therefore, the control unit 90 stops the liquid pump 40, and the liquid refrigerant separated in the gas-liquid separator 17 flows into the main pipe 41 via the path 42 by circulation caused by the operation of the compressors 11 and 12. That is, during heating operation, as in a normal two-stage compression cycle, the compressors 11 and 12 also perform the work of flowing the liquid refrigerant from the gas-liquid separator 17 to the heat-source-side heat exchanger 14. The control unit 90 opens the cooling throttle valve 45, and cools the refrigerant in the main pipe 41 using the subcooling heat exchanger 46. The control unit 90 also stops the external cooling device 47.

[0091] The refrigerant that has passed through the main pipe 41 passes through the heating throttle valve 60 of the second switching mechanism 52 and flows into the heat source side heat exchanger 14. The refrigerant absorbs heat and evaporates in the heat source side heat exchanger 14, passes through the suction side pipe 18 via the second heating valve 56 and the suction side on-off valve 19 of the first switching mechanism 51, and is two-stage compressed in the compressors 11 and 12. Note that the control unit 90 stops the water supply means 14b during heating operation. The control unit 90 also controls the opening of the heating throttle valve 60 so that the refrigerant passing through the heat source side heat exchanger 14 reaches a specified degree of superheat, thereby preventing liquid compression in the compressors 11 and 12.

[0092] [1-3. Effects, etc.] As described above, in the present embodiment, the refrigeration device 1 includes the refrigeration circuit 2 connecting the compressors 11, 12, the heat source side heat exchanger 14, the gas-liquid separator 17, and the user side heat exchanger 21, and is provided with a liquid pump 40 that sends the liquid refrigerant from the gas-liquid separator 17 to the cooling side heat exchanger of the heat source side heat exchanger 14 or the user side heat exchanger 21, and a path 42 that sends the liquid refrigerant from the gas-liquid separator 17 to the downstream side of the liquid pump 40 without passing through the liquid pump 40. This allows the liquid refrigerant in the gas-liquid separator 17 to be sent to the cooling side heat exchanger without relying on the compressors 11, 12, making it easier to reduce the workload of the compressors 11, 12 to compress the gas refrigerant. Furthermore, particularly when the gas-liquid separator 17 is installed on the rooftop of a building or the like and the cooling-side heat exchanger is installed on a lower floor of the building or the like, and the gas-liquid separator 17 is located higher than the cooling-side heat exchanger, the liquid refrigerant can easily circulate between the gas-liquid separator 17 and the cooling-side heat exchanger via the path 42 even after the liquid pump 40 has stopped. This makes it easier to reduce energy consumption and improve the efficiency of the refrigeration system 1.

[0093] As in the present embodiment, in the refrigeration system 1, the compressors 11, 12 may be configured to discharge the gas refrigerant from the gas-liquid separator 17 to the gas cooler of the heat source side heat exchanger 14 or the user side heat exchanger 21, return the gas-liquid mixed state to the gas-liquid separator 17 via the throttle valve 16, and the liquid pump 40 send the liquid refrigerant from the gas-liquid separator 17 to the cooling side heat exchanger, where it absorbs heat and then returns the liquid refrigerant to the gas-liquid separator 17. This allows the operation of the compressors 11, 12 to be separated from the sending of liquid refrigerant to the cooling side heat exchanger, and to be performed with the purpose of liquefying the gas refrigerant and returning it to the gas-liquid separator 17, thereby reducing the workload of the compressors 11, 12. This makes it easier to reduce energy consumption and improve the efficiency of the refrigeration system 1.

[0094] As in the present embodiment, the refrigeration apparatus 1 may be configured such that a check valve 43 is provided in the path 42 to prevent backflow of the refrigerant toward the gas-liquid separator 17. This prevents the liquid refrigerant sent to the liquid pump 40 from flowing back to the gas-liquid separator 17 via the path 42. This makes it easier for the liquid pump 40 to send the liquid refrigerant from the gas-liquid separator 17, thereby improving the efficiency of the refrigeration apparatus 1.

[0095] As in this embodiment, the refrigeration system 1 may be configured to include a main pipe 41 provided downstream of the liquid pump 40 and through which refrigerant flows toward the cooling-side heat exchanger, a cooling pipe 44 branching from the main pipe 41, a cooling throttle valve 45 that reduces the pressure of the refrigerant in the cooling pipe 44, and a subcooling heat exchanger 46 that cools the refrigerant in the main pipe 41 with the refrigerant reduced in pressure by the cooling throttle valve 45. This allows the liquid refrigerant to be cooled after passing through the gas-liquid separator 17, which has a large surface area, thereby reducing heat leakage from the liquid refrigerant. This increases the refrigeration effect while suppressing losses, thereby improving the efficiency of the refrigeration system 1.

[0096] As in the present embodiment, the refrigeration system 1 may be configured to be provided with an external cooling device 47 that cools the refrigerant after passing through the subcooling heat exchanger 46 in the main pipe 41. This allows the liquid refrigerant flowing into the cooling-side heat exchanger to be further cooled. This makes it possible to improve and stabilize the refrigeration capacity, thereby achieving high efficiency of the refrigeration system.

[0097] As in the present embodiment, the refrigeration circuit 2 may use carbon dioxide as a refrigerant, and the external cooling device 47 may be configured to cool the refrigerant in the main pipe 41 using a refrigeration cycle that utilizes a refrigerant that is more energy efficient than carbon dioxide. This allows the energy-efficient external cooling device 47 to improve the refrigeration capacity of the refrigeration system 1 that uses carbon dioxide, which has a small environmental impact, as a refrigerant. Furthermore, because the external cooling device 47 can be configured more simply than the refrigeration circuit 2 of the refrigeration system 1, even if a refrigerant such as an HFC or HFO, which is highly efficient but has a larger environmental impact than carbon dioxide, is used in the external cooling device 47, the risk of refrigerant leakage from the external cooling device 47 is less likely to increase. This allows the refrigeration system 1 to achieve high efficiency while suppressing environmental impact.

[0098] As in the present embodiment, the refrigeration system 1 may be configured to use the external cooling device 47 preferentially over the subcooling heat exchanger 46 to cool the refrigerant flowing through the cooling-side heat exchanger to a target temperature. This allows the external cooling device 47, which is more likely to be configured with high energy efficiency, to be used preferentially over the subcooling heat exchanger 46. This allows the refrigeration system 1 to be made more efficient.

[0099] As in this embodiment, the refrigeration system 1 may be configured to include a water supply means 14b that supplies water to lower the temperature of the intake air of the heat source side heat exchanger 14 by using the latent heat of evaporation. This makes it easier to improve the refrigeration capacity of the refrigeration system with small energy consumption, thereby achieving high efficiency of the refrigeration system.

[0100] As in the present embodiment, the compressor may be configured to include the high-stage compressor 12 and the low-stage compressor 11. This makes it easier to increase the efficiency of each compressor 11, 12, particularly when carbon dioxide or the like, which has a large pressure difference within the refrigeration circuit 2, is used as a refrigerant. This makes it possible to increase the efficiency of the refrigeration device 1.

[0101] As described above, in this embodiment, the refrigeration device 1 includes a refrigeration circuit 2 that connects the compressors 11, 12, the heat source side heat exchanger 14, the gas-liquid separator 17, and the use side heat exchanger 21, and includes a liquid pump 40 that sends liquid refrigerant from the gas-liquid separator 17 to the cooling side heat exchanger of the heat source side heat exchanger 14 or the use side heat exchanger 21, and a check valve 43 that is provided in parallel with the liquid pump 40 and prevents backflow of the refrigerant toward the gas-liquid separator 17. The refrigerant that has passed through the cooling side heat exchanger branches off and flows into the suction side piping 18 that is connected to the suction sides of the compressors 11, 12, and the return piping 70 that is connected to the gas-liquid separator 17, and the suction side piping 18 and the return piping 70 are provided with the suction side on-off valve 19 and the return side on-off valve 71, respectively. As a result, when the cooling load of the cooling-side heat exchanger is not high, the refrigerant in the cooling-side heat exchanger can be returned to the gas-liquid separator 17 via the return pipe 70 by operation of the liquid pump 40 or natural circulation via the check valve 43, thereby reducing the workload of the compressors 11 and 12. Furthermore, when the cooling load of the cooling-side heat exchanger is high, the refrigerant that has flowed into the cooling-side heat exchanger via the check valve 43 can be compressed by the compressors 11 and 12. This makes it easier to improve the APF and enables the efficiency of the refrigeration system to be increased.

[0102] As in the present embodiment, the refrigeration system 1 may be configured such that the compressor includes a low-stage compressor 11 and a high-stage compressor 12, and the gas vent pipe 30 that vents the gas refrigerant from the gas-liquid separator 17 is connected to the low-stage compressor 11 and the high-stage compressor 12 via a low-stage throttle valve 33 and a high-stage throttle valve 34, respectively. As a result, when liquid refrigerant is flowed to the cooling-side heat exchanger by the liquid pump 40 or natural circulation, if the load is small, the low-stage compressor 11 can be stopped and the gas refrigerant in the gas-liquid separator 17 can be liquefied by operating only the high-stage compressor 12. This makes it easier to improve the APF, and the efficiency of the refrigeration system 1 can be increased.

[0103] As in this embodiment, the refrigeration system 1 may be configured to include a heat exchanger 74 that exchanges heat between the refrigerant in the return pipe 70 and outside air. This allows the refrigerant in the return pipe 70 to dissipate heat to the outside air, making it easier to increase the liquid component of the refrigerant flowing into the gas-liquid separator 17 and reduce the work of the compressors 11 and 12. This makes it easier to improve the APF and increase the efficiency of the refrigeration system 1.

[0104] As in this embodiment, the refrigeration system 1 may be configured to include a water supply means 74b that supplies water to lower the temperature of the intake air of the heat exchanger 74 by using the latent heat of evaporation. This makes it easier to dissipate heat from the refrigerant in the return pipe 70 to the outside air, making it less likely that the liquid refrigerant in the gas-liquid separator 17 will be insufficient, and making it easier to reduce the work of the compressors 11 and 12. This makes it easier to improve the APF, and makes it possible to achieve high efficiency in the refrigeration system 1.

[0105] As in the present embodiment, the refrigeration system 1 may be configured to be provided with an oil separator 73 that recovers oil from the return pipe 70 and returns it to the suction sides of the compressors 11 and 12. This makes it possible to prevent oil from the compressors 11 and 12 from accumulating in the gas-liquid separator 17 when the liquid refrigerant in the gas-liquid separator 17 is circulated by flowing it through the cooling-side heat exchanger and returning it to the gas-liquid separator 17 via the return pipe 70. This makes it easier to ensure reliability while improving the efficiency of the refrigeration system 1.

[0106] As in the present embodiment, the refrigeration apparatus 1 includes a flow path switching mechanism 50 that switches the gas cooler, which dissipates heat into the refrigerant discharged from the compressors 11 and 12, between the user-side heat exchanger 21 and the heat-source-side heat exchanger 14, and the flow path switching mechanism 50 may be configured to cause the refrigerant that has passed through the gas cooler to flow into the gas-liquid separator 17 regardless of whether the user-side heat exchanger 21 or the heat-source-side heat exchanger 14 is functioning as the gas cooler. This allows the refrigerant liquefied in the gas cooler to be stored in the gas-liquid separator 17 and pumped by the liquid pump 40 while switching the heat exchanger functioning as the gas cooler between the user-side heat exchanger 21 and the heat-source-side heat exchanger 14. Therefore, when the refrigeration apparatus 1 is an air conditioner as in the present embodiment, it is easy to reduce the work of the compressors 11 and 12 during both cooling and heating operations.

[0107] As in the present embodiment, the refrigeration apparatus 1 includes a flow path switching mechanism 50 that switches the cooling-side heat exchanger between the use-side heat exchanger 21 and the heat-source-side heat exchanger 14. The flow path switching mechanism 50 may be configured to cause the refrigerant that has passed through the cooling-side heat exchanger to reach the suction-side piping 18 and the return piping 70 regardless of whether the use-side heat exchanger 21 or the heat-source-side heat exchanger 14 is functioning as the cooling-side heat exchanger. This allows the heat exchanger functioning as the cooling-side heat exchanger to be switched between the use-side heat exchanger 21 and the heat-source-side heat exchanger 14, and selects whether the refrigerant that has passed through the cooling-side heat exchanger is returned to the gas-liquid separator 17 or compressed by the compressors 11 and 12, depending on the load. Therefore, when the refrigeration apparatus 1 is an air conditioner as in the present embodiment, it is easy to reduce the work of the compressors 11 and 12 during both cooling and heating operations.

[0108] The following describes an embodiment that is a partial modification of embodiment 1. The following describes configurations that are different from embodiment 1, and omits a description of configurations that are the same as embodiment 1.

[0109] As described above, the refrigeration system 1 of the first embodiment operates in a manner similar to a normal two-stage compression cycle when the cooling load is high and when the refrigeration system 101 of the second embodiment operates in a manner similar to a normal two-stage compression cycle when the cooling load is high and when the refrigeration system 101 is in heating mode. In contrast, the refrigeration system 101 of the second embodiment is configured to facilitate improvement in energy efficiency even when the load is high.

[0110] [2-1. Configuration] Fig. 6 is a diagram showing a refrigeration circuit 102 of a refrigeration apparatus 101 according to a second embodiment. In the refrigeration circuit 102 according to the second embodiment, an ejector 116 is provided instead of the throttle valve 16 according to the first embodiment. The ejector has a nozzle, a suction port, and the like. The ejector 116 reduces the pressure of the liquid refrigerant flowing in from the high-pressure receiver 15 by spraying it from the nozzle. The ejector 116 also draws refrigerant from the suction port by utilizing the low pressure of the refrigerant sprayed from the nozzle, mixes the drawn refrigerant with the sprayed refrigerant, and allows the refrigerant to flow into the gas-liquid separator 17. In this embodiment, a suction pipe 116a is connected to the suction port of the ejector 116.

[0111] The suction pipe 116a is connected to one port of a flow path switching valve 175 provided in the return pipe 70. The flow path switching valve 175 is a so-called three-way valve. The flow path switching valve 175 is provided in a midpoint of the return pipe 70 downstream of the heat exchanger 74, and is connected to the suction pipe 116a, the upstream side of the return pipe 70, and the downstream side of the return pipe 70. That is, the suction pipe 116a is provided on the outlet side of the cooling-side heat exchanger of the heat-source-side heat exchanger 14 and the use-side heat exchanger 22 via the first switching mechanism 51, the return pipe 70, and the flow path switching valve 175. The flow path switching valve 175 can be switched between a first state and a second state under the control of the control unit 90. In the first state, the flow path switching valve 175 connects the upstream side of the flow path switching valve 175 in the return pipe 70 with the suction pipe 116a, and closes the downstream side of the flow path switching valve 175 in the return pipe 70. As a result, when the flow path switching valve 175 is in the first state, the refrigerant that has passed through the cooling-side heat exchanger flows into the suction pipe 116a. In the second state, the flow path switching valve 175 connects the upstream side of the flow path switching valve 175 with the downstream side of the return pipe 70, and closes the suction pipe 116a.

[0112] Furthermore, in the second embodiment, a venting throttle valve 135 is provided to adjust the flow rate of the refrigerant in the venting pipe 30. The venting throttle valve 135 is a valve whose opening degree can be adjusted under the control of the control unit 90. More specifically, the venting throttle valve 135 is provided in the venting pipe 30 upstream of the connection portion with the cooling pipe 44, i.e., on the side closer to the gas-liquid separator 17.

[0113] Furthermore, in the second embodiment, unlike the suction side piping 18 in the first embodiment, the suction side piping 118, which is the piping on the suction side of the low-stage compressor 11, is not connected to the first switching mechanism 51. Furthermore, the suction side on-off valve 19 in the first embodiment is not provided. The suction side piping 118 is connected only to the low-stage side branch pipe 31 of the gas vent piping 30. For this reason, in the second embodiment, the compressors 11 and 12 cannot directly draw in the refrigerant that has passed through the cooling side heat exchanger, but can draw in the gas refrigerant separated in the gas-liquid separator 17.

[0114] [2-2. Operation] The operation of the refrigeration device 101 configured as above will be described below.

[0115] [2-2-1. Operation during cooling operation at medium load or less] Fig. 7 shows the refrigeration circuit 102 during cooling operation at medium load. Note that Fig. 6 described above shows the refrigeration circuit 102 during cooling operation at low load. As shown in Figs. 6 and 7, when the cooling load is medium load or less, the control unit 90 controls each unit other than the flow path switching valve 175, the gas vent throttle valve 135, and the cooling throttle valve 45 in the same manner as in the first embodiment.

[0116] In the second embodiment, when the cooling load is a medium load or less, the control unit 90 sets the flow path switching valve 175 to the second state and closes the suction pipe 116a. As a result, the refrigerant flow path in the refrigeration circuit 102 becomes the same as in the first embodiment. That is, similar to the first embodiment, the compressors 11 and 12 only perform the work of liquefying the gas refrigerant in the gas-liquid separator 17 and returning it to the gas-liquid separator 17. The liquid refrigerant in the gas-liquid separator 17 is sent to the user-side heat exchanger 21 by the liquid pump 40 or natural circulation. Therefore, similar to the first embodiment, the workload of the compressors 11 and 12 can be reduced.

[0117] In addition, in the second embodiment, the control unit 90 controls the gas vent throttle valve 175 and the cooling throttle valve 45 so that the refrigeration effect in the utilization side heat exchanger 21 is increased and the discharge gas temperature of the compressors 11 and 12 is optimized.

[0118] The temperature of the refrigerant in the gas-liquid separator 17 is equal to the saturation temperature corresponding to the pressure in the gas-liquid separator 17. Therefore, when the control unit 90 increases the opening of the gas vent throttle valve 175, the pressure in the gas-liquid separator 17 decreases, and the temperature of the refrigerant in the gas-liquid separator 17 also decreases. When the control unit 90 increases the opening of the cooling throttle valve 45, the cooling by the subcooling heat exchanger 46 increases, the temperature of the liquid refrigerant in the main pipe 41 decreases, and the refrigeration effect in the user-side heat exchanger 21 increases. Furthermore, when the control unit 90 increases the opening of the cooling throttle valve 45, the flow rate of refrigerant flowing from the cooling pipe 44 into the gas vent pipe 30 increases, and the suction temperature and discharge gas temperature of the compressors 11, 12 decrease.

[0119] [2-2-2. Operation During Air-Cooling Operation] FIG. 8 shows the refrigeration circuit 102 during air-cooling operation. In the second embodiment, as in the first embodiment, air-cooling operation using the heat exchanger 74 is possible with the compressors 11 and 12 stopped. In air-cooling operation, the control unit 90 stops the compressors 11 and 12 and closes the cooling throttle valve 45, the gas vent throttle valve 135, and the third cooling valve 57 when the cooling load is medium or lower. As a result, neither the discharge side nor the suction side of the compressors 11 and 12 communicates with the gas-liquid separator 17. Similarly to the first embodiment, the control unit 90 uses the liquid pump 40 and natural circulation to circulate supercooled liquid refrigerant through the user-side heat exchanger 21, thereby cooling the space to be conditioned.

[0120] [2-2-3. Operation during high-load cooling operation] Fig. 9 is a diagram showing the refrigeration circuit 102 during high-load cooling operation. As shown in Fig. 9, when the cooling load is high, the control unit 90 switches the flow path switching valve 175 from a medium-load cooling load state to the first state. As a result, the refrigerant in the return pipe 70 cooled by the heat exchanger 74 is not returned directly to the gas-liquid separator 17, but is instead sucked into the suction port of the ejector 116 via the suction pipe 116a.

[0121] When the cooling load is high, the gas refrigerant in the gas-liquid separator 17 passes through the gas vent pipe 30, is compressed in two stages by the compressors 11 and 12, and dissipates heat in the heat source-side heat exchanger 14. The refrigerant that has dissipated heat in the heat source-side heat exchanger 14 flows into the ejector 116 via the high-pressure receiver 15, is decompressed, and returns to the gas-liquid separator 17. When the refrigerant passes through the ejector 116, the ejector 116 draws the refrigerant in the return pipe 70 that has been cooled to the heat exchanger 74 via the suction port and suction pipe 116a.

[0122] Here, the heat exchanger 74 is connected to the liquid side outlet of the gas-liquid separator 17 via the return pipe 70, the user-side heat exchanger 21, the main pipe 41, the passage 42, etc. Therefore, when the ejector 116 sucks the refrigerant from the return pipe 70, the liquid refrigerant from the gas-liquid separator 17 flows toward the user-side heat exchanger 21 via the passage 42 and the main pipe 41. In other words, the ejector 116 can perform the work of returning the liquid refrigerant from the gas-liquid separator 17 to the gas-liquid separator 17 through the user-side heat exchanger 21.

[0123] In addition, when the cooling load is high, as well as when the cooling load is medium or lower, the control unit 90 adjusts the opening of the gas vent throttle valve 175 and the cooling throttle valve 45 to improve the refrigeration effect in the user side heat exchanger 21 and to optimize the discharge gas temperature of the compressors 11 and 12.

[0124] [2-2-4. Operation during heating operation] Figure 10 is a diagram showing the refrigeration circuit 102 during heating operation. During heating operation, the control unit 90 closes the cooling valves 53, 55, 57, and 59 and opens the heating valves 54, 56, and 58 and the heating throttle valve 60, since the cooling load is high. As a result, the gas refrigerant in the gas-liquid separator 17 is drawn into the compressors 11 and 12 via the gas vent pipe 30, and after being compressed in two stages, flows into the user-side heat exchanger 21 via the oil separator 13 and dissipates heat. In this way, the space to be conditioned is heated.

[0125] Similarly to the cooling operation, the refrigerant that has released heat in the user-side heat exchanger 21 flows into the ejector 116 via the high-pressure receiver 15, is decompressed, and flows into the gas-liquid separator 17. At this time, the ejector 116 sucks the refrigerant from the return pipe 70 that has passed through the heat exchanger 74 via the suction pipe 116a.

[0126] Here, the heat exchanger 74 is connected to the liquid side outlet of the gas-liquid separator 17 via the return pipe 70, the heat source side heat exchanger 14, the main pipe 41, the passage 42, etc. Therefore, when the ejector 116 sucks the refrigerant from the return pipe 70, the liquid refrigerant from the gas-liquid separator 17 flows toward the heat source side heat exchanger 14 via the passage 42 and the main pipe 41. In other words, the ejector 116 can perform the work of returning the liquid refrigerant from the gas-liquid separator 17 to the gas-liquid separator 17 through the heat source side heat exchanger 14.

[0127] During heating operation, the control unit 90 stops the external cooling device 47 and the water supply means 14b, 74b. Similarly to cooling operation, the control unit 90 adjusts the openings of the gas vent throttle valve 175 and the cooling throttle valve 45 to improve the refrigeration effect in the use-side heat exchanger 21 and to optimize the discharge gas temperatures of the compressors 11, 12.

[0128] [2-3. Effects, etc.] As described above, in this embodiment, the refrigeration device 101 includes a refrigeration circuit 102 that connects the compressors 11, 12, the heat source side heat exchanger 14, the gas-liquid separator 17, and the user side heat exchanger 21, a liquid pump 40 that sends liquid refrigerant from the gas-liquid separator 17 to the cooling side heat exchanger of the heat source side heat exchanger 14 or the user side heat exchanger 21, a check valve 43 that is provided in parallel with the liquid pump 40 and prevents backflow of the refrigerant toward the gas-liquid separator 17, and an ejector 116 into which the refrigerant that has flowed through a gas cooler of the heat source side heat exchanger 14 or the user side heat exchanger 21 flows and which sends the inflowing refrigerant to the gas-liquid separator 17, and a suction port of the ejector 116 is connected to a suction pipe 116a that is provided on the outlet side of the cooling side heat exchanger. This makes it easier to return the refrigerant in the cooling-side heat exchanger to the gas-liquid separator by utilizing the suction force of the ejector. This makes it easier to reduce the workload of the liquid pump 40, thereby improving the efficiency of the refrigeration system. In particular, in this embodiment, a flow path switching mechanism 50 is provided that causes the refrigerant that has passed through the gas cooler to flow into the gas-liquid separator 17 via the ejector 116, while causing the refrigerant that has passed through the cooling-side heat exchanger to flow into the return pipe 70, during both cooling and heating operations. This makes it easier to reduce the workload of the liquid pump 40 during both cooling and heating operations.

[0129] Furthermore, as in the present embodiment, the refrigeration apparatus 101 may be configured such that a return pipe 70 for returning the refrigerant to the gas-liquid separator 17 is provided at the outlet side of the cooling-side heat exchanger, the suction pipe 116a branches off from the return pipe 70, and the return pipe 70 is provided with a flow path switching valve 175 for directing the refrigerant that has passed through the cooling-side heat exchanger to either the suction pipe 116a or the gas-liquid separator 17. In this way, by returning the refrigerant to the gas-liquid separator 17 without passing through the ejector 116, it is possible to avoid the resistance of the ejector 116 and facilitate natural circulation returning to the gas-liquid separator 17 through the return pipe 70. Therefore, the ejector 116 can be effectively used under high load conditions, and natural circulation can be utilized under stable low load conditions, thereby achieving high efficiency of the refrigeration apparatus 101.

[0130] As in the present embodiment, the return pipe 70 may be configured to include a heat exchanger 74, located upstream of the flow path switching valve 175, for exchanging heat between the refrigerant in the return pipe 70 and outside air. This makes it easier to increase the liquid component of the refrigerant returning to the gas-liquid separator 17 when the outside temperature is low, making it harder for the liquid refrigerant in the gas-liquid separator 17 to run out, making it easier to maintain natural circulation. This makes it easier to reduce the workload of the compressor, and improves the efficiency of the refrigeration system.

[0131] As in the present embodiment, the refrigeration system 101 may be configured to include a vent pipe 30 that vents gas refrigerant from the gas-liquid separator 17 and returns it to the compressors 11 and 12, a vent throttle valve 135 for adjusting the flow rate of the vent pipe 30, a main pipe 41 that is provided downstream of the liquid pump 40 and through which refrigerant flows toward the cooling-side heat exchanger, a cooling pipe 44 that branches off from the main pipe 41 and is connected to the vent pipe 30 downstream of the vent throttle valve 135, and a cooling throttle valve 45 that adjusts the flow rate of refrigerant in the cooling pipe 44. As a result, the refrigerant temperature in the gas-liquid separator 17 can be adjusted by adjusting the aperture of the vent throttle valve 135, and the suction temperatures of the compressors 11 and 12 can be adjusted by adjusting the aperture of the cooling throttle valve 45. This makes it possible to adjust the discharge temperatures of the compressors 11 and 12, thereby improving the reliability of the refrigeration system.

[0132] As in the present embodiment, a configuration may be adopted in which a subcooling heat exchanger 46 is provided that cools the refrigerant in the main pipe 41 with refrigerant decompressed by the cooling throttle valve 45. This allows the refrigerant heading to the cooling-side heat exchanger to be subcooled, improving the refrigeration capacity of the refrigeration device 101. This allows for higher efficiency of the refrigeration device.

[0133] (Embodiment 3) [3-1. Configuration] Fig. 11 is a diagram showing a refrigeration circuit 202 of a refrigeration device 201 according to Embodiment 3. As shown in Fig. 11, the refrigeration circuit 202 of Embodiment 3 is provided with an ejector 216 instead of the throttle valve 16 of Embodiment 1. The ejector 216 reduces the pressure of the refrigerant in the high-pressure receiver 15 and discharges it toward the gas-liquid separator 17.

[0134] Furthermore, the refrigeration circuit 202 does not include the cooling pipe 44, the cooling throttle valve 45, and the subcooling heat exchanger 46 of the first embodiment. Instead, the refrigeration circuit 202 is provided with a cooling suction pipe 244 that branches off from the main pipe 41 and is connected to the suction port of the ejector 216, and a cooling throttle valve 245 that reduces the pressure of the refrigerant in the cooling suction pipe 244. Therefore, when the refrigerant in the high-pressure receiver 15 flows into the ejector 216, the refrigerant in the main pipe 41 flows into the cooling suction pipe 244, is reduced in pressure by the cooling throttle valve 245, and is sucked into the ejector 216.

[0135] The refrigeration circuit 202 is also provided with a heat exchanger 246 that exchanges heat between the refrigerant decompressed by the cooling throttle valve 245 and the refrigerant flowing through the ejector 216 toward the gas-liquid separator 17. The refrigerant flowing through the ejector 216 toward the gas-liquid separator 17 is cooled and liquefied by the heat exchanger 246.

[0136] Furthermore, the refrigeration circuit 202 is provided with a bypass pipe 248 that connects the downstream side of the heat exchanger 246, i.e., the suction port side of the ejector 216, of the cooling suction pipe 244 with the gas vent pipe 30. The bypass pipe 248 is also provided with a bypass pipe throttle valve 249 that adjusts the flow rate of the refrigerant passing through the bypass pipe 248.

[0137] [3-2. Operation] The operation of the refrigeration circuit 202 according to the third embodiment is the same as that of the refrigeration circuit 2 according to the first embodiment, except for the operation of the cooling throttle valve 245 and the bypass pipe throttle valve 249. Only the differences in operation from the first embodiment will be described below.

[0138] [3-2-1. Operation during Compressor Driving] Fig. 12 is a diagram showing the refrigeration circuit 202 during medium-load cooling operation. Fig. 13 is a diagram showing the refrigeration circuit 202 during high-load cooling operation. Fig. 14 is a diagram showing the refrigeration circuit 202 during heating operation. Fig. 11 shows the refrigeration circuit 202 during low-load cooling operation.

[0139] When the compressors 11, 12 are driven, such as during low- to high-load cooling operation and heating operation shown in Figures 11 to 14, the control unit 90 opens the cooling throttle valve 245. As a result, the refrigerant in the main pipe 41 is sucked into the ejector 216 via the cooling suction pipe 244. Then, the refrigerant decompressed by the cooling throttle valve 245 flows into the heat exchanger 246, where it can cool and liquefy the refrigerant that has passed through the gas cooler, the high-pressure receiver 15, and the ejector 216. When the ejector 216 can suck in a sufficient amount of refrigerant to be cooled by the heat exchanger 246, the control unit 90 closes the bypass pipe throttle valve 249.

[0140] On the other hand, for example, when the rotation speed of the compressors 11 and 12 is low, the refrigerant drawn from the main pipe 41 through the cooling suction pipe 244 to the suction port of the ejector 216 may not be enough to cool the refrigerant in the heat exchanger 246. In such a case, the control unit 90 opens the bypass pipe throttle valve 249 and connects the cooling suction pipe 244 to the gas vent pipe 30 via the bypass pipe 248. Since the gas vent pipe 30 is connected to the suction sides of the compressors 11 and 12, when the bypass pipe throttle valve 249 is open, the liquid refrigerant in the main pipe 41 flows into the cooling suction pipe 244 by being drawn into the compressors 11 and 12, and passes through the cooling throttle valve 245 and the heat exchanger 246. Therefore, the refrigerant that has passed through the ejector 216 can be cooled and liquefied by the heat exchanger 246.

[0141] In this way, in the third embodiment, the liquefaction of the refrigerant flowing into the gas-liquid separator 17 can be promoted both when the suction force of the ejector 216 is sufficient and when the suction force is insufficient.

[0142] 15 illustrates the refrigeration circuit 202 during air-cooling operation. When the compressors 11 and 12 are stopped, such as during air-cooling operation, the control unit 90 closes the cooling throttle valve 245 and the bypass pipe throttle valve 249 to block the flow of refrigerant through the cooling suction pipe 244 and the bypass pipe 248. During air-cooling operation, the control unit 90 also closes the third cooling valve 57, the low-stage throttle valve 33, and the high-stage throttle valve 34, thereby preventing communication between the suction and discharge sides of the compressors 11 and 12 and the gas-liquid separator 17. As a result, similar to the first embodiment, the liquid pump 40 or natural circulation is used to send the liquid refrigerant from the gas-liquid separator 17 to the user-side heat exchanger 21 for cooling, and the refrigerant is liquefied in the heat exchanger 74 before being returned to the gas-liquid separator 17.

[0143] [3-3. Effects, etc.] As described above, in this embodiment, the refrigeration device 201 includes a refrigeration circuit 202 that connects the compressors 11, 12, the heat source side heat exchanger 14, the gas-liquid separator 17, and the use side heat exchanger 21, and includes a liquid pump 40 that sends liquid refrigerant from the gas-liquid separator 17 to the cooling side heat exchanger of the heat source side heat exchanger 14 or the use side heat exchanger 21, a check valve 43 that is provided in parallel with the liquid pump 40 and prevents the refrigerant from flowing back toward the gas-liquid separator 17, and a gas cooler that cools the gas-liquid separator of the heat source side heat exchanger 14 or the use side heat exchanger 21. The refrigeration system 201 includes an ejector 216 into which the refrigerant flowing through the cooler flows and which directs the inflowing refrigerant to the gas-liquid separator 17, a main pipe 41 provided downstream of the liquid pump 40 and through which the refrigerant flowing toward the cooling-side heat exchanger flows, a cooling suction pipe 244 branching from the main pipe 41 and connected to the suction port of the ejector 216, a cooling throttle valve 245 which depressurizes the refrigerant in the cooling suction pipe 244, and a heat exchanger 246 which cools the refrigerant flowing from the ejector 216 to the gas-liquid separator 17 with the refrigerant depressurized by the cooling throttle valve 245. As a result, the suction force of the ejector 216 can be used to increase the flow rate of the cooling suction pipe 244, enabling cooling by the heat exchanger 246, and making it easier to liquefy the refrigerant flowing into the gas-liquid separator 17. This reduces the workload of the compressors 11 and 12, and improves the efficiency of the refrigeration system 201.

[0144] As in the present embodiment, the refrigeration apparatus 201 may be configured to include a gas vent pipe 30 that vents the gas refrigerant from the gas-liquid separator 17 and returns it to the compressors 11 and 12, a bypass pipe 248 that connects the gas vent pipe 30 to the downstream side of the heat exchanger 246 of the cooling suction pipe 244, and a bypass pipe throttle valve 249 provided in the bypass pipe 248. As a result, when the suction force of the ejector 216 is insufficient, the flow rate of the cooling suction pipe 244 can be increased by utilizing the suction of the compressors 11 and 12, and the subcooling of the refrigerant flowing into the gas-liquid separator 17 can be increased. This improves the refrigeration capacity and increases the efficiency of the refrigeration apparatus 201.

[0145] As in this embodiment, the refrigeration system 201 may be configured to be provided with an external cooling device 47 that cools the refrigerant in the main pipe 41. This allows the refrigerant flowing into the cooling-side heat exchanger to be more subcooled. This improves the refrigeration capacity and enables the refrigeration system 201 to be more efficient.

[0146] As in the present embodiment, the refrigeration circuit 202 of the refrigeration device 201 may be configured to use carbon dioxide as a refrigerant, and the external cooling device 47 may be configured to cool the refrigerant in the main pipe 41 using a refrigeration cycle that uses a refrigerant that is more energy efficient than carbon dioxide. This allows the energy-efficient external cooling device 47 to improve the refrigeration capacity of the refrigeration device 201, which uses carbon dioxide as a refrigerant with a small environmental impact. Furthermore, because the external cooling device 47 can be configured more simply than the refrigeration device 201, even if a refrigerant such as an HFC or HFO, which is highly efficient but has a larger environmental impact than carbon dioxide, is used in the external cooling device, the risk of refrigerant leakage from the external cooling device 47 is unlikely to increase. This allows the refrigeration device 201 to be made highly efficient while minimizing environmental impact.

[0147] As in this embodiment, the refrigeration device 201 may be configured to include a water supply means 14b that supplies water to lower the temperature of the intake air of the heat source side heat exchanger 14 by using the latent heat of evaporation. This makes it easier to improve the refrigeration capacity of the refrigeration device 201 with small energy consumption. Therefore, the efficiency of the refrigeration device 201 can be improved.

[0148] As described above, the refrigeration system 1 of the first embodiment operates in a manner similar to a normal two-stage compression cycle when the cooling load is high and when the refrigeration system 1 is in heating operation. In contrast, the refrigeration system 301 of the fourth embodiment is configured to facilitate improvement of energy efficiency even when the load is high.

[0149] [4-1. Configuration] Fig. 16 is a diagram showing a refrigeration circuit 302 of a refrigeration device 301 according to a fourth embodiment. In the refrigeration circuit 302 of the fourth embodiment, an expansion mechanism 316 is provided instead of the throttle valve 16 of the first embodiment. The expansion mechanism 316 is a device that recovers the pressure difference caused by the flow of the refrigerant as power and reduces the pressure of the refrigerant. The power recovered by the expansion mechanism 316 can be used for generating electricity using a generator, driving the compressors 11 and 12, and the like. In this embodiment, carbon dioxide, which has a particularly large pressure difference in the refrigeration circuit 302, is used as the refrigerant, making it easy to recover power using the expansion mechanism 316. Note that the refrigeration device 301 of the present embodiment is not provided with the external cooling device 47 of the first embodiment.

[0150] The refrigeration apparatus 301 of the fourth embodiment is also provided with a pressure sensor 381 that measures the pressure inside the gas-liquid separator 17. The pressure sensor 381 transmits the measured value of the pressure inside the gas-liquid separator 17 to the control unit 90. The refrigeration apparatus 301 is also provided with a temperature sensor 382 that measures the outlet temperature of the liquid refrigerant in the gas-liquid separator 17. In the present embodiment, the temperature sensor 382 measures the temperature of the refrigerant at one of the liquid side outlets of the gas-liquid separator 17, which is connected to the liquid pump 40. The temperature sensor 382 transmits the measured value of the outlet temperature of the liquid refrigerant in the gas-liquid separator 17 to the control unit 90.

[0151] [4-2. Operation] The operation of each part of the refrigeration circuit 302 during cooling operation and heating operation of the refrigeration device 301 is the same as the operation of each part of the refrigeration circuit 2 in embodiment 1, except for the operation of the cooling throttle valve 45 and the expansion mechanism 316. Note that in embodiment 4 as well, during both heating operation and cooling operation, the flow path switching mechanism 50 causes the refrigerant that has passed through the gas cooler to flow into the expansion mechanism 316 from the same direction via the high-pressure receiver 15. Therefore, during both cooling operation and heating operation, the expansion mechanism 316 can reduce the pressure of the refrigerant and recover power.

[0152] As described above, during operation of the compressors 11 and 12, the refrigerant that has flowed through the gas cooler flows into the expansion mechanism 316, where it is decompressed and flows into the gas-liquid separator 17. However, it is more difficult to control the amount of decompression of the refrigerant in the expansion mechanism 316 than in the throttle valve 16, and refrigerant that is not sufficiently decompressed may flow into the gas-liquid separator 17. In such a case, the pressure of the refrigerant in the gas-liquid separator 17 increases. Furthermore, since the temperature of the refrigerant in the gas-liquid separator 17 is equivalent to the saturation temperature converted from the pressure of the refrigerant in the gas-liquid separator 17, the temperature of the refrigerant in the gas-liquid separator 17 also increases as the pressure in the gas-liquid separator 17 increases. In such a case, the temperature of the liquid refrigerant flowing from the main pipe 41 into the cooling-side heat exchanger increases, inhibiting the refrigerant from absorbing heat in the cooling-side heat exchanger and reducing the refrigeration effect.

[0153] In contrast, in this embodiment, when the refrigerant is not sufficiently depressurized by the expansion mechanism 316, the opening of the cooling throttle valve 45 is increased and the cooling of the refrigerant in the main pipe 41 by the subcooling heat exchanger 46 is strengthened, thereby stabilizing the temperature of the refrigerant flowing into the cooling side heat exchanger.

[0154] 17 is a flowchart of the refrigeration apparatus 301, and shows the operation of the control unit 90 while at least one of the compressors 11 and 12 is operating. The control unit 90 repeatedly executes the operation of FIG. 17 while at least one of the compressors 11 and 12 is operating.

[0155] First, in step SA1 , the control unit 90 acquires the measurement value of the pressure sensor 381 or the temperature sensor 382 .

[0156] In step SA2, the control unit 90 determines whether the pressure reduction by the expansion mechanism 316 is insufficient based on the measurement value acquired in step SA1. Specifically, if the measurement value of the pressure sensor 381 was acquired in step SA1, the control unit 90 determines whether the acquired measurement value is equal to or greater than a first pressure. If the measurement value of the pressure sensor 381 is equal to or greater than the first pressure, the control unit 90 determines that the pressure reduction by the expansion mechanism 316 is insufficient (step SA2: YES) and proceeds to step SA3. If the measurement value of the pressure sensor 381 is less than the first pressure, the control unit 90 determines that the pressure reduction by the expansion mechanism 316 is not insufficient (step SA2: NO) and ends the operation of FIG. 17 .

[0157] Furthermore, in step SA2, if the control unit 90 has acquired a measurement value from the temperature sensor 382 in step SA1, it determines whether the acquired measurement value is equal to or higher than the first temperature. If the measurement value from the temperature sensor 382 is equal to or higher than the first pressure, the control unit 90 determines that the pressure reduction by the expansion mechanism 316 is insufficient (step SA2: YES) and proceeds to step SA3. If the measurement value from the temperature sensor 382 is less than the first pressure, the control unit 90 determines that the pressure reduction by the expansion mechanism 316 is not insufficient (step SA2: NO) and proceeds to step SA4.

[0158] The first pressure or first temperature used in the determination in step SA2 may be stored as a predetermined constant value in the control unit 90. Alternatively, the first pressure and the first temperature may be values ​​calculated based on the current opening of the cooling throttle valve 45, the target temperature of the refrigerant in the main pipe 41 for cooling by the subcooling heat exchanger 46, etc. For example, the configuration may be such that the value of the first pressure or the first temperature increases when the current opening of the cooling throttle valve 45 is large, and the value of the first pressure or the first temperature decreases when the target temperature of the refrigerant in the main pipe 41 is low.

[0159] In step SA3, the control unit 90 increases the opening of the cooling throttle valve 45. This increases the flow rate of refrigerant in the cooling pipe 44, and strengthens the cooling of the refrigerant in the main pipe 41 by the subcooling heat exchanger 46. Therefore, even if the pressure reduction by the expansion mechanism 316 is insufficient, the temperature of the refrigerant flowing into the cooling-side heat exchanger can be stabilized. Note that in step SA3, the control unit 90 may be configured to increase the opening of the cooling throttle valve 45 the greater the difference between the first pressure or first temperature and the measurements of the sensors 381, 382. After executing step SA3, the operation of the control unit 90 proceeds to step SA4.

[0160] In step SA4, the control unit 90 determines whether the intermediate pressure, i.e., the suction pressure P1 of the high-stage compressor 12, is equal to or less than a specified value. For example, if the opening of the cooling throttle valve 45 is increased in step SA3, the flow rate of the refrigerant flowing into the gas vent pipe 30 after heat absorption in the subcooling heat exchanger 46 increases, and the intermediate pressure rises. If the suction pressure P1 of the high-stage compressor 12 is equal to or less than the specified value (step SA4: YES), the control unit 90 ends the operation of Fig. 17, but if the suction pressure P1 of the high-stage compressor 12 exceeds the specified value (step SA4: NO), the control unit 90 proceeds to step SA5.

[0161] In step SA5, the control unit 90 increases the operating rotation speed of the high-stage compressor 12. This allows the intermediate pressure to be reduced until it reaches a pressure that matches the liquid temperature in the gas-liquid separator 17. After step SA5, the control unit 90 ends the operation of FIG.

[0162] [4-3. Effects, etc.] As described above, in this embodiment, the refrigeration device 301 includes a refrigeration circuit 302 that connects the compressors 11, 12, the heat source side heat exchanger 14, the gas-liquid separator 17, and the use side heat exchanger 21, and includes a liquid pump 40 that sends the liquid refrigerant from the gas-liquid separator 17 to the cooling side heat exchanger of the heat source side heat exchanger 14 or the use side heat exchanger 21, a check valve 43 that is provided in parallel with the liquid pump 40 and prevents the refrigerant from flowing back toward the gas-liquid separator 17, and a check valve 44 that connects the heat source side heat exchanger 14 and the use side heat exchanger 21. The refrigerant exchanger 301 includes an expansion mechanism 316 that expands the refrigerant that has flowed through the gas cooler of the heat exchanger 21 and flows it to the gas-liquid separator 17, a main pipe 41 that is provided downstream of the liquid pump 40 and through which the refrigerant flows toward the cooling-side heat exchanger, a cooling pipe 44 that branches off from the main pipe 41 and returns the refrigerant to the suction side of the compressors 11 and 12, a cooling throttle valve 45 that adjusts the flow rate of the cooling pipe 44, and a subcooling heat exchanger 46 that cools the refrigerant in the main pipe 41 with the refrigerant decompressed by the cooling throttle valve 45. This allows the refrigerant entering the gas-liquid separator 17 to be decompressed while recovering power using the expansion mechanism 316, and the refrigerant flowing into the cooling-side heat exchanger to be subcooled by the subcooling heat exchanger 46, thereby improving refrigeration capacity. This allows refrigeration capacity to be improved while recovering power, thereby achieving high efficiency in the refrigeration device 301.

[0163] As in the present embodiment, the control unit 90 of the refrigeration system 301 may be configured to increase the opening of the cooling throttle valve 45 when it determines that the expansion mechanism 316 has insufficiently reduced the pressure. This allows the refrigerant flowing into the cooling-side heat exchanger to be stably subcooled. This makes it possible to improve the refrigeration capacity while recovering power, thereby achieving high efficiency in the refrigeration system 301. In particular, in this embodiment, when the opening of the cooling throttle valve 45 is increased and the intermediate pressure, i.e., the suction pressure P1 of the high-stage compressor 12, exceeds a specified value, the control unit 90 increases the operating speed of the high-stage compressor 12. This suppresses an increase in the intermediate pressure. This suppresses a temperature rise of the liquid refrigerant in the gas-liquid separator 17.

[0164] As in the present embodiment, the control unit 90 may be configured to determine that the pressure reduction by the expansion mechanism 316 is insufficient when the pressure inside the gas-liquid separator 17 is equal to or higher than the first pressure, or when the outlet temperature of the liquid refrigerant from the gas-liquid separator 17 is equal to or higher than the first temperature. This allows the refrigerant flowing into the cooling-side heat exchanger to be stably supercooled. This makes it possible to improve the refrigeration capacity while recovering power, thereby achieving high efficiency in the refrigeration device.

[0165] (Other Embodiments) As described above, embodiments 1 to 4 have been described as examples of the technology disclosed in this application. However, the technology in this disclosure is not limited to these and can be applied to embodiments in which modifications, substitutions, additions, omissions, etc. are made. Furthermore, it is also possible to combine the components described in embodiments 1 to 4 to create new embodiments. Therefore, other embodiments will be described below as examples.

[0166] In the above embodiment, the refrigeration device 1 has been described as an air conditioner, but this is merely an example. The refrigeration device 1 may be any device other than an air conditioner that heats or cools an object using a refrigeration cycle. For example, the refrigeration device 1 may be a freezer such as a refrigerator or a showcase.

[0167] In the above embodiment, the refrigeration circuit 2 is configured to include the low-stage compressor 11 and the high-stage compressor 12 as compressors, enabling two-stage compression. However, this is merely an example. For example, instead of the low-stage compressor 11 and the high-stage compressor 12, a compound compressor capable of two-stage compression may be provided as the compressor of the refrigeration circuit 2. Furthermore, instead of the low-stage compressor 11 and the high-stage compressor 12, the refrigeration circuit 2 may be configured to include a single-stage compressor. Furthermore, the single-stage compressor may be configured to include an injection port through which refrigerant can be injected. In this case, the high-stage branch pipe 32 may be connected to the injection port. Note that two or more of the low-stage compressor 11, the high-stage compressor 12, or compressors replacing these may be connected in parallel.

[0168] In the above embodiment, the flow path switching mechanism 50 has been described as including the first switching mechanism 51 having the valves 53 to 56 connected in a ring and the second switching mechanism 52 having the valves 57 to 63 connected in a ring, but this is just one example. The flow path switching mechanism 50 switches the heat exchanger that functions as a gas cooler between the use-side heat exchanger 21 and the heat-source-side heat exchanger 14, and it is sufficient that the refrigerant that has passed through the gas cooler can flow toward the gas-liquid separator 17 regardless of which heat exchanger is set to function as the gas cooler. The flow path switching mechanism 50 also switches the heat exchanger that functions as a cooling-side heat exchanger between the use-side heat exchanger 21 and the heat-source-side heat exchanger 14, and it is sufficient that the refrigerant that has passed through the cooling-side heat exchanger can flow toward the suction-side piping 18 and the return piping 70 regardless of which heat exchanger is set to function as the cooling-side heat exchanger. That is, as long as it has the same function as the flow path switching mechanism 50 of this embodiment, part or all of the flow path switching mechanism 50 may be replaced with an on-off valve, a check valve, a throttle valve, a four-way valve, or the like.

[0169] In the above embodiment, carbon dioxide is used as the refrigerant in the refrigeration circuit 2, but this is just one example. The type of refrigerant in the refrigeration circuit 2 is not particularly limited, and may be a natural refrigerant other than carbon dioxide, or a refrigerant other than a natural refrigerant such as an HFC refrigerant or an HFO refrigerant. However, when carbon dioxide is used as the refrigerant in the refrigeration circuit 2, the risk of refrigerant leakage, such as environmental impact, can be reduced.

[0170] In the above embodiment, the suction-side valve 19 is opened and the return-side valve 71 is closed during heating operation, but this is merely an example. The refrigeration system 1 may be configured such that the suction-side valve 19 is closed and the return-side valve 71 is open during heating operation, similar to cooling operation, when the heating load is medium or less. This allows the compressors 11 and 12 to drive and store liquid refrigerant in the gas-liquid separator 17, and the liquid pump 40 to drive and send the liquid refrigerant from the gas-liquid separator 17 to the heat-source-side heat exchanger 14, to be performed independently, thereby reducing energy consumption during operation of the compressors 11 and 12.

[0171] In the second embodiment, a three-way valve is used as the flow path switching valve 175, but this is merely an example. The flow path switching valve 175 may be configured to allow the refrigerant in the return pipe 70 to flow to either the suction pipe 116a or the gas-liquid separator 17 as an inlet destination and switch the inlet destination. For example, the flow path switching valve 175 may be configured with a plurality of on-off valves or throttle valves, etc.

[0172] In the fourth embodiment, the refrigeration device 301 is described as being provided with both the pressure sensor 381 and the temperature sensor 382, ​​but this is merely an example. The refrigeration device 301 may be provided with either the pressure sensor 381 or the temperature sensor 382. The operation of step SA2 in Fig. 17 may be performed using the measurement value of either the pressure sensor 381 or the temperature sensor 382 provided in the refrigeration device 301.

[0173] 17 in the fourth embodiment is an example, and the operation of the control unit 90 is not limited thereto. For example, in addition to the operation of FIG. 17 , the control unit 90 may be configured to compare the measurement values ​​of the sensors 381 and 382 with a second pressure and a second temperature that are lower than the first pressure and the first temperature, after step SA3, etc., to determine whether the pressure reduction by the expansion mechanism 316 is excessive. Furthermore, the control unit 90 may be configured to reduce the opening of the cooling throttle valve 45 when the measurement values ​​of the sensors 381 and 382 are lower than the second pressure and the second temperature and it is determined that the pressure reduction by the expansion mechanism 316 is excessive.

[0174] Furthermore, the step units of operation shown in Figure 17 are divided according to the main processing content in order to make it easier to understand the operation of each part of the refrigeration device 301, and the present disclosure is not limited by the way in which the processing units are divided or their names.

[0175] It should be noted that the above-described embodiments are intended to illustrate the technology of the present disclosure, and various modifications, substitutions, additions, omissions, etc. may be made within the scope of the claims or their equivalents.

[0176] (Additional Notes) The above embodiments disclose the following technologies: (Technology 1) A refrigeration system including a refrigeration circuit connecting a compressor, a heat source-side heat exchanger, a gas-liquid separator, and a user-side heat exchanger, a liquid pump that sends liquid refrigerant from the gas-liquid separator to a cooling-side heat exchanger of the heat source-side heat exchanger and the user-side heat exchanger, and a check valve that is arranged in parallel with the liquid pump and prevents backflow of the refrigerant toward the gas-liquid separator, wherein the refrigerant that has passed through the cooling-side heat exchanger branches into a suction-side pipe connected to the suction side of the compressor and a return pipe connected to the gas-liquid separator, and the suction-side pipe and the return pipe are each provided with an on-off valve. As a result, when the cooling load of the cooling-side heat exchanger is not high, the refrigerant from the cooling-side heat exchanger can be returned to the gas-liquid separator through the return pipe by operation of the liquid pump or natural circulation via the check valve, thereby reducing the workload of the compressor. When the cooling load of the cooling-side heat exchanger is high, the refrigerant flowing into the cooling-side heat exchanger via the check valve can be compressed by the compressor, which makes it easier to improve the APF and improve the efficiency of the refrigeration system.

[0177] (Technology 2) The refrigeration apparatus according to Technology 1, wherein the compressor includes a low-stage compressor and a high-stage compressor, and a gas vent pipe for venting the gas refrigerant from the gas-liquid separator is connected to the low-stage compressor and the high-stage compressor via a throttle valve, respectively. This allows the low-stage compressor to be stopped and the gas refrigerant in the gas-liquid separator to be liquefied by operating only the high-stage compressor when the load is small, for example, when liquid refrigerant is flowed to the cooling-side heat exchanger by a liquid pump or natural circulation. This makes it easier to improve the APF and enables the efficiency of the refrigeration apparatus to be increased.

[0178] (Technology 3) The refrigeration system according to Technology 1 or 2, further comprising a heat exchanger that exchanges heat between the refrigerant in the return pipe and outside air. This allows the refrigerant in the return pipe to dissipate heat to the outside air, making it easier to increase the liquid component of the refrigerant flowing into the gas-liquid separator and reduce the work of the compressor. This makes it easier to improve the APF and increase the efficiency of the refrigeration system.

[0179] (Technology 4) The refrigeration apparatus according to Technology 3 further includes a water supply means for supplying water to lower the temperature of the intake air of the heat exchanger by using the latent heat of evaporation. This makes it easier to dissipate heat from the refrigerant in the return pipe to the outside air, further reducing the work of the compressor. This makes it easier to improve the APF and achieve high efficiency of the refrigeration apparatus.

[0180] (Technology 5) The refrigeration apparatus according to any one of Technologies 1 to 4, further comprising an oil separator that recovers oil from the return pipe and returns it to the suction side of the compressor. This prevents oil from accumulating in the gas-liquid separator when the liquid refrigerant in the gas-liquid separator flows through the cooling-side heat exchanger and is returned to the gas-liquid separator via the return pipe for circulation. This makes it easier to ensure reliability while improving the efficiency of the refrigeration apparatus.

[0181] (Technology 6) The refrigeration apparatus according to any one of Technologies 1 to 5, further comprising a flow path switching mechanism that switches a gas cooler that dissipates heat into the refrigerant discharged from the compressor between the user-side heat exchanger and the heat-source-side heat exchanger, and the flow path switching mechanism causes the refrigerant that has passed through the gas cooler to flow into the gas-liquid separator regardless of whether the user-side heat exchanger or the heat-source-side heat exchanger is functioning as the gas cooler. This allows the refrigerant liquefied in the gas cooler to be stored in the gas-liquid separator and pumped by a liquid pump while switching the heat exchanger that functions as the gas cooler. Therefore, for example, when the refrigeration apparatus is an air conditioner, it is easy to reduce the work of the compressor during both cooling and heating operations.

[0182] (Technology 7) The refrigeration apparatus according to any one of Technologies 1 to 6, further comprising a flow path switching mechanism that switches the cooling-side heat exchanger between the user-side heat exchanger and the heat-source-side heat exchanger, and the flow path switching mechanism allows the refrigerant that has passed through the cooling-side heat exchanger to reach the suction-side pipe and the return pipe regardless of whether the user-side heat exchanger or the heat-source-side heat exchanger is functioning as the cooling-side heat exchanger. This allows the refrigerant that has passed through the cooling-side heat exchanger to be returned to the gas-liquid separator or drawn into the compressor, depending on the load, while switching the heat exchanger that functions as the cooling-side heat exchanger. This makes it easier to reduce the work of the compressor, for example, when the refrigeration apparatus is an air conditioner, during both cooling and heating operations.

[0183] (Technology 8) A refrigeration system including a refrigeration circuit connecting a compressor, a heat source-side heat exchanger, a gas-liquid separator, and a user-side heat exchanger, the refrigeration system further including a liquid pump for sending liquid refrigerant from the gas-liquid separator to a cooling-side heat exchanger among the heat source-side heat exchanger and the user-side heat exchanger, and a path for sending liquid refrigerant from the gas-liquid separator downstream of the liquid pump without passing through the liquid pump. This allows the liquid refrigerant in the gas-liquid separator to be sent to the cooling-side heat exchanger without using a compressor, thereby reducing the workload of the compressor to compress the gas refrigerant. Furthermore, particularly when the gas-liquid separator is located higher than the cooling-side heat exchanger, such as when the gas-liquid separator is installed on the roof of a building and the cooling-side heat exchanger is installed on a lower floor of the building, the liquid refrigerant can easily circulate between the gas-liquid separator and the cooling-side heat exchanger through the path even after the liquid pump is stopped. This makes it easier to reduce energy consumption and improve the efficiency of the refrigeration device.

[0184] (Technology 9) A refrigeration apparatus according to Technology 8, wherein the compressor discharges the gas refrigerant from the gas-liquid separator to a gas cooler of the heat source-side heat exchanger or the user-side heat exchanger, and returns the gas-liquid mixed state to the gas-liquid separator via a throttle valve, and the liquid pump sends the liquid refrigerant from the gas-liquid separator to the cooling-side heat exchanger, where it absorbs heat and then returns the liquid refrigerant to the gas-liquid separator. This allows the compressor to be operated separately from sending liquid to the cooling-side heat exchanger, with the purpose of liquefying the gas refrigerant and returning it to the gas-liquid separator, thereby reducing the workload of the compressor. This makes it easier to reduce energy consumption and improves the efficiency of the refrigeration apparatus.

[0185] (Technology 10) The refrigeration apparatus according to Technology 8 or 9, wherein the path is provided with a check valve that prevents the refrigerant from flowing back toward the gas-liquid separator. This prevents the liquid refrigerant sent to the liquid pump from flowing back to the gas-liquid separator via the path. This makes it easier for the liquid pump to send the liquid refrigerant from the gas-liquid separator, thereby improving the efficiency of the refrigeration apparatus.

[0186] (Technology 11) The refrigeration system according to any one of Technologies 8 to 10, further comprising: a main pipe provided downstream of the liquid pump through which refrigerant flows toward the cooling-side heat exchanger; a cooling pipe branched from the main pipe; a cooling throttle valve that reduces the pressure of the refrigerant in the cooling pipe; and a subcooling heat exchanger that cools the refrigerant in the main pipe with the refrigerant reduced in pressure by the cooling throttle valve. This allows the liquid refrigerant to be cooled after passing through a gas-liquid separator with a large surface area, thereby reducing heat leakage from the liquid refrigerant. This increases the refrigeration effect while suppressing losses, thereby improving the efficiency of the refrigeration system.

[0187] (Technology 12) The refrigeration apparatus according to Technology 11, further comprising an external cooling device that cools the refrigerant in the main pipe after passing through the subcooling heat exchanger. This allows the liquid refrigerant flowing into the cooling-side heat exchanger to be further cooled. This improves and stabilizes the refrigeration capacity, thereby enabling the efficiency of the refrigeration apparatus to be improved.

[0188] (Technology 13) The refrigeration system according to Technology 12, wherein the refrigeration circuit uses carbon dioxide as a refrigerant, and the external cooling device cools the refrigerant in the main pipe using a refrigeration cycle that uses a refrigerant that is more energy-efficient than carbon dioxide. This allows the energy-efficient external cooling device to improve the refrigeration capacity of a refrigeration system that uses carbon dioxide as a refrigerant, which has a small environmental impact. Furthermore, because the external cooling device can be configured more simply than the refrigeration system, even if a refrigerant such as an HFC or HFO, which is highly efficient but has a larger environmental impact than carbon dioxide, is used in the external cooling device, the risk of refrigerant leakage from the external cooling device is less likely to increase. This allows for a high efficiency refrigeration system while minimizing environmental impact.

[0189] (Technology 14) The refrigeration apparatus according to Technology 13, wherein the refrigerant flowing through the cooling-side heat exchanger is cooled to a target temperature by using the external cooling device in preference to the subcooling heat exchanger. This allows the external cooling device, which is more likely to be configured with high energy efficiency, to be used in preference to the subcooling heat exchanger. This allows for high efficiency of the refrigeration apparatus.

[0190] (Technology 15) The refrigeration device according to any one of Technologies 8 to 14, further comprising a water supply means for supplying water to lower the temperature of the intake air of the heat source side heat exchanger by using latent heat of evaporation. This makes it easier to improve the refrigeration capacity of the refrigeration device with small energy consumption, thereby achieving high efficiency of the refrigeration device.

[0191] (Technology 16) The refrigeration device according to any one of Technologies 8 to 15, wherein the compressor includes a high-stage compressor and a low-stage compressor. This makes it easy to increase the efficiency of each compressor, particularly when using carbon dioxide or the like as a refrigerant, which has a large pressure difference within the refrigeration circuit. This makes it possible to increase the efficiency of the refrigeration device.

[0192] (Technology 17) A refrigeration system including a refrigeration circuit connecting a compressor, a heat source-side heat exchanger, a gas-liquid separator, and a user-side heat exchanger, the refrigeration system further including a liquid pump for pumping liquid refrigerant from the gas-liquid separator to a cooling-side heat exchanger of the heat source-side heat exchanger and the user-side heat exchanger, a check valve arranged in parallel with the liquid pump for preventing backflow of refrigerant toward the gas-liquid separator, and an ejector into which refrigerant flowing through a gas cooler of the heat source-side heat exchanger or the user-side heat exchanger flows and which directs the inflowing refrigerant to the gas-liquid separator, the suction port of the ejector being connected to a suction pipe arranged on the outlet side of the cooling-side heat exchanger. This facilitates the use of suction force by the ejector to return refrigerant from the cooling-side heat exchanger to the gas-liquid separator. This facilitates reducing the workload of the liquid pump and improves the efficiency of the refrigeration system.

[0193] (Technology 18) The refrigeration apparatus according to Technology 17, further comprising: a return pipe provided at the outlet side of the cooling-side heat exchanger for returning the refrigerant to the gas-liquid separator; a suction pipe branching from the return pipe; and a flow path switching valve provided in the return pipe for directing the refrigerant that has passed through the cooling-side heat exchanger to either the suction pipe or the gas-liquid separator. This allows the refrigerant to be returned to the gas-liquid separator without passing through the ejector, thereby avoiding the resistance of the ejector and facilitating natural circulation returning to the gas-liquid separator through the return branch pipe. This allows the ejector to be effectively utilized under high loads and natural circulation to be utilized under stable low loads, thereby improving the efficiency of the refrigeration apparatus.

[0194] (Technology 19) The refrigeration apparatus according to Technology 18, wherein the return pipe is provided with a heat exchanger located upstream of the flow path switching valve, which exchanges heat between the refrigerant in the return pipe and outside air. This makes it easier to increase the liquid component of the refrigerant returning to the gas-liquid separator when the outside air temperature is low, making it harder for the liquid refrigerant in the gas-liquid separator to run out, and thus making it easier to maintain natural circulation. This makes it easier to reduce the workload of the compressor, and improves the efficiency of the refrigeration apparatus.

[0195] (Technology 20) The refrigeration system according to any one of Technologies 17 to 19, further comprising: a gas vent pipe for venting gas refrigerant from the gas-liquid separator and returning it to the compressor; a gas vent throttle valve for adjusting the flow rate of the gas vent pipe; a main pipe provided downstream of the liquid pump through which refrigerant flows toward the cooling-side heat exchanger; a cooling pipe branching from the main pipe and connected to the gas vent pipe downstream of the gas vent throttle valve; and a cooling throttle valve for adjusting the flow rate of refrigerant in the cooling pipe. This allows the refrigerant temperature in the gas-liquid separator to be adjusted by adjusting the aperture of the gas vent throttle valve, and the intake temperature of the compressor to be adjusted by adjusting the aperture of the cooling throttle valve. This allows the compressor discharge temperature to be adjusted, improving the reliability of the refrigeration system.

[0196] (Technology 21) The refrigeration apparatus according to Technology 20, further comprising a subcooling heat exchanger that cools the refrigerant in the main pipe with refrigerant decompressed by the cooling throttle valve. This allows the refrigerant flowing to the cooling-side heat exchanger to be subcooled, improving the refrigeration capacity. This allows the efficiency of the refrigeration apparatus to be improved.

[0197] (Technology 22) A refrigeration system including a refrigeration circuit connecting a compressor, a heat source side heat exchanger, a gas-liquid separator, and a user side heat exchanger, the refrigeration system including: a liquid pump that sends liquid refrigerant from the gas-liquid separator to a cooling side heat exchanger of the heat source side heat exchanger or the user side heat exchanger; a check valve that is provided in parallel with the liquid pump and prevents backflow of refrigerant toward the gas-liquid separator; an ejector that receives refrigerant that has flowed through a gas cooler of the heat source side heat exchanger or the user side heat exchanger and directs the inflowing refrigerant to the gas-liquid separator; a main pipe that is provided downstream of the liquid pump and through which refrigerant toward the cooling side heat exchanger flows; a cooling suction pipe that branches off from the main pipe and is connected to a suction port of the ejector; a cooling throttle valve that decompresses the refrigerant in the cooling suction pipe; and a heat exchanger that cools the refrigerant flowing from the ejector to the gas-liquid separator with the refrigerant decompressed by the cooling throttle valve. This allows the suction force of the ejector to be used to increase the flow rate of the cooling suction pipe, enabling cooling by the heat exchanger, and liquefying the refrigerant flowing into the gas-liquid separator, thereby reducing the workload of the compressor and improving the efficiency of the refrigeration system.

[0198] (Technology 23) The refrigeration system according to Technology 22, further comprising a gas vent pipe that vents gas refrigerant from the gas-liquid separator and returns it to the compressor, a bypass pipe that connects the gas vent pipe with the downstream side of the heat exchanger of the cooling suction pipe, and a bypass pipe throttle valve provided in the bypass pipe. This allows the suction of the compressor to be used to increase the flow rate of the cooling suction pipe when the suction force of the ejector is insufficient, thereby increasing the degree of subcooling of the refrigerant flowing into the gas-liquid separator. This improves the refrigeration capacity and increases the efficiency of the refrigeration system.

[0199] (Technology 24) The refrigeration apparatus according to Technology 22 or 23, further comprising an external cooling device for cooling the refrigerant in the main pipe. This allows for greater subcooling of the refrigerant flowing into the cooling-side heat exchanger. This improves the refrigeration capacity and increases the efficiency of the refrigeration apparatus.

[0200] (Technology 25) The refrigeration system according to Technology 24, wherein the refrigeration circuit uses carbon dioxide as a refrigerant, and the external cooling device cools the refrigerant in the main pipe using a refrigeration cycle that utilizes a refrigerant that is more energy-efficient than carbon dioxide. This allows the energy-efficient external cooling device to improve the refrigeration capacity of a refrigeration system that uses carbon dioxide, which has a small environmental impact, as a refrigerant. Furthermore, because the external cooling device can be configured more simply than the refrigeration system, even if a refrigerant such as an HFC or HFO, which is highly efficient but has a larger environmental impact than carbon dioxide, is used in the external cooling device, the risk of refrigerant leakage from the external cooling device is less likely to increase. This allows for a high efficiency refrigeration system while minimizing environmental impact.

[0201] (Technology 26) The refrigeration device according to any one of Technologies 22 to 25, further comprising a water supply means for supplying water to lower the temperature of the intake air of the heat source side heat exchanger by using latent heat of evaporation. This makes it easier to improve the refrigeration capacity of the refrigeration device with small energy consumption, thereby achieving high efficiency of the refrigeration device.

[0202] (Technology 27) A refrigeration system including a refrigeration circuit connecting a compressor, a heat source side heat exchanger, a gas-liquid separator, and a user side heat exchanger, the refrigeration system including: a liquid pump that sends liquid refrigerant from the gas-liquid separator to a cooling side heat exchanger of the heat source side heat exchanger and the user side heat exchanger; a check valve that is provided in parallel with the liquid pump and prevents backflow of refrigerant toward the gas-liquid separator; an expansion mechanism that expands refrigerant that has flowed through a gas cooler of the heat source side heat exchanger or the user side heat exchanger and supplies the refrigerant to the gas-liquid separator; a main pipe that is provided downstream of the liquid pump and through which refrigerant toward the cooling side heat exchanger flows; a cooling pipe that branches off from the main pipe and returns refrigerant to the suction side of the compressor; a cooling throttle valve that adjusts the flow rate of the cooling pipe; and a subcooling heat exchanger that cools the refrigerant in the main pipe with refrigerant decompressed by the cooling throttle valve. This allows the refrigeration capacity to be improved by reducing the pressure of the refrigerant entering the gas-liquid separator while recovering power using the expansion mechanism, and by subcooling the refrigerant flowing into the cooling-side heat exchanger using the subcooling heat exchanger, thereby improving the refrigeration capacity while recovering power and achieving high efficiency in the refrigeration device.

[0203] (Technology 28) The refrigeration apparatus according to Technology 27, wherein the opening of the cooling throttle valve is increased when it is determined that the pressure reduction by the expansion mechanism is insufficient. This allows the refrigerant flowing into the cooling-side heat exchanger to be stably supercooled. This makes it possible to improve the refrigeration capacity while recovering power, thereby achieving high efficiency of the refrigeration apparatus.

[0204] (Technology 29) The refrigeration apparatus according to Technology 28, wherein when the pressure in the gas-liquid separator is equal to or higher than a first pressure, or when the outlet temperature of the liquid refrigerant from the gas-liquid separator is equal to or higher than a first temperature, it is determined that the pressure reduction by the expansion mechanism is insufficient. This allows the refrigerant flowing into the cooling-side heat exchanger to be stably supercooled. This allows the refrigeration capacity to be improved while recovering power, thereby achieving high efficiency of the refrigeration apparatus.

[0205] The present disclosure is applicable to refrigeration devices, and more specifically, to devices such as air conditioners that include a refrigeration circuit.

[0206] DESCRIPTION OF SYMBOLS 1 Refrigeration device 2 Refrigeration circuit 10 Outdoor unit 11 Low-stage compressor (compressor) 12 High-stage compressor (compressor) 13 Oil separator 14 Heat source side heat exchanger 14a Blower 14b Water supply means 15 High-pressure receiver 16 Throttle valve 17 Gas-liquid separator 18 Suction side piping 19 Suction side on-off valve (on-off valve) 20, 20H, 20L Indoor unit 21 Use side heat exchanger 22 Use side throttle valve 30 Gas vent piping 31 Low-stage side branch pipe 32 High-stage side branch pipe 33 Low-stage side throttle valve 34 High-stage side throttle valve 40 Liquid pump 41 Main piping 42 Path 43 Check valve 44 Cooling piping 45 Cooling throttle valve 46 Cooling heat exchanger 47 External cooling equipment 50 Flow path switching mechanism 51 First switching mechanism 52 Second switching mechanism 53 First cooling valve 54 First heating valve 55 Second cooling valve 56 Second heating valve 57 Third cooling valve 58 Third heating valve 59 Fourth cooling valve 60 Heating throttle valve 61-63 Check valve 70 Return pipe 71 Return side opening / closing valve (opening / closing valve) 72 Check valve 73 Oil separator 74 Heat exchanger 74a Blower 74b Water supply means 90 Control unit 101 Refrigeration device 102 Refrigeration circuit 116 Ejector 116a Suction pipe 118 Suction side pipe 135 Gas vent throttle valve 175 Flow path switching valve 201 Refrigeration device 202 Refrigeration circuit 216 Ejector 244 Cooling suction pipe 245 Cooling throttle valve 246 Heat exchanger 248 Bypass piping 249 Bypass pipe throttle valve 301 Refrigeration device 302 Refrigeration circuit 316 Expansion mechanism 381 Pressure sensor 382 Temperature sensor

Claims

1. A refrigeration system comprising a refrigeration circuit connecting a compressor, a heat source side heat exchanger, a gas-liquid separator, and a user side heat exchanger, and comprising: a liquid pump that sends liquid refrigerant from the gas-liquid separator to a cooling side heat exchanger out of the heat source side heat exchanger and the user side heat exchanger; and a check valve that is provided in parallel with the liquid pump and prevents backflow of refrigerant toward the gas-liquid separator, wherein the refrigerant that has passed through the cooling side heat exchanger branches off and flows into a suction side pipe connected to the suction side of the compressor and a return pipe connected to the gas-liquid separator, and the suction side pipe and the return pipe are each provided with an on-off valve.

2. The refrigeration system according to claim 1, wherein the compressor includes a low-stage compressor and a high-stage compressor, and gas vent pipes for venting gas refrigerant from the gas-liquid separator are connected to the low-stage compressor and the high-stage compressor via throttle valves, respectively.

3. The refrigeration system according to claim 1, further comprising a heat exchanger for exchanging heat between the refrigerant in the return pipe and outside air.

4. The refrigeration system according to claim 3, further comprising a water supply means for supplying water to lower the temperature of the intake air of the heat exchanger by means of latent heat of vaporization.

5. The refrigeration system according to claim 1, further comprising an oil separator for recovering oil from the return pipe and returning it to the suction side of the compressor.

6. A refrigeration device as described in claim 1, further comprising a flow path switching mechanism that switches a gas cooler that dissipates heat into the refrigerant discharged from the compressor between the user side heat exchanger and the heat source side heat exchanger, and the flow path switching mechanism causes the refrigerant that has passed through the gas cooler to flow into the gas-liquid separator regardless of whether the user side heat exchanger or the heat source side heat exchanger is made to function as the gas cooler.

7. A refrigeration device as described in claim 1, further comprising a flow path switching mechanism that switches the cooling side heat exchanger between the utilization side heat exchanger and the heat source side heat exchanger, and the flow path switching mechanism allows the refrigerant that has passed through the cooling side heat exchanger to reach the suction side piping and the return piping regardless of whether the utilization side heat exchanger or the heat source side heat exchanger is made to function as the cooling side heat exchanger.

8. A refrigeration system comprising a refrigeration circuit connecting a compressor, a heat source side heat exchanger, a gas-liquid separator, and a user side heat exchanger, and further comprising: a liquid pump that sends liquid refrigerant from the gas-liquid separator to the cooling side heat exchanger of the heat source side heat exchanger and the user side heat exchanger; and a path that sends the liquid refrigerant from the gas-liquid separator to the downstream side of the liquid pump without passing through the liquid pump.

9. The refrigeration system according to claim 8, wherein the compressor discharges the gas refrigerant from the gas-liquid separator to a gas cooler in the heat source side heat exchanger or the user side heat exchanger, and returns the gas-liquid mixed state to the gas-liquid separator via a throttle valve, and the liquid pump sends the liquid refrigerant from the gas-liquid separator to the cooling side heat exchanger, where it absorbs heat and then returns it to the gas-liquid separator.

10. The refrigeration system according to claim 8, wherein the path is provided with a check valve for preventing backflow of the refrigerant toward the gas-liquid separator.

11. A refrigeration system as described in claim 8, comprising: a main pipe provided downstream of the liquid pump through which refrigerant flows toward the cooling side heat exchanger; a cooling pipe branching off from the main pipe; a cooling throttle valve that reduces the pressure of the refrigerant in the cooling pipe; and a subcooling heat exchanger that cools the refrigerant in the main pipe with the refrigerant reduced in pressure by the cooling throttle valve.

12. The refrigeration system according to claim 11, further comprising an external cooling device for cooling the refrigerant in the main pipe after passing through the subcooling heat exchanger.

13. The refrigeration system according to claim 12, wherein the refrigeration circuit uses carbon dioxide as a refrigerant, and the external cooling device cools the refrigerant in the main pipe using a refrigeration cycle that utilizes a refrigerant that is more energy efficient than carbon dioxide.

14. The refrigeration system according to claim 13, wherein the refrigerant flowing through the cooling-side heat exchanger is cooled to a target temperature by using the external cooling device with priority over the subcooling heat exchanger.

15. The refrigeration system according to claim 8, further comprising a water supply means for supplying water to lower the temperature of the intake air of the heat source side heat exchanger by means of latent heat of evaporation.

16. The refrigeration system of claim 8, wherein the compressor includes a high-stage compressor and a low-stage compressor.

17. A refrigeration system comprising a refrigeration circuit connecting a compressor, a heat source side heat exchanger, a gas-liquid separator, and a user side heat exchanger, the refrigeration system comprising: a liquid pump that sends liquid refrigerant from the gas-liquid separator to the cooling side heat exchanger of the heat source side heat exchanger and the user side heat exchanger; a check valve that is provided in parallel with the liquid pump and prevents backflow of refrigerant toward the gas-liquid separator; and an ejector into which refrigerant that has flowed through a gas cooler of the heat source side heat exchanger or the user side heat exchanger flows and which directs the inflowing refrigerant to the gas-liquid separator, the suction port of the ejector being connected to a suction pipe provided on the outlet side of the cooling side heat exchanger.

18. A refrigeration system as described in claim 17, wherein a return pipe for returning refrigerant to the gas-liquid separator is provided on the outlet side of the cooling side heat exchanger, the suction pipe branches off from the return pipe, and the return pipe is provided with a flow path switching valve for directing refrigerant that has passed through the cooling side heat exchanger to either the suction pipe or the gas-liquid separator.

19. The refrigeration system according to claim 18, wherein the return pipe is provided with a heat exchanger, located upstream of the flow path switching valve, for exchanging heat between the refrigerant in the return pipe and outside air.

20. A refrigeration system as described in claim 17, comprising: a gas vent pipe that draws gas refrigerant from the gas-liquid separator and returns it to the compressor; a gas vent throttle valve for adjusting the flow rate of the gas vent pipe; a main pipe that is provided downstream of the liquid pump and through which refrigerant flows toward the cooling side heat exchanger; a cooling pipe that branches off from the main pipe and is connected to the gas vent pipe downstream of the gas vent throttle valve; and a cooling throttle valve that adjusts the flow rate of refrigerant in the cooling pipe.

21. The refrigeration system according to claim 20, further comprising a subcooling heat exchanger that cools the refrigerant in the main pipe with the refrigerant decompressed by the cooling throttle valve.

22. A refrigeration system comprising a refrigeration circuit connecting a compressor, a heat source side heat exchanger, a gas-liquid separator, and a user side heat exchanger, the refrigeration system comprising: a liquid pump that sends liquid refrigerant from the gas-liquid separator to the cooling side heat exchanger of the heat source side heat exchanger or the user side heat exchanger; a check valve that is provided in parallel with the liquid pump and prevents backflow of refrigerant toward the gas-liquid separator; an ejector that receives refrigerant that has flowed through a gas cooler of the heat source side heat exchanger or the user side heat exchanger and directs the inflowing refrigerant to the gas-liquid separator; a main pipe that is provided downstream of the liquid pump and through which refrigerant toward the cooling side heat exchanger flows; a cooling suction pipe that branches off from the main pipe and is connected to the suction port of the ejector; a cooling throttle valve that decompresses the refrigerant in the cooling suction pipe; and a heat exchanger that cools the refrigerant flowing from the ejector to the gas-liquid separator with the refrigerant decompressed by the cooling throttle valve.

23. A refrigeration system as claimed in claim 22, comprising: a gas vent pipe for extracting gas refrigerant from the gas-liquid separator and returning it to the compressor; a bypass pipe connecting the gas vent pipe with the downstream side of the heat exchanger of the cooling suction pipe; and a bypass pipe throttle valve provided in the bypass pipe.

24. The refrigeration system according to claim 22, further comprising an external cooling device for cooling the refrigerant in the main pipe.

25. The refrigeration system according to claim 24, wherein the refrigeration circuit uses carbon dioxide as a refrigerant, and the external cooling device cools the refrigerant in the main pipe using a refrigeration cycle that utilizes a refrigerant that is more energy efficient than carbon dioxide.

26. The refrigeration system according to claim 22, further comprising a water supply means for supplying water to lower the temperature of the intake air of the heat source side heat exchanger by means of latent heat of evaporation.

27. A refrigeration system comprising a refrigeration circuit connecting a compressor, a heat source side heat exchanger, a gas-liquid separator, and a user side heat exchanger, and comprising: a liquid pump that sends liquid refrigerant from the gas-liquid separator to the cooling side heat exchanger of the heat source side heat exchanger and the user side heat exchanger; a check valve that is provided in parallel with the liquid pump and prevents backflow of refrigerant toward the gas-liquid separator; an expansion mechanism that expands refrigerant that has flowed through a gas cooler of the heat source side heat exchanger or the user side heat exchanger and sends it to the gas-liquid separator; a main pipe that is provided downstream of the liquid pump and through which refrigerant toward the cooling side heat exchanger flows; a cooling pipe that branches off from the main pipe and returns refrigerant to the suction side of the compressor; a cooling throttle valve that adjusts the flow rate of the cooling pipe; and a subcooling heat exchanger that cools the refrigerant in the main pipe with refrigerant decompressed by the cooling throttle valve.

28. The refrigeration system according to claim 27, wherein the opening of the cooling throttle valve is increased when it is determined that the pressure reduction by the expansion mechanism is insufficient.

29. The refrigeration device according to claim 28, wherein when the pressure inside the gas-liquid separator is equal to or higher than a first pressure, or when the outlet temperature of the liquid refrigerant from the gas-liquid separator is equal to or higher than a first temperature, it is determined that the pressure reduction by the expansion mechanism is insufficient.

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