Refrigeration unit

Abstract

To provide a refrigeration unit which can achieve high efficiency.SOLUTION: A refrigeration unit includes a refrigeration circuit in which a compressor, a heat source side heat exchanger, a gas-liquid separator, and a utilization side heat exchanger are connected to one another. The refrigeration unit is provided with a liquid pump which delivers liquid refrigerant from the gas-liquid separator to a cooling side heat exchanger being either of the heat source side heat exchanger and the utilization side heat exchanger, and a passage through which the liquid refrigerant from the gas-liquid separator flows to downstream side of the liquid pump without passing through the liquid pump.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to refrigeration devices. [Background technology]

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

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

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

[0005] [Patent Document 1] Patent No. 6292480

[0006] [Patent Document 2] Patent No. 5213986

[0007] [Patent Document 3] Patent No. 7193706 Summary of the Invention [Problem to be solved by the invention]

[0008] The present disclosure provides a refrigeration device that can achieve high efficiency. [Means for solving the problem]

[0009] The refrigeration device of the present disclosure includes a refrigeration circuit connecting a compressor, a heat source side heat exchanger, a gas-liquid separator, and a utilization side heat exchanger, and is provided with a liquid pump that sends liquid refrigerant from the gas-liquid separator to the cooling side heat exchanger of the heat source side heat exchanger and the utilization side heat exchanger, and a path that flows the liquid refrigerant from the gas-liquid separator downstream of the liquid pump without passing through the liquid pump. [Effects of the Invention]

[0010] In the refrigeration apparatus according to the present disclosure, the liquid refrigerant in the gas-liquid separator can be sent to the cooling-side heat exchanger without relying on a compressor, which makes it easier to reduce the workload of the compressor compressing the gas refrigerant. Furthermore, the liquid refrigerant can easily circulate between the gas-liquid separator and the cooling-side heat exchanger through the path even after the liquid pump is stopped. This contributes to improving the efficiency of the refrigeration apparatus. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a diagram showing a refrigeration circuit of a refrigeration device according to a first embodiment. [Figure 2] Diagram showing the refrigeration circuit during medium load cooling operation [Figure 3] Diagram showing the refrigeration circuit during air-cooling operation [Figure 4] Diagram showing the refrigeration circuit during high-load cooling operation [Figure 5] Diagram showing the refrigeration circuit during heating operation DETAILED DESCRIPTION OF THE INVENTION

[0012] (Findings that formed the basis of this disclosure) At the time the inventors conceived the present disclosure, there was a technology in the field of refrigeration equipment that uses carbon dioxide, a type of natural refrigerant, as a refrigerant. Carbon dioxide has a low global warming potential, is nonflammable, and is nontoxic, making it expected to be widely used as a refrigerant with a low environmental impact. Because carbon dioxide's critical temperature is within the operating temperature range, it was previously thought to have issues with efficiency. However, in low-temperature equipment operating at temperatures around -45°C to -5°C, the high suction density of the compressor can be utilized, and refrigeration units using carbon dioxide as a refrigerant have been put into practical use with performance similar to that of units using fluorocarbons. However, when using carbon dioxide as a refrigerant, it is difficult to take advantage of the high suction density, particularly in equipment operating in the air-conditioning temperature range. This challenge posed a need for technological development to further improve efficiency. The inventors discovered this issue, and the subject matter of the present disclosure was formed to address this challenge. Therefore, the present disclosure provides a refrigeration device that can achieve high efficiency.

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

[0014] (Embodiment 1) Hereinafter, the first embodiment will be described with reference to the drawings. [1-1.Configuration] [1-1-1. Overall structure] 1 is a diagram showing a refrigeration circuit 2 of a refrigeration device 1 according to embodiment 1. In the figure, open valves and throttle valves are shown in white, and closed valves and throttle valves are shown in white. In the figure, wiring through which a refrigerant flows is shown in thick lines, and pipes through which no refrigerant flows are shown in thin lines.

[0015] The refrigeration device 1 is a device having a refrigeration circuit 2 that transfers heat through a refrigeration cycle. The refrigeration device 1 of this 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 refrigeration circuit 2 is formed as a circuit through which a refrigerant circulates by connecting the outdoor unit 10 and the indoor unit 20. In this embodiment, the refrigeration circuit 2 uses carbon dioxide (R744), a natural refrigerant that is non-flammable, non-toxic, and has little impact on the environment.

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

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

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

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

[0020] First switching mechanism 51 is a mechanism for switching the flow path of the refrigerant. First switching mechanism 51 has first cooling valve 53, first heating valve 54, second cooling valve 55, and heating throttle valve 56, which are connected in this order in a ring shape.

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

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

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

[0024] Second switching mechanism 52 is a mechanism for switching the refrigerant flow path. Second switching mechanism 52 has third cooling valve 57, third heating valve 58, fourth cooling valve 59, and heating throttle valve 60, which are connected in this order in a ring shape.

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

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

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

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

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

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

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

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

[0033] Further, the refrigeration circuit 2 is provided with a path 42 that is parallel to the liquid pump 40. The 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. The path 42 connects the main pipe 41 to a liquid side outlet of the gas-liquid separator 17 that is different from the liquid side outlet to which the liquid pump is connected.

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

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

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

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

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

[0039] For this reason, a refrigerant that is more flammable, toxic, and has a greater environmental impact in the event of leakage than carbon dioxide but is more energy efficient than carbon dioxide can be used in the refrigeration cycle of the external cooling device 47. In this embodiment, the external cooling device 47 can appropriately perform leakage management even if it uses 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 pipe 41 is connected to the second switching mechanism 52 between the fourth cooling valve 59 and the heating throttle valve 60 downstream of the external cooling device 47.

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

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

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

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

[0046] An oil separator 73 is provided in the return pipe 70. The oil separator 73 separates oil mixed in the refrigerant in the return pipe 70 and returns the oil to the suction sides of the compressors 11 and 12. In this embodiment, the oil separator 73 returns the oil in the return pipe 70 to the gas vent 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. That is, the heat exchanger 74 can liquefy the gas component of the refrigerant in the return pipe 70 that has evaporated in the cooling-side heat exchanger.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

[0066] The refrigerant that has passed through the use-side heat exchanger 21 flows into the first switching mechanism 51, passes through the second cooling valve 55, and reaches the suction-side piping 18 and the return piping 70. As described above, when the cooling load is medium or less, the suction-side on-off valve 19 is closed and the return-side on-off valve 71 is open, so the refrigerant that has passed through the first switching mechanism 51 is not sucked into the compressors 11 and 12, and returns to the gas-liquid separator 17 via the return 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 less, the control unit 90 operates the water supply means 74b to facilitate liquefaction of the refrigerant in the return pipe 70. The refrigerant that has passed through the heat exchanger 74 is returned to the gas-liquid separator 17.

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

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

[0070] In order to achieve the above-described operation, when the cooling load is low, the control unit 90 controls each part of the refrigeration device 1 so that the pressure in each part of the refrigeration circuit 2 satisfies the following inequality (A). P1 <P5≦P9<P8≦P0<P7 (A) 1, in inequality (A), P0 represents the pressure on the outlet side of liquid pump 40, P1 represents the suction pressure of high-stage compressor 12, P5 represents the pressure inside gas-liquid separator 17, P7 represents the pressure in the piping on the inlet side of indoor unit 20L on a low floor, P8 represents the pressure in the piping on the inlet side of indoor unit 20H on a high 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 medium or less, as described above, the liquid pump 40 operates to return the liquid refrigerant in the gas-liquid separator 17 to the gas-liquid separator 17 through a closed cycle that does not pass through the compressors 11 and 12. In this closed cycle, even if the liquid pump 40 is stopped after the liquid pump 40 operates, natural circulation of the refrigerant may occur between the gas-liquid separator 17 and the user-side heat exchanger 21.

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

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

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

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

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

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

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

[0079] [1-2-3. Operation during high load cooling operation] FIG. 4 shows the refrigeration circuit 2 during high-load cooling operation. When the cooling load is medium or less, supercooled liquid refrigerant flows through the user-side heat exchanger 21, which can lead to significant heat leakage when the ambient temperature is high and the cooling load is high. This heat leakage is particularly pronounced in the gas-liquid separator 17. To reduce this heat leakage, the refrigerant temperature drop in the gas-liquid separator 17 is suppressed, and the liquid refrigerant is cooled by the subcooling heat exchanger 46 and the external cooling device 47, thereby increasing the subcooling effect. Furthermore, when the cooling load is high, the refrigeration system 1 switches to superheat control, which creates a temperature difference between the inlet and outlet of the user-side heat exchanger 21 (the cooling-side heat exchanger), thereby utilizing the latent heat of evaporation to cool the air in the conditioned space.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

[0094] As in this embodiment, the refrigeration device 1 may be configured such that the check valve 43 for preventing the refrigerant from flowing back toward the gas-liquid separator 17 is provided in the path . This prevents the liquid refrigerant sent to liquid pump 40 from flowing back into gas-liquid separator 17 via path 42. This makes it easier for the liquid pump 40 to pump the liquid refrigerant from the gas-liquid separator 17, and the efficiency of the refrigeration device 1 can be improved.

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

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

[0097] As in this embodiment, the refrigeration circuit 2 may be configured to use carbon dioxide as a refrigerant, and the external cooling device 47 may be configured to cool the refrigerant in the main pipe 41 using a refrigeration cycle that uses a refrigerant that is more energy efficient than carbon dioxide. As a result, the refrigeration capacity of the refrigeration device 1 that uses carbon dioxide, which has a small environmental impact, as a refrigerant can be improved by using the highly energy-efficient external cooling device 47. Furthermore, since the external cooling device 47 can be configured more simply than the refrigeration circuit 2 of the refrigeration device 1, even if a refrigerant such as an HFC or HFO, which is highly efficient but has a greater environmental impact than carbon dioxide, is used in the external cooling device 47, the risk of refrigerant leakage from the external cooling device 47 is unlikely to increase. Therefore, the efficiency of the refrigeration device 1 can be increased while suppressing environmental impact.

[0098] As in this embodiment, the refrigeration device 1 may be configured to use the external cooling device 47 preferentially over the subcooling heat exchanger 46 to cool the refrigerant flowing through the cooling-side heat exchanger to a target temperature. This allows the external cooling device 47, which can be easily configured to be highly energy efficient, to be used in preference to the subcooling heat exchanger . Therefore, the efficiency of the refrigeration device 1 can be increased.

[0099] As in this embodiment, the refrigeration device 1 may be configured to have water supply means 14b for supplying water to lower the temperature of the air drawn into the heat source side heat exchanger 14 by using latent heat of evaporation. This makes it easier to improve the refrigeration capacity of the refrigeration device with small energy consumption. This allows the refrigeration device to be made more efficient.

[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 easy to increase the efficiency of the compressors 11, 12, particularly when carbon dioxide or the like, which has a large pressure difference in the refrigeration circuit 2, is used as a refrigerant. Therefore, the efficiency of the refrigeration device 1 can be increased.

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

[0102] As in this embodiment, in the refrigeration device 1, the compressor may include a low-stage compressor 11 and a high-stage compressor 12, and the gas vent pipe 30 that vents the gas refrigerant from the gas-liquid separator 17 may be configured to be 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 caused to flow into the cooling side heat exchanger by the liquid pump 40 or natural circulation, if the load is small, the low stage compressor 11 can be stopped and the gas refrigerant in the gas-liquid separator 17 can be liquefied by operating only the high stage compressor 12. This makes it easier to improve the APF, and the efficiency of the refrigeration device 1 can be increased.

[0103] As in this embodiment, the refrigeration device 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 allows the refrigerant in the return pipe 70 to dissipate heat to the outside air, making it easier to increase the liquid component of the refrigerant flowing into the gas-liquid separator 17, and making it easier to reduce the work of the compressors 11 and 12. This makes it easier to improve the APF, and the efficiency of the refrigeration device 1 can be increased.

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

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

[0106] As in this embodiment, the refrigeration device 1 is provided with a flow path switching mechanism 50 that switches the gas cooler that causes the refrigerant discharged from the compressors 11 and 12 to release heat between the user side heat exchanger 21 and the heat source side heat exchanger 14, and the flow path switching mechanism 50 may be configured to cause the refrigerant that has passed through the gas cooler to flow into the gas-liquid separator 17 regardless of whether the user side heat exchanger 21 or the heat source side heat exchanger 14 is made to function as the gas cooler. This allows the heat exchanger functioning 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 pumped out by the liquid pump 40. Therefore, when the refrigeration device 1 is an air conditioner as in this embodiment, the work of the compressors 11, 12 can be easily reduced during both cooling and heating operations.

[0107] As in this embodiment, the refrigeration device 1 is provided with a flow path switching mechanism 50 that switches the cooling side heat exchanger between the use side heat exchanger 21 and the heat source side heat exchanger 14, and the flow path switching mechanism 50 may be configured to allow the refrigerant that has passed through the cooling side heat exchanger to reach the suction side piping 18 and the return piping 70 regardless of whether the use side heat exchanger 21 or the heat source side heat exchanger 14 is functioning as the cooling side heat exchanger. This allows the heat exchanger functioning as the cooling side heat exchanger to be switched between the utilization side heat exchanger 21 and the heat source side heat exchanger 14, and allows the refrigerant that has passed through the cooling side heat exchanger to be selected depending on the load, either returned to the gas-liquid separator 17 or compressed by the compressors 11 and 12. Therefore, when the refrigeration device 1 is an air conditioner as in this embodiment, the work of the compressors 11, 12 can be easily reduced during both cooling and heating operations.

[0108] (Other embodiments) As described above, the first embodiment has been described as an example of the technology disclosed in the present application. However, the technology in the present disclosure is not limited to this, and can be applied to embodiments in which modifications, substitutions, additions, omissions, etc. are made. Furthermore, it is also possible to combine the components described in the first embodiment above to create new embodiments. Therefore, other embodiments will be exemplified below.

[0109] In the above embodiment, the refrigeration device 1 has been described as an air conditioner, but this is merely an example. The refrigeration device 1 may be any device other than an air conditioner that heats or cools an object using a refrigeration cycle. For example, the refrigeration device 1 may be a freezer such as a refrigerator or a showcase.

[0110] In the above embodiment, the refrigeration circuit 2 is provided with the low-stage compressor 11 and the high-stage compressor 12 as compressors, and is configured to be capable of two-stage compression. However, this is merely an example. For example, instead of the low-stage compressor 11 and the high-stage compressor 12, a compound compressor capable of two-stage compression may be provided as the compressor of the refrigeration circuit 2. Furthermore, instead of the low-stage compressor 11 and the high-stage compressor 12, the refrigeration circuit 2 may be configured to be provided with a single-stage compressor. Furthermore, the single-stage compressor may be configured to be provided with an injection port through which refrigerant can be injected. In this case, the high-stage branch pipe 32 may be connected to the injection port. Note that two or more of the low-stage compressor 11, the high-stage compressor 12, or compressors replacing these may be connected in parallel.

[0111] In the above embodiment, the flow path switching mechanism 50 has been described as including the first switching mechanism 51 having the valves 53-56 connected in a ring and the second switching mechanism 52 having the valves 57-63 connected in a ring, but this is just one example. The flow path switching mechanism 50 switches the heat exchanger that functions as a gas cooler between the use-side heat exchanger 21 and the heat-source-side heat exchanger 14, and regardless of which one functions as the gas cooler, it is sufficient that the refrigerant that has passed through the gas cooler can flow toward the gas-liquid separator 17. The flow path switching mechanism 50 also switches the heat exchanger that functions as a cooling-side heat exchanger between the use-side heat exchanger 21 and the heat-source-side heat exchanger 14, and regardless of which one functions as the cooling-side heat exchanger, it is sufficient that the refrigerant that has passed through the cooling-side heat exchanger can flow toward the suction-side piping 18 and the return piping 70. That is, as long as it has the same function as the flow path switching mechanism 50 of this embodiment, part or all of the flow path switching mechanism 50 may be replaced with an on-off valve, a check valve, a throttle valve, a four-way valve, or the like.

[0112] In the above embodiment, carbon dioxide is used as the refrigerant in the refrigeration circuit 2, but this is just one example. The type of refrigerant in the refrigeration circuit 2 is not particularly limited, and may be a natural refrigerant other than carbon dioxide, or a refrigerant other than a natural refrigerant such as an HFC refrigerant or an HFO refrigerant. However, when carbon dioxide is used as the refrigerant in the refrigeration circuit 2, the risk of refrigerant leakage, such as environmental impact, can be reduced.

[0113] In the above embodiment, it has been described that the suction-side on-off valve 19 is open and the return-side on-off valve 71 is closed during heating operation, but this is just one example. The refrigeration system 1 may be configured such that the suction-side on-off valve 19 is closed and the return-side on-off valve 71 is open during heating operation as well, when the heating load is medium or less, as in cooling operation. This makes it possible to independently store liquid refrigerant in the gas-liquid separator 17 by driving the compressors 11 and 12 and deliver the liquid refrigerant from the gas-liquid separator 17 to the heat-source-side heat exchanger 14 by driving the liquid pump 40, thereby reducing energy consumption by driving the compressors 11 and 12.

[0114] It should be noted that the above-described embodiments are intended to illustrate the technology of the present disclosure, and various modifications, substitutions, additions, omissions, etc. may be made within the scope of the claims or their equivalents.

[0115] (Addendum) The above description of the embodiments discloses the following techniques. (Technology 1) A refrigeration system including a refrigeration circuit connecting a compressor, a heat source side heat exchanger, a gas-liquid separator, and a user side heat exchanger, the refrigeration system being characterized by comprising: a liquid pump that sends liquid refrigerant from the gas-liquid separator to a cooling side heat exchanger out of the heat source side heat exchanger and the user side heat exchanger; and a path that sends the liquid refrigerant from the gas-liquid separator to the downstream side of the liquid pump without passing through the liquid pump. This allows the liquid refrigerant in the gas-liquid separator to be sent to the cooling-side heat exchanger without relying on a compressor, making it easier to reduce the amount of work the compressor has to do to compress the gas refrigerant. Furthermore, particularly when the gas-liquid separator is installed higher than the cooling-side heat exchanger, such as when the gas-liquid separator is installed on the roof of a building and the cooling-side heat exchanger is installed on a lower floor of the building, the liquid refrigerant can easily circulate between the gas-liquid separator and the cooling-side heat exchanger via the path even after the liquid pump is stopped. This makes it easier to reduce energy consumption and improve the efficiency of the refrigeration system.

[0116] (Technology 2) The compressor discharges the gas refrigerant from the gas-liquid separator to a gas cooler in the heat source side heat exchanger or the user side heat exchanger, and returns the gas-liquid mixed state to the gas-liquid separator via a throttle valve, and the liquid pump sends the liquid refrigerant from the gas-liquid separator to the cooling side heat exchanger, where it absorbs heat and then returns the liquid refrigerant to the gas-liquid separator. This refrigeration apparatus is described in Technology 1. This allows the compressor to be operated separately from the liquid supply to the cooling-side heat exchanger, with the purpose of liquefying the gas refrigerant and returning it to the gas-liquid separator, reducing the workload of the compressor, making it easier to reduce energy consumption and improving the efficiency of the refrigeration system.

[0117] (Technical Technique 3) The refrigeration device according to Technical Technique 1 or 2, wherein the path is provided with a check valve that prevents the refrigerant from flowing back toward the gas-liquid separator. This prevents the liquid refrigerant pumped to the liquid pump from flowing back through the path to the gas-liquid separator, making it easier for the liquid pump to pump the liquid refrigerant from the gas-liquid separator and improving the efficiency of the refrigeration system.

[0118] (Technology 4) A refrigeration device according to any one of Technologies 1 to 3, comprising: a main pipe provided downstream of the liquid pump and through which a refrigerant flows toward the cooling-side heat exchanger; a cooling pipe branched from the main pipe; a cooling throttle valve that reduces the pressure of the refrigerant in the cooling pipe; and a subcooling heat exchanger that cools the refrigerant in the main pipe with the refrigerant reduced in pressure by the cooling throttle valve. This allows the liquid refrigerant to be cooled after passing through the gas-liquid separator, which has a large surface area, reducing heat leakage from the liquid refrigerant. This increases the refrigeration effect while suppressing losses, resulting in a more efficient refrigeration system.

[0119] (Technical Aspect 5) The refrigeration device according to Technical Aspect 4, further comprising an external cooling device that cools the refrigerant in the main pipe after passing through the subcooling heat exchanger. This allows the liquid refrigerant flowing into the cooling-side heat exchanger to be further cooled, thereby improving and stabilizing the refrigeration capacity and increasing the efficiency of the refrigeration device.

[0120] (Technology 6) The refrigeration circuit uses carbon dioxide as a refrigerant, and the external cooling device cools the refrigerant in the main pipe using a refrigeration cycle that uses a refrigerant that is more energy efficient than carbon dioxide. As a result, the highly energy-efficient external cooling device can improve the refrigeration capacity of a refrigeration unit that uses carbon dioxide, which has a small environmental impact, as a refrigerant. Furthermore, because the external cooling device can be configured more simply than a refrigeration unit, even if a refrigerant such as an HFC or HFO, which is highly efficient but has a larger environmental impact than carbon dioxide, is used in the external cooling device, the risk of refrigerant leakage from the external cooling device is less likely to increase. This makes it possible to increase the efficiency of a refrigeration unit while minimizing environmental impact.

[0121] (Technical Aspect 7) The refrigeration apparatus according to Technical Aspect 6, wherein the refrigerant flowing through the cooling-side heat exchanger is cooled to a target temperature by using the external cooling device preferentially over the subcooling heat exchanger. This allows the use of an external cooling device, which is more likely to be configured with high energy efficiency, in preference to the subcooling heat exchanger, thereby achieving high efficiency in the refrigeration device.

[0122] (Technology 8) The refrigeration device according to any one of Technologies 1 to 7, further comprising a water supply means for supplying water to lower the temperature of the intake air of the heat source side heat exchanger by using latent heat of evaporation. This makes it easier to improve the refrigeration capacity of the refrigeration device with small energy consumption, thereby enabling the refrigeration device to be made more efficient.

[0123] (Technology 9) The refrigeration device according to any one of Technologies 1 to 8, wherein the compressor includes a high-stage compressor and a low-stage compressor. This makes it easy to increase the efficiency of each compressor, particularly when using carbon dioxide or the like as a refrigerant, which has a large pressure difference in the refrigeration circuit, and therefore makes it possible to increase the efficiency of the refrigeration device. [Industrial Applicability]

[0124] The present disclosure is applicable to refrigeration devices, and more specifically, to devices such as air conditioners that include a refrigeration circuit. [Explanation of symbols]

[0125] 1 Refrigeration equipment 2 Refrigeration circuit 10 Outdoor unit 11 Low-stage compressor (compressor) 12 High-stage compressor (compressor) 13 Oil separator 14 Heat source side heat exchanger 14a Blower 14b Water supply means 15 High-pressure receiver 16 Throttle valve 17 Gas-liquid separator 18 Suction side piping 19 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 vent pipe 31 Lower stage branch pipe 32 High-stage branch pipe 33 Low-stage throttle valve 34 High stage throttle valve 40 Liquid Pump 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 pipe 71 Return side on-off valve (on-off valve) 72 Check valve 73 Oil separator 74 Heat exchanger 74a Air blower 74b Water supply means 90 Control Unit

Claims

1. A refrigeration circuit is provided which connects a compressor, a heat source side heat exchanger, a gas-liquid separator, and a user side heat exchanger, a liquid pump that sends the liquid refrigerant from the gas-liquid separator to a cooling-side heat exchanger of the heat source-side heat exchanger and the user-side heat exchanger; a path for causing the liquid refrigerant in the gas-liquid separator to flow to the downstream side of the liquid pump without passing through the liquid pump; A refrigeration device characterized by:

2. the compressor discharges the gas refrigerant from the gas-liquid separator to a gas cooler in one of the heat source side heat exchanger and the user side heat exchanger, and returns the gas refrigerant to the gas-liquid separator in a gas-liquid mixed state via a throttle valve; the liquid pump sends the liquid refrigerant from the gas-liquid separator to the cooling-side heat exchanger, absorbs heat, and then returns the liquid refrigerant to the gas-liquid separator; The refrigeration system of claim 1.

3. a check valve is provided in the path to prevent backflow of the refrigerant toward the gas-liquid separator; The refrigeration system of claim 1.

4. a main pipe provided downstream of the liquid pump, through which a refrigerant flows toward the cooling-side heat exchanger; a cooling pipe branched from the main pipe; a cooling throttle valve for reducing the pressure of the refrigerant in the cooling pipe; a subcooling heat exchanger that cools the refrigerant in the main pipe by the refrigerant decompressed by the cooling throttle valve; The refrigeration system of claim 1.

5. An external cooling device is provided to cool the refrigerant in the main pipe after passing through the subcooling heat exchanger.

5. The refrigeration system of claim 4.

6. The refrigeration circuit uses carbon dioxide as a refrigerant, The external cooling device cools the refrigerant in the main pipe using a refrigeration cycle that uses a refrigerant that is more energy efficient than carbon dioxide.

6. The refrigeration system of claim 5.

7. The refrigerant flowing through the cooling-side heat exchanger is cooled to a target temperature by using the external cooling device preferentially over the subcooling heat exchanger.

7. The refrigeration system of claim 6.

8. a water supply means for supplying water to lower the temperature of the intake air of the heat source side heat exchanger by using latent heat of evaporation; The refrigeration system of claim 1.

9. The compressor includes a high-stage compressor and a low-stage compressor. The refrigeration system of claim 1.

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