Refrigeration system

Abstract

Provided is a refrigeration system that can improve energy efficiency.　A refrigeration system 1 comprises a refrigeration circuit 2 provided with a plurality of compressors, a heat source-side heat exchanger, a plurality of usage-side heat exchangers, and a gas-liquid separator 16 that separates a refrigerant cooled by at least one of the plurality of usage-side heat exchangers into a liquid refrigerant and a gas refrigerant. The plurality of compressors include a low-stage compressor 11 and a high-stage compressor 12, and the plurality of usage-side heat exchangers include a first usage-side heat exchanger and a second usage-side heat exchanger having a lower evaporation temperature of the refrigerant than that of the first usage-side heat exchanger. The high-stage compressor 12 is provided with a high-stage injection port 19 that supplies the refrigerant to a compression mechanism of the high-stage compressor 12 via a route different from that of an intake unit that takes in the refrigerant.

Description

Refrigeration system

[0001] The present invention relates to refrigeration systems.

[0002] Patent Document 1 discloses a refrigeration system including a low-stage compressor, a high-stage compressor, multiple user-side heat exchangers, and a heat-source-side heat exchanger shared with the user-side heat exchangers in a single refrigeration circuit, with each user-side heat exchanger operating at a different evaporation temperature range. A known example of such a refrigeration system includes a gas-liquid separator. In this refrigeration system, refrigerant discharged from the compressor flows through the gas-liquid separator to the user-side heat exchangers, thereby improving refrigeration capacity. Another example of a refrigeration system including a gas-liquid separator is one in which refrigerant is drawn into the compressor from multiple user-side heat exchangers with different evaporation temperature ranges.

[0003] Japanese Patent Application Laid-Open No. 2022-039365

[0004] The present disclosure provides a refrigeration system that can improve energy efficiency.

[0005] This specification includes the entire contents of Japanese Patent Application No. 2024-148161 filed on August 30, 2024. The refrigeration system of the present disclosure includes a refrigeration circuit provided with a plurality of compressors, a heat source-side heat exchanger, a plurality of user-side heat exchangers, and a gas-liquid separator that separates a refrigerant cooled by at least one of the plurality of user-side heat exchangers into a liquid refrigerant and a gas refrigerant, 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 refrigerant evaporation temperature lower than that of the first user-side heat exchanger, and the high-stage compressor is provided with a high-stage injection port that supplies refrigerant to a compression mechanism of the high-stage compressor via a path different from a suction port that draws in refrigerant.

[0006] According to the present disclosure, it is possible to improve energy efficiency.

[0007] 1 is a circuit diagram showing a refrigeration circuit of a refrigeration system according to embodiment 1; FIG. 2 is a block diagram of the refrigeration system; FIG. 3 is a p-h diagram showing the state of refrigerant in the refrigeration circuit; FIG. 4 is a p-h diagram showing the state of refrigerant in the refrigeration circuit; FIG. 5 is a p-h diagram showing the state of refrigerant in the refrigeration circuit;

[0008] At the time the inventors conceived the present disclosure, a refrigeration system existed that included a low-stage compressor, a high-stage compressor, multiple user-side heat exchangers, and a heat-source-side heat exchanger shared with the user-side heat exchangers in a single refrigeration circuit, with each user-side heat exchanger operating at a different evaporation temperature range. In this refrigeration system, refrigerant flowing out of the user-side heat exchanger with a lower evaporation temperature range is drawn into the low-stage compressor, and refrigerant flowing out of the user-side heat exchanger with a higher evaporation temperature range is drawn into the high-stage compressor. This refrigeration system, for example, air-conditions a conditioned space and cools the interior of a refrigeration unit. Known refrigeration systems include a gas-liquid separator. In this refrigeration system, refrigerant discharged from the compressor flows through the gas-liquid separator to the user-side heat exchangers, thereby improving refrigeration capacity.

[0009] In the above-described refrigeration system, when the evaporating temperature zones of the multiple user-side heat exchangers are different, in order for all the user-side heat exchangers to reach their respective target temperatures, they must be operated so that the evaporating temperature is set to the lowest of the target temperatures. The inventors discovered that this refrigeration system may have a problem of reduced energy efficiency, and the subject of the present disclosure was formed to solve this problem. Therefore, the present disclosure provides a refrigeration system that includes a refrigeration circuit with a simple configuration and can achieve improved energy efficiency.

[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 Refrigeration System] FIG. 1 is a circuit diagram showing a refrigeration system 1 in Embodiment 1. In FIG. 1, for ease of explanation, an open-close device is shown in white, and a closed-close device and an expansion mechanism 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 the subsequent circuit diagrams, the open-close device and pipes are shown in the same manner as in FIG. 1. As shown in FIG. 1, the refrigeration system 1 includes an outdoor unit 10, an indoor unit 20, and a cooling device 30. These are connected to each other by refrigerant pipes to form a refrigeration circuit 2 that functions as a flow path for the refrigerant. In this embodiment, the refrigeration circuit 2 uses, for example, refrigerant carbon dioxide (R744), a natural refrigerant that is non-flammable and non-toxic.

[0012] The indoor unit 20 includes an indoor heat exchanger 22, which is a user-side heat exchanger. The indoor unit 20 conditions the interior of a store, which is a space to be conditioned, based on a temperature setting set by a user in a store such as a supermarket. The refrigeration equipment 30 includes a refrigeration heat exchanger 32, which is a user-side heat exchanger. The refrigeration equipment 30 cools the interior of a refrigerated showcase or a freezer showcase, which serves as refrigerated storage equipment installed in the store, based on a temperature setting set by a user.

[0013] The outdoor unit 10 functions as a heat source device. The outdoor unit 10 is formed by sequentially connecting multiple compressors, a first switching mechanism 50, an outdoor heat exchanger 15, a second switching mechanism 54, and a gas-liquid separator 16. The outdoor heat exchanger 15 corresponds to the "heat source-side heat exchanger" in this disclosure.

[0014] In this embodiment, the outdoor unit 10 is equipped with a two-stage compressor including a low-stage compressor 11 and two high-stage compressors 12, 12. The two high-stage compressors 12, 12 are both connected in series to the low-stage compressor 11. The two high-stage compressors 12, 12 are connected in parallel to each other downstream of the low-stage compressor 11. Each of the compressors is, for example, a rotary compressor in which a scroll-type compression mechanism is driven by a motor.

[0015] The compressor in this embodiment has a compression mechanism that includes a fixed scroll and an orbiting scroll combined with the fixed scroll. The compressor draws refrigerant into the compression mechanism through a suction port, and compresses the drawn refrigerant as the orbiting scroll oscillates together with the crankshaft. The compressed refrigerant is discharged from the compressor through a discharge port provided in each compressor.

[0016] The low-stage compressor 11 has an inlet 7 and a discharge port 6, and each of the two high-stage compressors 12 has an inlet 9 and a discharge port 8. The inlets 7 and 9 are both suction portions that draw in a refrigerant, and the discharge ports 6 and 8 are both discharge portions that discharge the refrigerant. The low-stage compressor 11 has a low-stage injection port 17, and each of the two high-stage compressors 12 has a high-stage injection port 19. The low-stage injection ports 17 and 19 are both refrigerant supply portions that supply refrigerant to the compression mechanisms of the low-stage compressor 11 and the high-stage compressor 12 via a route different from the inlets 7 and 9.

[0017] The low-stage injection ports 17, 19 are both tubular portions that communicate the inside and outside of the low-stage compressor 11 and the high-stage compressor 12. In the low-stage compressor 11, refrigerant is supplied through the low-stage injection port 17 during the compression process, thereby cooling the low-stage compressor 11 and the refrigerant compressed in the low-stage compressor 11. In each of the two high-stage compressors 12, refrigerant is supplied through the high-stage injection port 19 during the compression process, thereby cooling the high-stage compressor 12 and the refrigerant compressed in the high-stage compressor 12.

[0018] An accumulator 13 is disposed between the low-stage compressor 11 and the high-stage compressor 12. The accumulator 13 is a flow divider that distributes oil flowing out from the oil separator 14 approximately evenly to each of the high-stage compressors 12. The oil separator 14 is connected to the discharge port 8 of the high-stage compressor 12. A first switching mechanism 50 is connected to the oil separator 14. Therefore, the first switching mechanism 50 is connected to the discharge pipe of the high-stage compressor 12 via the oil separator 14.

[0019] The first switching mechanism 50 includes a pipe 40 that connects the oil separator 14 and the outdoor heat exchanger 15. A first cooling valve 51, which is an opening / closing device that opens and closes the pipe 40, is provided in the pipe 40 at a location between the high-stage compressor 12 and the outdoor heat exchanger 15.

[0020] In the piping 40, one end of a first heating piping 41 is connected between the oil separator 14 and the first cooling valve 51. The first heating piping 41 is provided with a first heating valve 52, which is an opening and closing device that opens and closes the first heating piping 41.

[0021] The other end of the first heating pipe 41 is connected to a pipe 71 that connects the indoor heat exchanger 22 of the indoor unit 20 and the suction port 9 of the high-stage compressor 12. As a result, the discharge port 8 is connected to the indoor heat exchanger 22 via the first heating pipe 41. An on-off valve 23, which is an on-off device that opens and closes the pipe 71, is provided in the pipe 71 between the point where the other end of the first heating pipe 41 is connected and the accumulator 13.

[0022] In the piping 40, one end of a first outdoor return piping 42 is connected between the first cooling valve 51 and the outdoor heat exchanger 15. The other end of the first outdoor return piping 42 is connected between the cooling heat exchanger 32 of the refrigeration equipment 30 and the suction port 7 of the low-stage compressor 11. The first outdoor return piping 42 is provided with an outdoor refrigerant return valve 53, which is an opening and closing device that opens and closes the first outdoor return piping 42.

[0023] A cooling-unit outlet pressure adjustment mechanism 33, which is an opening / closing device that can change its opening degree from fully closed to fully open, is provided in the piping 72 between the point where the other end of the first outdoor return piping 42 is connected and the cooling-unit heat exchanger 32. By adjusting its opening degree, the cooling-unit outlet pressure adjustment mechanism 33 functions as a throttle valve that adjusts the evaporation pressure of the refrigerant flowing through the cooling-unit heat exchanger 32 and controls the evaporation temperature to an optimum value.

[0024] In this way, the first switching mechanism 50 is connected to the outdoor heat exchanger 15, the indoor heat exchanger 22, the refrigeration heat exchanger 32, and the low-stage compressor 11. The first switching mechanism 50 switches the refrigerant flow path in the refrigeration circuit 2 by opening and closing the first cooling valve 51, the first heating valve 52, and the outdoor refrigerant return valve 53, and causes the refrigerant discharged from the high-stage compressor 12 to flow to either the outdoor heat exchanger 15 or the indoor heat exchanger 22.

[0025] In this embodiment, the first cooling valve 51, the first heating valve 52, and the outdoor refrigerant return valve 53 are electrically operated on-off valves that are opened and closed by an actuator or the like. Therefore, the first switching mechanism 50 can switch the refrigerant flow path in the refrigeration circuit 2 and switch between operations related to air conditioning and cooling inside the showcase without stopping the low-stage compressor 11 and the high-stage compressor 12. Note that in the first switching mechanism 50, the first cooling valve 51, the first heating valve 52, and the outdoor refrigerant return valve 53 may be on-off devices whose opening degree can be adjusted from fully closed to fully open.

[0026] A second switching mechanism 54 is provided in the piping 40 on the opposite side of the first switching mechanism 50 across the outdoor heat exchanger 15. The second switching mechanism 54 interconnects the outdoor heat exchanger 15, the indoor heat exchanger 22, the chilled heat exchanger 32, and the gas-liquid separator 16. The second switching mechanism 54 is a mechanism that switches the refrigerant flow to one of a plurality of flow paths that interconnect the outdoor heat exchanger 15, the indoor heat exchanger 22, the chilled heat exchanger 32, and the gas-liquid separator 16.

[0027] The second switching mechanism 54 is formed by connecting the ends of the first to fourth pipes 73, 74, 75, and 76 in an annular shape at connection points A, B, C, and D. Check valves 59 are disposed in the first pipe 73, the third pipe 75, and the fourth pipe 76. The check valve 59 prevents backflow of the first pipe 73 from connection point D to connection point A, allowing the refrigerant to flow from connection point A to connection point D. The check valve 59 prevents backflow of the third pipe 75 from connection point C to connection point B, allowing the refrigerant to flow from connection point B to connection point C. The check valve 59 prevents backflow of the fourth pipe 76 from connection point D to connection point C, allowing the refrigerant to flow from connection point C to connection point D. In this way, the second switching mechanism 54 is formed in the shape of a bridge circuit provided with check valves. In this embodiment, the check valve 59 is a self-acting automatic valve that opens and closes depending on the flow of refrigerant.

[0028] A refrigerant return expansion mechanism 58, which is a flow control valve whose opening can be changed from fully closed to fully open, is disposed in the second pipe 74. By adjusting its opening, the refrigerant return expansion mechanism 58 controls the flow rate of the refrigerant flowing through the second pipe 74 and also functions as a throttle valve that can change the pressure of the refrigerant.

[0029] A piping 40 provided with the outdoor heat exchanger 15 is connected to a connection part A between the check valve 59 provided in the first piping 73 and the refrigerant return expansion mechanism 58. A piping part B between the refrigerant return expansion mechanism 58 and the check valve 59 provided in the third piping 75 is connected to a midpoint of a piping 77 connecting the gas-liquid separator 16 and the chilled heat exchanger 32. A chilled inlet expansion mechanism 31, which is a throttle valve, is provided in the piping 77 between the point where connection part B is connected and the chilled heat exchanger 32.

[0030] A connection C between the check valve 59 provided in the third pipe 75 and the check valve 59 provided in the fourth pipe 76 is connected to the indoor heat exchanger 22 via a pipe 78. An indoor expansion mechanism 21 of the indoor unit 20 is provided in the pipe 78 between one end connected to the connection C and the indoor heat exchanger 22. The indoor expansion mechanism 21 functions as a throttle valve that can change the pressure of the refrigerant flowing through the pipe 78 by adjusting its opening degree.

[0031] A connection D between the check valve 59 provided in the fourth pipe 76 and the check valve 59 provided in the first pipe 73 is connected to the gas-liquid separator 16 via a pipe 79. A throttling mechanism 63 is disposed in the pipe 79. The throttling mechanism 63 functions as a throttling valve that can change the pressure and flow rate of the refrigerant flowing through the second pipe 74 by adjusting its opening degree. The pressure of the refrigerant flowing from the second switching mechanism 54 to the gas-liquid separator 16 is adjusted by the throttling mechanism 63. When the refrigeration system 1 is operating, the refrigerant flows into the gas-liquid separator 16 from the pipe 79, which is the inlet pipe, and flows out from the pipe 77, which is the outlet pipe.

[0032] One end of an injection pipe 90 is connected to a midpoint of the pipe 77. The injection pipe 90 is connected to the pipe 77 between the connection part B and the cold-set heat exchanger 32. The other end of the injection pipe 90 is connected to the low-stage injection port 17 of the low-stage compressor 11.

[0033] As a result, a refrigerant having a pressure higher than the pressure of the refrigerant sucked into the low-stage compressor 11 and lower than the pressure of the refrigerant discharged from the low-stage compressor 11 is supplied to the low-stage compressor 11 via the low-stage injection port 17. Therefore, the refrigerant can be supplied to the low-stage compressor 11 via the low-stage injection port 17.

[0034] A control valve 92 is provided in the middle of the injection pipe 90. The control valve 92 is an opening / closing device that can change its opening degree from fully closed to fully open. In the refrigeration system 1, the flow rate of the refrigerant flowing through the injection pipe 90 is adjusted by adjusting the opening degree of the control valve 92.

[0035] One end of an injection pipe 94 is connected to a midpoint of the pipe 79. The injection pipe 94 is connected to the pipe 79 between the connection part D and the throttle mechanism 63. The other end of the injection pipe 94 branches into two and is connected to the high-stage injection ports 19 provided in each of the high-stage compressors 12.

[0036] As a result, a refrigerant having a pressure higher than the pressure of the refrigerant sucked into the high-stage compressor 12 and lower than the pressure of the refrigerant discharged from the high-stage compressor 12 is supplied to the high-stage compressor 12 via the high-stage injection port 19. Therefore, the refrigerant can be supplied to the high-stage compressor 12 via the high-stage injection port 19.

[0037] In the refrigeration system 1, during cooling operation, high-pressure refrigerant cooled in the outdoor heat exchanger 15 is supplied to the high-stage compressor 12 via the injection pipe 94, and during heating operation, high-pressure refrigerant cooled in the indoor heat exchanger 22 is supplied to the high-stage compressor 12. The high-pressure refrigerant supplied to the high-stage compressor 12 via the injection pipe 94 evaporates during the compression process of the high-stage compressor 12. This reduces the temperature of the refrigerant discharged in a gaseous state from the high-stage compressor 12, thereby improving volumetric efficiency.

[0038] In the refrigeration system 1, the flow of refrigerant differs between cooling operation and heating operation. In the refrigeration system 1, in both cooling operation and heating operation, high-pressure liquid refrigerant is supplied to each compression process of the low-stage compressor 11 and the high-stage compressor 12 via a path different from the suction port 9, and the temperature of the gas refrigerant discharged from each of these compressors can be appropriately controlled. Therefore, in the refrigeration system 1, it is possible to improve volumetric efficiency in both cooling operation and heating operation.

[0039] A control valve 96 is provided midway through the injection pipe 94. The control valve 96 is an opening / closing device whose opening degree can be changed from fully closed to fully open. In the refrigeration system 1, adjusting the opening degree of the control valve 96 adjusts the flow rate of the refrigerant flowing through the injection pipe 94 and also functions as a throttling mechanism that adjusts the pressure of the refrigerant. The opening degree of the control valve 96 is adjusted so that the refrigerant flowing through the injection pipe 94 reaches a pressure at which it can evaporate in the compression process of the high-stage compressor 12. The injection pipes 90, 94 correspond to the "refrigerant supply pipe" in this disclosure.

[0040] Next, we will explain the user-side heat exchanger provided in the refrigeration system 1. When the indoor unit 20 performs cooling operation, the indoor heat exchanger 22 functions as an evaporator. During air conditioning operation in the refrigeration system 1, the temperature of the blown air is determined based on the difference between the set temperature and the intake air temperature (room temperature), and the flow rate of the refrigerant and the evaporation temperature are controlled to achieve that temperature. The evaporation temperature range of the indoor heat exchanger 22 is, for example, 3°C to 6°C.

[0041] The refrigeration heat exchanger 32 functions as an evaporator, and the evaporation temperature thereof is determined by the opening degree of the refrigeration inlet-side expansion mechanism 31. In this embodiment, the evaporation temperature of the refrigeration heat exchanger 32 is determined according to the internal temperature set in the refrigeration equipment 30. The evaporation temperature range of the refrigeration heat exchanger 32 is, for example, from −40° C. to 0° C.

[0042] In this way, two use-side heat exchangers with different evaporation temperature ranges are provided in the refrigeration system 1. Of these two use-side heat exchangers with different evaporation temperature ranges, the indoor heat exchanger 22 is connected to the inlet side of the high-stage compressor 12, and the cooling heat exchanger 32, which has a lower evaporation temperature range than the indoor heat exchanger 22, is connected to the inlet side of the low-stage compressor 11. The indoor heat exchanger 22 corresponds to the "first use-side heat exchanger" in the present disclosure, and the cooling heat exchanger 32 corresponds to the "first use-side heat exchanger" in the present disclosure.

[0043] Next, the gas-liquid separator 16 will be described. The gas-liquid separator 16 is a flash tank that separates the two-phase refrigerant flowing thereinto into a low-density refrigerant and a high-density refrigerant. In this embodiment, when the refrigeration system 1 performs various operations, the refrigerant flows into the gas-liquid separator 16 through the second switching mechanism 54, with the flow rate controlled by the throttling mechanism 63. The gas-liquid separator 16 extracts gas refrigerant from the flowing refrigerant, thereby obtaining liquid refrigerant corresponding to the amount of extracted gas refrigerant. As a result, the refrigerant inside the gas-liquid separator 16 is in a gas-liquid two-phase state. By providing the second switching mechanism 54, the refrigeration system 1 can, with a simple circuit configuration, allow the refrigerant discharged from the high-stage compressor 12 to flow into the gas-liquid separator 16 through the throttling mechanism 63, regardless of whether the refrigeration system 1 is performing cooling operation or heating operation.

[0044] 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 rate control valve 61 is connected to the gas refrigerant return pipe 60. This gas refrigerant flow rate control valve 61 is an opening / closing device that can change its opening degree from fully closed to fully open. In the refrigeration system 1, the flow rate of gas refrigerant flowing through the gas refrigerant return pipe 60 is adjusted by the opening degree of the gas refrigerant flow rate control valve 61.

[0045] 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, flows into the accumulator 13, and is returned to the suction port 9 of the high-stage compressor 12. In this way, in the gas-liquid separator 16, a predetermined amount of gas refrigerant is extracted according to the aperture of the gas refrigerant flow control valve 61, thereby reducing the pressure and lowering the internal temperature through heat exchange, and producing liquid refrigerant at a predetermined temperature. Therefore, in the refrigeration system 1, the gas-liquid separator 16 functions as a heat exchanger that cools the liquid refrigerant, thereby increasing the refrigeration effect of the refrigeration system 1 and enabling higher efficiency.

[0046] Additionally, in the refrigeration system 1, a pressure difference is generated before and after the indoor expansion mechanism 21 by controlling the aperture of the gas refrigerant flow control valve 61 and adjusting the amount of gas refrigerant returning. This makes it possible to generate a refrigerant pressure difference between the inlet and outlet of the indoor unit 20 in the refrigeration circuit 2 in the refrigeration system 1. This prevents refrigerant flow from stagnating in the refrigeration system 1, particularly during cooling operation. Furthermore, in the refrigeration system 1, in the indoor heat exchanger 22 where the evaporation temperature of the refrigerant is high, it is possible to 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.

[0047] An internal heat exchanger 64 is provided midway between the gas refrigerant return pipe 60 and the pipe 77. The internal heat exchanger 64 is an economizer heat exchanger. This internal heat exchanger 64 is disposed in the pipe 77 between the gas-liquid separator 16 and connection part B, and is disposed in the gas refrigerant return pipe 60 between the gas refrigerant flow rate control valve 61 and the accumulator 13. The internal heat exchanger 64 houses the pipe 77 and the gas refrigerant return pipe 60 at the above-mentioned position, and exchanges heat between the liquid refrigerant flowing through the pipe 77 and the gas refrigerant flowing through the gas refrigerant return pipe 60.

[0048] As a result, in the refrigeration system 1, the liquid refrigerant is cooled by the gas refrigerant in the internal heat exchanger 64. The liquid refrigerant is then more reliably brought into a subcooled state, and the degree of subcooling increases. Therefore, even if the temperature of the liquid refrigerant in the gas-liquid separator 16 does not decrease to the saturation temperature in the gas-liquid separator 16, the liquid refrigerant is cooled in the internal heat exchanger 64, and the temperature is reduced to below the saturation temperature. In the refrigeration system 1, the cooled refrigerant flows through the third pipe 75, the pipe 77, and the injection pipe 90, thereby increasing the refrigeration effect of the indoor heat exchanger 22 and the chilled heat exchanger 32 and suppressing an increase in the discharge temperature of the low-stage compressor 11. In other words, the refrigeration system 1 ensures the degree of subcooling of the refrigerant flowing through the internal heat exchanger 64, thereby improving energy efficiency.

[0049] The refrigeration circuit 2 is provided with a connection pipe 66 that connects the pipe 77 between the internal heat exchanger 64 and the connection part B, and the gas refrigerant return pipe 60 between the gas refrigerant flow rate control valve 61 and the internal heat exchanger 64. A part of the liquid refrigerant that has exchanged heat with the gas refrigerant in the internal heat exchanger 64 flows through this connection pipe 66. The liquid refrigerant flowing through this connection pipe 66 is mixed with the gas refrigerant before it has exchanged heat with the liquid refrigerant in the internal heat exchanger 64.

[0050] In the internal heat exchanger 64, heat is exchanged between the liquid refrigerant and the mixed refrigerant of the liquid refrigerant and the gas refrigerant that has been cooled by heat exchange with the gas refrigerant in the internal heat exchanger 64. This makes it possible to increase the degree of subcooling of the liquid refrigerant in the internal heat exchanger 64. Therefore, the refrigeration system 1 can improve energy efficiency.

[0051] A liquid refrigerant flow control valve 65 is provided in the connecting pipe 66. The liquid refrigerant flow control valve 65 is an opening / closing device that can change its opening degree from fully closed to fully open. In the refrigeration system 1, the flow rate and pressure of the liquid refrigerant flowing through the connecting pipe 66 are adjusted by the opening degree of the liquid refrigerant flow control valve 65.

[0052] [1-1-2. Configuration Related to Control of Refrigeration System] Figure 2 is a block diagram of the refrigeration system 1. As shown in Figures 1 and 2, multiple refrigerant pressure sensors 140, 142, 144, 146, and 148 that detect refrigerant pressure are provided at predetermined locations in the refrigeration circuit 2. As shown in Figure 1, the refrigerant pressure sensor 140 is provided in the pipe 77 between the gas-liquid separator 16 and the internal heat exchanger 64. The refrigerant pressure sensor 142 is provided in the gas refrigerant return pipe 60 between the gas refrigerant flow control valve 61 and the accumulator 13. The refrigerant pressure sensor 144 is provided in the pipe 71 between the connection point of the pipe 71 and the first heating pipe 41 and the indoor heat exchanger 22. The refrigerant pressure sensor 146 is provided in the pipe 72 between the cooling outlet pressure adjustment mechanism 33 and the suction port 7 of the low-stage compressor 11. The refrigerant pressure sensor 148 is provided on a refrigerant pipe connecting the discharge port 8 and the oil separator 14 .

[0053] 1 and 2 , a plurality of refrigerant temperature sensors 81, 82, 83, 84, 85, 86, 87, 88, 89, and 91 for detecting the temperature of the refrigerant are provided at predetermined locations in the refrigeration circuit 2. As shown in FIG. 1 , two refrigerant temperature sensors 81 are provided on refrigerant pipes connected to the suction ports 9 of the high-stage compressors 12. Two refrigerant temperature sensors 82 are provided on refrigerant pipes connected to the discharge port 8 of the high-stage compressor 12. Refrigerant temperature sensor 83 is provided on pipe 72 connected to the suction port 7 of the low-stage compressor 11, between the cooling outlet pressure adjustment mechanism 33 and the suction port 7 of the low-stage compressor 11. Refrigerant temperature sensor 84 is provided on the refrigerant pipe connected to the discharge port 6.

[0054] The refrigerant temperature sensor 85 is provided at a location where the pipe 40 is connected to the outdoor heat exchanger 15. The refrigerant temperature sensor 86 is provided at a location where the second switching mechanism 54 and the outdoor heat exchanger 15 are connected.

[0055] The refrigerant temperature sensor 87 is provided in the refrigerant piping connected to the inlet side of the chilled-service heat exchanger 32, between the chilled-service inlet expansion mechanism 31 and the inlet side of the chilled-service heat exchanger 32. The refrigerant temperature sensor 88 is provided in the first outdoor return piping 42, between the chilled-service outlet pressure adjustment mechanism 33 and the outlet side of the chilled-service heat exchanger 32. The refrigerant temperature sensor 89 is provided in the piping 78, between the indoor expansion mechanism 21 and the indoor heat exchanger 22. The refrigerant temperature sensor 91 is provided in the piping 71, at a location adjacent to the connection between the piping 71 and the indoor heat exchanger 22.

[0056] 2, the refrigeration system 1 includes a space temperature sensor 27 that is disposed in the space to be conditioned by the indoor unit 20 and detects the temperature of the space to be conditioned. The refrigeration system 1 also includes an internal temperature sensor 37 that is disposed in the refrigerated showcase or freezer showcase included in the cooling equipment 30 and detects the internal temperature.

[0057] The outdoor unit 10, the indoor unit 20, and the cooling equipment 30 are provided with fans 18, 28, and 38, respectively. The fans 18, 28, and 38 send air to the outdoor heat exchanger 15, the indoor heat exchanger 22, and the cooling heat exchanger 32, respectively, to promote heat exchange between the air and the refrigerant flowing through the outdoor heat exchanger 15, the indoor heat exchanger 22, and the cooling heat exchanger 32.

[0058] The outdoor unit 10 includes an outdoor unit communication unit 106 that communicates with the indoor unit 20 via control wiring. The outdoor unit communication unit 106 is configured with communication hardware such as a connector and a communication circuit that conforms to a predetermined communication standard.

[0059] The outdoor unit 10 includes a control device 100. The outdoor unit I / F 105 includes communication hardware, such as connectors and communication circuits, that conform to a predetermined communication standard. The outdoor unit I / F 105 communicates with the low-stage compressor 11, the high-stage compressor 12, the blower 18, refrigerant pressure sensors 140, 142, 144, 146, and 148, refrigerant temperature sensors 81, 82, 83, 84, 85, and 86, and the outdoor unit communication unit 106. The outdoor unit I / F 105 communicates with the first cooling valve 51, the first heating valve 52, the outdoor refrigerant return valve 53, the throttling mechanism 63, the refrigerant return expansion mechanism 58, the on-off valve 23, the gas refrigerant flow control valve 61, and the liquid refrigerant flow control valve 65. Furthermore, the outdoor unit I / F 105 communicates with the indoor unit I / F 115 , the space temperature sensor 27 , and the cooling equipment I / F 125 .

[0060] The outdoor unit 10 includes a control device 100. The control device 100 includes an outdoor unit control unit 101 and a storage unit 103. The outdoor unit control unit 101 is a processor such as a CPU (Central Processing Unit) or an MPU (Micro Processing Unit) that operates based on a program stored in advance in the storage unit 103. The outdoor unit control unit 101 may be configured with a single processor or multiple processors. Note that a DSP (Digital Signal Processor) or the like may be used as the outdoor unit control unit 101. Furthermore, the outdoor unit control unit 101 may be a control circuit such as an LSI (large scale integration), an ASIC (application specific integrated circuit), or an FPGA (field-programming gate array).

[0061] The outdoor unit control unit 101 receives various signals from each part of the outdoor unit 10, the indoor unit 20, and the cooling equipment 30 via the outdoor unit I / F 105, and controls each part of the outdoor unit 10, the indoor unit 20, and the cooling equipment 30. The outdoor unit control unit 101 is connected to each part of the refrigeration system 1 by wire or wirelessly.

[0062] The outdoor unit control unit 101 reads the computer program stored in the storage unit 103 and operates in accordance with the read computer program, thereby functioning as an operation control unit 101a and a determination unit 101b.

[0063] The operation control unit 101a controls various devices such as the low-stage compressor 11, the high-stage compressor 12, and the opening and closing devices provided in the outdoor unit 10. The operation control unit 101a transmits control signals to the indoor unit 20 and the cooling equipment 30 via the outdoor unit I / F 105, and causes the refrigeration system 1 to operate in coordination with each other.

[0064] The operation control unit 101a can change the rotation speed of the compression mechanism of each compressor and can change the discharge pressure of the refrigerant. The operation control unit 101a can adjust the apertures of the gas refrigerant flow control valve 61, the throttling mechanism 63, the indoor expansion mechanism 21, the cooling-service inlet expansion mechanism 31, the cooling-service outlet pressure adjustment mechanism 33, the refrigerant return expansion mechanism 58, and the control valves 92 and 96. The operation control unit 101a can switch the opening and closing devices and the opening and closing valve 23 included in each of the first switching mechanism 50 and the second switching mechanism 54 between an open state and a closed state.

[0065] The determination unit 101b compares the detection values ​​of each of the refrigerant pressure sensors 140, 142, 144, 146, and 148 and the detection values ​​of each of the refrigerant temperature sensors 81, 82, 83, 84, 85, and 86 with data such as a reference temperature and a reference pressure included in the setting data 103a stored in the memory unit 103. The operation control unit 101a controls each part of the refrigeration system 1 based on the determination of the determination unit 101b.

[0066] The storage unit 103 includes a memory device such as a RAM (Random Access Memory) or a ROM (Read Only Memory), a fixed disk device such as a hard disk, or a portable storage device such as a flexible disk or an optical disk. The storage unit 103 also stores computer programs, databases, tables, etc. used for various operations of the refrigeration system 1. These computer programs, etc. may be installed into the storage unit 103 from a computer-readable portable recording medium using a known setup program, etc. The portable recording medium may be, for example, a semiconductor storage device such as a CD-ROM (compact disc read-only memory), a DVD-ROM (digital versatile disc read-only memory), a USB (universal serial bus) memory, or an SSD (solid state drive). The computer program may be installed from a predetermined server. The storage unit 103 may also have a volatile storage area and may constitute a work area for the outdoor unit control unit 101.

[0067] Setting data 103a is stored in the storage unit 103. The setting data 103a includes data on the set temperatures of the indoor units 20 and the cooling equipment 30. The setting data 103a includes data such as the rotation speed that is a specified value for each compressor, and a reference pressure value that is a specified value indicating the differential pressure at a specified location in the refrigeration circuit 2.

[0068] The setting data 103a includes data related to the operation of the refrigeration system 1. Specifically, the setting data 103a includes information on the opening / closing or opening degree of each of the opening / closing devices provided in the refrigeration circuit 2 when the system is operating. The outdoor unit control unit 101 controls each part of the refrigeration circuit 2 in accordance with the data related to the operation.

[0069] The control device 100 adjusts the openings of the control valves 92 and 96 so that the temperature difference between the temperature of the refrigerant discharged from each of the low-stage compressor 11 and the high-stage compressor 12 and the temperature of the refrigerant flowing out of the outdoor heat exchanger 15 becomes a predetermined value. The predetermined value is included in the setting data 103a.

[0070] The control device 100 acquires detection values ​​from refrigerant temperature sensors 82, 84 provided on the discharge sides of the low-stage compressor 11 and the high-stage compressor 12. Furthermore, the control device 100 acquires detection values ​​from a refrigerant temperature sensor 86 provided in the piping 40 between the outdoor heat exchanger 15 and the connection part A, thereby determining the temperatures of the refrigerant discharged from each of the low-stage compressor 11 and the high-stage compressor 12.

[0071] In the refrigeration system 1, the control device 100 adjusts the opening degree of the control valve 92 so as to satisfy the following equation (1): DT1-LT≦SH1 (1) In the above equation (1), DT1 is the temperature of the refrigerant discharged from the low-stage compressor 11. LT is the temperature of the refrigerant flowing out from the outdoor heat exchanger 15. SH1 is a predetermined value included in the setting data 103a.

[0072] In the refrigeration system 1, the control device 100 adjusts the opening degree of the control valve 96 so as to satisfy the following equation (2): DTh-LT≦SHh (2) In the above equation (1), DTh is the temperature of the refrigerant discharged from the high-stage compressor 12. SHh is a predetermined value included in the setting data 103a.

[0073] In this way, the control device 100 controls each part of the refrigeration system 1 so that the temperature difference between the refrigerant temperature flowing out from the outdoor heat exchanger 15 and the refrigerant temperature discharged from the low-stage compressor 11 or the high-stage compressor 12 is equal to or less than a predetermined value. As a result, the refrigeration system 1 can suppress an increase in the discharge refrigerant temperature of the low-stage compressor 11 or the high-stage compressor 12, suppress a high load, and suppress a decrease in the volumetric efficiency of the refrigerant.

[0074] The outdoor unit I / F 105 includes communication hardware such as a communication interface circuit and a connector that allows the outdoor unit 10 to communicate with each device via a cable or the like in accordance with a predetermined communication protocol. The outdoor unit I / F 105 sends data received from each device to the control device 100, and also transmits data received from the control device 100 to each device. The control device 100 corresponds to the "control unit" in this disclosure.

[0075] The indoor unit 20 includes an indoor unit control device 110 and an indoor unit I / F 115. The indoor unit control device 110 includes an indoor unit control section 111 and an indoor unit storage section 113.

[0076] The indoor unit control unit 111 is a processor such as a CPU or MPU, similar to the outdoor unit control unit 101. The indoor unit control unit 111 operates in accordance with a computer program stored in the indoor unit memory unit 113 to control various devices such as the blower 28 mounted in the indoor unit 20, and receives output signals from various sensors mounted in the indoor unit 20, such as the space temperature sensor 27. Similar to the memory unit 103, the indoor unit memory unit 113 has storage devices such as RAM and ROM, and stores computer programs and the like used for various operations of the indoor unit 20.

[0077] The indoor unit I / F 115 is equipped with communication hardware such as a communication interface circuit and connectors that allow the indoor unit 20 to communicate with each device, and sends data received from the space temperature sensor 27 and each device to the indoor unit control device 110, and also sends data received from the indoor unit control device 110 to each device.

[0078] The refrigeration equipment 30 includes a refrigeration equipment control device 120 and a refrigeration equipment I / F 125. The refrigeration equipment control device 120 includes a refrigeration equipment control unit 121 and a refrigeration equipment storage unit 123.

[0079] The refrigeration equipment control unit 121 is a processor such as a CPU or an MPU, similar to the outdoor unit control unit 101. The refrigeration equipment control unit 121 operates in accordance with a computer program stored in the refrigeration equipment storage unit 123 to control various devices such as the blower 38 mounted in the refrigeration equipment 30, and receives output signals from various sensors such as the internal temperature sensor 37 mounted in the refrigeration equipment 30. Similar to the storage unit 103, the refrigeration equipment storage unit 123 has a storage device such as a RAM or a ROM, and stores computer programs and the like used for various operations of the refrigeration equipment 30.

[0080] The refrigeration equipment I / F 125 is equipped with communication hardware such as a communication interface circuit and connectors that allow the refrigeration equipment 30 to communicate with each device, and sends data received from the internal temperature sensor 37 and each device to the refrigeration equipment control device 120, and also sends data received from the refrigeration equipment control device 120 to each device.

[0081] The operation control unit 101a and the determination unit 101b are not limited to being provided in the outdoor unit control unit 101, and may also be provided in the indoor unit control unit 111 or the refrigeration equipment control unit 121. For example, the operation control unit 101a and the determination unit 101b may be provided in a processor provided in another location in the refrigeration system 1. For example, the operation control unit 101a and the determination unit 101b may also be provided in a processor provided in a server device or the like provided outside the refrigeration system 1. Such a server device may be able to control each unit of the refrigeration system 1 via a network configured, for example, of a public line network, a dedicated line, other communication lines, and various communication facilities.

[0082] 1, when the refrigeration system 1 performs cooling operation, the outdoor heat exchanger 15 is used as a gas cooler or radiator, and the indoor heat exchanger 22 and the cooling heat exchanger 32 are used as evaporators. When performing cooling operation, in the first switching mechanism 50, the control device 100 opens the first cooling valve 51 and closes the remaining first heating valve 52 and the outdoor refrigerant return valve 53. In addition, in the second switching mechanism 54, the control device 100 closes the refrigerant return expansion mechanism 58.

[0083] [1-2-2. State of Refrigerant in Refrigeration Circuit] Fig. 3 is a p-h diagram showing the state of refrigerant in the refrigeration circuit 2. In Fig. 3, the vertical axis p represents pressure (MPa), and the horizontal axis h represents enthalpy (kJ / kg). When the refrigeration system 1 performs cooling operation, the refrigerant is located at point PA1 in Fig. 3 at the suction port 7 of the low-stage compressor 11. The refrigerant is refrigerant that has evaporated in the cooling heat exchanger 32, and is a gas refrigerant at point PA1. Hereinafter, for convenience of explanation, the pressure at point PA1 will be referred to as low-pressure pressure.

[0084] When low-pressure refrigerant is drawn into the low-stage compressor 11 and adiabatically compressed, the refrigerant reaches a state located at point PA2 in Fig. 3. For ease of explanation, the pressure at point PA2 will be referred to as medium pressure hereinafter. In this embodiment, the pressure difference between the pressure at point PA1 and the pressure at point PA2 is, for example, 1.0 MPa. This refrigerant is mixed with the refrigerant evaporated in the indoor heat exchanger 22 and the gas refrigerant flowing through the gas refrigerant return pipe 60. The temperature of these mixed refrigerants decreases while maintaining the medium pressure, and the refrigerant reaches a state located at point PA3 in Fig. 3.

[0085] When the refrigerant in the state of point PA3 is adiabatically compressed, the refrigerant reaches a state of point PA4 in Figure 3. For convenience of explanation, the pressure at point PA4 will be referred to as the high-pressure pressure below. When this refrigerant is discharged from high-stage compressor 12, heat is dissipated in outdoor heat exchanger 15 while the pressure is maintained at high pressure. As a result, the refrigerant reaches a state of point PA5 in Figure 3.

[0086] The refrigerant at point PA5 is decompressed by the throttle mechanism 63 to reach point PA6 in FIG. 3 . At point PA6, the refrigerant pressure is higher than the pressure at point PA2. Hereinafter, for convenience of explanation, the pressure at point PA6 will be referred to as the intermediate pressure. In this embodiment, the differential pressure between point PA6 and point PA2 is, for example, 0.5 MPa.

[0087] As described above, in the refrigeration system 1, in both the cooling operation and the heating operation, the low-pressure liquid refrigerant decompressed by the throttling mechanism 63 flows into the gas-liquid separator 16. This makes it possible to adjust the pressure of the refrigerant entering the gas-liquid separator 16 in the refrigeration system 1.

[0088] The refrigerant in a state located at point PA6 is separated into liquid refrigerant and gas refrigerant in the gas-liquid separator 16. Of these refrigerants, the gas refrigerant is discharged from the gas-liquid separator 16 via the gas refrigerant return pipe 60. As the gas refrigerant is separated and discharged from the gas-liquid separator 16, the liquid refrigerant is cooled to a state of point PA7 on the saturated liquid line, as shown in FIG.

[0089] As described above, the gas refrigerant return pipe 60 is connected to the suction port 9 of the high-stage compressor 12. The gas refrigerant is sucked by the high-stage compressor 12 through the gas refrigerant return pipe 60, and is discharged from the gas-liquid separator 16. As a result, in the refrigeration system 1, the liquid refrigerant stored in the gas-liquid separator 16 is cooled to a state of point PA7 on the saturated liquid line.

[0090] The refrigeration system 1 includes one low-stage compressor 11 and two high-stage compressors 12. Therefore, in the refrigeration system 1, the high-stage compressors 12 have a larger capacity than the low-stage compressors 11. By drawing gas refrigerant into these high-stage compressors 12, the refrigeration system 1 can cool the liquid refrigerant inside the gas-liquid separator 16 to a state of point PA7 on the saturated liquid line, even when the outside air temperature of the conditioned space or the cooling equipment 30 is high, such as in summer. In this way, the refrigeration system 1 can operate stably even when the ambient temperature of the user-side heat exchanger is high.

[0091] The liquid refrigerant exchanges heat with the gas refrigerant in the internal heat exchanger 64, and reaches a state located at point PA8 in Fig. 3. At point PA8, the liquid refrigerant is in a subcooled state. The gas refrigerant that has exchanged heat with the liquid refrigerant in the internal heat exchanger 64 reaches a state located at point PA11 in Fig. 3.

[0092] The liquid refrigerant flowing out from the internal heat exchanger 64 branches off at connection point B and flows to the indoor unit 20 and the cooling equipment 30. The liquid refrigerant flowing into the indoor unit 20 is decompressed by the indoor expansion mechanism 21 to a pressure substantially equal to the pressure at point PA2, and reaches a state located at point PA9 in Figure 3. After this, the liquid refrigerant flowing into the indoor unit 20 evaporates in the indoor heat exchanger 22, and reaches a state located at point PA3 in Figure 3. The refrigerant flows out from the indoor unit 20 and is drawn into the suction port 9 of the high-stage compressor 12. The gas refrigerant flowing out from the internal heat exchanger 64 is also drawn into the suction port 9 of the high-stage compressor 12.

[0093] The liquid refrigerant flowing into the refrigeration equipment 30 is decompressed by the refrigeration inlet-side expansion mechanism 31, and reaches a state located at point PA10 in Fig. 3. Thereafter, the liquid refrigerant flowing into the refrigeration equipment 30 evaporates in the refrigeration heat exchanger 32, and reaches a state located at point PA1 in Fig. 3. The refrigerant flows out of the refrigeration equipment 30 and is drawn into the suction port 7 of the low-stage compressor 11. As shown in Fig. 1, the refrigeration system 1 of this embodiment is a system that performs a two-stage compression, two-stage expansion cycle by including a refrigeration circuit 2.

[0094] In this way, in the refrigeration system 1, the outlet side of the indoor heat exchanger 22 is set to an intermediate pressure by controlling the aperture of the gas refrigerant flow control valve 61 and adjusting the return amount of gas refrigerant. Also, in the refrigeration system 1, the inlet side of the indoor heat exchanger 22 is set to an intermediate pressure by controlling the aperture of the indoor expansion mechanism 21. Therefore, in the refrigeration system 1, it is possible to generate a refrigerant pressure difference between the inlet and outlet sides of the indoor expansion mechanism 21 in the refrigeration circuit 2.

[0095] As a result, in the refrigeration system 1, in the indoor heat exchanger 22 where the evaporation temperature of the refrigerant is high, it is possible to 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 which the refrigerant evaporates. Therefore, in the refrigeration system 1, carbon dioxide (R744), a natural refrigerant with high environmental friendliness, is used, which makes it possible to improve the efficiency of the air conditioning temperature range and the efficiency of the refrigeration system as a whole.

[0096] As described above, in the refrigeration system 1, the refrigerant pressure is adjusted by the throttle mechanism 63 and the gas refrigerant flow control valve 61, and the refrigerant temperature is adjusted by the gas-liquid separator 16, thereby making it possible to stably change the state of the refrigerant as shown in Fig. 3. Therefore, in the refrigeration system 1, the pressure and temperature of the refrigerant can be adjusted in accordance with the load on the indoor unit 20 and the cooling equipment 30, which is caused by the outside air temperature, etc., and stable operation can be achieved.

[0097] Furthermore, in the refrigeration system 1, heat is exchanged between the liquid refrigerant separated in the gas-liquid separator 16 and the gas refrigerant in the internal heat exchanger 64. This causes the liquid refrigerant flowing into the indoor unit 20 and the cooling equipment 30 to be subcooled. Therefore, even if the temperature of the liquid refrigerant fluctuates due to external heat radiation or heat capacity of the gas-liquid separator 16 or fluctuations in the operating load of the refrigeration system 1, the liquid refrigerant is prevented from rising to a temperature at which flash gas is generated, for example. Thus, in the refrigeration system 1, stable evaporation of the refrigerant can be achieved in the indoor heat exchanger 22 and the cooling heat exchanger 32.

[0098] Additionally, in the refrigeration system 1, a portion of the liquid refrigerant that has exchanged heat with the gas refrigerant in the internal heat exchanger 64 is mixed with the gas refrigerant before heat exchange with the liquid refrigerant via the connecting pipe 66. As a result, in the internal heat exchanger 64, heat exchange occurs between the liquid refrigerant and the mixed refrigerant of the liquid refrigerant and gas refrigerant that has been cooled by heat exchange with the gas refrigerant in the internal heat exchanger 64. As a result, the degree of subcooling of the liquid refrigerant is increased in the internal heat exchanger 64, and the energy efficiency of the refrigeration system 1 can be improved.

[0099] [1-2-3. State of Refrigerant in Refrigeration Circuit When Compression Ratio of High-Stage Compressor Increases] Here, a description will be given of the refrigerant in the refrigeration system 1 when the compression ratio of the high-stage compressor 12 increases during cooling operation. In the refrigeration system 1, there are cases where the temperature difference between the refrigerant temperature DTh discharged from the high-stage compressor 12 and the refrigerant temperature LT flowing out of the outdoor heat exchanger 15 becomes higher than a predetermined value SHh. In this case, a high load is applied to the high-stage compressor 12 in the refrigeration system 1, which may increase the refrigerant discharge temperature of the high-stage compressor 12 and reduce the volumetric efficiency of the refrigerant.

[0100] In this embodiment, when the temperature difference between the refrigerant temperature DTh discharged from the high-stage compressor 12 and the refrigerant temperature LT flowing out from the outdoor heat exchanger 15 is higher than a predetermined value SHh, the control device 100 determines that the compression ratio of the high-stage compressor 12 has increased. When the control device 100 determines that the compression ratio of the high-stage compressor 12 has increased, it increases the opening degree of the adjustment valve 96 so as to satisfy the above-described formula (2).

[0101] FIG. 4 is a ph diagram showing the state of the refrigerant in the refrigeration circuit 2. FIG. 4 shows the state of the refrigerant in the refrigeration circuit 2 when the compression ratio of the high-stage compressor 12 is high. Under the control of the control device 100, refrigerant having the temperature and pressure at point PB8 in FIG. 4 is supplied to the high-stage compressor 12 via the high-stage injection port 19. The refrigerant supplied via the high-stage injection port 19 then cools the high-stage compressor 12 and the refrigerant compressed by the high-stage compressor 12 to the temperature shown at point PB5 in FIG. 4. After this, the high-stage compressor 12 again compresses the refrigerant inside the high-stage compressor 12, together with the refrigerant supplied via the high-stage injection port 19, to the pressure and temperature at PB6 and discharges it.

[0102] This makes it possible to suppress an increase in the compression ratio of the high-stage compressor 12 in the refrigeration system 1. As a result, the refrigeration system 1 can operate more efficiently.

[0103] [1-2-4. State of Refrigerant in the Refrigeration Circuit When the Compression Ratio of the Low-Stage Compressor is Increasing] In the refrigeration system 1, during cooling operation, the temperature difference between the refrigerant temperature DTl discharged from the low-stage compressor 11 in addition to the high-stage compressor 12 and the refrigerant temperature LT flowing out from the outdoor heat exchanger 15 may be higher than a predetermined value SHl. For example, in the refrigeration system 1, the temperature zone inside the refrigerator of the cooling equipment 30 may be set to a partial temperature zone or a freezing temperature zone. In this case, a large difference occurs between the evaporation temperature of the indoor heat exchanger 22 and the evaporation temperature of the chilled heat exchanger 32. In this case, in the refrigeration system 1, the discharge refrigerant temperatures of the high-stage compressor 12 and the low-stage compressor 11 increase, and the volumetric efficiency of the refrigerant may decrease.

[0104] In this embodiment, when the temperature difference between the refrigerant temperature DTl discharged from the low-stage compressor 11 and the refrigerant temperature LT flowing out from the outdoor heat exchanger 15 is higher than a predetermined value SHl, the control device 100 determines that the compression ratio of the low-stage compressor 11 has increased. When the control device 100 determines that the compression ratio of the low-stage compressor 11 has increased, it increases the opening degree of the adjustment valve 92 so as to satisfy the above-described formula (1).

[0105] Fig. 5 is a ph diagram showing the state of the refrigerant in the refrigeration circuit 2. Fig. 5 shows the state of the refrigerant in the refrigeration circuit 2 when the compression ratio of the low-stage compressor 11 is high. Under the control of the control device 100, refrigerant having the temperature and pressure at point PC14 in Fig. 5 is supplied to the low-stage compressor 11 via the low-stage injection port 17. Then, the refrigerant supplied via the low-stage injection port 17 cools the low-stage compressor 11 and the refrigerant compressed by the low-stage compressor 11, and the temperature reaches the temperature shown by point PC3 in Fig. 5.

[0106] Thereafter, the low-stage compressor 11 again compresses the refrigerant inside the low-stage compressor 11 to the pressure and temperature of PC4 together with the refrigerant supplied via the low-stage injection port 17, and discharges the refrigerant. This makes it possible to suppress an increase in the compression ratio of the low-stage compressor 11 and to suppress an increase in the discharge temperature of the low-stage compressor 11 in the refrigeration system 1. This allows the refrigeration system 1 to operate more efficiently.

[0107] The refrigerant discharged from the low-stage compressor 11 is drawn into each of the high-stage compressors 12. Under the control of the control device 100, refrigerant having the temperature and pressure at point PC10 in FIG. 5 is supplied to the high-stage compressor 12 via the high-stage injection port 19. The refrigerant supplied via the high-stage injection port 19 cools the high-stage compressor 12 and the refrigerant compressed in the high-stage compressor 12, resulting in a temperature indicated by point PC7 in FIG. 5. After this, the high-stage compressor 12 again compresses the refrigerant inside the high-stage compressor 12, together with the refrigerant supplied via the high-stage injection port 19, to the pressure and temperature indicated by PC8 and discharges the refrigerant. This allows the refrigeration system 1 to suppress an increase in the compression ratio of the high-stage compressor 12 and to suppress an increase in the discharge temperature of the low-stage compressor 11. This allows the refrigeration system 1 to operate more efficiently.

[0108] [1-2-5. Heating Operation] Figure 6 is a circuit diagram of the refrigeration system 1 showing the operation of the heating operation. In the refrigeration system 1, the heating operation is performed using the indoor heat exchanger 22 as a gas cooler or radiator and the cooling heat exchanger 32 as an evaporator. As shown in Figure 6, when performing the heating operation, in the first switching mechanism 50, the control device 100 opens the first heating valve 52 and closes the remaining first cooling valve 51 and outdoor refrigerant return valve 53. In addition, in the second switching mechanism 54, the control device 100 closes the throttling mechanism 63 and the refrigerant return expansion mechanism 58.

[0109] In this state, by driving each of the low-stage compressor 11 and the high-stage compressor 12, the refrigerant compressed by the low-stage compressor 11 is further compressed by each of the high-stage compressors 12 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 flows into the indoor heat exchanger 22, where it exchanges heat with the indoor air, heating the indoor air.

[0110] The refrigerant that has exchanged heat in the indoor heat exchanger 22 passes through the indoor expansion mechanism 21, and flows into the gas-liquid separator 16 via the check valve 59 and the throttling mechanism 63 provided in the fourth pipe 76. The refrigerant separated in the gas-liquid separator 16 passes through the pipe 77 and flows into the chilled-unit heat exchanger 32 via the chilled-unit inlet-side expansion mechanism 31. This refrigerant exchanges heat in the chilled-unit heat exchanger 32 and cools the chilled-unit equipment 30.

[0111] The refrigerant that has exchanged heat in the chiller heat exchanger 32 passes through the pipe 72 and is returned to the suction port 7 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 operation, the indoor heat exchanger 22 functions as a gas cooler or a radiator, and the outdoor heat exchanger 15 is not used. In the refrigeration system 1, during heating operation, liquid refrigerant flows only through the chiller equipment 30, so the opening of the gas refrigerant flow control valve 61 is smaller than during cooling operation.

[0112] During heating operation of the refrigeration system 1, the refrigerant discharged from the high-stage compressor 12 dissipates heat while maintaining its pressure at high in the indoor heat exchanger 22. The refrigerant is reduced in pressure by the indoor expansion mechanism 21 to an intermediate pressure, and then flows into the gas-liquid separator 16.

[0113] 7 is a circuit diagram of the refrigeration system 1 showing the operation of the heating operation when the amount of heat exhausted to the cooling equipment 30 is insufficient. As shown in Fig. 7, when heating is performed at full capacity, the control device 100 opens the first heating valve 52, the outdoor refrigerant return valve 53, and the refrigerant return expansion mechanism 58, and closes the first cooling valve 51.

[0114] 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 sucked into each high-stage compressor 12, further compressed by each high-stage compressor 12, and discharged toward the oil separator 14. The refrigerant that has passed through the oil separator 14 flows through the first heating valve 52 into the indoor heat exchanger 22, where it exchanges heat with the indoor air, heating the indoor air.

[0115] The refrigerant that has exchanged heat in the indoor heat exchanger 22 flows into the gas-liquid separator 16 via the check valve 59 provided in the fourth pipe 76, and then flows into the chilled-unit heat exchanger 32 via the chilled-unit inlet-side expansion mechanism 31. The refrigerant exchanges heat in the chilled-unit heat exchanger 32 and cools the chilled-unit equipment 30. Thereafter, the refrigerant is adjusted via the chilled-unit outlet-side pressure adjustment mechanism 33 so that its pressure is the same as that of the refrigerant flowing through the first outdoor return pipe 42, and is returned to the low-stage compressor 11. This is the operation when the outside air temperature is lower than the temperature inside the chilled-unit equipment 30.

[0116] Meanwhile, part of the refrigerant from the gas-liquid separator 16 flows into the outdoor heat exchanger 15 via the refrigerant return expansion mechanism 58, and after heat exchange in the outdoor heat exchanger 15, is returned to the low-stage compressor 11. This allows the exhaust heat from the chiller heat exchanger 32 and the heat pumped up by the outdoor heat exchanger 15 to be used as heat for the indoor heat exchanger 22, making it possible to increase the heating capacity when the amount of heat exhausted to the chiller equipment 30 is insufficient.

[0117] During heating operation when the amount of heat exhausted to the cooling equipment 30 is insufficient, the refrigerant in the refrigeration circuit 2 changes state in the same manner as the refrigerant state shown in the ph diagram of FIG.

[0118] 8 is a circuit diagram of the refrigeration system 1 showing the heating operation when a large capacity is required in the cooling equipment 30 and a large amount of heating heat is not required. As shown in Fig. 8, when a large capacity is required in the cooling equipment 30 and a large amount of heating heat is not required, the control device 100 opens the first cooling valve 51, the first heating valve 52, and the check valve 59 provided in the fourth pipe 76, and closes the refrigerant return valve 53 and the check valve 59 provided in the third pipe 75.

[0119] 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 sucked into each high-stage compressor 12, further compressed by each high-stage compressor 12, and discharged toward the oil separator 14. The refrigerant that has passed through the oil separator 14 flows through the first cooling valve 51 into the outdoor heat exchanger 15, where it exchanges heat with outside air. The refrigerant after heat exchange flows into the gas-liquid separator 16 via the throttling mechanism 63.

[0120] On the other hand, the refrigerant that has passed through the oil separator 14 flows through the first heating valve 52 into the indoor heat exchanger 22, where it exchanges heat with the indoor air to heat the indoor air. The refrigerant that has exchanged heat in the indoor heat exchanger 22 merges with the refrigerant that has flowed out from the outdoor heat exchanger 15 via the check valve 59 provided in the fourth pipe 76, and flows into the gas-liquid separator 16.

[0121] The refrigerant flowing out of the gas-liquid separator 16 flows into the refrigeration heat exchanger 32 via the inlet expansion mechanism for the refrigeration equipment 30. Heat exchange occurs in the refrigeration heat exchanger 32, cooling the refrigeration equipment 30, and the refrigerant that has exchanged heat in the refrigeration heat exchanger 32 is returned to the low-stage compressor 11 via the refrigeration outlet pressure adjustment mechanism 33. Meanwhile, a portion of the refrigerant flowing out of the gas-liquid separator 16 flows into the outdoor heat exchanger 15 via the refrigerant return expansion mechanism 58, and after heat exchange in the outdoor heat exchanger 15, is returned to the low-stage compressor 11.

[0122] In the refrigeration system 1, the compression ratio of the high-stage compressor may be increased during heating operation when the cooling equipment 30 requires a large capacity but does not require a large amount of heating heat. In this case, the control device 100 may increase the opening degree of the control valve 96 so as to satisfy the above-described formula (2). In this case, the state of the refrigerant in the refrigeration circuit 2 changes in the same manner as the state of the refrigerant shown in the p-h diagram of FIG. 4.

[0123] [1-3. Effects, etc.] As described above, in this embodiment, the refrigeration system 1 includes a refrigeration circuit 2 provided with multiple compressors, an outdoor heat exchanger 15, multiple user-side heat exchangers, and a gas-liquid separator 16. The multiple compressors include a low-stage compressor 11 and a high-stage compressor 12, and the multiple user-side heat exchangers include an indoor heat exchanger 22 and a chilled heat exchanger 32 having a refrigerant evaporation temperature lower than that of the indoor heat exchanger 22. The high-stage compressor 12 is provided with an inlet 9 that draws in refrigerant, and a high-stage injection port 19 that supplies refrigerant to the high-stage compressor 12 via a path different from the inlet 9.

[0124] This makes it possible to suppress an increase in the compression ratio of the high-stage compressor 12 in the refrigeration system 1. As a result, the refrigeration system 1 can operate more efficiently.

[0125] As in the present embodiment, an injection pipe 94 branching from the pipe 79 that supplies refrigerant to the gas-liquid separator 16 may be connected to the high-stage injection port 19. As a result, high-pressure refrigerant cooled in the outdoor heat exchanger 15 or the indoor heat exchanger 22 is supplied to the high-stage compressor 12 via the injection pipe 94. Therefore, in the refrigeration system 1, it is possible to supply refrigerant via a route different from the suction port 9 while suppressing a decrease in the compression efficiency of the refrigerant in the high-stage compressor 12.

[0126] As in the present embodiment, the low-stage compressor 11 may be provided with an inlet 7 that draws in refrigerant, and a low-stage injection port 17 that supplies refrigerant to the low-stage compressor 11 via a path different from the inlet 7. This makes it possible to suppress an increase in the compression ratio of the low-stage compressor 11 in the refrigeration system 1. This allows the refrigeration system 1 to operate more efficiently.

[0127] The low-stage compressor 11 may be supplied with liquid refrigerant separated in the gas-liquid separator 16 via the low-stage injection port 17. As a result, the low-stage compressor 11 is supplied with liquid refrigerant, which is a higher-pressure refrigerant among the refrigerants flowing into the gas-liquid separator 16, via the low-stage injection port 17. As a result, in the refrigeration system 1, it is possible to supply refrigerant while suppressing a decrease in the compression efficiency of the refrigerant in the low-stage compressor 11.

[0128] As in the present embodiment, an internal heat exchanger 64 may be provided between the gas-liquid separator 16 and the indoor heat exchanger 22 and the cooling heat exchanger 32 to exchange heat between the liquid refrigerant flowing from the gas-liquid separator 16 to the indoor heat exchanger 22 and the cooling heat exchanger 32 and the gas refrigerant flowing out of the gas-liquid separator 16. This allows the refrigeration system 1 to cool the liquid refrigerant flowing out of the gas-liquid separator 16 to a lower temperature. This allows the refrigeration system 1 to increase the refrigeration effect.

[0129] As in the present embodiment, the refrigeration system 1 includes a control device 100 that controls each component of the refrigeration circuit 2. The control device 100 may supply refrigerant to each of the low-stage compressor 11 and the high-stage compressor 12 via the low-stage injection ports 17 and 19 in an amount such that a predetermined value is obtained as a difference between the temperature of the refrigerant discharged from each of the low-stage compressor 11 and the high-stage compressor 12 and the temperature of the refrigerant flowing out of the outdoor heat exchanger 15. This allows the refrigeration system 1 to supply an appropriate amount of refrigerant via the low-stage injection ports 17 and 19. This prevents an increase in the compression ratio of the refrigerant in the low-stage compressor 11 and the high-stage compressor 12, enabling more efficient operation.

[0130] As in the present embodiment, the refrigerant may be carbon dioxide, which is a natural refrigerant, and thus the refrigeration system 1 can operate more efficiently.

[0131] (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 also 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 and second embodiments above to create new embodiments. Therefore, other embodiments will be described below as examples.

[0132] Fig. 9 is a circuit diagram showing the refrigeration circuit 2 included in the refrigeration system 1 according to Modification 1. As shown in Fig. 9, the refrigeration system 1 may include an injection pipe 190 instead of the injection pipe 90. One end of this injection pipe 190 is connected to a midpoint of the gas refrigerant return pipe 60, and the other end is connected to a low-stage injection port 17 of the low-stage compressor 11. The refrigerant that is heat exchanged in the internal heat exchanger 64 is supplied to the low-stage compressor 11 via the low-stage injection port 17.

[0133] As a result, a refrigerant having a pressure higher than the pressure of the refrigerant sucked into the low-stage compressor 11 and lower than the pressure of the refrigerant discharged from the low-stage compressor 11 is supplied to the low-stage compressor 11 via the low-stage injection port 17. Therefore, the refrigerant is supplied to the low-stage compressor 11 via the low-stage injection port 17 while suppressing backflow.

[0134] In the refrigeration system 1, the flow rate of the refrigerant flowing through the injection pipe 190 is adjusted by adjusting the aperture of at least one of the gas refrigerant flow control valve 61 and the liquid refrigerant flow control valve 65. As a result, in the refrigeration system 1, the flow rate of the refrigerant flowing through the injection pipe 190 is adjusted without providing a flow rate adjustment mechanism such as an opening and closing device in the injection pipe 190. Therefore, in the refrigeration system 1, the flow rate of the refrigerant flowing through the injection pipe 190 can be adjusted with a simpler configuration and control. In addition, because the injection pipe 190 is a pipe branching off from the gas refrigerant return pipe 60, it can be installed more easily. Therefore, in the refrigeration system 1 in this modified example, refrigerant can be supplied to the low-stage compressor 11 via a route different from the suction port 7 with a simpler configuration.

[0135] FIG. 10 is a circuit diagram showing a refrigeration circuit 2 included in a refrigeration system 1 according to Modification 2. As shown in FIG. 10 , the refrigeration system 1 may omit the internal heat exchanger 64. In this case, the refrigeration system 1 may include an injection pipe 290. One end of the injection pipe 290 is connected to a midpoint of the piping 77. The injection pipe 290 is connected to the piping 77 between the gas-liquid separator 16 and the connection part B. The other end of the injection pipe 290 is connected to the low-stage injection port 17 of the low-stage compressor 11. Therefore, the refrigerant flowing out from the gas-liquid separator 16 is supplied to the low-stage compressor 11 via the low-stage injection port 17.

[0136] A control valve 292 may be provided in the middle of the injection pipe 290. The control valve 292 is an opening / closing device that can change the opening degree from fully closed to fully open. In the refrigeration system 1, the flow rate of the refrigerant flowing through the injection pipe 90 is adjusted by adjusting the opening degree of the control valve 292.

[0137] In the above-described embodiment, the refrigeration system 1 includes the injection pipes 90 and 94. However, the present invention is not limited to this, and the refrigeration system 1 may include only one of the injection pipes 90 and 94.

[0138] The low-stage compressor 11 and the high-stage compressor 12 in the above-described embodiment are not limited to scroll compressors, and may be compressors having other compression mechanisms such as rotary compressors. In either type of compressor, the low-stage injection port 17 is connected to the low-stage compressor 11, and the high-stage injection port 19 is connected to the high-stage compressor 12.

[0139] In the above-described embodiment, the refrigeration system 1 includes one indoor heat exchanger 22 and one chilled-use heat exchanger 32. However, this is not limited to this. The refrigeration system 1 may include another chilled-use heat exchanger 32 instead of the indoor heat exchanger 22. That is, the refrigeration system 1 may omit the indoor unit 20 and include multiple chilled-use devices 30. In this case, the multiple chilled-use heat exchangers 32 have different evaporation temperature ranges. Of the multiple chilled-use heat exchangers 32, the chilled-use heat exchanger 32 with a higher evaporation temperature range is connected to the inlet side of the high-stage compressor 12, and the chilled-use heat exchanger 32 with a lower evaporation temperature range is connected to the inlet side of the low-stage compressor 11.

[0140] 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 32 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 32 is connected to the inlet side of the low-stage compressor 11.

[0141] 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.

[0142] 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. Also in this case, one or more indoor heat exchangers 22 and one or more cooling heat exchangers 32 may be provided in parallel to one another in the pipe 78 and the pipe 71.

[0143] A plurality of chilled-use heat exchangers 32 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 31 may be provided on the inlet side of each chilled-use heat exchanger 32. In this case, at least one of the chilled-use heat exchangers 32 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 32.

[0144] The components shown in FIG. 2 are merely examples, and the specific implementation is not particularly limited. In other words, it is not necessary to implement hardware corresponding to each component individually, and it is of course possible to configure the components so that the functions of each component are realized by a single processor executing a program. Furthermore, some of the functions realized by software in the above-described embodiment may be implemented by hardware, or some of the functions realized by hardware may be implemented by software. In addition, the specific detailed configurations of the other components, such as the outdoor unit 10, the indoor unit 20, and the cooling equipment 30, may also be changed as desired without departing from the spirit of the present disclosure.

[0145] 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.

[0146] (Additional Notes) The above description of the embodiments discloses the following techniques.

[0147] (Technology 1) A refrigeration system including a refrigeration circuit including multiple compressors, a heat source heat exchanger, multiple user-side heat exchangers, and a gas-liquid separator that separates refrigerant cooled by at least one of the multiple user-side heat exchangers into liquid refrigerant and gas refrigerant, wherein the multiple compressors are configured as low-stage compressors and high-stage compressors, and the multiple user-side heat exchangers are configured as first user-side heat exchangers and second user-side heat exchangers having a lower refrigerant evaporation temperature than the first user-side heat exchanger, and the high-stage compressor is provided with a high-stage injection port that supplies refrigerant to the compression mechanism of the high-stage compressor via a path different from the suction port that draws in refrigerant. This allows the refrigeration system to suppress an increase in the compression ratio of the high-stage compressor. This allows the refrigeration system to operate more efficiently.

[0148] (Technology 2) In the refrigeration system according to Technology 1, a refrigerant supply pipe branching from a pipe supplying refrigerant to the gas-liquid separator is connected to the high-stage injection port. As a result, high-pressure refrigerant cooled in the outdoor heat exchanger 15 or the indoor heat exchanger 22 is supplied to the high-stage compressor via the refrigerant supply pipe. Therefore, in the refrigeration system, refrigerant can be supplied via a route different from the suction port while suppressing a decrease in the compression efficiency of the refrigerant in the high-stage compressor.

[0149] (Technology 3) The refrigeration system according to Technology 1 or Technology 2, wherein the low-stage compressor is provided with a low-stage injection port that supplies refrigerant to the compression mechanism of the low-stage compressor via a path different from the suction port that draws in the refrigerant. This makes it possible to suppress an increase in the compression ratio of the low-stage compressor in the refrigeration system. As a result, the refrigeration system 1 can operate more efficiently.

[0150] (Technology 4) The refrigeration system according to Technology 3, wherein the liquid refrigerant separated in the gas-liquid separator is supplied to the low-stage compressor via the low-stage injection port. As a result, the low-stage compressor is supplied with liquid refrigerant, which is a refrigerant with a higher pressure than the refrigerant flowing into the gas-liquid separator, via the low-stage injection port. This allows the refrigeration system to supply refrigerant while suppressing a decrease in the compression efficiency of the refrigerant in the low-stage compressor.

[0151] (Technology 5) The refrigeration system according to any one of Technologies 1 to 4, wherein an internal heat exchanger is provided between the gas-liquid separator and the first and second user-side heat exchangers, and the internal heat exchanger exchanges heat between the liquid refrigerant flowing from the gas-liquid separator to the first and second user-side heat exchangers and the gas refrigerant flowing out of the gas-liquid separator. This allows the refrigeration system to cool the liquid refrigerant flowing out of the gas-liquid separator to a lower temperature. This increases the refrigeration effect of the refrigeration system.

[0152] (Technology 6) The low-stage compressor is provided with a low-stage injection port that supplies refrigerant to the compression mechanism of the low-stage compressor via a path different from the suction port that draws in the refrigerant, and the gas refrigerant that has been heat exchanged in the internal heat exchanger is supplied to the low-stage compressor via the low-stage injection port. In the refrigeration system, the flow rate of the refrigerant supplied to the low-stage injection port is adjusted by adjusting the opening of a throttling mechanism used to adjust the flow rate of the internal heat exchanger. As a result, in the refrigeration system, the flow rate of the refrigerant supplied to the low-stage compressor is adjusted without providing a mechanism for adjusting the flow rate of the low-stage injection port. As a result, the refrigeration system can adjust the flow rate of the refrigerant supplied to the low-stage compressor with a simpler configuration and control.

[0153] (Technology 7) The refrigeration system according to any one of Technology 1 to Technology 6, further comprising a control unit that controls each unit of the refrigeration circuit, and the control unit supplies the compressor with an amount of refrigerant through the refrigerant injection port such that a difference between a temperature of the refrigerant discharged from the compressor and a temperature of the refrigerant flowing out of the heat source-side heat exchanger is a predetermined value. This allows the refrigeration system to supply an appropriate amount of refrigerant through the high-stage injection port and the low-stage injection port. This prevents an increase in the compression ratio of the refrigerant in the low-stage compressor and the high-stage compressor, enabling more efficient operation.

[0154] (Technology 8) The refrigeration system according to any one of Techniques 1 to 7, wherein the refrigerant is carbon dioxide. This allows the refrigeration system to operate more efficiently by using carbon dioxide, which is a natural refrigerant, as the refrigerant.

[0155] INDUSTRIAL APPLICABILITY The present disclosure can be suitably used as a refrigeration system that uses a natural refrigerant and can improve the operating efficiency of the entire system.

[0156] DESCRIPTION OF SYMBOLS 1 Refrigeration system 2 Refrigeration circuit 6, 8 Discharge port 7, 9 Intake port (suction section) 17 Low-stage injection port 19 High-stage injection port 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 18, 28, 38 Blower 20 Indoor unit 21 Indoor expansion mechanism 22 Indoor heat exchanger (first use side heat exchanger) 23 Opening / closing valve 27 Space temperature sensor 30 Refrigeration equipment 31 Refrigeration inlet side expansion mechanism 32 Refrigeration heat exchanger (second use side heat exchanger) 33 Refrigeration outlet side pressure adjustment mechanism 37 In-cabinet temperature sensor 40 Piping 41 First heating pipe 42 DESCRIPTION OF SYMBOLS 50 First outdoor return pipe 50 First switching mechanism (another switching mechanism) 51 First cooling valve 52 First heating valve 53 Outdoor refrigerant return valve 54 Second switching mechanism (switching mechanism) 55 Throttle mechanism 58 Refrigerant return expansion mechanism 59 Check valve 60 Gas refrigerant return pipe 61 Gas refrigerant flow control valve 64 Internal heat exchanger 65 Liquid refrigerant flow control valve 66 Connecting pipe 71 Pipe 72 Pipe 73 First pipe 74 Second pipe 75 Third pipe 76 Fourth pipe 77 Pipe 78 Pipe 79 Pipe 81, 82, 83, 84, 85, 86, 87, 88, 89, 91 Refrigerant temperature sensor 90, 94, 190, 290 Injection pipe (refrigerant supply pipe) 92, 96, 292 Control valve 100 Control device 101 Outdoor unit control unit 101a Operation control unit 101b Determination unit 103 Memory unit 103a Setting data 105 Outdoor unit I / F 106 Outdoor unit communication unit 110 Indoor unit control device 111 Indoor unit control unit 113 Indoor unit memory unit 115 Indoor unit I / F 120 Refrigeration equipment control device 121 Refrigeration equipment control unit 123 Refrigeration equipment memory unit 125 Refrigeration equipment I / F 140, 142, 144, 146, 148 Refrigerant pressure sensor 150 Refrigerant recovery device 152 Vacuum drawing unit 154 Refrigerant sealing unit 156 Connection piping A, B, C, D Connection unit

Claims

1. A refrigeration system comprising a refrigeration circuit provided with a plurality of compressors, a heat source side heat exchanger, a plurality of user side heat exchangers, and a gas-liquid separator that separates refrigerant cooled by at least one of the plurality of user side heat exchangers into liquid refrigerant and gas refrigerant, 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, and the high-stage compressor is provided with a high-stage injection port that supplies refrigerant to a compression mechanism of the high-stage compressor via a route different from a suction section that draws in refrigerant.

2. The refrigeration system according to claim 1, wherein a refrigerant supply pipe branching from a pipe for supplying refrigerant to the gas-liquid separator is connected to the high-stage injection port.

3. A refrigeration system as described in claim 1 or claim 2, wherein the low-stage compressor is provided with a low-stage injection port that supplies refrigerant to the compression mechanism of the low-stage compressor via a route different from the suction port that draws in the refrigerant.

4. A refrigeration system according to claim 3, wherein the liquid refrigerant separated in the gas-liquid separator is supplied to the low-stage compressor via the low-stage injection port.

5. A refrigeration system according to any one of claims 1 to 4, wherein an internal heat exchanger is provided between the gas-liquid separator and the first and second user-side heat exchangers, for exchanging heat between liquid refrigerant flowing from the gas-liquid separator to the first and second user-side heat exchangers and gas refrigerant flowing out of the gas-liquid separator.

6. A refrigeration system as described in claim 5, wherein the low-stage compressor is provided with a low-stage injection port that supplies refrigerant to the compression mechanism of the low-stage compressor via a route different from the suction section that draws in the refrigerant, and the low-stage compressor is supplied with gas refrigerant that has been heat exchanged in the internal heat exchanger via the low-stage injection port.

7. A refrigeration system as described in any one of claims 1 to 6, comprising a control unit that controls each part of the refrigeration circuit, wherein the control unit supplies the compressor with an amount of refrigerant via the high-stage injection port such that the difference between the temperature of the refrigerant discharged from the compressor and the temperature of the refrigerant flowing out of the heat source side heat exchanger is a predetermined value.

8. A refrigeration system according to any one of claims 1 to 7, wherein the refrigerant is carbon dioxide.

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