Refrigeration equipment

Abstract

This disclosure provides a refrigeration system that can achieve high efficiency. [Solution] The refrigeration system in this disclosure comprises a refrigeration circuit connecting a high-stage compressor, a low-stage compressor, 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, a gas venting pipe that removes gaseous refrigerant from the gas-liquid separator, and a control unit, the gas venting pipe is connected to the high-stage compressor via a high-stage side valve and to the low-stage compressor via a low-stage side valve, the control unit determines a target compression ratio based on the ambient temperature, and based on the target compression ratio, opens and closes the low-stage side valve to switch between two-stage compression operation, which drives the high-stage compressor and the low-stage compressor, and single-stage compression operation, which stops the low-stage compressor and drives the high-stage compressor.

Description

Technical Field

[0005] , ,

[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 decompression tank provided downstream of the gas cooler, an auxiliary circuit that sucks the refrigerant in the decompression tank into the intermediate pressure section of the throttle compression means, and a main circuit that exchanges heat between the refrigerant flowing out of the decompression tank and the refrigerant throttled in the auxiliary circuit and flows it to the main throttle means. 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 the compressor and passed through the outdoor heat exchanger flows and discharges the refrigerant to the gas-liquid separator, and an internal heat exchanger that cools the refrigerant flowing from the gas-liquid separator to the indoor heat exchanger by a part of the liquid refrigerant sucked by the ejector.

[0003] Patent Document 3 discloses a refrigeration cycle device that improves efficiency by an expansion mechanism and a sub-refrigerant circuit independent of the main refrigerant circuit. This refrigeration cycle device includes a main expansion mechanism that expands the refrigerant flowing toward the 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 it to the utilization-side heat exchanger. Patent Document 4 discloses a refrigeration device that uses an ejector and enables the refrigerant to easily circulate through the evaporator while maintaining the efficiency of the refrigerant circuit. This refrigeration device includes a bypass passage branched from a pipe between the downstream side of the radiator and the inlet of the ejector, and an adjustment mechanism that adjusts the amount of refrigerant in the bypass passage.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

[0005] [Patent Document 2] Patent No. 5213986

[0006] [Patent Document 3] Patent No. 7193706

[0007] [Patent Document 4] Patent No. 5786481 [Overview of the project] [Problems that the invention aims to solve]

[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 refrigeration circuit connecting a high-stage compressor, a low-stage compressor, 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, a gas venting pipe that removes gaseous refrigerant from the gas-liquid separator, and a control unit, wherein the gas venting pipe is connected to the high-stage compressor via a high-stage side valve and to the low-stage compressor via a low-stage side valve, and the control unit determines a target compression ratio based on the ambient temperature, and based on the target compression ratio, opens and closes the low-stage side valve to switch between a two-stage compression operation that drives the high-stage compressor and the low-stage compressor, and a single-stage compression operation that stops the low-stage compressor and drives the high-stage compressor. [Effects of the Invention]

[0010] The refrigeration system described in this disclosure can easily maintain an appropriate compression ratio and suppress compressor starting and stopping by switching between single-stage compression operation and double-stage compression operation based on the target compression ratio. Therefore, the efficiency of the refrigeration system can be improved.

Brief Description of the Drawings

[0011] [Figure 1] Figure showing the refrigeration circuit of the refrigeration device according to Embodiment 1 [Figure 2] Figure showing the refrigeration circuit during medium-load cooling operation [Figure 3] Figure showing the refrigeration circuit during air-cooled cooling operation [Figure 4] Figure showing the refrigeration circuit during high-load cooling operation [Figure 5] Figure showing the refrigeration circuit during heating operation [Figure 6] Figure showing the refrigeration circuit of the refrigeration device according to Embodiment 2 [Figure 7] Figure showing the refrigeration circuit during medium-load cooling operation [Figure 8] Figure showing the refrigeration circuit during air-cooled cooling operation [Figure 9] Figure showing the refrigeration circuit during high-load cooling operation [Figure 10] Figure showing the refrigeration circuit during heating operation [Figure 11] Figure showing the refrigeration circuit of the refrigeration device according to Embodiment 3 [Figure 12] Figure showing the refrigeration circuit during medium-load cooling operation [Figure 13] Figure showing the refrigeration circuit during high-load cooling operation [Figure 14] Figure showing the refrigeration circuit during heating operation <_{ [Figure 15] Figure showing the refrigeration circuit during air-cooled cooling operation [Figure 16] Figure showing the refrigeration circuit of the refrigeration device according to Embodiment 4 [Figure 17] Flowchart showing the operation of the refrigeration device [Figure 18] Flowchart showing the operation of the refrigeration device [Figure 19] Flowchart showing the operation of the refrigeration device

Modes for Carrying Out the Invention

[0012] (Findings etc. on which the present disclosure is based) 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 this disclosure and are not intended to limit the subject matter described in the claims.

[0014] (Embodiment 1) Embodiment 1 will be described below with reference to the drawings. [1-1. Structure] [1-1-1. Overall Structure] Figure 1 shows the refrigeration circuit 2 of the 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. Also, in the figure, wiring through which refrigerant flows is shown with thick lines, and piping through which refrigerant does not flow is shown with thin lines.

[0015] The refrigeration system 1 is a device having a refrigeration circuit 2 that transfers heat through a refrigeration cycle. The refrigeration system 1 in this embodiment is an air conditioner installed in buildings such as commercial buildings, office buildings, and hotels. The refrigeration system 1 has an outdoor unit 10 and an indoor unit 20. The refrigeration circuit 2 is formed as a circuit through which a refrigerant circulates when the outdoor unit 10 and the indoor unit 20 are connected. In this 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 refrigeration circuit 2.

[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 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 space to be conditioned. 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 space to be conditioned by heating or cooling the air in the space to be conditioned using the user-side heat exchanger 21. In this embodiment, of the components of the refrigeration 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. Configuration of the Refrigeration Circuit] The refrigeration 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 refrigeration 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 separated from the refrigerant in the refrigeration circuit 2.

[0038] The external cooling equipment 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 equipment 47 can be simpler than that of the refrigeration circuit 2, and refrigerant leakage from the external cooling equipment 47 is less likely to occur. In addition, since the external cooling equipment 47 can be easily configured to operate with a smaller amount of refrigerant than the refrigeration circuit 2, even if refrigerant leaks from the external cooling equipment 47, the amount of leakage can be easily reduced. In other words, the external cooling equipment 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 refrigeration circuit 2 during medium-load cooling operation. Figure 1 shows the refrigeration circuit 2 during low-load cooling operation. As shown in Figures 1 and 2, during medium-load or lower 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.

[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 refrigeration 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 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) 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 refrigeration 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, it is possible to perform air-cooled cooling operation by using only the heat exchanger 74 to liquefy the refrigerant without operating the compressors 11 and 12. For example, when the refrigeration system 1 is operated in a cooling operation to prevent the room temperature from rising due to exhaust heat from equipment installed in the air-conditioned space in an environment with a low outside temperature, air-cooled cooling operation is easy to perform.

[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 refrigeration circuit 2 during high-load cooling operation. In operation when the cooling load is medium or lower, as described above, 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 be large. 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 a 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 refrigeration circuit 2 during heating operation. The refrigeration device 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 refrigeration 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 refrigeration 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 refrigeration 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 the 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 as refrigerants that have a large pressure difference within the refrigeration circuit 2. 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 refrigeration 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 intake 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 intake side pipe 18 and the return pipe 70 are equipped with an intake 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 101 of Embodiment 2 is configured to easily improve energy efficiency even under high load conditions.

[0110] [2-1. Structure] Figure 6 shows the refrigeration circuit 102 of the refrigeration device 101 according to Embodiment 2. In the refrigeration circuit 102 of Embodiment 2, an ejector 116 is provided instead of the throttle valve 16 of Embodiment 1. The ejector has a nozzle and a suction port, etc. The ejector 116 reduces the pressure of the liquid refrigerant flowing in from the high-pressure receiver 15 by injecting it from the nozzle. The ejector 116 also uses the low pressure of the refrigerant injected from the nozzle to suck in refrigerant from the suction port, mixes the sucked refrigerant with the injected refrigerant, and flows it into the gas-liquid separator 17. In this embodiment, a suction pipe 116a is connected to the suction port of the ejector 116.

[0111] The suction pipe 116a is connected to one port of a flow path switching valve 175 provided in the return pipe 70. The flow path switching valve 175 is a so-called three-way valve. The flow path switching valve 175 is provided in the middle of the return pipe 70 on the downstream side of the heat exchanger 74 and is connected to the aforementioned suction pipe 116a, the upstream side of the return pipe 70, and the downstream side of the return pipe 70. In other words, the suction pipe 116a is provided on the outlet side of the cooling-side heat exchanger, of the heat source-side heat exchanger 14 and the utilization-side heat exchanger 21, via the first switching mechanism 51, the return pipe 70, and the flow path switching valve 175. The flow path switching valve 175 can be switched between a first state and a second state by control of the control unit 90. In the first state, the flow path switching valve 175 connects the upstream side of the return pipe 70 to the suction pipe 116a and closes the downstream side of the return pipe 70 to the flow path switching valve 175. As a result, when the flow path switching valve 175 is in the first state, refrigerant that has passed through the cooling side heat exchanger flows into the suction pipe 116a. In the second state, the flow path switching valve 175 connects the upstream and downstream sides of the return pipe 70 to the flow path switching valve 175 and closes the suction pipe 116a.

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

[0113] Furthermore, in Embodiment 2, unlike the suction-side piping 18 in Embodiment 1, the suction-side piping 118, which is the suction-side piping of the low-stage compressor 11, is not connected to the first switching mechanism 51. Also, the suction-side on-off valve 19 of Embodiment 1 is not provided. The suction-side piping 118 is connected only to the low-stage side branch pipe 31 of the gas venting piping 30. For this reason, in Embodiment 2, the compressors 11 and 12 cannot directly inhale the refrigerant that has passed through the cooling-side heat exchanger, but can inhale the gaseous refrigerant separated by the gas-liquid separator 17.

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

[0115] [2-2-1. Operation during cooling operation at medium load or lower] Figure 7 shows the refrigeration circuit 102 during medium-load cooling operation. Figure 6, mentioned above, shows the refrigeration circuit 102 during low-load cooling operation. As shown in Figures 6 and 7, when the cooling load is medium or less, the control unit 90 performs the same control as in Embodiment 1 for each part except the flow path switching valve 175, the gas venting throttle valve 135, and the cooling throttle valve 45.

[0116] In Embodiment 2, when the cooling load is medium load or lower, the control unit 90 sets the flow path switching valve 175 to the second state and closes the suction pipe 116a. As a result, the flow path of the refrigerant in the refrigeration circuit 102 becomes the same as in Embodiment 1. That is, as in Embodiment 1, the compressors 11 and 12 only perform the work of liquefying the gaseous refrigerant in the gas-liquid separator 17 and returning it to the gas-liquid separator 17. The liquid refrigerant in the gas-liquid separator 17 is then supplied to the user-side heat exchanger 21 by the liquid pump 40 or by natural circulation. Therefore, as in Embodiment 1, the workload of the compressors 11 and 12 can be reduced.

[0117] In the second embodiment, the control unit 90 controls the gas venting throttle valve 135 and the cooling throttle valve 45 so that the cooling effect in the user-side heat exchanger 21 is enhanced and the discharge gas temperature of the compressors 11 and 12 is optimized.

[0118] The temperature of the refrigerant in the gas-liquid separator 17 is equivalent to the saturation temperature corresponding to the pressure in the gas-liquid separator 17. Therefore, when the control unit 90 increases the opening of the gas venting throttle valve 135, the pressure in the gas-liquid separator 17 decreases, and the temperature of the refrigerant in the gas-liquid separator 17 also decreases. When the control unit 90 increases the opening of the cooling throttle valve 45, the cooling by the subcooled heat exchanger 46 increases, the temperature of the liquid refrigerant in the main piping 41 decreases, and the refrigeration effect in the user-side heat exchanger 21 increases. In addition, when the control unit 90 increases the opening of the cooling throttle valve 45, the flow rate of refrigerant flowing from the cooling piping 44 to the gas venting piping 30 increases, so the suction temperature and discharge gas temperature of the compressors 11 and 12 decrease.

[0119] [2-2-2. Operation during cooling operation using air cooling] Figure 8 shows the refrigeration circuit 102 during air-cooled cooling operation. In Embodiment 2, as in Embodiment 1, air-cooled cooling operation of the heat exchanger 74 is possible with the compressors 11 and 12 stopped. In air-cooled cooling operation, the control unit 90 stops the compressors 11 and 12 when the cooling load is medium load or lower, and closes the cooling throttle valve 45, the gas venting throttle valve 135, and the third cooling valve 57. As a result, the discharge and suction sides of the compressors 11 and 12 are no longer in communication with the gas-liquid separator 17. Also, as in Embodiment 1, the control unit 90 cools the conditioned space by using the liquid pump 40 and natural circulation to flow the supercooled liquid refrigerant to the utilization-side heat exchanger 21.

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

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

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

[0123] Furthermore, when the cooling load is high, the control unit 90 adjusts the opening of the gas venting throttle valve 135 and the cooling throttle valve 45 in the same way as when the cooling load is medium or low, in order to improve the cooling effect in the user-side heat exchanger 21 and to optimize the discharge gas temperature of the compressors 11 and 12.

[0124] [2-2-4. Operation during heating operation] Figure 10 shows the refrigeration circuit 102 during heating operation. During heating operation, the control unit 90 closes the cooling valves 53, 55, 57, and 59 when the cooling load is high, and opens the heating valves 54, 56, 58 and the heating throttle valve 60. As a result, the gaseous refrigerant from the gas-liquid separator 17 is drawn into the compressors 11 and 12 via the gas venting pipe 30, compressed in two stages, and then flows into the utilization-side heat exchanger 21 via the oil separator 13 to dissipate heat. This heats the heated space.

[0125] Furthermore, the refrigerant that has released heat in the user-side heat exchanger 21 flows into the ejector 116 via the high-pressure receiver 15, just as during cooling operation, and is depressurized before flowing into the gas-liquid separator 17. At this time, the ejector 116 draws the refrigerant from the return pipe 70 after it has passed through the heat exchanger 74 via the suction pipe 116a.

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

[0127] During heating operation, the control unit 90 stops the external cooling equipment 47 and the water supply means 14b and 74b. Also, similar to during cooling operation, the control unit 90 adjusts the opening of the gas venting throttle valve 135 and the cooling throttle valve 45 to improve the cooling effect in the user-side heat exchanger 21 and to optimize the discharge gas temperature of the compressors 11 and 12.

[0128] [2-3. Effects, etc.] As described above, in this embodiment, the refrigeration system 101 includes a refrigeration circuit 102 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 includes 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 an ejector 116 into which the refrigerant that has flowed through the gas cooler among the heat source side heat exchanger 14 and the utilization side heat exchanger 21 flows and directs the incoming refrigerant toward the gas-liquid separator 17. The suction port of the ejector 116 is connected to a suction pipe 116a provided on the outlet side of the cooling side heat exchanger. This makes it easier to return the refrigerant from the cooling heat exchanger to the gas-liquid separator by utilizing the suction force of the ejector. Therefore, it becomes easier to reduce the workload of the liquid pump 40, and the efficiency of the refrigeration system can be improved. In particular, in this embodiment, a flow path switching mechanism 50 is provided that, during both cooling and heating operations, directs the refrigerant that has passed through the gas cooler into the gas-liquid separator 17 via the ejector 116, while simultaneously directing the refrigerant that has passed through the cooling-side heat exchanger into the return pipe 70. As a result, the workload of the liquid pump 40 can be reduced during both cooling and heating operations.

[0129] Furthermore, as in this embodiment, in the refrigeration system 101, a return pipe 70 for returning the refrigerant to the gas-liquid separator 17 may be provided on the outlet side of the cooling-side heat exchanger, the suction pipe 116a may branch off from the return pipe 70, and the return pipe 70 may be provided with a flow path switching valve 175 that directs the refrigerant that has passed through the cooling-side heat exchanger to either the suction pipe 116a or the gas-liquid separator 17. This allows the refrigerant to be returned to the gas-liquid separator 17 without going through the ejector 116, thereby facilitating a natural circulation that avoids the resistance of the ejector 116 and returns to the gas-liquid separator 17 through the return pipe 70. Therefore, the ejector 116 can be effectively utilized under high load conditions, and natural circulation can be utilized under low load conditions, thereby improving the efficiency of the refrigeration system 101.

[0130] As in this embodiment, the return pipe 70 may be configured to include a heat exchanger 74 located upstream of the flow path switching valve 175, which 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 returning to the gas-liquid separator 17 when the outside temperature is low, and the liquid refrigerant in the gas-liquid separator 17 is less likely to be depleted, thus making it easier to maintain natural circulation. Therefore, it becomes easier to reduce the workload of the compressor, and the efficiency of the refrigeration system can be improved.

[0131] As in this embodiment, the refrigeration system 101 may be configured to include a gas venting pipe 30 that removes gaseous refrigerant from the gas-liquid separator 17 and returns it to the compressors 11 and 12, a gas venting throttle valve 135 for adjusting the flow rate of the gas venting pipe 30, a main pipe 41 provided downstream of the liquid pump 40 through which refrigerant flows toward the cooling-side heat exchanger, a cooling pipe 44 that branches off from the main pipe 41 and is connected to the gas venting pipe 30 downstream of the gas venting throttle valve 135, and a cooling throttle valve 45 for adjusting the flow rate of refrigerant in the cooling pipe 44. This allows the refrigerant temperature in the gas-liquid separator 17 to be adjusted by adjusting the opening of the gas venting throttle valve 135, and the suction temperature of the compressors 11 and 12 to be adjusted by adjusting the opening of the cooling throttle valve 45. Therefore, the discharge temperature of the compressors 11 and 12 can be adjusted, improving the reliability of the refrigeration system.

[0132] As in this embodiment, a configuration may be provided in which a subcooled heat exchanger 46 is used to cool the refrigerant in the main pipe 41 with the reduced pressure refrigerant at the cooling throttle valve 45. This allows the refrigerant heading towards the cooling-side heat exchanger to be supercooled, thereby improving the cooling capacity of the refrigeration system 101. Therefore, it is possible to improve the efficiency of refrigeration equipment.

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

[0134] Furthermore, the refrigeration circuit 202 does not have the cooling pipe 44, cooling throttle valve 45, and subcooling heat exchanger 46 of Embodiment 1. Instead, the refrigeration circuit 202 is provided with a cooling suction pipe 244, which is a pipe that branches off from the main pipe 41 and is connected to the suction port of the ejector 216, and a cooling throttle valve 245 that reduces the pressure of the refrigerant in the cooling suction pipe 244. Therefore, when the refrigerant from the high-pressure receiver 15 flows into the ejector 216, the refrigerant from the main pipe 41 flows into the cooling suction pipe 244, is reduced in pressure by the cooling throttle valve 245, and is drawn into the ejector 216.

[0135] Furthermore, the refrigeration circuit 202 is equipped with a heat exchanger 246 that exchanges heat between the refrigerant, which has been depressurized by the cooling throttle valve 245, and the refrigerant that flows through the ejector 216 toward the gas-liquid separator 17. The heat exchanger 246 cools and liquefies the refrigerant that flows through the ejector 216 toward the gas-liquid separator 17.

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

[0137] [3-2. Operation] The operation of the refrigeration circuit 202 according to Embodiment 3 is the same as that of the refrigeration circuit 2 according to Embodiment 1, except for the operation of the cooling throttle valve 245 and the bypass pipe throttle valve 249. Below, only the differences in operation from Embodiment 1 will be described.

[0138] [3-2-1. Operation of the compressor while it is running] Figure 12 shows the refrigeration circuit 202 during medium-load cooling operation. Figure 13 shows the refrigeration circuit 202 during high-load cooling operation. Figure 14 shows the refrigeration circuit 202 during heating operation. Figure 11 shows the refrigeration circuit 202 during low-load cooling operation.

[0139] During low to high load cooling operation and heating operation as shown in Figures 11 to 14, when the compressors 11 and 12 are driven, the control unit 90 opens the cooling throttle valve 245. As a result, the refrigerant in the main piping 41 is drawn into the ejector 216 via the cooling suction pipe 244. Then, the refrigerant, depressurized by the cooling throttle valve 245, flows into the heat exchanger 246, and the refrigerant that has passed through the gas cooler, high-pressure receiver 15, and ejector 216 is cooled and liquefied. When the control unit 90 can draw in enough refrigerant for cooling by the heat exchanger 246 through the ejector 216, it closes the bypass pipe throttle valve 249.

[0140] In contrast, for example, when the rotational speed of the compressors 11 and 12 is low, the refrigerant drawn from the main piping 41 through the cooling suction pipe 244 to the suction port of the ejector 216 may not be sufficient to cool the heat exchanger 246. In such cases, the control unit 90 opens the bypass pipe throttle valve 249 and connects the cooling suction pipe 244 and the gas vent pipe 30 via the bypass piping 248. Since the gas vent pipe 30 is connected to the suction side of the compressors 11 and 12, when the bypass pipe throttle valve 249 is open, the liquid refrigerant in the main piping 41 flows into the cooling suction pipe 244 due to the suction of the compressors 11 and 12, and passes through the cooling throttle valve 245 and the heat exchanger 246. As a result, the refrigerant that has passed through the ejector 216 can be cooled and liquefied by the heat exchanger 246.

[0141] Thus, in Embodiment 3, the liquefaction of the refrigerant flowing into the gas-liquid separator 17 can be promoted both when the suction force of the ejector 216 is sufficient and when the suction force is insufficient.

[0142] [3-2-2. Operation while the compressor is stopped] Figure 15 shows the refrigeration circuit 202 during air-cooled cooling operation. When the compressors 11 and 12 are stopped, such as during air-cooled cooling operation, the control unit 90 closes the cooling throttle valve 245 and the bypass pipe throttle valve 249, blocking the flow of refrigerant in the cooling suction pipe 244 and the bypass piping 248. In addition, during air-cooled cooling operation, the control unit 90 closes the third cooling valve 57, the low-stage throttle valve 33, and the high-stage throttle valve 34, etc., so that the suction and discharge sides of the compressors 11 and 12 are not in communication with the gas-liquid separator 17. As a result, similar to Embodiment 1, the liquid refrigerant from the gas-liquid separator 17 can be sent to the utilization-side heat exchanger 21 for cooling using the liquid pump 40 or natural circulation, and the refrigerant can be liquefied in the heat exchanger 74 before being returned to the gas-liquid separator 17.

[0143] [3-3. Effects, etc.] As described above, in this embodiment, the refrigeration system 201 includes a refrigeration circuit 202 connecting compressors 11 and 12, a heat source side heat exchanger 14, a gas-liquid separator 17, and a utilization side heat exchanger 21, and 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 a gas-liquid separator 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 The system includes an ejector 216 into which the refrigerant flowing through the air flows and which directs the incoming refrigerant to a gas-liquid separator 17; a main pipe 41 located downstream of the liquid pump 40 through which the refrigerant toward the cooling-side heat exchanger flows; a cooling suction pipe 244 branching off from the main pipe 41 and connected to the suction port of the ejector 216; a cooling throttle valve 245 that reduces the pressure of the refrigerant in the cooling suction pipe 244; and a heat exchanger 246 that cools the refrigerant flowing from the ejector 216 to the gas-liquid separator 17 with the refrigerant reduced in pressure by the cooling throttle valve 245. This allows the flow rate of the cooling suction pipe 244 to be increased using the suction force of the ejector 216, enabling cooling by the heat exchanger 246, and thus making it easier to liquefy the refrigerant flowing into the gas-liquid separator 17. Therefore, the workload of the compressors 11 and 12 can be reduced, and the efficiency of the refrigeration system 201 can be improved.

[0144] As in this embodiment, the refrigeration system 201 may be configured to include a gas venting pipe 30 that removes gaseous refrigerant from the gas-liquid separator 17 and returns it to the compressors 11 and 12, a bypass pipe 248 that connects the gas venting pipe 30 to the downstream side of the cooling suction pipe 244 of the heat exchanger 246, and a bypass pipe throttle valve 249 provided on the bypass pipe 248. This allows the flow rate of the cooling suction pipe 244 to be increased by utilizing the suction of the compressors 11 and 12 when the suction force of the ejector 216 is insufficient, thereby increasing the subcooling of the refrigerant flowing into the gas-liquid separator 17. Therefore, the freezing capacity can be improved, and the efficiency of the refrigeration device 201 can be increased.

[0145] As in this embodiment, the refrigeration system 201 may be configured to include an external cooling device 47 for cooling the refrigerant in the main piping 41. This allows for greater supercooling of the refrigerant flowing into the cooling-side heat exchanger. Therefore, the freezing capacity can be improved, and the efficiency of the refrigeration device 201 can be increased.

[0146] As in this embodiment, the refrigeration circuit 202 of the refrigeration device 201 may use carbon dioxide as the refrigerant, and the external cooling device 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 the refrigeration system 201, which uses carbon dioxide as a refrigerant with minimal environmental impact, to be improved by the energy-efficient external cooling device 47. Furthermore, because the external cooling device 47 can be made with a simpler configuration than the refrigeration system 201, 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 201 while suppressing environmental impact.

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

[0148] (Embodiment 4) Next, the refrigeration apparatus 401 according to Embodiment 4 will be described.

[0149] [4-1. Structure] Figure 16 shows the refrigeration circuit 402 of the refrigeration device 401 according to Embodiment 4. The refrigeration circuit 402 of the refrigeration device 401 has the same configuration as the refrigeration circuit 102 of Embodiment 2, in addition to having a pressure sensor 481. The pressure sensor 481 measures the pressure P5 inside the gas-liquid separator 17. The pressure sensor 481 also transmits the measured value of the pressure P5 inside the gas-liquid separator 17 to the control unit 90.

[0150] The refrigeration circuit 402 has a first refrigerant temperature sensor 482. The first refrigerant temperature sensor 482 measures the temperature T1 of the liquid refrigerant in the gas-liquid separator 17. More specifically, the first refrigerant temperature sensor 482 measures the temperature T1 as the outlet temperature of the liquid refrigerant in the gas-liquid separator 17. The first refrigerant temperature sensor 482 transmits the measured value of the liquid refrigerant temperature T1 in the gas-liquid separator 17 to the control unit 90.

[0151] The refrigeration circuit 402 has a second refrigerant temperature sensor 483. The second refrigerant temperature sensor 483 measures the temperature T2 of the refrigerant between the heat source side heat exchanger 14 and the second switching mechanism 52. That is, when the refrigeration system 401 is performing cooling operation, the second refrigerant temperature sensor 483 measures the temperature T2 of the refrigerant on the outlet side of the heat source side heat exchanger 14, which is a gas cooler. The second refrigerant temperature sensor 483 transmits the measured temperature T2 to the control unit 90.

[0152] Furthermore, the refrigeration unit 401 has an outside air temperature sensor 484. The outside air temperature sensor 484 is installed, for example, on the outdoor unit 10. The outside air temperature sensor 484 measures the outside air temperature T0 at the location where the refrigeration unit 401 is installed. The outside air temperature sensor 484 transmits the measured value of the outside air temperature T0 to the control unit 90.

[0153] Furthermore, in this embodiment, the ejector 116 is configured to allow adjustment of the throttle opening under the control of the control unit 90. When the throttle opening of the ejector 116 is reduced, the amount of pressure reduction of the liquid refrigerant flowing in from the high-pressure receiver 15 becomes greater than when the throttle opening is large.

[0154] [4-2. Operation] The operation of the refrigeration system 401, configured as described above, will be explained below. The control of the refrigeration system 401 when it performs cooling operation will be explained below. Specifically, in the following operation, the cooling valves 53, 55, 57, and 59 are set to the open state, and the heating valves 54, 56, and 58 and the heating throttle valve 60 are set to the closed state. In addition, during the following operation, the return side on / off valve 71 is set to the open state. As a result, during the following operation, 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.

[0155] [4-2-1. Operation to switch between single-stage and double-stage compression operation] Figure 17 is a flowchart of the refrigeration unit 401, showing the operation when switching between single-stage compression operation and double-stage compression operation during cooling operation of the refrigeration unit 401. The operation in Figure 17 may be repeatedly performed at predetermined time intervals (for example, every 5 minutes) while the refrigeration unit 401 is performing cooling operation, or it may be configured to be performed when the refrigeration unit 401 starts cooling operation. In this specification, single-stage compression operation means operation in which only the high-stage compressor 12 of the compressors 11 and 12 is driven, and two-stage compression operation means operation in which both compressors 11 and 12 are driven.

[0156] At the beginning of the operation of FIG. 17, in step SA1, the control unit 90 executes a determination regarding the outside air temperature T0. The control unit 90 uses the measured value of the outside air temperature sensor 484 for the determination. Specifically, the control unit 90 determines whether the outside air temperature T0 is less than the low-temperature reference temperature TL, whether the outside air temperature T0 is greater than or equal to the low-temperature reference temperature TL and less than or equal to the high-temperature reference temperature TH, or whether the outside air temperature T0 exceeds the high-temperature reference temperature TH.

[0157] The high-temperature reference temperature TH and the low-temperature reference temperature TL are stored in advance in the storage medium of the control unit 90. The high-temperature reference temperature TH is set to a temperature higher than the low-temperature reference temperature TL. In the present embodiment, the high-temperature reference temperature TH is 25°C. Also, in the present embodiment, the low-temperature reference temperature TL is 20°C.

[0158] In step SA1, when the control unit 90 determines that the outside air temperature T0 is greater than or equal to the low-temperature reference temperature TL and less than or equal to the high-temperature reference temperature TH (step SA1: TL ≤ T0 ≤ TH), the operation of the control unit 90 proceeds to step SA2.

[0159] In step SA1, when the control unit 90 determines that the outside air temperature T0 is less than the low-temperature reference temperature TL (step SA1: T0 < TL), the operation of the control unit 90 proceeds to step SA3.

[0160] In step SA1, when the control unit 90 determines that the outside air temperature T0 exceeds the high-temperature reference temperature TH (step SA1: TH < T0), the operation of the control unit 90 proceeds to step SA4.

[0161] In step SA2, the control unit 90 determines whether the temperature T2 of the refrigerant at the outlet side of the heat source side heat exchanger 14, which is a gas cooler, exceeds the sum of the outside air temperature T0 and the reference temperature difference dT. In other words, in step SA2, the control unit 90 determines whether the temperature difference obtained by subtracting the outside air temperature T0 from the temperature T2 of the refrigerant at the outlet side of the heat source side heat exchanger 14 exceeds the reference temperature difference dT. In step SA2, the control unit 90 uses the measurement value from the ambient air temperature sensor 484 as the ambient air temperature T0 and the measurement value from the second refrigerant temperature sensor 483 as the temperature T2. The reference differential temperature dT is stored in the storage medium of the control unit 90. In this embodiment, the reference differential temperature is 2K.

[0162] When the temperature T2 exceeds the sum of the ambient temperature T0 and the reference temperature difference dT, that is, when the temperature difference obtained by subtracting the ambient temperature T0 from the temperature T2 exceeds the reference temperature difference dT, it can be estimated that the refrigerant in the heat source side heat exchanger 14, which is a gas cooler, is sufficiently hotter than the ambient temperature T0 and can dissipate heat sufficiently. Conversely, when the temperature T2 does not exceed the sum of the ambient temperature T0 and the reference temperature difference dT, that is, when the temperature difference obtained by subtracting the ambient temperature T0 from the temperature T2 does not exceed the reference temperature difference dT, it can be estimated that the refrigerant in the heat source side heat exchanger 14, which is a gas cooler, is not sufficiently hotter than the ambient temperature T0 and cannot dissipate heat sufficiently. Thus, in step SA2, the control unit 90 can be said to be determining whether sufficient heat is being dissipated in the heat source side heat exchanger 14, which is a gas cooler.

[0163] In step SA2, if the temperature T2 exceeds the sum of the ambient temperature T0 and the reference temperature difference dT (step SA2: YES), the control unit 90 proceeds to step SA3. In step SA2, if the temperature T2 does not exceed the sum of the ambient temperature T0 and the reference temperature difference dT (step SA2: NO), the control unit 90 proceeds to step SA4.

[0164] In step SA3, the control unit 90 sets a target high pressure according to the ambient temperature T0. The target high pressure is the target value of the high pressure, which is the pressure of the refrigerant in the range from the discharge port of the high-stage compressor 12 to the ejector 116 during the operation of the refrigeration system 401. The target high pressure set by the control unit 90 in step SA3 is the pressure of the first pressure zone. The first pressure zone is a range of pressures. In this embodiment, the first pressure zone is the subcritical pressure of carbon dioxide, which is the refrigerant of the refrigeration circuit 402.

[0165] In step SA4, the control unit 90 sets a target high pressure according to the ambient temperature T0, similar to step SA3. The target high pressure set by the control unit 90 in step SA4 is the pressure in the second pressure band. The second pressure band is a range of pressures higher than the first pressure band. In this embodiment, the second pressure band is the supercritical pressure for carbon dioxide, which is the refrigerant in the refrigeration circuit 402.

[0166] In detail, in step SA3 and step SA4, the control unit 90 sets the target high pressure so that when the gaseous refrigerant in the gas-liquid separator 17 is compressed and raised to the target high pressure, the temperature of the pressurized refrigerant becomes higher than the ambient temperature T0 by a predetermined temperature difference. The predetermined temperature difference is, for example, 10K. This allows the refrigerant, which has been pressurized to the target high pressure, to dissipate heat sufficiently in the heat source side heat exchanger 14, which is a gas cooler. For example, the control unit 90 may store a table or the like that associates the temperature of the pressurized refrigerant with the value of the target high pressure of the ambient temperature T0 for a combination of the refrigerant pressure P5 or temperature T1 in the gas-liquid separator 17 during cooling operation and the ambient temperature T0.

[0167] Thus, in each of steps SA3 and SA4, the control unit 90 sets a target high pressure that is higher when the ambient temperature T0 is high than when the ambient temperature T0 is low. After the completion of step SA3 and step SA4, the operation of the control unit 90 proceeds to step SA5.

[0168] In step SA5, the control unit 90 determines whether the target compression ratio is less than a specified value. The target compression ratio is a value calculated based on the target high pressure set in steps SA3 and SA4 and the refrigerant pressure P5 of the gas-liquid separator 17 during cooling operation. The specified value is, for example, a value stored in the storage medium of the control unit 90.

[0169] If the control unit 90 determines in step SA5 that the target compression ratio is less than the specified value (step SA5: YES), the operation of the control unit 90 proceeds to step SA6. In step SA6, the control unit 90 closes the low-stage throttle valve 33 and opens the high-stage throttle valve 34. After step SA6, the control unit 90 proceeds to step SA7. In step SA7, the control unit 90 stops the low-stage compressor 11 and drives the high-stage compressor 12 to start single-stage compression operation. After step SA7, the control unit 90 completes the operation shown in Figure 17. The high-stage throttle valve 34 is an example of a "high-stage valve" in this disclosure. The low-stage throttle valve 33 is an example of a "low-stage valve" in this disclosure.

[0170] If the control unit 90 determines in step SA5 that the target compression ratio is not below the specified value (step SA5: NO), the operation of the control unit 90 proceeds to step SA8. In step SA8, the control unit 90 opens the lower-stage throttle valve 33 and closes the upper-stage throttle valve 34. After step SA8, the control unit 90 proceeds to step SA9. In step SA9, the control unit 90 drives the lower-stage compressor 11 and the upper-stage compressor 12 to start two-stage compression operation. After step SA9, the control unit 90 terminates the operation shown in Figure 17.

[0171] Thus, when the target compression ratio is below a specified value, the increase in energy consumption can be suppressed by single-stage compression operation, and when the target compression ratio is not below a specified value, the load on each compressor 11 and 12 can be reduced by two-stage compression operation.

[0172] [4-2-2. Control of the flow path switching valve] Figure 18 is a flowchart showing the operation of the refrigeration unit 401, illustrating the operation of switching the flow path switching valve 175. The operation shown in Figure 18 may be repeatedly performed at predetermined time intervals (for example, every 5 minutes) while the refrigeration unit 401 is performing cooling operation, or it may be configured to be performed when the refrigeration unit 401 starts cooling operation.

[0173] At the start of the operation shown in Figure 18, in step SB1, the control unit 90 determines whether the ambient temperature T0 exceeds the first specified temperature Tc. The first specified temperature Tc is stored in the storage medium of the control unit 90. If the control unit 90 determines in step SB1 that the ambient temperature T0 exceeds the first specified temperature Tc (step SB1: YES), the operation of the control unit 90 proceeds to step SB2. If the control unit determines in step SB1 that the ambient temperature T0 does not exceed the first specified temperature Tc (step SB1: NO), the operation of the control unit 90 proceeds to step SB4.

[0174] In step SB2, the control unit 90 determines whether the rotational speed N of the operating low-stage compressor 11 or high-stage compressor 12 exceeds the first specified rotational speed Nc. During single-stage compression operation, the control unit 90 uses the rotational speed N of the high-stage compressor 12 to make the determination in step SB2. During two-stage compression operation, the control unit 90 uses the rotational speed N of either the low-stage compressor 11 or the high-stage compressor 12 to make the determination in step SB2. The first specified rotational speed Nc is stored, for example, in the storage medium of the control unit 90. In step SB2, if the control unit 90 determines that the rotational speed N of the operating low-stage compressor 11 or high-stage compressor 12 exceeds the first specified rotational speed Nc (step SB2: YES), the operation of the control unit 90 proceeds to step SB3. In step SB2, if the control unit 90 determines that the rotational speed N of the operating low-stage compressor 11 or high-stage compressor 12 does not exceed the first specified rotational speed Nc (step SB2: NO), the operation of the control unit 90 proceeds to step SB4.

[0175] In step SB3, the control unit 90 switches the state of the flow path switching valve 175 to the first state. That is, in step SB3, the control unit 90 controls the flow path switching valve 175 to direct the refrigerant that has passed through the utilization-side heat exchanger 21, which is the cooling-side heat exchanger, to the suction port of the ejector 116 via the suction pipe 116a. After step SB3, the control unit 90 terminates the operation shown in Figure 18. Note that if the flow path switching valve 175 was originally in the first state in step SB3, the control unit 90 maintains the flow path switching valve 175 in the first state. Thus, when the ambient temperature T0 exceeds the first specified temperature Tc (step SB1: YES) and the rotational speed N exceeds the first specified rotational speed Nc (step SB2: YES), the control unit 90 controls the flow path switching valve 175 to draw in the refrigerant using the ejector 116. As a result, the control unit 90 can draw in the refrigerant using the ejector 116 when the refrigerant circulation volume is large and the ejector 116 can draw in sufficiently.

[0176] In step SB4, the control unit 90 switches the state of the flow path switching valve 175 to the second state. That is, in step SB4, the control unit 90 controls the flow path switching valve 175 to allow the refrigerant that has passed through the cooling-side heat exchanger, the utilization-side heat exchanger 21, to flow to the gas-liquid separator 17, and not to flow to the suction port of the ejector 116 via the suction pipe 116a. After step SB4, the control unit 90 terminates the operation shown in Figure 18. Note that if the flow path switching valve 175 was originally in the second state in step SB4, the control unit 90 maintains the flow path switching valve 175 in the second state. Furthermore, in step SB4, the control unit 90 controls the aperture opening of the ejector 116 to a first aperture opening or greater. The first aperture opening is stored in the storage medium of the control unit 90. In this embodiment, the first aperture opening is approximately the fully open position of the ejector 116. Thus, when the ambient temperature T0 is below the first specified temperature Tc (step SB1: NO), or when the rotational speed N is below the first specified rotational speed Nc (step SB2: NO), the control unit 90 controls the flow path switching valve 175 to return the refrigerant that has passed through the utilization-side heat exchanger 21, which is the cooling-side heat exchanger, back to the gas-liquid separator 17. This allows the control unit 90 to return the refrigerant that has passed through the utilization-side heat exchanger 21 to the gas-liquid separator 17 without being sucked in by the ejector 116 when the refrigerant circulation rate is small and the ejector 116 cannot adequately suction. Furthermore, by controlling the throttle opening of the ejector 116 to a first throttle opening or higher, the throttling loss in the ejector 116 can be reduced when the refrigerant circulation rate is small.

[0177] [4-2-3. Operation during cooling operation] Figure 19 is a flowchart showing the operation of the refrigeration unit 401, illustrating its operation when performing a cooling operation. A cooling operation is an operation that starts after a pull-down operation, which lowers the temperature of the heated space to the set temperature, and is a cooling operation performed to maintain the temperature of the heated space at the set temperature. The operation shown in Figure 19 may be performed repeatedly at predetermined time intervals (for example, every 5 minutes) while the refrigeration unit 401 is performing a cooling operation, or it may be configured to be performed when the refrigeration unit 401 starts a cooling operation after a pull-down operation.

[0178] In step SC1, the control unit 90 determines whether the temperature T1 of the liquid refrigerant in the gas-liquid separator 17, or the pressure P5 of the liquid refrigerant in the gas-liquid separator 17, is within a specified range. In step SC1, the control unit 90 may determine only the temperature T1 of the liquid refrigerant in the gas-liquid separator 17, or only the pressure P5 of the liquid refrigerant in the gas-liquid separator 17. The specified range is a range of temperature or a range of pressure, and is stored, for example, in the storage medium of the control unit 90. The control unit 90 also uses the measured value of the first refrigerant temperature sensor 482 or the measured value of the pressure sensor 481 for the determination in step SC1.

[0179] In step SC1, if it is determined that the temperature T1 of the liquid refrigerant in the gas-liquid separator 17, or the pressure P5 of the liquid refrigerant in the gas-liquid separator 17, is within the specified range (step SC1: YES), the operation of the control unit 90 proceeds to step SC2. In step SC2, the control unit 90 maintains the throttle opening of the ejector 116 and the rotational speeds of the compressors 11 and 12. This makes it easier to maintain the temperature T1 of the liquid refrigerant in the gas-liquid separator 17 and the pressure P5 of the liquid refrigerant in the gas-liquid separator 17 within the specified range.

[0180] Furthermore, if, in step SC1, the temperature T1 of the liquid refrigerant in the gas-liquid separator 17, or the pressure P5 of the liquid refrigerant in the gas-liquid separator 17, is determined to be lower than the specified range (step SC1: lower than the specified range or lower than the specified range), the operation of the control unit 90 proceeds to step SC3. In step SC3, the control unit 90 increases the throttle opening of the ejector 116 and decreases the rotational speed of the compressors 11 and 12. As a result, the amount of pressure reduction in the ejector 116 decreases, and the amount of refrigerant drawn from the venting pipe 30 to the compressors 11 and 12 decreases, making it easier for the temperature T1 and pressure P5 of the liquid refrigerant in the gas-liquid separator 17 to rise. Therefore, it becomes easier to adjust the temperature T1 of the liquid refrigerant in the gas-liquid separator 17 and the pressure P5 of the liquid refrigerant in the gas-liquid separator 17 within the specified range.

[0181] Furthermore, if, in step SC1, the temperature T1 of the liquid refrigerant in the gas-liquid separator 17, or the pressure P5 of the liquid refrigerant in the gas-liquid separator 17, is determined to be higher or higher than the specified range (step SC1: higher temperature or higher pressure than the specified range), the operation of the control unit 90 proceeds to step SC4. In step SC4, the control unit 90 reduces the throttle opening of the ejector 116 and increases the rotational speed of the compressors 11 and 12. This increases the amount of pressure reduction in the ejector 116, and increases the amount of refrigerant drawn from the venting pipe 30 to the compressors 11 and 12, making it easier for the temperature T1 and pressure P5 of the liquid refrigerant in the gas-liquid separator 17 to decrease. As a result, it becomes easier to adjust the temperature T1 of the liquid refrigerant in the gas-liquid separator 17 and the pressure P5 of the liquid refrigerant in the gas-liquid separator 17 within the specified range.

[0182] [4-3. Effects, etc.] As described above, in this embodiment, the refrigeration system 401 includes a refrigeration circuit 402 connecting a high-stage compressor 12, a low-stage compressor 11, 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 a gaseous refrigerant from the gas-liquid separator 17 The system includes a gas venting pipe 30 and a control unit 90. The gas venting pipe 30 is connected to the high-stage compressor 12 via a high-stage throttle valve 34 and to the low-stage compressor 11 via a low-stage throttle valve 33. The control unit 90 determines a target compression ratio based on the ambient temperature T0 and, based on the target compression ratio, opens and closes the low-stage throttle valve to switch between two-stage compression operation, which drives the high-stage compressor 12 and the low-stage compressor 11, and single-stage compression operation, which stops the low-stage compressor 11 and drives the high-stage compressor 12. This makes it easier to maintain an appropriate compression ratio by switching between single-stage and two-stage compression operation based on the target compression ratio, and makes it easier to suppress the starting and stopping of compressors 11 and 12. As a result, the efficiency of the refrigeration system 401 can be increased.

[0183] As in this embodiment, the control unit 90 may be configured to determine a target high pressure based on the ambient temperature T0, and then determine a target compression ratio based on the target high pressure. This makes it easier to maintain an appropriate compression ratio by switching between single-stage and two-stage compression operation based on the target compression ratio, and makes it easier to suppress the starting and stopping of compressors 11 and 12. As a result, the efficiency of the refrigeration system 401 can be increased.

[0184] As in this embodiment, the control unit 90 may be configured to close the low-stage throttle valve 33 during single-stage compression operation. This suppresses oil leakage from the low-stage compressor 11, which is stopped during single-stage compression operation. As a result, the reliability of the compressors 11 and 12 can be ensured while improving the efficiency of the refrigeration system 401.

[0185] As in this embodiment, the refrigeration system 401 includes an ejector 116 into which the refrigerant that has flowed through the gas cooler flows in between the heat source side heat exchanger 14 and the utilization side heat exchanger 21, and which directs the incoming refrigerant to a gas-liquid separator 17; a return pipe 70 provided on the outlet side of the cooling side heat exchanger that returns the refrigerant to the gas-liquid separator 17; and a flow path switching valve 175 provided on the return pipe 70 that directs the refrigerant that has passed through the cooling side heat exchanger to either the suction port of the ejector 116 or the gas-liquid separator 17. The control unit 90 may be configured to switch the flow path switching valve 175 when the outside air temperature T0 is below a first specified temperature Tc, to direct the refrigerant that has passed through the cooling side heat exchanger to the gas-liquid separator 17, and to set the throttle opening of the ejector 116 to a first specified opening or greater. This reduces the throttling loss in the ejector 116 when the refrigerant circulation rate in the refrigeration circuit 402 is low. As a result, the efficiency of the refrigeration system 401 can be improved.

[0186] As in this embodiment, the control unit 90 may be configured to switch the flow path switching valve 175 based on the rotational speed N of the high-stage compressor 12 or low-stage compressor 11 during operation when the ambient temperature T0 exceeds a first specified temperature Tc. This allows switching between drawing the refrigerant from the return pipe 30 into the ejector 116 or returning it to the gas-liquid separator 17, depending on whether or not suction is possible with the ejector 116. Therefore, a highly efficient refrigeration system 401 utilizing the ejector can be realized. In particular, in this embodiment, when the ambient temperature T0 exceeds a first specified temperature Tc and the rotational speed N exceeds a first specified rotational speed Nc, the control unit 90 controls the flow path switching valve 175 to cause the ejector 116 to draw in the refrigerant. As a result, the control unit 90 can cause the ejector 116 to draw in the refrigerant when the refrigerant circulation amount is large and the ejector 116 can draw in sufficiently, thereby improving the efficiency of the refrigeration system 401.

[0187] As in this embodiment, the control unit 90 may be configured to switch the flow path switching valve 175 when the ambient temperature T0 exceeds a first specified temperature Tc and the rotational speed N of the operating high-stage compressor 12 or low-stage compressor 11 is less than the first specified rotational speed Nc, thereby allowing the refrigerant that has passed through the cooling-side heat exchanger to flow to the gas-liquid separator 17. This allows the refrigerant in the return pipe 30 to be returned directly to the gas-liquid separator 17 when suction by the ejector 116 is not possible. Therefore, a highly efficient refrigeration system 401 utilizing the ejector 116 can be realized.

[0188] As in this embodiment, the refrigeration circuit 402 may be configured to use carbon dioxide as a refrigerant. This reduces the environmental impact of refrigerants. Therefore, it is possible to improve the efficiency of the refrigeration system 401 while reducing the environmental impact of refrigerants.

[0189] (Other embodiments) As described above, Embodiments 1 to 4 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 4 above. Therefore, other embodiments are illustrated below.

[0190] 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.

[0191] In the above embodiment, the refrigeration circuit 2 was equipped with a low-stage compressor 11 and a high-stage compressor 12 as compressors, and was configured to enable 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 refrigeration 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 refrigeration circuit 2. Furthermore, the single-stage compressor may be equipped with 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.

[0192] 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.

[0193] In the above embodiment, carbon dioxide was described as being 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-based refrigerant or an HFO-based refrigerant. However, using carbon dioxide as the refrigerant in the refrigeration circuit 2 can reduce the risk of environmental impact and other risks in the event of refrigerant leakage.

[0194] 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.

[0195] In the above embodiment, a three-way valve was described as being used as the flow path switching valve 175, but this is just one example. The flow path switching valve 175 can be configured to allow the refrigerant from the return pipe 70 to flow through either the suction pipe 116a or the gas-liquid separator 17, and to switch the inlet destination. For example, the flow path switching valve 175 may be composed of multiple on-off valves or throttle valves.

[0196] In the above embodiment, a low-stage throttle valve 33 and a high-stage throttle valve 34 were described as examples of low-stage and high-stage valves provided on the suction side of each compressor 11 and 12, but this is just one example. The valves provided on the suction side of each compressor 11 and 12 only need to be able to switch between single-stage compression operation, in which the high-stage compressor is driven while the low-stage compressor 11 is stopped, and two-stage compression operation, in which both the low-stage compressor 11 and the high-stage compressor 12 are driven. Therefore, the valves provided on the suction side of each compressor 11 and 12 are not limited to a low-stage throttle valve 33 and a high-stage throttle valve 34 that can be switched between an open state and a closed state and the degree of opening can be adjusted. For example, instead of a low-stage throttle valve 33 and a high-stage throttle valve 34, an on-off valve that can only be switched between an open state and a closed state may be used. Alternatively, for example, instead of the low-stage throttle valve 33, an on-off valve that can only be switched between an open state and a closed state may be used, and instead of the high-stage throttle valve 34, a check valve may be provided to block the refrigerant flowing back from the discharge side of the low-stage compressor 11 to the venting pipe 30 via the high-stage branch pipe 32.

[0197] In Embodiment 4, the refrigeration system 401 was described as having an ambient temperature sensor 484 for measuring the ambient temperature T0, but this is just one example. The refrigeration system 401 only needs to be configured so that the control unit 90 can acquire the ambient temperature T0 at the location where the refrigeration system 401 is installed. For example, the control unit 90 may be configured to be able to connect to an external server or terminal such as a smartphone via a communication network such as the Internet, and to acquire the ambient temperature at the location where the refrigeration system 401 is installed from an external server or terminal. In this case, the ambient temperature sensor 484 may be omitted.

[0198] The operational step units shown in Figures 17 to 19 are divided according to the main processing content to facilitate understanding of the operation, and the operation is not limited by the way the processing units are divided or the names of the processing units. Depending on the processing content, it may be further divided into more step units. Alternatively, it may be divided so that one step unit includes even more processing. Furthermore, the order of the steps may be changed as appropriate, as long as it does not impede the intent of this disclosure.

[0199] Since the embodiments described above are for illustrative purposes of the technology described herein, various modifications, substitutions, additions, omissions, etc., can be made within the claims or their equivalents.

[0200] (Note) Based on the above description of embodiments, the following technologies are disclosed. (Technology 1) A refrigeration system comprising a refrigeration circuit connecting a high-stage compressor, a low-stage compressor, 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, a gas venting pipe that removes gaseous refrigerant from the gas-liquid separator, and a control unit, wherein the gas venting pipe is connected to the high-stage compressor via a high-stage side valve and to the low-stage compressor via a low-stage side valve, and the control unit determines a target compression ratio based on the ambient temperature, and based on the target compression ratio, opens and closes the low-stage side valve to switch between a two-stage compression operation that drives the high-stage compressor and the low-stage compressor, and a single-stage compression operation that stops the low-stage compressor and drives the high-stage compressor. This makes it easier to maintain an appropriate compression ratio by switching between single-stage and two-stage compression operation based on the target compression ratio, and also makes it easier to suppress compressor starting and stopping. As a result, the efficiency of the refrigeration system can be improved.

[0201] (Technical 2) The refrigeration apparatus according to Technical 1, wherein the control unit determines a target high pressure based on the ambient temperature and determines the target compression ratio based on the target high pressure. This makes it easier to maintain an appropriate compression ratio by switching between single-stage and two-stage compression operation based on the target compression ratio, and also makes it easier to suppress compressor starting and stopping. As a result, the efficiency of the refrigeration system can be improved.

[0202] (Technical 3) The refrigeration apparatus according to Technical 1 or 2, wherein the control unit closes the low-stage side valve during the single-stage compression operation. This suppresses oil leakage from the lower-stage compressor, which is stopped during single-stage compression operation. As a result, it is possible to improve the efficiency of the refrigeration system while ensuring the reliability of the compressor.

[0203] (Technology 4) A refrigeration apparatus according to any one of Technologies 1 to 3, comprising: an ejector into which refrigerant that has flowed through a gas cooler flows between the heat source side heat exchanger and the utilization side heat exchanger, and which directs the incoming refrigerant to the gas-liquid separator; a return pipe provided on the outlet side of the cooling side heat exchanger that returns the refrigerant to the gas-liquid separator; and a flow path switching valve provided in the return pipe that directs the refrigerant that has passed through the cooling side heat exchanger to either the suction port of the ejector or the gas-liquid separator, wherein the control unit switches the flow path switching valve when the outside air temperature is below a first specified temperature, directing the refrigerant that has passed through the cooling side heat exchanger to the gas-liquid separator, and setting the throttle opening of the ejector to a first specified opening or greater. This reduces throttling losses in the ejector when the refrigerant circulation rate in the refrigeration circuit is low. As a result, the efficiency of the refrigeration system can be improved.

[0204] (Technical 5) The refrigeration apparatus according to Technical 4, wherein the control unit switches the flow path switching valve based on the rotational speed of the high-stage compressor or the low-stage compressor during operation when the outside air temperature exceeds the first specified temperature. This allows switching between drawing the refrigerant from the return piping into the ejector or returning it to the gas-liquid separator, depending on whether or not suction is possible with the ejector. Therefore, a highly efficient refrigeration system utilizing the ejector can be realized.

[0205] (Technical 6) The refrigeration apparatus according to Technical 5, wherein the control unit switches the flow path switching valve when the ambient temperature exceeds the first specified temperature and the rotational speed of the high-stage compressor or the low-stage compressor in operation is less than the first specified rotational speed, thereby flowing the refrigerant that has passed through the cooling-side heat exchanger to the gas-liquid separator. This allows the refrigerant in the return piping to be returned directly to the gas-liquid separator when suction by the ejector is not possible. Therefore, a highly efficient refrigeration system utilizing the ejector can be realized.

[0206] (Technology 7) The refrigeration circuit is a refrigeration apparatus according to any one of the technologies 1 to 6, wherein carbon dioxide is used as the refrigerant. This reduces the environmental impact of refrigerants. Therefore, it is possible to improve the efficiency of refrigeration systems while reducing the environmental impact of refrigerants. [Industrial applicability]

[0207] This disclosure is applicable to refrigeration equipment. Specifically, this disclosure is applicable to devices such as air conditioners equipped with a refrigeration circuit. [Explanation of symbols]

[0208] 1. Refrigeration equipment 2 Refrigeration Circuit 10 Outdoor unit 11. Low-stage compressor 12 High-stage compressor 13 Oil Separator 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 on / 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 (low-stage valve) 34. High-stage throttle valve (high-stage 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 side on / off valve 72 Check valve 73 Oil Separator 74 Heat exchanger 74a Air blower 74b Water supply means 90 Control Unit 101 Refrigeration equipment 102 Refrigeration Circuit 116 Ejector 116a Suction tube 118 Intake side piping 135 Gas venting throttle valve 175 Flow path switching valve 201 Refrigeration equipment 202 Refrigeration Circuit 216 Ejector 244 Cooling suction pipe 245 Cooling throttle valve 246 Heat exchanger 248 Bypass piping 249 Bypass pipe throttle valve 481 Pressure Sensor 482 First refrigerant temperature sensor 483 Second refrigerant temperature sensor 484 Outdoor temperature sensor

Claims

1. It is equipped with a refrigeration circuit that connects a high-stage compressor, a low-stage compressor, 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, A gas venting pipe for removing gaseous refrigerant from the aforementioned gas-liquid separator, It comprises a control unit and, The aforementioned gas venting pipe is connected to the high-stage compressor via a high-stage side valve and to the low-stage compressor via a low-stage side valve. The control unit, The target compression ratio is determined based on the ambient temperature. Based on the target compression ratio, the system switches between a two-stage compression operation, in which the lower-stage side valve is opened and closed to drive the upper-stage compressor and the lower-stage compressor, and a single-stage compression operation, in which the lower-stage compressor is stopped and the upper-stage compressor is driven. Refrigeration equipment.

2. The control unit determines a target high pressure based on the ambient temperature, and determines the target compression ratio based on the target high pressure. The refrigeration apparatus according to claim 1.

3. The control unit closes the low-stage side valve during the single-stage compression operation. The refrigeration apparatus according to claim 1 or 2.

4. The heat source side heat exchanger and the utilization side heat exchanger include an ejector into which the refrigerant that has flowed through the gas cooler flows and which directs the flowing refrigerant to the gas-liquid separator, A return pipe is provided on the outlet side of the cooling heat exchanger and returns the refrigerant to the gas-liquid separator, The return piping includes a flow path switching valve that directs the refrigerant that has passed through the cooling-side heat exchanger to either the suction port of the ejector or the gas-liquid separator, The control unit switches the flow path switching valve when the ambient temperature is below a first specified temperature, allowing the refrigerant that has passed through the cooling-side heat exchanger to flow to the gas-liquid separator, and setting the throttle opening of the ejector to a first specified opening or greater. The refrigeration apparatus according to claim 1 or 2.

5. When the ambient temperature exceeds the first specified temperature, the control unit switches the flow path switching valve based on the rotational speed of the high-stage compressor or the low-stage compressor during operation. The refrigeration apparatus according to claim 4.

6. The control unit switches the flow path switching valve when the ambient temperature exceeds the first specified temperature and the rotational speed of the high-stage compressor or the low-stage compressor during operation is less than the first specified rotational speed, thereby allowing the refrigerant that has passed through the cooling-side heat exchanger to flow to the gas-liquid separator. The refrigeration apparatus according to claim 5.

7. The aforementioned refrigeration circuit uses carbon dioxide as a refrigerant. The refrigeration apparatus according to claim 1 or 2.

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