Refrigeration system

Abstract

Provided is a refrigeration system in which a ratio of cooling capacity of a use-side heat exchanger can be changed.　A refrigeration system 1 comprises a refrigeration circuit in which a plurality of compressors, a heat source-side heat exchanger, a plurality of use-side heat exchangers, and a gas-liquid separator 16 are connected. The plurality of compressors are composed of a low-stage compressor 11 and a high-stage compressor 12. The plurality of use-side heat exchangers are composed of a first use-side heat exchanger and a second use-side heat exchanger having a refrigerant evaporation temperature lower than that of the first use-side heat exchanger. The first use-side heat exchanger is connected to the high-stage compressor 12, and the second use-side heat exchanger is connected to the low-stage compressor 11. The refrigeration circuit is provided with a connection port capable of connecting an external cooling device that super-cools the refrigerant to between the gas-liquid separator 16 and the first use-side heat exchanger, and / or between the gas-liquid separator 16 and the first use-side heat exchanger.

Description

Refrigeration system

[0001] The present disclosure relates to refrigeration systems.

[0002] Patent Document 1 discloses a refrigeration system that includes a cascade heat exchanger that exchanges heat between the low-pressure side of an air-conditioning refrigerant circuit and the high-pressure side of a refrigerant circuit for a cooling storage facility, and during cooling operation of the air-conditioning refrigerant circuit, the refrigerant on the high-pressure side of the refrigerant circuit for the cooling storage facility flows through a condenser to the cascade heat exchanger, and during heating operation of the air-conditioning refrigerant circuit, the refrigerant on the high-pressure side of the refrigerant circuit for the cooling storage facility flows through the cascade heat exchanger and then flows to the condenser.

[0003] Patent No. 4169638

[0004] The present disclosure provides a refrigeration system that can change the ratio of the cooling capacity of the utilization side heat exchangers, increasing the degree of freedom in selecting the load on the utilization side heat exchangers and expanding the range of use of the system.

[0005] This specification includes the entire contents of Japanese Patent Application No. 2023-168985, filed on September 29, 2023. A refrigeration system in the present disclosure includes a refrigeration circuit connecting a plurality of compressors, a heat source-side heat exchanger, a plurality of user-side heat exchangers, and a gas-liquid separator, the plurality of compressors being configured with low-stage compressors and high-stage compressors, the plurality of user-side heat exchangers being configured with a first user-side heat exchanger and a second user-side heat exchanger having a refrigerant evaporation temperature lower than that of the first user-side heat exchanger, the first user-side heat exchanger being connected to the high-stage compressor, and the second user-side heat exchanger being connected to the low-stage compressor, and the refrigeration circuit being provided with a connection port between the gas-liquid separator and the first user-side heat exchanger and between the gas-liquid separator and the second user-side heat exchanger, capable of connecting an external cooling device that subcools refrigerant.

[0006] The refrigeration system according to the present disclosure includes a refrigeration circuit connecting a plurality of compressors, a heat source-side heat exchanger, a plurality of user-side heat exchangers, and a gas-liquid separator, the plurality of compressors being composed of low-stage compressors and high-stage compressors, the plurality of user-side heat exchangers being composed of a first user-side heat exchanger and a second user-side heat exchanger having a refrigerant evaporation temperature lower than that of the first user-side heat exchanger, the first user-side heat exchanger being connected to the high-stage compressor, and the second user-side heat exchanger being connected to the low-stage compressor, the refrigeration circuit including a gas vent pipe that sends gas refrigerant separated in the gas-liquid separator to the high-stage compressor, and a flow rate adjustment mechanism that adjusts the flow rate of the gas refrigerant flowing through the gas vent pipe, and the gas vent pipe has a plurality of connection ports between the flow rate adjustment mechanism and the gas-liquid separator that can be connected to an external cooling device that cools the refrigerant.

[0007] According to the present disclosure, by connecting an external cooling device to any selected connection port, the ratio of the cooling capacity of the user-side heat exchanger can be changed, increasing the freedom in selecting the load for each heat exchanger and expanding the range of use of the system.

[0008] 1 is a circuit diagram of a refrigeration system showing operation during cooling operation in embodiment 1. FIG. 2 is a circuit diagram showing a first external cooling device. FIG. 3 is a circuit diagram showing a second external cooling device. FIG. 4 is a circuit diagram showing a third external cooling device. FIG. 5 is a circuit diagram showing a refrigerant amount adjustment tank. FIG. 6 is a circuit diagram of a refrigeration system showing operation during heating operation in embodiment 1. FIG. 7 is a circuit diagram of a refrigeration system showing operation during heating operation when the amount of heat exhausted to the cooling equipment is insufficient in embodiment 1. FIG. 8 is a circuit diagram of a refrigeration system showing operation when a large capacity is required in the cooling equipment and no amount of heat for heating is required in embodiment 1.

[0009] (Knowledge, etc. that Forms the Basis of the Present Disclosure) When the inventors arrived at the present disclosure, there were refrigeration systems in stores such as convenience stores that combined refrigeration and freezing equipment and air conditioning equipment into a single refrigeration circuit and used the exhaust heat from the refrigeration and freezing equipment for heating in winter to save energy. However, the inventors discovered a problem with this conventional refrigeration system: it was unable to accommodate the need to change the ratio of the cooling capacities of the indoor heat exchanger and the cold-side heat exchanger depending on the installation location. To solve this problem, the inventors came up with the subject matter of the present disclosure. The present disclosure provides a refrigeration system that can change the ratio of the cooling capacities of the user-side heat exchangers.

[0010] Hereinafter, embodiments will be described in detail with reference to the drawings. However, more detailed description than necessary may be omitted. For example, detailed description of already well-known matters or redundant description of substantially identical configurations may be omitted. This is to avoid unnecessary redundancy in the following description and to facilitate understanding by those skilled in the art. Note that the accompanying drawings and the following description are provided to enable those skilled in the art to fully understand the present disclosure, and are not intended to limit the subject matter described in the claims.

[0011] (Embodiment 1) Hereinafter, Embodiment 1 will be described with reference to the drawings. [1-1-1. Configuration of the Refrigeration System] FIG. 1 is a diagram showing a refrigeration circuit of a refrigeration system 1 in Embodiment 1. In FIG. 1, for ease of explanation, a valve body in an open state is shown in white, and a valve body in a closed state and a throttling mechanism in a closed state are shown in black. In FIG. 1, for ease of explanation, pipes through which a refrigerant flows are shown in thick lines, and pipes through which no refrigerant flows are shown in thin lines. In subsequent circuit diagrams, the valve body, throttling mechanism, and pipes are shown in the same manner as in FIG. 1. The refrigeration circuit uses carbon dioxide (R744), a natural refrigerant that is non-flammable and non-toxic. As shown in FIG. 1, the refrigeration system 1 includes an outdoor unit 10, an indoor unit 20, and a cooling unit 30. The indoor unit 20 provides air conditioning for the interior of a store, such as a convenience store or supermarket, and the cooling unit 30 provides cooling for the interior of a refrigerated showcase or freezer showcase, which serves as refrigerated storage equipment installed in the store.

[0012] The refrigeration system 1 includes an outdoor unit 10 configured by sequentially connecting a two-stage compressor including a low-stage compressor 11 and high-stage compressors 12, 12, a first switching mechanism 50, an outdoor heat exchanger 15, a second switching mechanism 54, and a gas-liquid separator 16. The two high-stage compressors 12, 12 are connected in parallel to the low-stage compressor 11. An accumulator 13 is disposed between the low-stage compressor 11 and the high-stage compressor 12. Refrigerant discharged from the low-stage compressor 11 is separated into gas and liquid by the accumulator 13, and the gas refrigerant is sent to the high-stage compressor 12.

[0013] An oil separator 14 is connected to the discharge side of the high-stage compressor 12. A first switching mechanism 50 is connected to the oil separator 14, and an outdoor heat exchanger 15 is connected to the first switching mechanism 50. The first switching mechanism 50 includes a pipe 40 connecting the oil separator 14 and the outdoor heat exchanger 15, and a first cooling valve (first on-off valve) 51 is connected to the pipe 40. A first heating pipe 41 is connected to the pipe 40 upstream of the first cooling valve 51. The first heating pipe 41 includes a first heating valve 52 (second on-off valve). The first heating pipe 41 is connected to a pipe 71 connecting the indoor heat exchanger 22 of the indoor unit 20 and the suction side of the high-stage compressor 12. An on-off valve 23 is connected to the pipe 71.

[0014] A first outdoor return pipe 42 is connected to the pipe 40 downstream of the first cooling valve 51. The first outdoor return pipe 42 is equipped with an outdoor refrigerant return valve (third on-off valve) 53. The first outdoor return pipe 42 is connected to a pipe 72 that connects the cooling-use heat exchanger 31 of the cooling equipment 30 to the suction side of the low-stage compressor 11, and the cooling-use outlet-side pressure adjustment mechanism 33 of the cooling equipment 30 is connected to this pipe 72.

[0015] A second switching mechanism 54 is connected to the outdoor heat exchanger 15, and the second switching mechanism 54 is connected to the gas-liquid separator 16. The second switching mechanism 54 is formed by annularly connecting the ends of first to fourth pipes 73, 74, 75, and 76 at connectors A, B, C, and D. A second cooling valve (first control valve) 55 and a check valve 59 are disposed in the first pipe 73, a refrigerant return expansion mechanism (second control valve) 58 that controls the flow rate is disposed in the second pipe 74, and a third cooling valve (third control valve) 56 and a check valve 59 are disposed in the third pipe 75. Furthermore, a second heating valve (fourth control valve) 57 and a check valve 59 are disposed in the fourth pipe 76.

[0016] A connection A between the second cooling valve 55 and the refrigerant return expansion mechanism 58 is connected to the outdoor heat exchanger 15, and a connection B between the refrigerant return expansion mechanism 58 and the third cooling valve 56 is connected to a pipe 77 that connects the gas-liquid separator 16 and the cooling heat exchanger 31. The cooling inlet expansion mechanism 32 is connected to this pipe 77. A connection C between the third cooling valve 56 and the second heating valve 57 is connected to the indoor heat exchanger 22 via a pipe (second cooling pipe) 78. The indoor expansion mechanism 21 of the indoor unit 20 is connected to the second cooling pipe 78. A connection D between the second heating valve 57 and the second cooling valve 55 is connected to the gas-liquid separator 16 via a pipe 79. A throttle mechanism 17 is arranged in the pipe 79.

[0017] A gas refrigerant return pipe 60 is connected to the gas-liquid separator 16, and the gas refrigerant return pipe 60 is connected to a pipe 71 and then to the accumulator 13. A gas refrigerant flow control valve 61 is connected to the gas refrigerant return pipe 60. In the present embodiment, a portion of the gas refrigerant separated in the gas-liquid separator 16 has its flow rate adjusted by the gas refrigerant flow control valve 61, is sent to the accumulator 13, and is returned to the suction side of the high-stage compressor 12.

[0018] In the refrigeration system 1, by controlling the aperture of the gas refrigerant flow control valve 61 and adjusting the return amount of gas refrigerant, the refrigerant pressure is higher at the outlet side of the indoor heat exchanger 22 than at the inlet side of the indoor heat exchanger 22. That is, in the refrigeration system 1, a refrigerant pressure difference can be generated between the inlet and outlet sides of the indoor expansion mechanism 21 in the refrigeration circuit. As a result, in the refrigeration system 1, in the indoor heat exchanger 22 where the evaporation temperature of the refrigerant is high, the refrigeration system 1 can control the refrigerant flowing through the indoor heat exchanger 22 at a pressure value obtained by adding a specified pressure value to the pressure value at the evaporation temperature of the refrigerant. Therefore, the refrigeration system 1 uses carbon dioxide (R744), a natural refrigerant with high environmental friendliness, thereby improving the efficiency of the air-conditioning temperature range and the efficiency of the entire refrigeration system.

[0019] The gas refrigerant return pipe 60 is provided with a connection port H and a connection port I. The connection port H and the connection port I are connection ports to which predetermined external devices can be connected. The connection port H and the connection port I are arranged in the gas refrigerant return pipe 60 between the gas-liquid separator 16 and the gas refrigerant flow control valve 61. In the first embodiment, the connection port H is arranged at a position closer to the gas-liquid separator 16 than the connection port I, and the connection port I is arranged at a position closer to the gas refrigerant flow control valve 61 than the connection port H. That is, in the flow of gas refrigerant in the refrigerant return pipe 60, the connection port H is located upstream of the connection port I.

[0020] In the first embodiment, a plurality of connection ports 110, 120 are arranged in a first piping region 101 between the connection portion B of the second switching mechanism 54 and the refrigeration heat exchanger 31, a second piping region 102 between the connection portion C of the second switching mechanism 54 and the indoor heat exchanger 22, and a third piping region 103 between the connection portion B of the second switching mechanism 54 and the gas-liquid separator 16. FIG. 1 shows an example in which the external cooling device 200 is connected to the first piping region 101. The first piping region 101 to the third piping region 103 are regions through which liquid refrigerant flows.

[0021] In the first piping region 101, more preferably, the connection port 110 at one end is arranged at connection portion B (branch point), and the connection port 120 at the other end is arranged at connection portion E between the cooling heat exchanger 31 and the liquid piping (piping 77). In the second piping region 102, the connection port 110 at one end is arranged at connection portion C, and the connection port 120 at the other end is arranged at connection portion F between the indoor heat exchanger 22 and the second cooling piping 78. The connection port 110 at one end of the second piping region 102 may be arranged at connection portion B (branch point). In the third piping region 103, the connection port 110 at one end is arranged at connection portion G between the gas-liquid separator 16 and the liquid piping (piping 77), and the connection port 120 at the other end is arranged closer to connection portion B than the connection port 110 at one end, and is preferably arranged at connection portion B. The connection port 110 at one end may be arranged on the outlet pipe of the outdoor unit 10 , and the connection port 120 at the other end may be arranged on the inlet pipe of the indoor unit 20 or the cooling equipment 30 .

[0022] When the external cooling device 200 is not connected, pipes 157 to 159 for sending refrigerant are connected between the connection ports 110, 120 of the first piping region 101 to the third piping region 103 by brazing or the like. It is possible to connect them using a valve such as a three-way valve instead of brazing. When the external cooling device 200 is to be connected to any of the first piping region 101 to the third piping region 103 afterwards, the brazing of one of the piping regions is removed and the external cooling device 200 is connected to that piping region.

[0023] 2 is a circuit diagram of a first external cooling device 201, which is an example of a device connected between the connection ports 110 and 120. The first external cooling device 201 includes a cascade heat exchanger 243 connected to the connection ports 110 and 120, and a cooling unit 247 connected to a circuit 243A of the cascade heat exchanger 243 and including an auxiliary compressor 244, a heat exchanger (controller) 245 capable of controlling the cooling capacity, and an expansion valve 246.

[0024] The cooling unit 247 circulates the refrigerant as shown by arrow X1 by driving the auxiliary compressor 244. Arrow X2 indicates the flow of refrigerant in the main circuit. The cascade heat exchanger 243 can supercool the refrigerant flowing through the connection ports 110 and 120. While the cooling unit 247 has been described as including the expansion valve 246, it may also include another type of throttle mechanism, such as a capillary tube.

[0025] The first external cooling device 201 can be connected to any of the connection ports 110, 120 of the piping regions 101 to 103. If it is connected to the first piping region 101, the cooling capacity of the cold-set heat exchanger 31 can be increased, and if it is connected to the second piping region 102, the cooling capacity of the indoor heat exchanger 22 can be increased. If it is connected to the third piping region 103, the overall cooling capacity of the cold-set heat exchanger 31 and the indoor heat exchanger 22 can be increased.

[0026] Because the refrigeration circuit of the refrigeration system 1 has a long piping length, making it difficult to identify the location of a refrigerant leak, the refrigeration circuit uses a non-flammable and non-toxic refrigerant, carbon dioxide (R744), which does not require leakage management. In contrast, the first external cooling device 201 cools the high-temperature refrigerant (e.g., 30 to 50°C) on the refrigeration system 1 side, so the evaporation temperature of the refrigerant in the cooling unit 247 should be relatively high (e.g., 10 to 20°C). The cooling unit 247 of the first external cooling device 201 has a short piping length, making it relatively easy to identify the location of a refrigerant leak. Therefore, a high GWP refrigerant or a flammable or toxic refrigerant can be selected. By selecting a refrigerant that performs well in high-temperature ranges, regardless of its GWP, flammability, or toxicity, the amount of refrigerant charged in the cooling unit 247 can be reduced, improving performance while lowering the GWP of the entire system.

[0027] 3 is a circuit diagram of a second external cooling device 202, which is an example of a device connected between connection ports 110 and 120 in Modification 1. In Modification 1, second external cooling device 202 includes a refrigerant / cooling medium heat exchanger 251 connected to connection ports 110 and 120, and a water-cooled cooling unit 255 connected to a cooling medium circuit 251A of refrigerant / cooling medium heat exchanger 251 and including a tank 252 for storing a cooling medium (water or brine), a pump 253 for circulating the cooling medium, and a flow rate adjustment valve 254.

[0028] In variant 1, by connecting the second external cooling device 202 to the connection ports 110, 120 of any of the piping areas 101 to 103, the cooling capacity of the cold-set heat exchanger 31 or the indoor heat exchanger 22 can be increased, or the overall cooling capacity of the cold-set heat exchanger 31 and the indoor heat exchanger 22 can be increased.

[0029] 4 is a circuit diagram of a third external cooling device 203, which is an example of a device connected between the connection ports 110 and 120 in Modification 2. In Modification 2, the third external cooling device 203 includes a refrigerant / cooling medium heat exchanger 261 connected to the connection ports 110 and 120, and a water-cooled cooling unit 265 connected to a cooling medium circuit 261A of the refrigerant / cooling medium heat exchanger 261 and including a tank 262 for storing the cooling medium, a pump 263 for circulating the cooling medium (water or brine), an auxiliary heat exchanger (auxiliary controller) 266 capable of controlling the cooling capacity, and a flow rate adjustment valve 264. A cooling unit 270 including an auxiliary compressor 267, a heat exchanger (controller) 268 capable of controlling the cooling capacity, and an expansion valve 269 is connected to the circuit 266A of the auxiliary heat exchanger 266.

[0030] In variant example 2, by connecting the third external cooling device 203 to the connection ports 110, 120 of any of the piping areas 101 to 103, the cooling capacity of the cold-air heat exchanger 31 or the indoor heat exchanger 22 can be increased, or the overall cooling capacity of the cold-air heat exchanger 31 and the indoor heat exchanger 22 can be increased.

[0031] Next, a case will be described in which any one of the first external cooling device 201, the second external cooling device 202, and the third external cooling device 203 is connected to the gas refrigerant return pipe 60 in the refrigeration system 1. In the refrigeration system 1, the gas refrigerant return pipe 60 is formed so that any one of the first external cooling device 201, the second external cooling device 202, and the third external cooling device 203 can be connected. The first external cooling device 201, the second external cooling device 202, and the third external cooling device 203 are attached to the gas refrigerant return pipe 60 by connecting the connection port 110 to the connection port H and connecting the connection port 120 to the connection port I.

[0032] Next, a case will be described in which the refrigeration system 1 is operated with any one of the first external cooling device 201, the second external cooling device 202, and the third external cooling device 203 connected to the gas refrigerant return pipe 60. The gas refrigerant delivered from the gas-liquid separator 16 via the gas refrigerant return pipe 60 is introduced into any one of the first external cooling device 201, the second external cooling device 202, and the third external cooling device 203 via the connection port 110 and the connection port H. This gas refrigerant is cooled by the cascade heat exchanger 243 or the refrigerant-cooling medium heat exchanger 151, 261. The cooled gas refrigerant is returned to the gas refrigerant return pipe 60 again via the connection port 120 and the connection port I, and delivered to the high-stage compressor 12.

[0033] As a result, in the refrigeration system 1, the density of the refrigerant sent from the gas-liquid separator 16 to the high-stage compressor 12 increases. Therefore, in the refrigeration system 1, overheating operation of the high-stage compressor 12 is suppressed, the load on the high-stage compressor 12 can be reduced, and an increase in the temperature of the gas refrigerant discharged from the high-stage compressor 12 can be suppressed. In addition, in the refrigeration system 1, the gas refrigerant is cooled by any one of the first external cooling device 201, the second external cooling device 202, and the third external cooling device 203, and the gas refrigerant return pipe 60 connected to the gas-liquid separator 16 is cooled by thermal conduction. Therefore, in the refrigeration system 1, the temperature of the refrigerant stored inside the gas-liquid separator 16 can be reduced.

[0034] FIG. 5 is a circuit diagram of a refrigerant amount adjustment tank 204, which is an example of a device connected between the connection ports 110 and 120. As shown in FIG. 1 , in the first embodiment, a throttling mechanism 17 is connected to the piping 79 between the second switching mechanism 54 and the gas-liquid separator 16. A first service valve 235 is disposed upstream of the throttling mechanism 17 in the piping 79, and a second service valve 236 is disposed downstream of the throttling mechanism 17 in the piping 79. A third service valve 237 is disposed in the piping 71 connecting the indoor heat exchanger 22 and the suction side of the high-stage compressor 12. A fourth service valve 238 is disposed in the piping 72 connecting the refrigerant heat exchanger 31 and the suction side of the low-stage compressor 11. As shown in FIG. 5 , a refrigerant amount adjustment tank 204 (not shown in FIG. 1 ) for storing refrigerant is connected between the first service valve 235, the second service valve 236, and the fourth service valve 238. This refrigerant amount adjustment tank 204 can be optionally connected later.

[0035] The refrigerant quantity adjustment tank 204 is connected to a first service valve 235 by a pipe 91, and a motor-operated valve 92 that adjusts the flow rate is connected to the pipe 91. The motor-operated valve 92 is a throttle mechanism that can change the pressure of the refrigerant. The refrigerant quantity adjustment tank 204 is connected to a second service valve 236 by a pipe 93, and a first electromagnetic on-off valve 94 that adjusts the flow rate is connected to the pipe 93. The refrigerant quantity adjustment tank 204 is connected to a fourth service valve 238 by a pipe 95, and a second electromagnetic on-off valve 96 that adjusts the flow rate is connected to the pipe 95. A capillary tube 97 that decompresses the refrigerant is connected between the second electromagnetic on-off valve 96 and the fourth service valve 238.

[0036] According to this configuration, when the cooling capacity of the refrigeration system 1 increases or decreases, the refrigerant is stored in or discharged from the refrigerant quantity adjustment tank 204 in accordance with the increase or decrease in cooling capacity, thereby absorbing any excess or deficiency in the amount of refrigerant. Furthermore, when flow rate adjustment is not required, the internal pressure of the refrigerant quantity adjustment tank 204 can be maintained at a high pressure by closing the first electromagnetic on-off valve 94 and the second electromagnetic on-off valve 96 and opening only the motor-operated valve 92 connected to the first service valve 235, thereby preventing liquid sealing in the refrigerant quantity adjustment tank 204. Note that the refrigerant quantity adjustment tank 204 is not limited to being provided with a capillary tube 97, and various types of throttle mechanisms capable of adjusting the pressure of the refrigerant, such as a pressure adjustment valve, may be provided.

[0037] The refrigerant amount adjustment tank 204 is used in the refrigerant recovery mode, refrigerant replenishment mode, and refrigerant amount adjustment stop mode, and the three valves 92, 94, and 96 are opened and closed by comparing the target high pressure (determined by the outside air temperature) with the current high pressure.

[0038] <Refrigerant Recovery Mode> The refrigerant recovery mode is executed when "high pressure" > "target high pressure (determined by outside air temperature) + specified value." The motor-operated valve 92 connected to the first service valve 235 and the first electromagnetic on-off valve 94 connected to the second service valve 236 are opened, and the second electromagnetic on-off valve 96 connected to the fourth service valve 238 is closed. The opening degree of the motor-operated valve 92 is adjusted based on the pressure difference between the "high pressure" and "target high pressure + specified value." In this manner, refrigerant is stored in the refrigerant amount adjustment tank 204 by opening and closing the three valves 92, 94, and 96.

[0039] <Refrigerant Refill Mode> The refrigerant refill mode is executed when "high pressure" < "target high pressure - specified value." The second electromagnetic on-off valve 96 connected to the fourth service valve 238 is opened, and the motor-operated valve 92 connected to the first service valve 235 and the first electromagnetic on-off valve 94 connected to the second service valve 236 are closed. In this manner, the refrigerant is discharged from the refrigerant amount adjustment tank 204 by opening and closing the three valves 92, 94, and 96.

[0040] <Refrigerant Amount Adjustment Stop Mode> The refrigerant amount adjustment stop mode is executed when "target high pressure" - "specified value" ≦ "high pressure" ≦ "target high pressure + specified value." The motor-operated valve 92 connected to the first service valve 235 is opened, and the first electromagnetic on-off valve 94 connected to the second service valve 236 and the second electromagnetic on-off valve 96 connected to the fourth service valve 238 are closed. This stops the storage of refrigerant in the refrigerant amount adjustment tank 204 or the discharge of refrigerant from the refrigerant amount adjustment tank 204.

[0041] [1-2. Operation and Effects] Next, the operation of this embodiment will be described. First, the operation of performing cooling operation will be described. During cooling operation, as shown in FIG. 1 , the outdoor heat exchanger 15 functions as a gas cooler or radiator, and the indoor heat exchanger 27 and the cooling heat exchanger 31 function as evaporators. When performing cooling operation, the first switching mechanism 50 opens the first cooling valve 51 and closes the remaining first heating valve 52 and outdoor refrigerant return valve 53. The second switching mechanism 54 opens the second cooling valve 55 and the third cooling valve 56 and closes the second heating valve 57 and the refrigerant return expansion mechanism 58. In this state, by driving the low-stage compressor 11 and each high-stage compressor 12, the refrigerant compressed by the low-stage compressor 11 is sent to each high-stage compressor 12, where it is further compressed and discharged toward the oil separator 14.

[0042] The refrigerant that has passed through the oil separator 14 is sent through the first cooling valve 51 of the first switching mechanism 50 to the outdoor heat exchanger 15, where it exchanges heat with outdoor air. The refrigerant after heat exchange is sent from connection A of the second switching mechanism 54 to the gas-liquid separator 16 via the second cooling valve 55. The refrigerant separated in the gas-liquid separator 16 passes through piping 77 to connection B of the second switching mechanism 54. One of the refrigerants branched at connection B is sent to the indoor heat exchanger 22 via the third cooling valve 56 and the indoor expansion mechanism 21 of the indoor unit 20. In the indoor heat exchanger 22, the refrigerant exchanges heat with indoor air to cool it. The refrigerant that has exchanged heat with the indoor air passes through piping 71, the on-off valve 23, and the accumulator 13, and is returned to the suction side of each high-stage compressor 12.

[0043] The other refrigerant branched at connection point B is sent to the refrigeration heat exchanger 31 via the refrigeration inlet expansion mechanism 32 of the refrigeration equipment 30, where it undergoes heat exchange and cools the refrigeration equipment 30. The refrigerant that has undergone heat exchange in the refrigeration heat exchanger 31 is returned to the low-stage compressor 11 via the refrigeration outlet pressure adjustment mechanism 33.

[0044] In the present refrigeration system 1, when the first external cooling device 201 is connected to the first piping region 101, the refrigerant that branches off at the connection portion B and flows into the chilled heat exchanger 31 is supercooled by the first external cooling device 201, thereby increasing the cooling capacity of the chilled heat exchanger 31 and changing the ratio of the cooling capacities of the indoor heat exchanger 22 and the chilled heat exchanger 31. Furthermore, when the first external cooling device 201 is connected to the second piping region 102, the refrigerant that branches off at the connection portion B and flows into the indoor heat exchanger 22 is supercooled by the first external cooling device 201, thereby increasing the cooling capacity of the indoor heat exchanger 22 and changing the ratio of the cooling capacities of the indoor heat exchanger 22 and the chilled heat exchanger 31. Furthermore, when the first external cooling device 201 is connected to the third piping area 103, the refrigerant that branches at connection point B and flows to both the indoor heat exchanger 22 and the refrigerated heat exchanger 31 is supercooled by the first external cooling device 201, thereby increasing the overall cooling capacity of the indoor heat exchanger 22 and the refrigerated heat exchanger 31.

[0045] In the present refrigeration system 1, it is necessary to change the ratio of the cooling capacities of the indoor heat exchanger 22 and the cold-use heat exchanger 31 depending on the usage situation.

[0046] In the first embodiment, by retrofitting the first external cooling device 201 to any of the piping regions 101 to 103, the cooling capacity of either the indoor heat exchanger 22 or the cold-air heat exchanger 31 can be increased, and the ratio of the cooling capacities can be changed. This increases the degree of freedom in selecting the load for each of the heat exchangers 22 and 31, and broadens the range of use of the refrigeration system.

[0047] Next, the operation of the first heating operation (heating operation) will be described. FIG. 6 is a circuit diagram of the refrigeration system 1 showing the heating operation. The connection ports and service valves shown in FIG. 1 are omitted from FIG. 6 . The refrigerant flow is indicated by arrows in the figure. The first heating operation is performed using the indoor heat exchanger 22 as a gas cooler or radiator and the cooling heat exchanger 31 as an evaporator. As shown in FIG. 6 , when the heating operation is performed, the first switching mechanism 50 opens the first heating valve 52 and closes the first cooling valve 51 and the outdoor refrigerant return valve 53. The second switching mechanism 54 opens the second heating valve 57 and closes the second cooling valve 55, the third cooling valve 56, and the refrigerant return expansion mechanism 58.

[0048] In this state, by driving the low-stage compressor 11 and each high-stage compressor 12, the refrigerant compressed by the low-stage compressor 11 is sent to each high-stage compressor 12, where it is further compressed and discharged toward the oil separator 14. The refrigerant that has passed through the oil separator 14 passes through the first heating valve 52 of the first switching mechanism 50 and is sent to the indoor heat exchanger 22, where it exchanges heat with the indoor air and heats the indoor air.

[0049] The refrigerant that has exchanged heat in the indoor heat exchanger 22 passes through the indoor expansion mechanism 21, reaches the connection C of the second switching mechanism 54, and is sent to the gas-liquid separator 16 via the second heating valve 57. The refrigerant separated in the gas-liquid separator 16 passes through piping 77, reaches the connection B of the second switching mechanism 54, and is sent to the chiller heat exchanger 31 via the chiller inlet expansion mechanism 32. This refrigerant undergoes heat exchange in the chiller heat exchanger 31 and cools the chiller equipment 30. The refrigerant that has exchanged heat in the chiller heat exchanger 31 passes through piping 72 and is returned to the suction side of the low-stage compressor 11 via the chiller outlet pressure adjustment mechanism 33. In the refrigeration system 1 of the present disclosure, during heating, the indoor heat exchanger 22 functions as a gas cooler or a radiator, and the outdoor heat exchanger 15 is not used.

[0050] Next, we will explain the operation of the second heating operation at full capacity when the heat exhausted to the cooling equipment 30 is insufficient, for example, when the outdoor air temperature is lower than the temperature inside the cooling equipment 30. FIG. 7 is a circuit diagram of the refrigeration system 1 illustrating the heating operation when the heat exhausted to the cooling equipment is insufficient. In FIG. 7, the connection ports and service valves shown in FIG. 1 are omitted. The refrigerant flow is indicated by arrows in the figure. The second heating operation is performed using the indoor heat exchanger 22 as a gas cooler or radiator, and the cooling heat exchanger 31 and the outdoor heat exchanger 15 as evaporators. When the second heating operation at full capacity is performed, the first switching mechanism 50 opens the first heating valve 52 and the outdoor refrigerant return valve 53 and closes the first cooling valve 51. In the second switching mechanism 54, the second heating valve 57 and the refrigerant return expansion mechanism 58 are opened, and the second cooling valve 55 and the third cooling valve 56 are closed.

[0051] In this state, by driving the low-stage compressor 11 and each high-stage compressor 12, the refrigerant compressed by the low-stage compressor 11 is sent to each high-stage compressor 12, where it is further compressed and discharged toward the oil separator 14. The refrigerant that has passed through the oil separator 14 is sent to the indoor heat exchanger 22 through the first heating valve 52 of the first switching mechanism 50, where it exchanges heat with the indoor air and heats the indoor air.

[0052] The refrigerant that has exchanged heat in the indoor heat exchanger 22 is sent to the gas-liquid separator 16 via the second heating valve 57 of the second switching mechanism 54. The refrigerant separated in the gas-liquid separator 16 reaches the connection B of the second switching mechanism 54 through piping 77. One of the refrigerants branched at connection B is sent to the outdoor heat exchanger 15 via the refrigerant return expansion mechanism 58 of the second switching mechanism 54 and connection A, where it exchanges heat with outside air. The other refrigerant branched at connection B is sent to the cooling-unit heat exchanger 31 via the cooling-unit inlet expansion mechanism 32, where it exchanges heat and cools the cooling-unit equipment 30. The refrigerant that has exchanged heat in the cooling-unit heat exchanger 31 and the refrigerant that has exchanged heat in the outdoor heat exchanger 15 and is sent from the first outdoor return piping 42 are joined at piping 72 and returned to the suction side of the low-stage compressor 11.

[0053] The refrigerant that has exchanged heat in the refrigeration heat exchanger 31 is adjusted by the refrigeration outlet pressure adjustment mechanism 33 so that its pressure is the same as that of the refrigerant sent from the first outdoor return pipe 42. This is the operation when the outside air temperature is lower than the temperature inside the refrigeration equipment 30.

[0054] This allows the exhaust heat from the refrigeration heat exchanger 31 and the heat pumped up by the outdoor heat exchanger 15 to be used as heat for the indoor heat exchanger 22, thereby increasing the heating capacity when the amount of heat exhausted to the refrigeration equipment 30 is insufficient.

[0055] In this case, if the outside air temperature becomes lower than the temperature inside the refrigerator 30, heat cannot be pumped from the outdoor heat exchanger 15 unless the evaporation temperature of the refrigerator 30 is lowered. Lowering the evaporation temperature of the refrigerator 30 will result in a temperature lower than the specified temperature, shortening the thermocycle, resulting in short-cycle operation and possibly causing frozen products. In this embodiment, the above-mentioned problems can be avoided by controlling the opening of the refrigerator outlet pressure adjustment mechanism 33 to balance the pressure with the refrigerant sent from the outdoor heat exchanger 15.

[0056] Next, an operation when a large capacity of the cooling equipment 30 is required but a large amount of heat is not required for heating will be described. FIG. 8 is a circuit diagram of the refrigeration system 1 illustrating the operation when a large amount of heat is not required for heating. The connection ports and service valves shown in FIG. 1 are omitted from FIG. 8 . The refrigerant flow is indicated by arrows in the figure. The third heating operation is performed using the outdoor heat exchanger 15 and the indoor heat exchanger 22 as gas coolers or radiators, and the cooling heat exchanger 31 as an evaporator. When performing the third heating operation, the first switching mechanism 50 opens the first cooling valve 51 and the first heating valve 52 and closes the outdoor refrigerant return valve 53. The second switching mechanism 54 opens the second cooling valve 55 and the second heating valve 57 and closes the third cooling valve 56 and the refrigerant return expansion mechanism 58.

[0057] In this state, by driving the low-stage compressor 11 and each high-stage compressor 12, the refrigerant compressed by the low-stage compressor 11 is sent to each high-stage compressor 12, where it is further compressed and discharged toward the oil separator 14.

[0058] The refrigerant that has passed through the oil separator 14 is sent to the outdoor heat exchanger 15 through the first cooling valve 51 of the first switching mechanism 50, and at the same time, is sent to the indoor heat exchanger 22 through the first heating valve 52. The outdoor heat exchanger 15 and the indoor heat exchanger 22 function as a gas cooler or a radiator, exchanging heat with outdoor air in the outdoor heat exchanger 15 and with indoor air in the indoor heat exchanger 22, thereby heating the indoor air. The refrigerant that has exchanged heat in the outdoor heat exchanger 15 reaches the second cooling valve 55 from the connection part A of the second switching mechanism 54, and the refrigerant that has exchanged heat in the indoor heat exchanger 22 reaches the second heating valve 57 from the connection part C of the second switching mechanism 54, where they join and are sent to the gas-liquid separator 16. The refrigerant separated in the gas-liquid separator 16 is sent through a pipe 77 to the chilled heat exchanger 31, where it undergoes heat exchange and cools the chilled equipment 30. The refrigerant that has exchanged heat in the chilled heat exchanger 31 is returned to the suction side of the low-stage compressor 11 via the chilled outlet pressure adjustment mechanism 33.

[0059] According to this, during heating operation, the exhaust heat from the cooling equipment 30 can be dissipated by the outdoor heat exchanger 15 and the indoor heat exchanger 22, thereby increasing the cooling capacity of the cooling equipment 30 and removing frost that has adhered to the outdoor heat exchanger 15.

[0060] (Other Embodiments) As described above, the first embodiment has been described as an example of the technology disclosed in the present application. However, the technology in the present disclosure is not limited to this, and can be applied to embodiments in which modifications, substitutions, additions, omissions, etc. are made. Furthermore, it is also possible to combine the components described in the first embodiment above to create new embodiments.

[0061] In the above-described embodiment, the refrigeration system 1 includes one indoor heat exchanger 22 and one chilled-use heat exchanger 31. However, the present invention is not limited to this. The refrigeration system 1 may omit the indoor heat exchanger 22 and include multiple chilled-use heat exchangers 31. That is, the refrigeration system 1 may be a chilled-use system that omits the indoor unit 20 and includes multiple chilled-use devices 30. In this case, the multiple chilled-use heat exchangers 31 have different evaporation temperature ranges. Of the multiple chilled-use heat exchangers 31, the chilled-use heat exchanger 31 with a higher evaporation temperature range is connected to the inlet side of the high-stage compressor 12, and the chilled-use heat exchanger 31 with a lower evaporation temperature range is connected to the inlet side of the low-stage compressor 11.

[0062] For example, when the refrigeration system 1 includes a refrigeration equipment 30 set to a freezing temperature range and a refrigeration equipment 30 set to a refrigeration temperature range, the refrigeration heat exchanger 31 in the refrigeration equipment 30 set to the refrigeration temperature range is connected to the inlet side of the high-stage compressor 12. On the other hand, in the refrigeration equipment 30 set to the freezing temperature range, the refrigeration heat exchanger 31 is connected to the inlet side of the low-stage compressor 11.

[0063] In the above-described embodiment, a plurality of use-side heat exchangers connected to the inlet side of the high-stage compressor 12 may be provided in parallel on the pipes 78 and 71. Similarly, a plurality of use-side heat exchangers connected to the inlet side of the low-stage compressor 11 may be provided in parallel on the pipes 77 and 72.

[0064] Furthermore, for example, a plurality of indoor heat exchangers 22 may be provided in parallel to one another in the pipe 78 and the pipe 71. In this case, an indoor expansion mechanism 21 may be provided on the inlet side of each of the indoor heat exchangers 22. In this case, the refrigeration system 1 includes a plurality of indoor units 20. Furthermore, in this case, one or more indoor heat exchangers 22 and one or more cooling heat exchangers 31 may be provided in parallel to one another in the pipe 78 and the pipe 71.

[0065] A plurality of chilled-use heat exchangers 31 may be provided in parallel to one another on the pipe 77 and the pipe 72. In this case, a chilled-use inlet-side expansion mechanism 32 may be provided on the inlet side of each chilled-use heat exchanger 31. In this case, at least one of the chilled-use heat exchangers 31 provided in parallel on the pipe 77 and the pipe 72 may have an evaporation temperature range different from that of the other chilled-use heat exchangers 31.

[0066] It should be noted that the above-described embodiments are intended to illustrate the technology of the present disclosure, and various modifications, substitutions, additions, omissions, etc. may be made within the scope of the claims or their equivalents.

[0067] (Additional Notes) The above description of the embodiments discloses the following techniques.

[0068] (Technology 1) A refrigeration system comprising a refrigeration circuit connecting a plurality of compressors, a heat source-side heat exchanger, a plurality of user-side heat exchangers, and a gas-liquid separator, wherein the plurality of compressors are composed of low-stage compressors and high-stage compressors, and the plurality of user-side heat exchangers are composed of a first user-side heat exchanger and a second user-side heat exchanger having a refrigerant evaporation temperature lower than that of the first user-side heat exchanger, the first user-side heat exchanger is connected to the high-stage compressor, and the second user-side heat exchanger is connected to the low-stage compressor, and the refrigeration circuit is provided with a connection port, at least either between the gas-liquid separator and the first user-side heat exchanger or between the gas-liquid separator and the second user-side heat exchanger, to which an external cooling device that subcools refrigerant can be connected. With this configuration, an external cooling device can be connected to any of the multiple connection ports, and the cooling capacity of the indoor heat exchanger or refrigerated heat exchanger can be changed depending on where the external cooling device is connected, or the overall cooling capacity of the indoor heat exchanger and refrigerated heat exchanger can be changed, increasing the freedom in selecting the load for each heat exchanger and expanding the range of uses for the refrigeration system.

[0069] (Technology 2) The refrigeration system according to Technology 1, wherein the refrigeration circuit uses carbon dioxide as a natural refrigerant. With this configuration, the natural refrigerant carbon dioxide (R744), which is highly environmentally friendly, can be used, improving the efficiency of the air conditioning temperature range and the efficiency of the entire refrigeration system.

[0070] (Technology 3) The refrigeration system according to Technology 1 or 2, wherein a first external cooling device is connected to at least one of the connection ports, and the first external cooling device comprises a cascade heat exchanger connected to the connection port, and a cooling unit connected to the cascade heat exchanger, the cooling unit including an auxiliary compressor, a controller capable of controlling cooling capacity, and a throttling mechanism. With this configuration, the first external cooling device supercools the refrigerant, and the cooling capacity of the indoor heat exchanger or the chilled heat exchanger can be changed or the overall cooling capacity of the indoor heat exchanger and the chilled heat exchanger can be changed depending on where the first external cooling device is connected, thereby increasing the flexibility in selecting the load for each heat exchanger and broadening the range of use of the refrigeration system.

[0071] (Technology 4) The refrigeration system according to Technology 1 or 2, wherein a second external cooling device is connected to at least one of the connection ports, and the second external cooling device comprises a refrigerant / cooling medium heat exchanger connected to the connection port, and a water-cooled cooling unit connected to the refrigerant / cooling medium heat exchanger, the water-cooled cooling unit including a tank for storing the cooling medium, a pump for circulating the cooling medium, and a flow control valve. With this configuration, the refrigerant is subcooled by the second external cooling device, and the cooling capacity of the indoor heat exchanger or the chilled heat exchanger can be changed or the overall cooling capacity of the indoor heat exchanger and the chilled heat exchanger can be changed depending on where the second external cooling device is connected, which increases the flexibility in selecting the load for each heat exchanger and broadens the range of use of the refrigeration system.

[0072] (Technology 5) The refrigeration system according to Technology 1 or 2, wherein a third external cooling device is connected to at least one of the connection ports, the third external cooling device comprising: a refrigerant / cooling medium heat exchanger connected to the connection port; and a water-cooled cooling unit connected to the refrigerant / cooling medium heat exchanger, the water-cooled cooling unit including a tank for storing the cooling medium, a pump for circulating the cooling medium, an auxiliary controller capable of controlling the cooling capacity, and a flow control valve, and the auxiliary controller is connected to the cooling unit including an auxiliary compressor, a controller capable of controlling the cooling capacity, and an expansion valve. With this configuration, the refrigerant is subcooled by the third external cooling device, and the cooling capacity of the indoor heat exchanger or the chilled heat exchanger can be changed or the overall cooling capacity of the indoor heat exchanger and the chilled heat exchanger can be changed depending on where the third external cooling device is connected, thereby increasing the flexibility in selecting the load for each heat exchanger and broadening the range of use of the refrigeration system.

[0073] (Technology 6) A refrigeration system according to any one of Technologies 1 to 5, further comprising a throttling mechanism between the heat source-side heat exchanger and the gas-liquid separator, a first service valve disposed upstream of the throttling mechanism, a second service valve disposed downstream of the throttling mechanism, a fourth service valve disposed in a pipe connecting the second user-side heat exchanger and a suction side of a low-stage compressor, a refrigerant quantity adjustment tank for storing refrigerant connected between the first service valve, the second service valve, and the fourth service valve, and the refrigerant quantity adjustment tank can be retrofitted to the first service valve, the second service valve, and the fourth service valve. With this configuration, when the cooling capacity of the refrigeration system increases or decreases, the refrigerant can be stored in or discharged from the refrigerant quantity adjustment tank in accordance with the increase or decrease in cooling capacity, thereby absorbing any excess or shortage of refrigerant.

[0074] (Technology 7) A refrigeration system according to Technology 6, further comprising: a piping connected to the first service valve; a first electromagnetic on-off valve that adjusts the flow rate; a piping connected to the second service valve; a second electromagnetic on-off valve 96 that adjusts the flow rate; and a throttling mechanism that depressurizes the refrigerant between the second electromagnetic on-off valve and the fourth service valve. With this configuration, when flow rate adjustment is not required, the first electromagnetic on-off valve and the second electromagnetic on-off valve are closed and only the throttling mechanism connected to the first service valve is opened, thereby maintaining the internal pressure of the refrigerant quantity adjustment tank at a high pressure and suppressing liquid seal.

[0075] (Technology 8) A refrigeration system including a refrigeration circuit connecting a plurality of compressors, a heat source-side heat exchanger, a plurality of user-side heat exchangers, and a gas-liquid separator, wherein the plurality of compressors are composed of low-stage compressors and high-stage compressors, the plurality of user-side heat exchangers are composed of a first user-side heat exchanger and a second user-side heat exchanger having a refrigerant evaporation temperature lower than that of the first user-side heat exchanger, the first user-side heat exchanger is connected to the high-stage compressor, and the second user-side heat exchanger is connected to the low-stage compressor, the refrigeration circuit includes a gas vent pipe that sends gas refrigerant separated by the gas-liquid separator to the high-stage compressor, and a flow rate adjustment mechanism that adjusts the flow rate of the gas refrigerant flowing through the gas vent pipe, the gas vent pipe having a plurality of connection ports between the flow rate adjustment mechanism and the gas-liquid separator that can be connected to an external cooling device that cools the refrigerant. With this configuration, in the refrigeration system, the gas refrigerant passing through the gas vent pipe is cooled. Therefore, in the refrigeration system, the load on the high-stage compressor can be reduced, and an increase in the discharge gas temperature can be suppressed.

[0076] The present disclosure can be suitably used as a refrigeration system that uses carbon dioxide (R744), a natural refrigerant with high environmental friendliness, and can improve the efficiency of the air conditioning temperature range and the efficiency of the entire system.

[0077] REFRIGERATION SYSTEM 10 OUTDOOR UNIT 11 LOW-STAGE COMPRESSOR 12 HIGH-STAGE COMPRESSOR 13 ACCUMULATOR 14 OIL SEPARATOR 15 OUTDOOR HEAT EXCHANGER (Heat Source Side Heat Exchanger) 16 GAS-LIQUID SEPARATOR 17 THROTTLE MECHANISM 20 INDOOR UNIT 21 INDOOR EXPANSION MECHANISM 22 INDOOR HEAT EXCHANGER (FIRST USE-SIDE HEAT EXCHANGER) 30 COOLING EQUIPMENT 31 COOLING EQUIPMENT HEAT EXCHANGER (SECOND USE-SIDE HEAT EXCHANGER) 50 FIRST SWITCHING MECHANISM 54 SECOND SWITCHING MECHANISM 60 GAS REFRIGERANTE RETURN PIPE 61 GAS REFRIGERANTE FLOW CONTROL VALVE 92 EXPANSION MECHANISM 94 FIRST SOLICITE ON / OFF VALVE 96 SECOND SOLICITE ON / OFF VALVE 97 CAPILLARY TUBE (THROTTLE MECHANISM) 101 FIRST PIPING AREA 102 SECOND PIPING AREA 103 THIRD PIPING AREA 110, 120 CONNECTION PORT 200 EXTERNAL COOLING DEVICE 201 First external cooling device 202 Second external cooling device 203 Third external cooling device 204 Refrigerant amount adjustment tank 235 First service valve 236 Second service valve 237 Third service valve 238 Fourth service valve 243 Cascade heat exchanger 244 Auxiliary compressor 245 Heat exchanger (controller) 246 Expansion valve 247, 255, 270 Cooling unit 251, 261 Refrigerant / cooling medium heat exchanger 252, 262 Tank 253, 263 Pump 254, 264 Flow rate adjustment valve 255, 265 Cooling unit 266 Auxiliary heat exchanger (auxiliary controller) 267 Auxiliary compressor 268 Heat exchanger (controller) 269 Expansion valve A to D, G Connections E, F, H, I Connection ports

Claims

1. A refrigeration system comprising a refrigeration circuit connecting a plurality of compressors, a heat source side heat exchanger, a plurality of user side heat exchangers, and a gas-liquid separator, wherein the plurality of compressors are composed of a low stage compressor and a high stage compressor, and the plurality of user side heat exchangers are composed of a first user side heat exchanger and a second user side heat exchanger having a lower evaporation temperature of a refrigerant than that of the first user side heat exchanger, the first user side heat exchanger is connected to the high stage compressor, and the second user side heat exchanger is connected to the low stage compressor, and the refrigeration circuit is provided with a connection port capable of connecting an external cooling device that supercools a refrigerant, at least either between the gas-liquid separator and the first user side heat exchanger, or between the gas-liquid separator and the second user side heat exchanger.

2. The refrigeration system according to claim 1, wherein the refrigeration circuit uses carbon dioxide as a natural refrigerant.

3. A refrigeration system as described in claim 1 or 2, wherein a first external cooling device is connected to at least one of the connection ports, the first external cooling device comprising: a cascade heat exchanger connected to the connection ports; and a cooling unit connected to the cascade heat exchanger, the cooling unit including an auxiliary compressor, a controller capable of controlling cooling capacity, and a throttling mechanism.

4. A refrigeration system as described in claim 1 or 2, wherein a second external cooling device is connected to at least one of the connection ports, the second external cooling device comprising: a refrigerant / cooling medium heat exchanger connected to the connection ports; and a water-cooled cooling unit connected to the refrigerant / cooling medium heat exchanger, the water-cooled cooling unit including a tank for storing the cooling medium, a pump for circulating the cooling medium, and a flow control valve.

5. A refrigeration system as described in claim 1 or 2, wherein a third external cooling device is connected to at least one of the connection ports, the third external cooling device comprising: a refrigerant / cooling medium heat exchanger connected to the connection ports; and a water-cooled cooling unit connected to the refrigerant / cooling medium heat exchanger, the water-cooled cooling unit including a tank for storing the cooling medium, a pump for circulating the cooling medium, an auxiliary controller capable of controlling the cooling capacity, and a flow control valve, and the cooling unit including an auxiliary compressor, a controller capable of controlling the cooling capacity, and an expansion valve is connected to the auxiliary controller.

6. A refrigeration system as described in claim 1 or 2, further comprising a throttling mechanism between the heat source side heat exchanger and the gas-liquid separator, a first service valve being arranged upstream of the throttling mechanism, a second service valve being arranged downstream of the throttling mechanism, a fourth service valve being arranged in a pipe connecting the second user side heat exchanger and the suction side of a low stage compressor, a refrigerant amount adjustment tank for storing refrigerant being connected between the first service valve, the second service valve and the fourth service valve, and the refrigerant amount adjustment tank being capable of being retrofitted and connected to the first service valve, the second service valve and the fourth service valve.

7. The refrigeration system of claim 6, further comprising: a throttling mechanism for adjusting the flow rate in a pipe connected to the first service valve; a first solenoid on-off valve for adjusting the flow rate in a pipe connected to the second service valve; a second solenoid on-off valve for adjusting the flow rate in a pipe connected to the fourth service valve; and a throttling mechanism for reducing the pressure of the refrigerant between the second solenoid on-off valve and the fourth service valve.

8. A refrigeration system comprising a refrigeration circuit connecting a plurality of compressors, a heat source side heat exchanger, a plurality of user side heat exchangers, and a gas-liquid separator, wherein the plurality of compressors are composed of a low stage compressor and a high stage compressor, and the plurality of user side heat exchangers are composed of a first user side heat exchanger and a second user side heat exchanger having a lower evaporation temperature of a refrigerant than that of the first user side heat exchanger, the first user side heat exchanger is connected to the high stage compressor, and the second user side heat exchanger is connected to the low stage compressor, the refrigeration circuit comprises: a gas vent pipe that sends gas refrigerant separated in the gas-liquid separator to the high stage compressor, and a flow rate adjustment mechanism that adjusts the flow rate of the gas refrigerant flowing through the gas vent pipe, and the gas vent pipe has a plurality of connection ports between the flow rate adjustment mechanism and the gas-liquid separator to which an external cooling device that cools the refrigerant can be connected.

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