Refrigeration equipment

Abstract

This disclosure provides a refrigeration system that can achieve high efficiency. [Solution] The refrigeration apparatus in this disclosure comprises a refrigerant circuit connecting a compression mechanism, a heat source side heat exchanger, a gas-liquid separator, and a utilization side heat exchanger, a liquid pump that sends the liquid refrigerant from the gas-liquid separator to the cooling side heat exchanger of the utilization side heat exchanger, a check valve provided in parallel with the liquid pump to prevent backflow of refrigerant toward the gas-liquid separator, and an expansion mechanism that expands the refrigerant that has flowed through the gas cooler of the heat source side heat exchanger and utilization side heat exchanger and sends it to the gas-liquid separator, the compression mechanism is provided in the gas venting pipe into which the gas refrigerant from the gas-liquid separator flows and operates coaxially with the expansion mechanism.

Description

Technical Field

[0001] The present disclosure relates to a refrigeration device.

Background Art

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

[0003] Patent Document 2 discloses a refrigeration cycle device that aims to improve efficiency by using an ejector. This refrigeration cycle device includes an ejector into which the refrigerant discharged from a compressor and passed through an outdoor heat exchanger flows and discharges the refrigerant to a gas-liquid separator, and an internal heat exchanger that cools the refrigerant flowing from the gas-liquid separator to an indoor heat exchanger by a part of the liquid refrigerant in the gas-liquid separator sucked by the ejector.

[0004] Patent Document 3 discloses a refrigeration cycle device that improves efficiency by an expansion mechanism and a sub-refrigerant circuit independent of a main refrigerant circuit. This refrigeration cycle device includes a main expansion mechanism that expands the refrigerant flowing toward a main utilization-side heat exchanger and recovers power, and a sub-utilization-side heat exchanger that further cools the refrigerant after power recovery and then flows the refrigerant to the utilization-side heat exchanger.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

[0006]

Patent Document 2

[0007]

Patent Document 3

[0008] This disclosure provides a refrigeration system that can achieve high efficiency. [Means for solving the problem]

[0009] The refrigeration system in this disclosure comprises a refrigerant circuit connecting a compression mechanism, a heat source side heat exchanger, a gas-liquid separator, and a utilization side heat exchanger, a liquid pump that sends the liquid refrigerant from the gas-liquid separator to the cooling side heat exchanger among the heat source side heat exchanger and the utilization side heat exchanger, a check valve provided in parallel with the liquid pump to prevent backflow of refrigerant toward the gas-liquid separator, and an expansion mechanism that expands the refrigerant that has flowed through the gas cooler among the heat source side heat exchanger and the utilization side heat exchanger and flows it toward the gas-liquid separator, the compression mechanism is provided in a gas vent pipe into which the gas refrigerant from the gas-liquid separator flows, and operates coaxially with the expansion mechanism. [Effects of the Invention]

[0010] The refrigeration system in this disclosure can reduce the pressure of the refrigerant entering the gas-liquid separator while recovering power using an expansion mechanism, and efficiently utilize the recovered power to operate the compression mechanism. Therefore, energy consumption can be suppressed and the efficiency of the refrigeration system can be improved. [Brief explanation of the drawing]

[0011] [Figure 1] Diagram showing the refrigerant circuit of the refrigeration system according to Embodiment 1. [Figure 2] Diagram showing the refrigerant circuit during cooling operation at medium load. [Figure 3] Diagram showing the refrigerant circuit during air-cooled cooling operation. [Figure 4] Diagram showing the refrigerant circuit during high-load cooling operation. [Figure 5] Diagram showing the refrigerant circuit during heating operation. [Figure 6]Diagram showing the refrigerant circuit of the refrigeration system according to Embodiment 2. [Figure 7] Flowchart of a refrigeration system [Figure 8] Diagram showing the refrigerant circuit of the refrigeration system according to Embodiment 3. [Figure 9] Diagram showing the refrigerant circuit during low-load cooling operation. [Figure 10] Diagram showing the refrigerant circuit during air-cooled cooling operation. [Figure 11] Diagram showing the refrigerant circuit during heating operation. [Modes for carrying out the invention]

[0012] (Knowledge and other information that formed the basis of this disclosure) At the time the inventors conceived this disclosure, there was a technology in the field of refrigeration equipment that used carbon dioxide, a type of natural refrigerant, as a refrigerant. Carbon dioxide has a low global warming potential, is non-flammable, and non-toxic, so it is expected to be used more widely as a refrigerant with a small environmental impact. Although carbon dioxide has been considered to have efficiency challenges because its critical temperature is within the range of operating temperatures, in low-temperature equipment of around -45°C to -5°C, the high intake density of the compressor can be utilized, and refrigeration equipment using carbon dioxide as a refrigerant has been put into practical use with performance close to that of equipment using fluorocarbons as a refrigerant. However, when using carbon dioxide as a refrigerant, it is difficult to utilize the high intake density, especially in equipment for air conditioning temperatures, making it difficult to achieve high efficiency, and the inventors discovered that further technological development for higher efficiency is required, and the subject of this disclosure was formed in order to solve this problem. Therefore, this disclosure provides a refrigeration system that can achieve high efficiency.

[0013] The embodiments will be described in detail below with reference to the drawings. However, unnecessary details may be omitted. For example, detailed explanations of already well-known matters or redundant explanations of substantially identical configurations may be omitted. This is to avoid the following explanation becoming unnecessarily verbose and to facilitate understanding for those skilled in the art. The attached 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 refrigerant circuit 2 of a refrigeration device 1 according to Embodiment 1. In the figure, open / close valves and throttle valves in the open state are shown in white, and open / close valves and throttle valves in the closed state are shown in white. Also, in the figure, the wiring through which the refrigerant flows is shown by a thick line, and the pipes through which the refrigerant does not flow are shown by a thin line.

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

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

[0017] The indoor unit 20 is a device installed primarily in a conditioned space 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 there is one or more, but Figure 1 shows one indoor unit 20 installed on the upper floor and one on the lower floor of the building. Hereafter, when distinguishing between the indoor units 20, the indoor unit 20 installed on the upper floor will be called indoor unit 20H, and the indoor unit 20 installed on the lower floor will be called indoor unit 20L. In other words, in this embodiment, the outdoor unit 10 is located at a higher position than the indoor unit 20H, and the indoor unit 20H is located at a higher position 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 and the air in the air-conditioned space. The user-side throttle valve 22 is a valve that adjusts the flow rate of the refrigerant flowing into the user-side heat exchanger 21. The indoor unit 20 conditioned the air in the air-conditioned space by heating or cooling the air in the air-conditioned space using the user-side heat exchanger 21. In this embodiment, of the components of the refrigerant circuit 2, all equipment and devices 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 installed in the outdoor unit 10.

[0019] [1-1-2. Refrigerant Circuit Configuration] The refrigerant circuit 2 includes 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 "compressors" in this disclosure. The low-stage compressor 11 and the high-stage compressor 12 are connected in series to enable 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 each of 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 flow path of the refrigerant. The first switching mechanism 51 has 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 an annular manner in order.

[0021] The discharge side of the high-stage compressor 12 described above is connected via an oil separator 13 to the first switching mechanism 51, specifically between the first cooling valve 53 and the first heating valve 54. 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 utilization 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 designated as the destination for the refrigerant discharged from the high-stage compressor 12 functions as a gas cooler. In this specification, a gas cooler means a heat exchanger that dissipates heat to the gaseous refrigerant inside. That is, during cooling operation of the refrigeration system 1, the heat source side heat exchanger 14 becomes a gas cooler, and during heating operation, the utilization side heat exchanger 21 becomes 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 utilization side heat exchanger 21 is connected to the second switching mechanism 52 via the utilization side throttle valve 22. In other words, regardless of whether the heat exchanger 14 or 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 flow path of the refrigerant. The second switching mechanism 52 has 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 an annular manner in 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 in 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. This allows the second switching mechanism 52 to allow the refrigerant that has passed through the gas cooler to flow into the gas-liquid separator 17, regardless of whether the heat exchanger 14 or 21 functions as the gas cooler. In this embodiment, the second switching mechanism 52 also has check valves 61 and 62 to prevent backflow of refrigerant from the high-pressure receiver 15 towards the gas cooler. Check valve 61 is provided between the high-pressure receiver 15 and the third cooling valve 57. 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 depends on which of the heat exchangers 14 and 21 the first switching mechanism 51 designates as the gas cooler. In other words, the first switching mechanism 51 and the second switching mechanism 52 are controlled to operate in conjunction. Hereafter, the first switching mechanism 51 and the second switching mechanism 52 together will be referred to as the flow path switching mechanism 50.

[0028] As described above, a 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 flows the liquid refrigerant from the stored refrigerant to the throttle valve 16.

[0029] The throttle valve 16 is located upstream of the inlet of the gas-liquid separator 17. The throttle valve 16 depressurizes the liquid refrigerant supplied from the high-pressure receiver 15, creating a gas-liquid mixture before allowing it to flow into the gas-liquid separator 17.

[0030] The gas-liquid separator 17 is a device that separates the incoming refrigerant into gaseous refrigerant and liquid refrigerant. The gas-liquid separator 17 flows the separated gaseous refrigerant into the gas venting pipe 30. The gas venting pipe 30 is a pipe that connects the gas-liquid separator 17 to the suction side of each compressor 11 and 12. The gas venting 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] Furthermore, a liquid pump 40 is provided at the liquid-side outlet of the gas-liquid separator 17. The liquid pump 40 is driven to send 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 the liquid pump 40. The main pipe 41 is the pipe that connects the outlet of the liquid pump 40 to the second switching mechanism 52. In other words, the main pipe 41 carries the liquid refrigerant from the gas-liquid separator 17, which has been supplied to the liquid pump 40, to the second switching mechanism 52.

[0033] Furthermore, the refrigerant circuit 2 is provided with a path 42 in parallel with the liquid pump 40. Path 42 is a pipe 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. Path 42 connects the liquid outlet of the gas-liquid separator 17, which is different from the liquid outlet to which the liquid pump is connected, to the main pipe 41.

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

[0035] Cooling pipe 44 branches off from main pipe 41. Cooling pipe 44 connects main pipe 41 to gas vent pipe 30. More specifically, cooling pipe 44 branches off from main pipe 41 upstream of the point where it merges with the check valve 43 downstream of main pipe 41. Cooling pipe 44 is equipped with a cooling throttle valve 45 for reducing the pressure of the refrigerant.

[0036] Downstream of the liquid pump 40, a subcooling heat exchanger 46 is provided to exchange heat between the liquid refrigerant in the main pipe 41 and the refrigerant in the cooling pipe 44 after it has passed through the cooling throttle valve 45. Since the refrigerant in the cooling pipe 44 is cooled after passing through the cooling throttle valve 45, in the subcooling heat exchanger 46, the refrigerant in the main pipe 41 is cooled by the refrigerant in the cooling pipe 44. In detail, 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 supplied to the liquid pump 40 and the refrigerant that has passed through the path 42.

[0037] Furthermore, the refrigerant downstream of the subcooled heat exchanger 46 in the main piping 41 is cooled by an external cooling device 47. The external cooling device 47 cools the refrigerant in the main piping 41 using a refrigeration cycle that uses refrigerant that has been disconnected from the refrigerant in the refrigerant circuit 2.

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

[0039] Therefore, the refrigeration cycle of the external cooling device 47 can use a refrigerant that is more flammable, toxic, and has a greater environmental impact in the event of leakage than carbon dioxide, but is more energy-efficient than carbon dioxide. In this embodiment, the external cooling device 47 can properly manage leakage even when using a refrigerant that is more energy-efficient in the refrigeration cycle than carbon dioxide, such as an HFC (Hydro Fluoro Carbon) refrigerant, an HFO (Hydro Fluoro Olefin) refrigerant, or a mixed refrigerant containing these.

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

[0041] The second switching mechanism 52 switches the destination of the liquid refrigerant inlet of the main piping 41 between the heat source side heat exchanger 14 and the utilization side heat exchanger 21 by opening either the fourth cooling valve 59 or the heating throttle valve 60. At this time, the heat exchanger designated as the destination of the liquid refrigerant inlet of the main piping 41 functions as the cooling side heat exchanger. In this specification, the cooling side heat exchanger means a heat exchanger that causes the refrigerant inside to absorb heat. That is, during cooling operation of the refrigeration system 1, the utilization side heat exchanger 21 becomes the cooling side heat exchanger, and during heating operation, the heat source side heat exchanger 14 becomes the cooling side heat exchanger. In this embodiment, the second switching mechanism 52 has a check valve 63 that prevents backflow from the utilization side throttle valve 22 toward the main piping 41. The check valve 63 is provided in the second switching mechanism 52 between the fourth cooling valve 59 and the utilization side throttle valve 22.

[0042] As described above, the high-temperature sides of the heat exchangers 14 and 21 are connected to the first switching mechanism 51, so that 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 piping 18, which is 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 piping 70 is connected between the second cooling valve 55 and the second heating valve 56. The return piping 70 is connected to the first switching mechanism 51 in parallel with the suction-side piping 18.

[0043] The first switching mechanism 51 opens one of the second cooling valve 55 and the second heating valve 56, which is located between the cooling-side heat exchanger and the suction-side piping 18. Therefore, regardless of whether the heat exchanger 14 or 21 functions as the cooling-side heat exchanger, the first switching mechanism 51 can allow the refrigerant from the cooling-side heat exchanger to flow to the suction-side piping 18 and the return piping 70.

[0044] An intake-side on-off valve 19 is provided in the intake-side piping 18. More specifically, the intake-side on-off valve 19 is located upstream of the confluence point between the low-stage branch pipe 31 and the intake-side piping 18 in the intake-side piping 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. The return pipe 70 is provided with a return-side on-off valve 71. The return pipe 70 is also provided with a check valve 72 to prevent backflow of refrigerant from the gas-liquid separator 17 side toward the first switching mechanism 51. The suction-side on-off valve 19 and the return-side on-off valve 71 correspond to the "on-off valves" in this disclosure.

[0046] An oil separator 73 is provided in the return pipe 70. The oil separator 73 separates the oil mixed in with the refrigerant in the return pipe 70 and returns it to the suction side of each compressor 11, 12. In this embodiment, the oil separator 73 returns the oil in the return pipe 70 to the vent pipe 30 located on the suction side of each compressor 11.

[0047] Furthermore, a heat exchanger 74 is 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. In other words, the heat exchanger 74 can liquefy the gaseous components of the refrigerant in the return pipe 70 that have evaporated in the cooling-side heat exchanger.

[0048] The refrigeration system 1 has a blower 74a that blows outside air into 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 to the heat exchanger 74 by latent heat of vaporization. As a result, the heat exchanger 74 can cool the refrigerant in the return pipe 70 even when the outside 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 a water supply means 14b that supplies water to lower the temperature of the intake air to the heat source side heat exchanger 14 by latent heat of vaporization. The water supply means 14b supplies water to lower the temperature of the intake air to the heat source side heat exchanger 14 by latent heat of vaporization when the heat source side heat exchanger 14 functions as a gas cooler. As a result, the efficiency of heat exchange when the heat source side heat exchanger 14 functions as a gas cooler is improved.

[0050] The water supply means 14b and 74b may be, for example, devices that directly spray water onto the heat exchangers 14 and 74. Alternatively, the water supply means 14b and 74b may be so-called indirect water-spraying devices that supply water to a permeable filter provided on the outside air intake side of the heat exchangers 14 and 74, thereby lowering the temperature of the intake air of the heat exchangers 14 and 74 due to the latent heat of vaporization of the water adhering to the filter. Furthermore, the water supply means 14b and 74b may be other devices, mechanisms, etc. that can lower the temperature of the intake air of the heat exchangers 14 and 74 by utilizing the latent heat of vaporization of water.

[0051] [1-1-3. Control device configuration] As shown in Figure 1, the refrigeration system 1 is provided with a control unit 90. The control unit 90 is a device that controls each part of the refrigeration system 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, flash memory, and optical disc. The control unit 90 controls each part of the refrigeration system 1 by having the processor read a program from the storage medium and executing the program using the processor. Alternatively, the control unit 90 may have wired logic such as an ASIC (Application Specific Integrated Circuit) instead of a processor and storage medium. Alternatively, the control unit 90 may have a combination of a processor, storage medium, and wired logic.

[0052] Furthermore, the control unit 90 is equipped with communication hardware such as connectors and communication circuits that conform to wireless or wired communication standards. The control unit 90 communicates with each part of the refrigeration system 1 via this communication hardware.

[0053] The control unit 90 individually controls the on / off state and rotational speed of each compressor 11, 12 and the liquid pump 40. The control unit 90 switches the open and closed states of each valve 19, 53-60, 71, which are on / off valves. The control unit 90 also switches the open and closed states and adjusts the opening degree of each throttle valve 16, 22, 33, 34, 45, 60, which are throttle valves with adjustable opening degrees. The control unit 90 switches the on / off state and controls the airflow rate of each blower 14a, 74a. The control unit 90 controls the presence or absence of water supply and the amount of water supplied by the water supply means 14b, 74b.

[0054] [1-2. Operation] The operation of the refrigeration system 1, configured as described above, will be explained below. The refrigeration system 1 is designed to easily improve its Annual Performance Factor (APF) by switching the refrigerant flow path according to the cooling load to increase energy efficiency. First, the operation during cooling when the cooling load is low or medium, that is, when the cooling load is medium or lower, will be explained.

[0055] [1-2-1. Operation during cooling operation under moderate load or less] Figure 2 shows the refrigerant circuit 2 during cooling operation at medium load. Figure 1 shows the refrigerant circuit 2 during cooling operation at low load. As shown in Figures 1 and 2, during cooling operation at medium load or lower, the control unit 90 opens the cooling valves 53, 55, 57, and 59. The control unit 90 also closes the heating valves 54, 56, 58 and the heating throttle valve 60. As a result, the heat source side heat exchanger 14 functions as a gas cooler, and the utilization side heat exchanger 21 functions as a cooling side heat exchanger.

[0056] Furthermore, the control unit 90 closes the intake-side on-off valve 19 and opens the return-side on-off valve 71. As a result, each compressor 11 and 12 no longer directly inhales the refrigerant that has passed through the utilization-side heat exchanger 21, which is the cooling-side heat exchanger, and instead inhales the gaseous refrigerant separated in the gas-liquid separator 17 through the gas venting pipe 30.

[0057] In detail, when the cooling load is low, the control unit 90 opens the high-stage throttle valve 34 and closes the low-stage throttle valve 33, as shown in Figure 1, and then drives only the high-stage compressor 12 among the compressors 11 and 12. As a result, the gaseous 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 gaseous refrigerant.

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

[0059] Regardless of whether the cooling load is low or medium, the refrigerant discharged by 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 gaseous refrigerant is cooled by releasing heat into the outside air. In addition, the control unit 90 activates the water supply means 14b during cooling operation to promote the cooling of the refrigerant. After releasing heat in the heat source side heat exchanger 14, the refrigerant flows into the second switching mechanism 52 and then into the high-pressure receiver 15 via the third cooling valve 57.

[0061] Of the refrigerant that flows into the high-pressure receiver 15, the liquid refrigerant is depressurized by the throttle valve 16 to become a medium-temperature gas-liquid mixture and flows into the gas-liquid separator 17. The refrigerant that flows into the gas-liquid separator 17 is separated into gaseous refrigerant and liquid refrigerant, and the separated gaseous refrigerant is drawn back into each compressor 11 and 12 via the venting pipe 30.

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

[0063] A liquid pump 40 is used to supply liquid refrigerant to the heat exchanger 21 on the user side. The control unit 90 drives the liquid pump 40 to supply the liquid refrigerant stored in the gas-liquid separator 17 to the heat exchanger 21 on the user side. When the liquid pump 40 is driven, the liquid refrigerant from the gas-liquid separator 17 flows into the main piping 41. A check valve 43 prevents backflow of the refrigerant supplied to the liquid pump 40 towards the gas-liquid separator 17.

[0064] The control unit 90 uses the subcooling heat exchanger 46 and the external cooling equipment 47 to cool the refrigerant in the main piping 41 to a predetermined target temperature. In this case, the control unit 90 prioritizes using the external cooling equipment 47 over the subcooling heat exchanger 46 to cool the refrigerant in the main piping 41. That is, when the refrigerant in the main piping 41 can be cooled to the target temperature using only the external cooling equipment 47, the control unit 90 closes the cooling throttle valve 45 and does not perform cooling by the subcooling heat exchanger 46. Also, when the refrigerant in the main piping 41 cannot be subcooled to the target temperature using only the external cooling equipment 47, 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 piping 41 flows into the second switching mechanism 52, then through the fourth cooling valve 59 and the check valve 63 to flow into each indoor unit 20, and then through the utilization-side throttle valve 22 to flow into the utilization-side heat exchanger 21. In the utilization-side heat exchanger 21, the liquid refrigerant absorbs heat from the air in the air-conditioned space, and a portion of it becomes gaseous refrigerant, which cools the air in the air-conditioned space. As a result, the air-conditioned space is cooled.

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

[0067] The refrigerant passing through the return pipe 70 is cooled by the heat exchanger 74. When the cooling load is medium or lower, the control unit 90 activates the water supply means 74b to facilitate the 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] Thus, when the cooling load is moderate or lower, 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 conditioned space, and returns to the gas-liquid separator 17 through a closed cycle without passing through the compressors 11 and 12. In other words, the refrigerant circuit 2 is configured to independently perform the storage of liquid refrigerant in the gas-liquid separator 17 by driving the compressors 11 and 12, and the sending of the liquid refrigerant from the gas-liquid separator 17 to the user-side heat exchanger 21 by driving the liquid pump 40.

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

[0070] To achieve the above operation, when the cooling load is low, the control unit 90 controls each part of the refrigeration system 1 so that the pressure in each part of the refrigerant circuit 2 satisfies the following inequality (A). P1 <P5≦P9<P8≦P0<P7 (A) However, as shown in Figure 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 lower floor, P8 represents the pressure in the piping on the inlet side of the indoor unit 20H on the upper floor, and P9 represents the pressure in the piping on the outlet side of indoor units 20L and 20H. Note that P7 is the pressure in the piping located at the same height as indoor unit 20L, and P8 is the pressure in the piping located at the same height as indoor unit 20H.

[0071] When the cooling load is moderate or lower, as described above, the liquid refrigerant in the gas-liquid separator 17 returns to the gas-liquid separator 17 through a closed cycle that bypasses the compressors 11 and 12, due to the operation of the liquid pump 40. In this closed cycle, even when the liquid pump 40 has stopped after it has operated, natural circulation of the refrigerant may occur between the gas-liquid separator 17 and the user-side heat exchanger 21.

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

[0073] In this embodiment, the refrigeration system 1 is installed under conditions that facilitate natural circulation. Specifically, since the outdoor unit 10 equipped with the gas-liquid separator 17 is located higher than the indoor units 20L and 20H, the difference in height between the gas-liquid separator 17 and the indoor units 20L and 20H makes it easy to circulate the refrigerant between the gas-liquid separator 17 and the indoor units 20L and 20H. Also, as described above, a portion of the liquid refrigerant evaporates due to heat absorption in the heat exchanger 21 on the utilization side. Therefore, the refrigerant with a lower specific gravity that has partially evaporated in the heat exchanger 21 on the utilization side is easily pushed back to the gas-liquid separator 17 by the liquid refrigerant with a higher specific gravity moving from the gas-liquid separator 17 towards the heat exchanger 21 on the utilization side of the indoor units 20L and 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 flows 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 flows 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-cooled cooling operation] Figure 3 shows the refrigerant circuit 2 during air-cooled cooling operation. When the cooling load is medium or lower, under conditions where all the refrigerant evaporated in the user-side heat exchanger 21 is returned to liquid refrigerant by the heat exchanger 74 in the return pipe 70, the amount of liquid refrigerant in the gas-liquid separator 17 does not decrease. In such cases, air-cooled cooling operation is possible, where the refrigerant is liquefied using only the heat exchanger 74 without operating the compressors 11 and 12. For example, in environments with low outside temperatures, air-cooled cooling operation is easily performed when the refrigeration system 1 is operated to prevent the room temperature from rising due to exhaust heat from equipment installed in the air-conditioned space.

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

[0077] During air-cooled cooling operation, the control unit 90 drives the liquid pump 40 to return the liquid refrigerant from the gas-liquid separator 17 to the user-side heat exchanger 21 and return piping 70 via a closed cycle similar to that used when the cooling load is medium or lower. In addition, the control unit 90 stops the liquid pump 40 when natural circulation of the refrigerant occurs in the closed cycle, similar to that used when the cooling load is medium or lower, and drives the liquid pump 40 only when natural circulation occurs or when natural circulation is reduced.

[0078] Thus, during air-cooled cooling operation, the compressors 11 and 12, which consume a particularly large amount of energy, are not driven, thus significantly reducing the energy required for cooling operation. The more frequently air-cooled cooling operation is possible 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 refrigerant circuit 2 during high-load cooling operation. In operation when the cooling load is medium or lower, the supercooled liquid refrigerant is flowed to the utilization-side heat exchanger 21, so when the ambient temperature is high and the cooling load is high, heat leakage tends to increase. Since such heat leakage occurs largely in the gas-liquid separator 17, in order to reduce heat leakage, the refrigerant temperature drop in the gas-liquid separator 17 is suppressed, and the liquid refrigerant is cooled by the supercooled heat exchanger 46 and external cooling equipment 47, thereby increasing supercooling and enhancing the refrigeration effect. Furthermore, when the cooling load is high, the refrigeration system 1 switches to superheat control where there is a temperature difference between the inlet and outlet of the utilization-side heat exchanger 21, which is the cooling-side heat exchanger, and cools the air in the conditioned space using the latent heat of vaporization.

[0080] 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, as it does when the load is moderate or lower. However, unlike when the load is moderate or lower, the control unit 90 opens the intake side on-off valve 19 and closes the return side on-off valve 71. As a result, the refrigerant that has passed through the utilization side heat exchanger 21, which is the cooling side heat exchanger, does not return to the gas-liquid separator 17 via the return pipe 70, but is compressed in two stages by the compressors 11 and 12.

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

[0082] When the cooling load is high, the suction-side shut-off valve 19 is open, so the main piping 41 and path 42 communicate with the suction side of the compressors 11 and 12. For this reason, the control unit 90 stops the liquid pump 40 and allows the liquid refrigerant separated in the gas-liquid separator 17 to flow into the main piping 41 via path 42 through circulation accompanying the operation of the compressors 11 and 12. The liquid refrigerant in the main piping 41 flows through the same path as in the case of medium load or lower, and flows into each indoor unit 20 while being cooled by the subcooled heat exchanger 46 and external cooling equipment 47.

[0083] The refrigerant flowing into each indoor unit 20 is depressurized at the utilization-side throttle valve 22, absorbs heat in the utilization-side heat exchanger 21, and evaporates. The refrigerant that has passed through the utilization-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, through the suction-side piping 18, and is compressed in two stages by the compressors 11 and 12. The control unit 90 controls the opening of the utilization-side throttle valve 22 so that the refrigerant flowing into the utilization-side heat exchanger 21 reaches a specified degree of superheating, thereby preventing liquid compression in the compressors 11 and 12. Furthermore, if 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] In other words, when the cooling load is high, the compressors 11 and 12 perform not only the work of liquefying the refrigerant and storing it in the gas-liquid separator 17, as in a normal two-stage compression cycle, but also the work of flowing the liquid refrigerant from the gas-liquid separator 17 to the heat exchanger 21 on the utilization side.

[0085] [1-2-4. Operation during heating operation] Figure 5 shows the refrigerant circuit 2 during heating operation. The refrigeration unit 1 is configured 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, 58 and the heating throttle valve 60 of the flow path switching mechanism 50, and closes the cooling valves 53, 55, 57, 59. As a result, the heat source side heat exchanger 14 functions as a cooling side heat exchanger, and the utilization side heat exchanger 21 functions as a gas cooler.

[0086] Furthermore, the control unit 90 opens the intake-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 the 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 flows into the first switching mechanism 51 flows into each indoor unit 20 via the first heating valve 54, and is cooled by releasing heat into the air of the heated space in the user-side heat exchanger 21. As a result, the heated space is heated.

[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 and check valve 62 of the second switching mechanism 52, and flows into the high-pressure receiver 15. Of the refrigerant that has flowed into the high-pressure receiver 15, the liquid refrigerant is depressurized by the throttle valve 16 to become 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 gaseous refrigerant separated in the gas-liquid separator 17 is drawn into the high-stage compressor 12 via the gas venting pipe 30, bringing the pressure inside the gas-liquid separator 17 to a specified value and lowering the discharge refrigerant temperature of the high-stage compressor 12.

[0090] Furthermore, during heating operation, the intake side shut-off valve 19 is open, so the main piping 41 and the path 42 communicate with the intake side of the compressors 11 and 12. For this reason, the control unit 90 stops the liquid pump 40 and allows the liquid refrigerant separated in the gas-liquid separator 17 to flow to the main piping 41 via the path 42 through circulation accompanying the operation of the compressors 11 and 12. In other words, during heating operation, just like 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 also opens the cooling throttle valve 45 and cools the refrigerant in the main piping 41 with the subcooled heat exchanger 46. The control unit 90 also stops the external cooling equipment 47.

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

[0092] [1-3. Effects, etc.] As described above, in this embodiment, the refrigeration system 1 is equipped with a refrigerant circuit 2 connecting compressors 11 and 12, a heat source side heat exchanger 14, a gas-liquid separator 17, and a utilization side heat exchanger 21. A liquid pump 40 is provided to send the liquid refrigerant from the gas-liquid separator 17 to the cooling side heat exchanger among the heat source side heat exchanger 14 and the utilization side heat exchanger 21, and a path 42 is provided to allow the liquid refrigerant from the gas-liquid separator 17 to flow downstream of the liquid pump 40 without passing through the liquid pump 40. As a result, the liquid refrigerant in the gas-liquid separator 17 can be sent to the cooling-side heat exchanger without relying on the compressors 11 and 12, thus reducing the amount of work that the compressors 11 and 12 have to do to compress the gaseous refrigerant. Furthermore, especially when the gas-liquid separator 17 is located higher than the cooling-side heat exchanger, such as when the gas-liquid separator 17 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 more 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. Therefore, it becomes easier to reduce energy consumption and improve the efficiency of the refrigeration system 1.

[0093] As in this embodiment, in the refrigeration system 1, the compressors 11 and 12 discharge the gaseous refrigerant from the gas-liquid separator 17 to the gas cooler among the heat source side heat exchanger 14 and the utilization side heat exchanger 21, and return it to the gas-liquid separator 17 in a gas-liquid mixed state via the throttle valve 16. The liquid pump 40 sends the liquid refrigerant from the gas-liquid separator 17 to the cooling side heat exchanger, where it absorbs heat before being returned to the gas-liquid separator 17. This allows the operation of compressors 11 and 12 to be separated from the supply of liquid refrigerant to the cooling-side heat exchanger, and to be performed with the purpose of liquefying the gaseous refrigerant and returning it to the gas-liquid separator 17, thereby reducing the workload of compressors 11 and 12. Therefore, it becomes easier to reduce energy consumption and improve the efficiency of the refrigeration system 1.

[0094] As in this embodiment, the refrigeration system 1 may be configured such that the path 42 is equipped with a check valve 43 to prevent backflow of refrigerant toward the gas-liquid separator 17. This prevents the liquid refrigerant supplied to the liquid pump 40 from flowing back into the gas-liquid separator 17 via the path 42. Therefore, the liquid pump 40 makes it easier to pump the liquid refrigerant from the gas-liquid separator 17, thereby improving the efficiency of the refrigeration system 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 heat exchanger, a cooling pipe 44 branched from the main pipe 41, a cooling throttle valve 45 that reduces the pressure of the refrigerant in the cooling pipe 44, and a subcooled 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 of the liquid refrigerant. Therefore, it is possible to increase the refrigeration effect while suppressing losses, thereby improving the efficiency of the refrigeration device 1.

[0096] As in this embodiment, the refrigeration system 1 may be configured to include an external cooling device 47 that cools the refrigerant after it has passed through the subcooling heat exchanger 46 in the main piping 41. This allows for further cooling of the liquid refrigerant flowing into the cooling-side heat exchanger. Therefore, it becomes possible to improve and stabilize the freezing capacity, and to increase the efficiency of the freezing equipment.

[0097] As in this embodiment, the refrigerant circuit 2 may use carbon dioxide as the refrigerant, and the external cooling equipment 47 may use a refrigeration cycle that utilizes a refrigerant with higher energy efficiency than carbon dioxide to cool the refrigerant in the main piping 41. As a result, the energy-efficient external cooling device 47 can improve the cooling capacity of the refrigeration system 1, which uses carbon dioxide as a refrigerant with minimal environmental impact. Furthermore, because the external cooling device 47 can be made with a simpler configuration than the refrigerant circuit 2 of the refrigeration system 1, even when using refrigerants such as HFCs or HFOs, which are highly efficient but have a greater environmental impact than carbon dioxide, in the external cooling device 47, the risk of refrigerant leakage from the external cooling device 47 is less likely to increase. Therefore, it is possible to improve the efficiency of the refrigeration system 1 while suppressing environmental impact.

[0098] As in this embodiment, the refrigeration system 1 may be configured to prioritize the use of the external cooling equipment 47 over the subcooled heat exchanger 46 in order to cool the refrigerant flowing to the cooling-side heat exchanger to the target temperature. This allows for the use of an external cooling device 47, which is easier to configure for high energy efficiency, as a preferred option over the supercooled heat exchanger 46. Therefore, the efficiency of the refrigeration device 1 can be improved.

[0099] As in this embodiment, the refrigeration device 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 latent heat of vaporization. This makes it easier to improve the cooling capacity of a refrigeration system with low energy consumption. Therefore, it is possible to improve the efficiency of refrigeration equipment.

[0100] As in this embodiment, the compressor may be configured to include a high-stage compressor 12 and a low-stage compressor 11. This makes it easier to increase the efficiency of each compressor 11 and 12, especially when using carbon dioxide or other substances with large pressure differences within the refrigerant circuit 2 as refrigerants. Therefore, the efficiency of the refrigeration device 1 can be improved.

[0101] As described above, in this embodiment, the refrigeration system 1 is equipped with a refrigerant circuit 2 connecting compressors 11 and 12, a heat source side heat exchanger 14, a gas-liquid separator 17, and a utilization side heat exchanger 21. It also has a liquid pump 40 that sends the liquid refrigerant from the gas-liquid separator 17 to the cooling side heat exchanger among the heat source side heat exchanger 14 and the utilization side heat exchanger 21, and a check valve 43 provided in parallel with the liquid pump 40 to prevent backflow of refrigerant toward the gas-liquid separator 17. The refrigerant that has passed through the cooling side heat exchanger branches and flows into an suction side pipe 18 connected to the suction side of the compressors 11 and 12 and a return pipe 70 connected to the gas-liquid separator 17. The suction side pipe 18 and the return pipe 70 are equipped with an suction side on-off valve 19 and a return side on-off valve 71, respectively. As a result, when the cooling load on the cooling-side heat exchanger is not high, the refrigerant from the cooling-side heat exchanger can be returned to the gas-liquid separator 17 via the return pipe 70 by the operation of the liquid pump 40 or by natural circulation via the check valve 43, thereby reducing the workload of the compressors 11 and 12. Also, when the cooling load on 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. Therefore, it becomes easier to improve the APF (Annual Performance Factor), and the efficiency of the refrigeration system can be increased.

[0102] As in this 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 venting pipe 30 for removing gaseous 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 side throttle valve 33 and a high-stage side throttle valve 34, respectively. As a result, when the liquid refrigerant is supplied to the cooling-side heat exchanger by the liquid pump 40 or natural circulation, the low-stage compressor 11 can be stopped and the gaseous refrigerant in the gas-liquid separator 17 can be liquefied by the operation of only the high-stage compressor 12 when the load is low. Therefore, it becomes 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 the outside air. This makes it easier to increase the liquid component of the refrigerant flowing into the gas-liquid separator 17 by allowing heat to dissipate from the refrigerant in the return pipe 70 to the outside air, thereby reducing the workload of the compressors 11 and 12. Therefore, it becomes easier to improve the APF, and the efficiency of the refrigeration system 1 can be increased.

[0104] As in this embodiment, the refrigeration device 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 latent heat of vaporization. This makes it easier for the refrigerant in the return pipe 70 to dissipate heat to the outside air, thus reducing the likelihood of a shortage of liquid refrigerant in the gas-liquid separator 17, and making it easier to reduce the workload of the compressors 11 and 12. Therefore, it becomes easier to improve the APF, and the efficiency of the refrigeration system 1 can be increased.

[0105] As in this embodiment, the refrigeration system 1 may be configured to include an oil separator 73 that recovers oil from the return pipe 70 and returns it to the suction side of the compressors 11 and 12. This prevents oil from the compressors 11 and 12 from accumulating in the gas-liquid separator 17 when the liquid refrigerant from the gas-liquid separator 17 is circulated to the cooling-side heat exchanger and then returned to the gas-liquid separator 17 via the return pipe 70. This makes it easier to improve the efficiency of the refrigeration system 1 while ensuring its reliability.

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

[0107] As in this embodiment, the refrigeration system 1 may be equipped with a flow path switching mechanism 50 that switches the cooling-side heat exchanger between the utilization-side heat exchanger 21 and the heat source-side heat exchanger 14, and the flow path switching mechanism 50 may be configured to ensure that the refrigerant that has passed through the cooling-side heat exchanger reaches the suction-side piping 18 and the return piping 70, regardless of whether the utilization-side heat exchanger 21 or the heat source-side heat exchanger 14 is functioning as the cooling-side heat exchanger. This allows the system to switch between the heat exchanger functioning as a cooling-side heat exchanger between the utilization-side heat exchanger 21 and the heat source-side heat exchanger 14, and to select, depending on the load, whether to return the refrigerant that has passed through the cooling-side heat exchanger to the gas-liquid separator 17 or to compress it in the compressors 11 and 12. Therefore, when the refrigeration unit 1 is an air conditioner, as in this embodiment, it becomes easier to reduce the workload of the compressors 11 and 12 during both cooling and heating operations.

[0108] The following describes an embodiment that modifies part of Embodiment 1. In the following, configurations that differ from Embodiment 1 will be described, and configurations that are the same as those in Embodiment 1 will not be described.

[0109] (Embodiment 2) As described above, the refrigeration system 1 of Embodiment 1 operates in a manner similar to a normal two-stage compression cycle when the cooling load is high and during heating operation. In contrast, the refrigeration system 301 of Embodiment 2 is configured to easily improve energy efficiency even under high load conditions.

[0110] [2-1. Structure] Figure 6 shows the refrigerant circuit 302 of the refrigeration system 301 according to Embodiment 2. In the refrigerant circuit 302 of Embodiment 2, an expansion mechanism 316 is provided instead of the throttle valve 16 of Embodiment 1. The expansion mechanism 316 is a device that recovers the pressure difference due to the flow of refrigerant as power and reduces the pressure of the refrigerant. The power recovered by the expansion mechanism 316 can be used for power generation by a generator, driving compressors 11 and 12, etc. In this embodiment, carbon dioxide is used as the refrigerant, which has a particularly large pressure difference in the refrigerant circuit 302, making it easier to recover power using the expansion mechanism 316. Note that the refrigeration system 301 of this embodiment does not have the external cooling equipment 47 of Embodiment 1.

[0111] Furthermore, the refrigeration system 301 of the second embodiment is provided with a pressure sensor 381 that measures the pressure inside the gas-liquid separator 17. The pressure sensor 381 transmits the measured pressure inside the gas-liquid separator 17 to the control unit 90. In addition, the refrigeration system 301 is provided with a temperature sensor 382 that measures the outlet temperature of the liquid refrigerant in the gas-liquid separator 17. In this embodiment, the temperature sensor 382 measures the temperature of the refrigerant at one of the liquid-side outlets of the gas-liquid separator 17 that is connected to the liquid pump 40. The temperature sensor 382 transmits the measured temperature of the outlet temperature of the liquid refrigerant in the gas-liquid separator 17 to the control unit 90.

[0112] [2-2. Operation] The operation of each part of the refrigerant circuit 302 during cooling and heating operation of the refrigeration unit 301 is the same as the operation of each part of the refrigerant circuit 2 in Embodiment 1, except for the operation of the cooling throttle valve 45 and the expansion mechanism 316. In Embodiment 2 as well, during both heating and cooling operation, the flow path switching mechanism 50 ensures that the refrigerant that has passed through the gas cooler flows into the expansion mechanism 316 from the same direction via the high-pressure receiver 15. Therefore, during both cooling and heating operation, the refrigerant pressure reduction and power recovery by the expansion mechanism 316 are possible.

[0113] During the operation of compressors 11 and 12, as described above, the refrigerant that has flowed through the gas cooler flows into the expansion mechanism 316, is depressurized, and flows into the gas-liquid separator 17. However, the expansion mechanism 316 is more difficult to control the amount of refrigerant depressurization than the throttle valve 16, and it is possible that refrigerant that has not been sufficiently depressurized may flow into the gas-liquid separator 17. In such cases, the pressure of the refrigerant in the gas-liquid separator 17 will rise. Also, since the temperature of the refrigerant in the gas-liquid separator 17 is equivalent to the saturation temperature calculated based on the pressure of the refrigerant in the gas-liquid separator 17, the temperature of the refrigerant in the gas-liquid separator 17 will rise as the pressure in the gas-liquid separator 17 rises. In such cases, the temperature of the liquid refrigerant flowing from the main pipe 41 to the cooling-side heat exchanger rises, inhibiting the heat absorption of the refrigerant in the cooling-side heat exchanger, and reducing the refrigeration effect.

[0114] In contrast, in this embodiment, when the refrigerant pressure reduction by the expansion mechanism 316 is insufficient, the opening of the cooling throttle valve 45 is increased, thereby strengthening the cooling of the refrigerant in the main pipe 41 by the subcooled heat exchanger 46 and stabilizing the temperature of the refrigerant flowing into the cooling-side heat exchanger.

[0115] Figure 7 is a flowchart of the refrigeration system 301, showing the operation of the control unit 90 while at least one of the compressors 11 and 12 is in operation. The control unit 90 repeatedly performs the operation shown in Figure 7 while at least one of the compressors 11 and 12 is in operation.

[0116] First, in step SA1, the control unit 90 acquires the measurement values ​​from the pressure sensor 381 or the temperature sensor 382.

[0117] In step SA2, the control unit 90 determines whether the pressure reduction by the expansion mechanism 316 is insufficient based on the measurement value obtained in step SA1. Specifically, if the control unit 90 obtained a measurement value from the pressure sensor 381 in step SA1, it determines whether the obtained measurement value is equal to or greater than the first pressure. If the measurement value from 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 from 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 terminates the operation shown in Figure 7.

[0118] Furthermore, in step SA2, if the control unit 90 obtained a measurement value from the temperature sensor 382 in step SA1, it determines whether the obtained measurement value is equal to or greater than the first temperature. If the measurement value from the temperature sensor 382 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 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.

[0119] The first pressure or first temperature used for the decision in step SA2 may be stored in the control unit 90 as a predetermined constant value. Alternatively, the first pressure and first temperature may be values ​​determined by the current opening of the cooling throttle valve 45, the target temperature of the refrigerant in the main piping 41 for cooling the subcooled heat exchanger 46, etc. For example, if the current opening of the cooling throttle valve 45 is large, the value of the first pressure or first temperature will be large, and if the target temperature of the refrigerant in the main piping 41 is low, the value of the first pressure or first temperature will be small.

[0120] 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. In step SA3, the control unit 90 may be configured to increase the opening of the cooling throttle valve 45 more as the difference between the first pressure or first temperature and the measured values ​​of sensors 381 and 382 increases. After step SA3 is executed, the operation of the control unit 90 proceeds to step SA4.

[0121] 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 below a specified value. For example, if the opening of the cooling throttle valve 45 is increased in step SA3, the flow rate of refrigerant flowing into the venting 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 below a specified value (step SA4: YES), the control unit 90 terminates the operation shown in Figure 7. If the suction pressure P1 of the high-stage compressor 12 exceeds a specified value (step SA4: NO), the control unit 90 proceeds to step SA5.

[0122] In step SA5, the control unit 90 increases the operating 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 terminates the operation shown in Figure 7.

[0123] [2-3. Effects, etc.] As described above, in this embodiment, the refrigeration system 301 includes a refrigerant circuit 302 connecting compressors 11 and 12, a heat source side heat exchanger 14, a gas-liquid separator 17, and a utilization side heat exchanger 21, a liquid pump 40 that sends the liquid refrigerant from the gas-liquid separator 17 to the cooling side heat exchanger among the heat source side heat exchanger 14 and the utilization side heat exchanger 21, a check valve 43 provided in parallel with the liquid pump 40 to prevent backflow of refrigerant toward the gas-liquid separator 17, and the heat source side heat exchanger 14 and the utilization side The heat exchanger 21 includes an expansion mechanism 316 that expands the refrigerant that has flowed through the gas cooler and sends it to the gas-liquid separator 17, a main pipe 41 provided downstream of the liquid pump 40 through which the refrigerant toward the cooling side heat exchanger flows, 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 subcooled 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 refrigerant entering the gas-liquid separator 17 to be depressurized while power is recovered using the expansion mechanism 316, and the refrigerant flowing into the cooling-side heat exchanger is supercooled by the supercooling heat exchanger 46 to improve the refrigeration capacity. Therefore, power can be recovered while improving the refrigeration capacity, and the efficiency of the refrigeration device 301 can be increased.

[0124] As in this embodiment, the control unit 90 of the refrigeration device 301 may be configured to increase the opening degree of the cooling throttle valve 45 when it determines that the pressure reduction by the expansion mechanism 316 is insufficient. This allows for stable supercooling of the refrigerant flowing into the cooling-side heat exchanger. Therefore, power can be recovered while improving the refrigeration capacity, and the efficiency of the refrigeration device 301 can be increased. 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 the increase in intermediate pressure. As a result, the temperature rise of the liquid refrigerant in the gas-liquid separator 17 can be suppressed.

[0125] As in this 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 greater than a first pressure, or when the outlet temperature of the liquid refrigerant from the gas-liquid separator 17 is equal to or greater than a first temperature. This allows for stable supercooling of the refrigerant flowing into the cooling-side heat exchanger. Therefore, it is possible to improve the refrigeration capacity while recovering power, thereby increasing the efficiency of the refrigeration system.

[0126] (Embodiment 3) In Embodiment 2, it was explained that the power recovered by the expansion mechanism 316 can be applied to purposes such as power generation or refrigerant compression. In Embodiment 3, a refrigeration system 401 is described that can efficiently utilize the power recovered by the expansion mechanism 316 to operate the compression mechanism 411, thereby achieving high efficiency. The following describes the differences between the refrigeration device 301 of Embodiment 2 and the present invention, while the same components will not be described.

[0127] [3-1. Structure] Figure 8 shows the refrigerant circuit 402 of the refrigeration system 401 according to Embodiment 3, and illustrates the refrigerant circuit 402 during high-load cooling operation. As shown in Figure 8, in Embodiment 3, a compression mechanism 411 is provided in place of the low-stage compressor 11 of Embodiment 2. Furthermore, in Embodiment 3, a compressor 412 is provided in place of the high-stage compressor 12.

[0128] The compression mechanism 411 is located in the venting pipe 30 that removes the gaseous refrigerant from the gas-liquid separator 17. More specifically, the suction side of the compression mechanism 411 is located downstream of the connection point with the oil separator 73 in the venting pipe 30. In other words, the oil separator 73 recovers oil from the return pipe 70 and returns the recovered oil to the suction side of the compression mechanism 411.

[0129] The compression mechanism 411, upon operation, draws in the gas refrigerant gas from the venting pipe 30, compresses it, and discharges it. In this embodiment, the venting pipe 30 does not have branch pipes 31 and 32, and the entire amount of refrigerant passing through the venting pipe 30 is drawn into the compression mechanism 411. As a result, the oil returned by the oil separator 73 is easily drawn into the compression mechanism 411, and the compression mechanism 411 is easily lubricated with oil.

[0130] Furthermore, in this embodiment, the cooling pipe 44 is connected to the venting pipe 30 between the suction side of the compression mechanism 411 and the gas-liquid separator 17. As a result, the suction force of the compression mechanism 411 makes it easier for the refrigerant in the cooling pipe 44 to flow toward the compression mechanism 411.

[0131] The compression mechanism 411 is coaxially connected to the expansion mechanism 316 via shaft 411a. The compression mechanism 411 is also operated by the power recovered by the expansion mechanism 316. Specifically, when the expansion mechanism 316 rotates using the power recovered from the refrigerant flow, the compression mechanism 411 rotates and operates coaxially with the expansion mechanism 316. By providing a compression mechanism 411 that operates coaxially with the expansion mechanism 316 in this way, energy loss can be reduced compared to, for example, a case where the power recovered by the expansion mechanism 316 is converted into electricity.

[0132] A low-stage discharge pipe 413 is connected to the discharge side of the compression mechanism 411. The low-stage discharge pipe 413 branches into a first branch pipe 414 and a second branch pipe 415. The first branch pipe 414 is connected to the suction side of the compressor 412. The first branch pipe 414 is also provided with a first on-off valve 414a for opening and closing the first branch pipe 414. The second branch pipe 415 is connected to the discharge side of the compressor 412. More specifically, the second branch pipe 415 merges with a discharge pipe 416 that connects the discharge side of the compressor 412 to the oil separator 13. The second branch pipe 415 is provided with a second on-off valve 415a for opening and closing the second branch pipe 415. The first on-off valve 414a and the second on-off valve 415a correspond to examples of "on-off valves" in this disclosure.

[0133] In other words, the discharge side of the compression mechanism 411 is connected to both the suction side and the discharge side of the compressor 412 via the on-off valves 414a and 415a, respectively. Furthermore, the control unit 90 can switch between single-stage and two-stage compression of the refrigerant in the gas venting pipe 30 by opening and closing the first on-off valve 414a and the second on-off valve 415a.

[0134] In detail, by opening the first on-off valve 414a and closing the second on-off valve 415a, the refrigerant in the venting pipe 30 is compressed in two stages by the compression mechanism 411 and the compressor 412 and flows into the discharge pipe 416. Alternatively, by opening the second on-off valve 415a and closing the first on-off valve 414a, the refrigerant in the venting pipe 30 is compressed in one stage by the compression mechanism 411 and then flows into the discharge pipe 416 without being compressed by the compressor 412. Note that each on-off valve 414a and 415a can be switched between an open state and a closed state by the control unit 90. Therefore, each on-off valve 414a and 415a may be a valve that can only be switched between an open state and a closed state, or it may be a flow control valve that allows adjustment of the opening degree.

[0135] The compressor 412 is powered by an electric motor or an engine powered by fuel. In this embodiment, the compressor 412 is powered by an electric motor. The compressor 412 compresses the gaseous refrigerant drawn in from the first branch pipe 414 and discharges it into the discharge pipe 416.

[0136] The discharge pipe 416 is connected to the oil separator 13. The oil separator 13 recovers the oil contained in the refrigerant flowing in from the discharge pipe 416. The oil separator 13 also flows the refrigerant, after the oil has been recovered, to the first switching mechanism 51. In this embodiment, the oil separator 13 has an oil tank 13a for storing the recovered oil.

[0137] Furthermore, in Embodiment 3, the refrigeration system 401 is provided with an oil return mechanism 420 that returns the oil recovered by the oil separator 13 to the expansion mechanism 316 and the compressor 412. The oil return mechanism 420 supplies the oil stored in the oil tank 13a to the expansion mechanism 316 and the compressor 412.

[0138] The oil return mechanism 420 is connected to the oil tank 13a and has an oil return pipe 421 through which oil flows. The oil return pipe 421 branches into a first oil return branch pipe 422 and a second oil return branch pipe 423. The first oil return branch pipe 422 is connected to the upstream side of the expansion mechanism 316. The second oil return branch pipe 423 is connected to the compressor 412.

[0139] A first oil return branch pipe 422 is provided with a first oil return volume adjustment valve 424. A second oil return volume adjustment valve 425 is provided with a second oil return branch pipe 423. Each oil return volume adjustment valve 424 and 425 is a valve whose opening and closing and degree of opening can be adjusted by the control unit 90. The first oil return volume adjustment valve 424 adjusts the amount of oil returned from the oil separator 13 to the expansion mechanism 316. The second oil return volume adjustment valve 425 adjusts the flow rate of oil returned from the oil separator 13 to the compressor 412. Each oil return volume adjustment valve 424 and 425 is controlled by the control unit 90 so that the sliding parts of the expansion mechanism 316 and the compressor 412 are sufficiently lubricated, and so that a large amount of oil does not accumulate downstream of the expansion mechanism 316 and the compressor 412. This allows for appropriate management of the oil circulation rate in the refrigerant circuit 402.

[0140] In this embodiment, the casing of the expansion mechanism 316 and the casing of the compression mechanism 411 are connected by an oil pipe 411b. The oil pipe 411b is a pipe that carries oil between the expansion mechanism 316 and the compression mechanism 411. In this embodiment, the pressure on the suction side of the compression mechanism 411 is lower than the pressure of the expansion mechanism 316. Therefore, the oil returned to the expansion mechanism 316 by the oil return mechanism 420 is distributed to the compression mechanism 411 via the oil pipe 411b.

[0141] Furthermore, in Embodiment 3, similar to Embodiment 1, an external cooling device 47 is provided to cool the refrigerant in the main piping 41 after it has passed through the subcooled heat exchanger 46. Similar to Embodiment 1, this external cooling device 47 uses a refrigeration cycle that employs a refrigerant with higher energy efficiency than carbon dioxide to cool the refrigerant in the main piping 41.

[0142] Furthermore, in Embodiment 3, the suction-side piping 18 and suction-side on-off valve 19 connected to the first switching mechanism 51 are not provided. Therefore, of the heat source-side heat exchanger 14 and the utilization-side heat exchanger 21, the refrigerant that has passed through the cooling-side heat exchanger always flows into the return piping 70 after passing through the first switching mechanism 51.

[0143] [3-2. Operation] [3-2-1. Operation during high-load cooling operation] As shown in Figure 8, during high-load cooling operation, 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.

[0144] Furthermore, the control unit 90 opens the first on-off valve 414a and closes the second on-off valve 415a. The control unit 90 also opens the return on-off valve 71.

[0145] During high-load cooling operation, the control unit 90 switches the opening and closing of each valve as described above, and then drives the compressor 412. As a result, the compressor 412 draws in refrigerant from the low-stage discharge pipe 413 and discharges it into the discharge pipe 416.

[0146] The refrigerant discharged into the discharge pipe 416 flows into the heat source side heat exchanger 14 via the oil separator 13 and the first switching mechanism 51. The heat source side heat exchanger 14 functions as a gas cooler, cooling the refrigerant by exchanging heat with air. At this time, the control unit 90 operates the water supply means 14b, as in embodiments 1 and 2, to lower the temperature of the intake air to the heat source side heat exchanger 14 by the latent heat of vaporization of water.

[0147] The refrigerant cooled by the heat source side heat exchanger 14 reaches the expansion mechanism 316 via the second switching mechanism 52 and the high-pressure receiver 15. The refrigerant that reaches the expansion mechanism 316 is depressurized by the expansion mechanism 316 and flows into the gas-liquid separator 17, where it is separated into gaseous refrigerant and liquid refrigerant.

[0148] As described above, the expansion mechanism 316 and the compression mechanism 411 operate coaxially, so when the expansion mechanism 316 reduces the pressure of the refrigerant, the compression mechanism 411 operates. Due to the operation of the compression mechanism 411, the gaseous refrigerant separated in the gas-liquid separator 17 is drawn into the compression mechanism 411 via the gas venting pipe 30.

[0149] In this embodiment, the expansion mechanism 316 is provided at the inlet of the gas-liquid separator 17, and the compression mechanism 411, which operates coaxially with the expansion mechanism 316, is provided at the gas venting pipe 30, which is the outlet for the gaseous refrigerant in the gas-liquid separator 17. That is, a portion of the refrigerant that flows into the gas-liquid separator 17 through the expansion mechanism 316 becomes gaseous refrigerant and is drawn into the compression mechanism 411. Therefore, the flow rates of the refrigerant passing through the expansion mechanism 316 and the refrigerant drawn into the compression mechanism 411 are correlated, and the ratio of their flow rates does not fluctuate significantly. Consequently, the power recovered by the expansion mechanism 316 can be effectively utilized for compression by the compression mechanism 411.

[0150] The gaseous refrigerant compressed by the compression mechanism 411 is drawn back into the compressor 412 via the low-stage discharge pipe 413. In other words, during high-load cooling operation, the refrigeration system 401 uses a two-stage compression system, with the compression mechanism 411 on the low-stage side and the compressor 412 on the high-stage side, to liquefy the gaseous refrigerant in the gas-liquid separator 17.

[0151] The liquid refrigerant separated in the gas-liquid separator 17 flows into the main piping 41 by driving the liquid pump 40. However, as in Embodiment 1, when natural circulation occurs between the user-side heat exchanger 21 and the gas-liquid separator 17, the control unit 90 may stop driving the liquid pump 40 and allow the liquid refrigerant from the gas-liquid separator 17 to flow into the main piping 41 via the path 42 and the check valve 43.

[0152] The liquid refrigerant flowing into the main pipe 41 branches off into the cooling pipe 44 midway through its flow, is depressurized by the cooling throttle valve 45, and passes through the subcooling heat exchanger 46. In the subcooling heat exchanger 46, the refrigerant in the cooling pipe 44 subcools the refrigerant in the main pipe 41. After passing through the subcooling heat exchanger 46, the refrigerant in the cooling pipe 44 flows into the venting pipe 30 and is drawn into the compression mechanism 411. Therefore, the suction force of the compression mechanism 411 can be used to facilitate the flow of the refrigerant in the cooling pipe 44, and the refrigerant in the main pipe 41 can be easily subcooled.

[0153] The refrigerant in the main pipe 41 passes through the subcooling heat exchanger 46 and is then supercooled by the external cooling device 47. Although the heat exchange by the subcooling heat exchanger 46 is within the refrigerant of the refrigerant circuit 402 and therefore less prone to losses, the amount of supercooling of the refrigerant in the main pipe 41 by the subcooling heat exchanger 46 is limited by the operating conditions of the refrigeration system 401. Furthermore, the external cooling device 47 uses a refrigerant that is more efficient than carbon dioxide, and the supercooling of the refrigerant in the main pipe 41 is easier to adjust, but unlike the subcooling heat exchanger 46, the operation of the external cooling device 47 requires additional power. For this reason, the control unit 90 may select the more efficient of the subcooling heat exchanger 46 and the external cooling device 47 and use them to cool the main pipe 41.

[0154] The refrigerant cooled by the external cooling device 47 flows into the utilization-side heat exchanger 21 via the second switching mechanism 52, cooling the air in the conditioned space. The refrigerant that has flowed through the utilization-side heat exchanger 21 flows into the return pipe 70 via the first switching mechanism 51. In the return pipe 70, the refrigerant passes through the oil separator 73 and reaches the heat exchanger 74, where it is cooled. The control unit 90 activates the water supply means 74b to lower the temperature of the intake air in the heat exchanger 74, making it easier to liquefy the refrigerant. The refrigerant cooled in the heat exchanger 74 flows back into the gas-liquid separator 17.

[0155] [3-2-2. Operation during low-load cooling operation] Figure 9 shows the refrigerant circuit 402 during low-load cooling operation. During low-load cooling operation, the control unit 90 switches the refrigerant circuit 402 from the state during high-load cooling operation to a state where the compressor 412 is stopped. The control unit 90 also switches the first on-off valve 414a to the closed state and the second on-off valve 415a to the open state.

[0156] As a result, the refrigerant discharged to the lower-stage discharge pipe 413 by the compression mechanism 411 flows into the discharge pipe 416 without being drawn into the compressor 412. The refrigerant that flows into the discharge pipe 416 reaches the expansion mechanism 316 via the oil separator 13, the first switching mechanism 51, and the high-pressure receiver 15. The refrigerant that reaches the expansion mechanism 316 is depressurized by the expansion mechanism 316 and flows into the gas-liquid separator 17, where it is separated into gaseous refrigerant and liquid refrigerant. The gaseous refrigerant separated in the gas-liquid separator 17 is then drawn back into the compression mechanism 411 via the gas vent pipe 30. In other words, during low-load cooling operation, the refrigeration system 401 liquefies the gaseous refrigerant in the gas-liquid separator 17 by single-stage compression by the compression mechanism 411.

[0157] The liquid refrigerant separated in the gas-liquid separator 17 flows into the utilization-side heat exchanger 21 via the same path as in high-load cooling operation, and cools the air in the air-conditioned space. The refrigerant that has flowed through the utilization-side heat exchanger 21 returns to the gas-liquid separator 17 via the same path as in high-load cooling operation.

[0158] If low-load cooling operation continues, the pressure difference between the upstream and downstream sides of the expansion mechanism 316 will gradually decrease, making it impossible to recover sufficient power from the expansion mechanism 316 and thus preventing the compression mechanism 411 from operating. For this reason, when the pressure difference between the upstream and downstream sides of the expansion mechanism 316 decreases, the control unit 90 switches the first on-off valve 414a to the open state and the second on-off valve 415a to the closed state, and then temporarily operates the compressor 412. After a sufficient pressure difference is secured between the upstream and downstream sides of the expansion mechanism 316, the control unit 90 stops the compressor 412 again and switches the first on-off valve 414a to the closed state and the second on-off valve 415a to the open state, thereby continuing low-load cooling operation.

[0159] [3-2-3. Operation during cooling operation using air cooling] The refrigeration device 401 of Embodiment 3 can perform cooling operation by air cooling, similar to Embodiment 1. Figure 10 shows the refrigerant circuit 402 during cooling operation by air cooling.

[0160] During air-cooled cooling operation, the refrigerant circuit 402 is configured to a state where the expansion mechanism 316 and the compression mechanism 411 are also stopped, in addition to the state during low-load cooling operation when the compressor 412 is stopped. Furthermore, during low-load cooling operation, the control unit 90 closes both the on-off valves 414a and 415a. As a result, the gaseous refrigerant separated in the gas-liquid separator 17 is no longer drawn into the compression mechanism 411 and compressor 412, and refrigerant no longer flows to the heat source side heat exchanger 14, which is a gas cooler.

[0161] Furthermore, during air-cooled cooling operation, the control unit 90 closes the cooling throttle valve 45. In addition, similar to Embodiment 1, the liquid refrigerant separated in the gas-liquid separator 17 flows into the utilization-side heat exchanger 21 by being pumped by the liquid pump 40 or by natural circulation via the path 42 and check valve 43, and returns to the gas-liquid separator 17 via the return pipe 70. At this time, the control unit 90 operates the external cooling equipment 47 to lower the temperature of the refrigerant flowing into the utilization-side heat exchanger 21 to the temperature required for air conditioning in the conditioned space. The control unit 90 also operates the water supply means 74b to lower the temperature of the intake air to the heat exchanger 74, thereby facilitating the liquefaction of the refrigerant returning to the gas-liquid separator 17.

[0162] [3-2-4. Operation during heating operation] Figure 11 shows the refrigerant circuit 402 during heating operation. As shown in Figure 11, during heating operation, the control unit 90 opens the heating valves 54, 56, 58 and the heating throttle valve 60 of the flow path switching mechanism 50, and closes the cooling valves 53, 55, 57, 59. As a result, the heat source side heat exchanger 14 functions as a cooling side heat exchanger, and the utilization side heat exchanger 21 functions as a gas cooler.

[0163] Furthermore, the control unit 90 opens the first on-off valve 414a and closes the second on-off valve 415a. The control unit 90 also opens the return on-off valve 71.

[0164] During heating operation, the control unit 90 switches the opening and closing of each valve as described above, and then drives the compressor 412. As a result, the compressor 412 draws in refrigerant from the low-stage discharge pipe 413 and discharges it into the discharge pipe 416. The refrigerant discharged into the discharge pipe 416 flows into the first switching mechanism 51 via the oil separator 13.

[0165] The refrigerant that flows into the first switching mechanism 51 flows into each indoor unit 20 via the first heating valve 54, and is cooled by releasing heat into the air of the heated space in the user-side heat exchanger 21. As a result, the heated space is heated.

[0166] The refrigerant that has passed through the user-side heat exchanger 21 reaches the expansion mechanism 316 via the second switching mechanism 52 and the high-pressure receiver 15, where it is depressurized and becomes a low-temperature gas-liquid mixture. Subsequently, the refrigerant flows into the gas-liquid separator 17, where it is separated into gaseous refrigerant and liquid refrigerant.

[0167] The gaseous refrigerant separated in the gas-liquid separator 17 is drawn into the compression mechanism 411 via the venting pipe 30, compressed, and discharged into the low-stage discharge pipe 413. The refrigerant discharged into the low-stage discharge pipe 413 is drawn back into the compressor 412 via the first branch pipe 414.

[0168] The liquid refrigerant separated in the gas-liquid separator 17 flows into the main pipe 41. The refrigerant that has passed through the main pipe 41 flows through the second switching mechanism 52 into the heat source side heat exchanger 14. The refrigerant absorbs heat in the heat source side heat exchanger 14 and returns to the gas-liquid separator 17 through the return pipe 70. The control unit 90 stops the water supply means 14b and 74b during heating operation.

[0169] [3-3. Effects, etc.] As described above, in this embodiment, the refrigeration system 401 is equipped with a refrigerant circuit 402 connecting a compression mechanism 411, a heat source side heat exchanger 14, a gas-liquid separator 17, and a utilization side heat exchanger 21. It includes a liquid pump 40 that sends the liquid refrigerant from the gas-liquid separator 17 to the cooling side heat exchanger of the utilization side heat exchanger 21, a check valve 43 provided in parallel with the liquid pump 40 to prevent backflow of refrigerant toward the gas-liquid separator 17, and an expansion mechanism 316 that expands the refrigerant that has flowed through the gas cooler of the heat source side heat exchanger 14 and utilization side heat exchanger 21 and sends it to the gas-liquid separator 17. The compression mechanism 411 is provided in the gas venting pipe 30 into which the gas refrigerant from the gas-liquid separator 17 flows, and operates coaxially with the expansion mechanism 316. This allows the refrigerant entering the gas-liquid separator 17 to be depressurized while power is recovered using the expansion mechanism 316, and the recovered power can be efficiently used to operate the compression mechanism 411. As a result, energy consumption can be suppressed and the efficiency of the refrigeration system 401 can be increased.

[0170] As in this embodiment, the refrigeration device 401 may have a motor-driven compressor 412, and the discharge side of the compression mechanism 411 may be connected to both the suction side and the discharge side of the compressor 412 via a first on-off valve 414a and a second on-off valve 415a, respectively. This allows switching between single-stage compression using only the compression mechanism 411 and two-stage compression using both the compression mechanism 411 and the compressor 412, depending on the load. As a result, energy consumption for operating the compressor 412 can be reduced, and the efficiency of the refrigeration system 401 can be improved.

[0171] As in this embodiment, the refrigeration system 401 is provided downstream of the liquid pump 40 and includes a main pipe 41 through which refrigerant flows toward the cooling heat exchanger, a cooling pipe 44 branching off from the main pipe 41, a cooling throttle valve 45 for adjusting the flow rate of the cooling pipe 44, and a subcooled heat exchanger 46 that cools the refrigerant in the main pipe 41 with the reduced-pressure refrigerant at the cooling throttle valve 45. The cooling pipe 44 may be connected between the compression mechanism 411 and the gas-liquid separator 17 in the venting pipe 30. This allows the refrigerant flowing into the cooling-side heat exchanger to be supercooled by utilizing the suction force of the compression mechanism 411, which operates coaxially with the expansion mechanism 316. As a result, the refrigeration effect can be increased while suppressing energy consumption, and the efficiency of the refrigeration system 401 can be improved.

[0172] As in this embodiment, the refrigeration system 401 may be configured to include an external cooling device 47 that cools the refrigerant after it has passed through the subcooling heat exchanger 46 in the main piping 41. This allows for supercooling of the refrigerant flowing toward the cooling-side heat exchanger even when the pressure reduction by the expansion mechanism 316 is insufficient. As a result, the efficiency of the refrigeration system 401 can be increased while stabilizing the refrigeration effect.

[0173] As in this embodiment, the refrigerant circuit 402 may use carbon dioxide as the refrigerant, and the external cooling equipment 47 may use a refrigeration cycle that utilizes a refrigerant with higher energy efficiency than carbon dioxide to cool the refrigerant in the main piping 41. This allows the refrigeration capacity of a refrigeration system using carbon dioxide, which has a low environmental impact, to be improved by using an energy-efficient external cooling device 47. Furthermore, because the external cooling device 47 can be made with a simpler configuration than the refrigeration system 401, even when using refrigerants such as HFCs or HFOs, which are highly efficient but have a greater environmental impact than carbon dioxide, the risk of refrigerant leakage from the external cooling device 47 is less likely to increase. Therefore, it is possible to improve the efficiency of the refrigeration system 401 while suppressing the environmental impact.

[0174] As in this embodiment, the system may also be configured to include a return pipe 70 through which the refrigerant that has passed through the cooling-side heat exchanger flows and which is connected to a gas-liquid separator 17, and a heat exchanger 74 that exchanges heat between the refrigerant in the return pipe 70 and the outside air. This allows heat to be released from the refrigerant in the return pipe 70 to the outside air, making it easier to increase the liquid component of the refrigerant flowing into the gas-liquid separator 17 and thus reducing the workload of the compressor 412. As a result, it becomes easier to improve the APF and increase the efficiency of the refrigeration system 401.

[0175] As in this embodiment, the refrigeration device 401 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 latent heat of vaporization. This makes it easier for the refrigerant in the return pipe 70 to dissipate heat to the outside air, thus reducing the workload of the compressor 412. As a result, it becomes easier to improve the APF and increase the efficiency of the refrigeration system 401.

[0176] As in this embodiment, the refrigeration device 401 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 latent heat of vaporization. This makes it easier to improve the cooling capacity of the refrigeration unit 401 with low energy consumption. Therefore, it is possible to increase the efficiency of the refrigeration unit 401.

[0177] As in this embodiment, the refrigeration system 401 may be configured to include a return pipe 70 through which the refrigerant that has passed through the cooling-side heat exchanger flows and which is connected to the gas-liquid separator 17, and an oil separator 73 that recovers oil from the return pipe 70 and returns it to the suction side of the compression mechanism 411. This prevents oil from the compression mechanism 411 from accumulating in the gas-liquid separator 17 when the liquid refrigerant from the gas-liquid separator 17 is circulated to the cooling-side heat exchanger and then returned to the gas-liquid separator 17 via the return pipe 70. As a result, it becomes easier to ensure reliability while increasing the efficiency of the refrigeration system 401.

[0178] As in this embodiment, the refrigeration system 401 may be configured to include an oil separator 13 that recovers oil from the discharge pipe 416 of the compressor 412, and an oil return mechanism 420 that returns the oil recovered by the oil separator 13 to the compressor 412 and the expansion mechanism 316. This allows for a stable supply of oil to the compressor 412 and the expansion mechanism 316. As a result, it becomes easier to ensure reliability while increasing the efficiency of the refrigeration system 401. In particular, in this embodiment, the oil return mechanism 420 has a first oil return amount adjustment valve 424 and a second oil return amount adjustment valve 425 that adjust the amount of oil returned to the expansion mechanism 316 and the compressor 412. Therefore, it is easy to supply an appropriate amount of oil to each of the expansion mechanism 316 and the compressor 412. Furthermore, in this embodiment, the refrigeration unit 401 is provided with an oil pipe 411b that allows oil to flow between the casing of the expansion mechanism 316 and the casing of the compression mechanism 411. Therefore, when oil is returned to the expansion mechanism 316 by the oil return mechanism 420, lubrication of the compression mechanism 411 can be easily ensured.

[0179] (Other embodiments) As described above, Embodiments 1 to 3 have been explained as examples of the technology disclosed in this application. However, the technology in this disclosure is not limited thereto and can be applied to embodiments that have been modified, replaced, added, or omitted. Furthermore, it is possible to create new embodiments by combining the components described in Embodiments 1 to 3 above. Therefore, other embodiments are illustrated below.

[0180] In the above embodiment, the refrigeration device 1 was described as an air conditioner, but this is just one example. The refrigeration device 1 may be any device other than an air conditioner that uses a refrigeration cycle to heat or cool an object. For example, the refrigeration device 1 may be a refrigerator, a display case, or other type of refrigeration device.

[0181] In the above embodiment, the refrigerant circuit 2 was configured to have a low-stage compressor 11 and a high-stage compressor 12 as compressors, enabling two-stage compression, but this is just one 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 refrigerant circuit 2. Alternatively, instead of the low-stage compressor 11 and the high-stage compressor 12, a single-stage compressor may be provided as the compressor of the refrigerant circuit 2. Furthermore, the single-stage compressor may be configured to have an injection port that allows for refrigerant injection. In this case, the high-stage side 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 that replace them may be connected in parallel.

[0182] In the above embodiment, the flow path switching mechanism 50 was described as comprising a first switching mechanism 51 having annularly connected valves 53 to 56 and a second switching mechanism 52 having annularly connected valves 57 to 63, but this is just one example. The flow path switching mechanism 50 can switch between the utilization-side heat exchanger 21 and the heat source-side heat exchanger 14 to function as a gas cooler, and in any case, it is sufficient that the refrigerant that has passed through the gas cooler can be directed toward the gas-liquid separator 17. Furthermore, the flow path switching mechanism 50 can switch between the utilization-side heat exchanger 21 and the heat source-side heat exchanger 14 to function as a cooling-side heat exchanger, and in any case, it is sufficient that the refrigerant that has passed through the cooling-side heat exchanger can be directed toward the suction-side piping 18 and the return piping 70. In other words, if 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, or a four-way valve, etc.

[0183] In the above embodiment, carbon dioxide was described as being used as the refrigerant in the refrigerant circuit 2, but this is just one example. The type of refrigerant in the refrigerant 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-based refrigerant or an HFO-based refrigerant. However, using carbon dioxide as the refrigerant in the refrigerant circuit 2 can reduce the risk of environmental impact and other risks in the event of refrigerant leakage.

[0184] In the above embodiment, it was explained that during heating operation, the intake valve 19 is open and the return valve 71 is closed, but this is just one example. The refrigeration system 1 may also be configured to close the intake valve 19 and open the return valve 71 during heating operation, just as during cooling operation, when the heating load is medium or lower. This makes it possible to independently store liquid refrigerant in the gas-liquid separator 17 by driving the compressors 11 and 12, and to independently send the liquid refrigerant from the gas-liquid separator 17 toward the heat source side heat exchanger 14 by driving the liquid pump 40, thereby reducing the energy consumed by driving the compressors 11 and 12.

[0185] In Embodiment 2, it was explained that the refrigeration device 301 is equipped with both a pressure sensor 381 and a temperature sensor 382, ​​but this is just one example. The refrigeration device 301 only needs to be equipped with either the pressure sensor 381 or the temperature sensor 382. Furthermore, the operation of step SA2 in Figure 7 may be performed using the measurement value of either the pressure sensor 381 or the temperature sensor 382 provided in the refrigeration device 301.

[0186] The operation shown in Figure 7 in Embodiment 2 is just one example, and the operation of the control unit 90 is not limited thereto. For example, in addition to the operation shown in Figure 7, the control unit 90 may, after step SA3 or the like, compare the measured values ​​of sensors 381 and 382 with a second pressure and a second temperature that are lower than the first pressure and first temperature, and determine whether the pressure reduction by the expansion mechanism 316 is excessive. Alternatively, the control unit 90 may be configured to reduce the opening of the cooling throttle valve 45 when it determines that the measured values ​​of sensors 381 and 382 are below the second pressure and second temperature, and that the pressure reduction by the expansion mechanism 316 is excessive.

[0187] Furthermore, the operational step units shown in Figure 7 are divided according to the main processing content in order to facilitate understanding of the operation of each part of the refrigeration device 301, and this disclosure is not limited by the way the processing units are divided or the names of those units.

[0188] Since the embodiments described above are for illustrative purposes only, various modifications, substitutions, additions, omissions, etc., can be made within the claims or their equivalents.

[0189] (Note) Based on the above description of embodiments, the following technologies are disclosed. (Technology 1) A refrigeration system comprising a refrigerant circuit connecting a compression mechanism, a heat source side heat exchanger, a gas-liquid separator, and a utilization side heat exchanger, wherein the refrigeration system includes a liquid pump that sends the liquid refrigerant from the gas-liquid separator to the cooling side heat exchanger among the heat source side heat exchanger and the utilization side heat exchanger, a check valve provided in parallel with the liquid pump to prevent backflow of refrigerant toward the gas-liquid separator, and an expansion mechanism that expands the refrigerant that has flowed through the gas cooler among the heat source side heat exchanger and the utilization side heat exchanger and flows it toward the gas-liquid separator, wherein the compression mechanism is provided in a gas venting pipe into which the gas refrigerant from the gas-liquid separator flows and operates coaxially with the expansion mechanism. This allows the refrigerant entering the gas-liquid separator to be depressurized while power is recovered using the expansion mechanism, and the recovered power can be efficiently used to operate the compression mechanism. As a result, energy consumption can be reduced and the efficiency of the refrigeration system can be improved.

[0190] (Technology 2) The refrigeration apparatus according to Technology 1, characterized in that it has a compressor operated by a motor, and the discharge side of the compression mechanism is connected to both the suction side and the discharge side of the compressor via on-off valves. This allows switching between single-stage compression using only the compression mechanism and two-stage compression using both the compression mechanism and the compressor, depending on the load. As a result, energy consumption for operating the compressor can be reduced, and the efficiency of the refrigeration system can be improved.

[0191] (Technology 3) The refrigeration apparatus according to Technology 1 or 2, comprising: a main pipe provided downstream of the liquid pump through which a refrigerant flows toward the cooling heat exchanger; a cooling pipe branching off from the main pipe; a cooling throttle valve for adjusting the flow rate of the cooling pipe; and a subcooling heat exchanger for cooling the refrigerant in the main pipe with the refrigerant reduced in pressure by the cooling throttle valve, wherein the cooling pipe is connected between the compression mechanism and the gas-liquid separator in the gas venting pipe. This allows the refrigerant flowing into the cooling-side heat exchanger to be supercooled by utilizing the suction force of the compression mechanism, which operates coaxially with the expansion mechanism. As a result, the refrigeration effect can be increased while suppressing energy consumption, thereby improving the efficiency of the refrigeration system.

[0192] (Technical 4) The refrigeration apparatus according to Technical 3, wherein an external cooling device is provided to cool the refrigerant after it has passed through the subcooled heat exchanger in the main piping. This allows for supercooling of the refrigerant flowing toward the cooling heat exchanger even when the pressure reduction by the expansion mechanism is insufficient. Therefore, it is possible to improve the efficiency of the refrigeration system while stabilizing the refrigeration effect.

[0193] (Technical 5) The refrigeration apparatus according to Technical 4, wherein the refrigerant circuit uses carbon dioxide as the refrigerant, and the external cooling equipment uses a refrigeration cycle that utilizes a refrigerant more energy-efficient than carbon dioxide to cool the refrigerant in the main piping. This allows for improved cooling capacity in refrigeration systems using energy-efficient external cooling equipment, thereby reducing the environmental impact of carbon dioxide as a refrigerant. Furthermore, because external cooling equipment can be designed with a simpler configuration than the refrigeration system itself, the risk of refrigerant leakage from the external cooling equipment is less significant, even when using highly efficient refrigerants such as HFCs or HFOs, which have a greater environmental impact than carbon dioxide. Therefore, it is possible to improve the efficiency of refrigeration systems while suppressing environmental impact.

[0194] (Technical 6) A refrigeration apparatus according to any one of Technical 1 to 5, comprising a return pipe through which the refrigerant that has passed through the cooling-side heat exchanger flows and which is connected to the gas-liquid separator, and a heat exchanger that exchanges heat between the refrigerant in the return pipe and the outside air. This allows heat to be released from the refrigerant in the return piping to the outside air, making it easier to increase the liquid component of the refrigerant flowing into the gas-liquid separator and thus reducing the workload of the compressor. As a result, it becomes easier to improve the APF (Annual Performance Factor) and increase the efficiency of the refrigeration system.

[0195] (Technical 7) The refrigeration apparatus according to Technical 6, further comprising a water supply means for supplying water to lower the temperature of the intake air of the heat exchanger by latent heat of vaporization. This makes it easier for the refrigerant in the return piping to dissipate heat to the outside air, thus reducing the workload on the compressor. As a result, it becomes easier to improve the APF (Annual Performance Factor) and increase the efficiency of the refrigeration system.

[0196] (Technical 8) A refrigeration apparatus according to any one of Technical 1 to 7, comprising a water supply means for supplying water to lower the temperature of the intake air of the heat source side heat exchanger by latent heat of vaporization. This makes it easier to improve the cooling capacity of a refrigeration system with less energy consumption. Therefore, it is possible to increase the efficiency of the refrigeration system.

[0197] (Technical 9) A refrigeration apparatus according to any one of Technical 1 to 8, wherein a return pipe through which the refrigerant that has passed through the cooling-side heat exchanger flows is connected to the gas-liquid separator, and an oil separator is provided for recovering oil from the return pipe and returning it to the suction side of the compression mechanism. This prevents oil from the compression mechanism from accumulating in the gas-liquid separator when the liquid refrigerant from the gas-liquid separator is circulated to the cooling-side heat exchanger and then returned to the gas-liquid separator via the return piping. As a result, it becomes easier to ensure reliability while increasing the efficiency of the refrigeration system.

[0198] (Technical 10) The refrigeration apparatus according to Technical 2, further comprising an oil separator for recovering oil from the discharge pipe of the compressor, and an oil return mechanism for returning the oil recovered by the oil separator to the compressor and the expansion mechanism. This allows for a stable supply of oil to the compressor and expansion mechanism. Therefore, it becomes easier to improve the efficiency and reliability of the refrigeration system. [Industrial applicability]

[0199] This disclosure is applicable to refrigeration equipment. Specifically, this disclosure is applicable to devices such as air conditioners that have a refrigerant circuit. [Explanation of symbols]

[0200] 1. Refrigeration equipment 2 Refrigerant Circuit 10 Outdoor unit 11. Low-stage compressor (compressor) 12. High-stage compressor (compressor) 13 Oil Separator 13a Oil Tank 14 Heat source side heat exchanger 14a Blower 14b Water supply means 15 High-voltage receiver 16 throttle valve 17 Gas-liquid separator 18. Intake side piping 19. Intake side shut-off valve (shut-off valve) 20, 20H, 20L indoor unit 21 User side heat exchanger 22 User-side throttle valve 30 Gas venting pipe 31. Lower-level branch pipe 32 High-level side branch pipe 33. Low-stage throttle valve 34 High-stage throttle valve 40 liquid pumps 41 Main piping 42 routes 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 piping 71. Return valve (on / off valve) 72 Check valve 73 Oil Separator 74 Heat exchanger 74a Air blower 74b Water supply means 90 Control Unit 301 Refrigeration equipment 302 Refrigerant Circuit 316 Expansion Mechanism 381 Pressure Sensor 382 Temperature Sensor 401 Refrigeration equipment 402 Refrigerant Circuit 411 Compression mechanism 411a axis 411b Oil pipe 412 Compressor 413 Stage-side discharge piping 414 First branch pipe 414a First shut-off valve (shut-off valve) 415 Second branch pipe 415a Second shut-off valve (shut-off valve) 416 Discharge piping 420 Oil return mechanism 421 Oil return piping 422 First oil return branch pipe 423 Second oil return branch pipe 424 First oil return volume adjustment valve 425 Second return oil volume adjustment valve

Claims

1. It is equipped with a refrigerant circuit connecting a compression mechanism, a heat source side heat exchanger, a gas-liquid separator, and a utilization side heat exchanger. A liquid pump that delivers the liquid refrigerant from the gas-liquid separator to the cooling-side heat exchanger among the heat source-side heat exchanger and the utilization-side heat exchanger, A check valve is provided in parallel with the liquid pump to prevent backflow of refrigerant toward the gas-liquid separator, The heat exchanger on the heat source side and the heat exchanger on the utilization side have an expansion mechanism that expands the refrigerant that has flowed through the gas cooler and flows it to the gas-liquid separator, The compression mechanism is provided in the venting pipe into which the gas refrigerant gas of the gas-liquid separator flows, and operates coaxially with the expansion mechanism. A refrigeration apparatus characterized by the following features.

2. It has a motor-driven compressor, The discharge side of the compression mechanism is connected to both the suction side and the discharge side of the compressor via on-off valves. The refrigeration apparatus according to feature 1.

3. A main pipe is provided downstream of the liquid pump, through which the refrigerant flows toward the cooling heat exchanger, Cooling pipes branching from the main pipe, A cooling throttle valve for adjusting the flow rate of the aforementioned cooling pipe, The system includes a subcooled heat exchanger that cools the refrigerant in the main piping with the reduced-pressure refrigerant at the cooling throttle valve, The cooling pipe is connected between the compression mechanism and the gas-liquid separator in the gas venting pipe. The refrigeration apparatus according to feature 1.

4. An external cooling device is provided to cool the refrigerant after it has passed through the subcooled heat exchanger in the main piping. The refrigeration apparatus according to claim 3.

5. The aforementioned refrigerant circuit uses carbon dioxide as the refrigerant. The aforementioned external cooling device uses a refrigeration cycle that utilizes a refrigerant more energy-efficient than carbon dioxide to cool the refrigerant in the main piping. The refrigeration apparatus according to claim 4.

6. The refrigerant that has passed through the cooling-side heat exchanger flows through a return pipe connected to the gas-liquid separator, The system includes a heat exchanger that exchanges heat between the refrigerant in the return piping and the outside air. The refrigeration apparatus according to claim 1.

7. The heat exchanger has a water supply means for supplying water to lower the temperature of the intake air by latent heat of vaporization, The refrigeration apparatus according to claim 6.

8. The heat source side heat exchanger has a water supply means for supplying water to lower the temperature of the intake air by latent heat of vaporization, The refrigeration apparatus according to claim 1.

9. The refrigerant that has passed through the cooling-side heat exchanger flows through a return pipe connected to the gas-liquid separator, The refrigeration apparatus according to claim 1, further comprising an oil separator that recovers oil from the return pipe and returns it to the suction side of the compression mechanism.

10. An oil separator for recovering oil from the discharge pipe of the compressor, The oil separator has an oil return mechanism that returns the oil recovered by the oil separator back to the compressor and the expansion mechanism, The refrigeration apparatus according to claim 2.

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