Refrigeration system

Abstract

To provide a refrigeration system which can continue to be operated even when defect occurs in any of compressors.SOLUTION: A refrigeration system includes: a plurality of low-stage compressors; and at least one high-stage compressor provided on the delivery side of the plurality of low-stage compressors. Each of the low-stage compressors and the high-stage compressors is provided with: delivery piping connected to the delivery side; and suction piping connected to the suction side. The delivery piping is provided with a delivery side opening / closing device capable of opening / closing the delivery piping. The suction piping is provided with a suction side opening / closing device capable of opening / closing the suction piping. The suction piping of the low-stage compressor is provided with a suction side connection pipe connecting the upper stream side than that of the suction side opening / closing device and the upper stream side than that of the suction side opening / closing device of the suction piping of the high-stage compressor. The delivery piping of the low-stage compressor is provided with a delivery side connection pipe connecting the downstream side than that of the delivery side opening / closing device and the downstream side than that of the delivery side opening / closing deice of the delivery piping of the high-stage compressor.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to refrigeration systems. [Background technology]

[0002] Patent Document 1 discloses a heat source unit and a refrigeration system that prevent gas refrigerant in a gas-liquid separator from being stopped from being sent to an intermediate flow path during high outdoor air temperatures. In this heat source unit and refrigeration system, a control unit executes a first operation to increase the rotation speed of the third compressor when a first condition is satisfied that an intermediate pressure corresponding to the pressure in the intermediate flow path is higher than a predetermined value during operation of the first, second, and third compressors. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2022-039365 Summary of the Invention [Problem to be solved by the invention]

[0004] The present disclosure provides a refrigeration system that can continue to operate even if a malfunction occurs in one of the compressors. [Means for solving the problem]

[0005] The refrigeration system of the present disclosure includes a refrigeration circuit provided with a plurality of compressors, a heat source side heat exchanger, and a plurality of use side heat exchangers, the plurality of use side heat exchangers being composed of a first use side heat exchanger and a second use side heat exchanger having a refrigerant evaporation temperature lower than that of the first use side heat exchanger, the plurality of compressors being composed of a plurality of low stage compressors and at least one high stage compressor provided on the discharge side of the plurality of low stage compressors, the low stage compressor and the high stage compressor each being provided with a discharge pipe which is a pipe connected to the discharge side, and a suction pipe which is a pipe connected to the suction side, and the discharge pipe Each of the pipes is provided with a discharge side opening and closing device that can open and close the discharge piping, each of the suction pipes is provided with a suction side opening and closing device that can open and close the suction piping, the suction pipe provided in the low-stage compressor is provided with a suction side connecting pipe that connects the upstream side of the suction side opening and closing device to the upstream side of the suction side opening and closing device of the suction pipe provided in the high-stage compressor, and the discharge pipe provided in the low-stage compressor is provided with a discharge side connecting pipe that connects the downstream side of the discharge side opening and closing device to the downstream side of the discharge side opening and closing device of the discharge piping provided in the high-stage compressor. [Effects of the Invention]

[0006] According to the present disclosure, operation can be continued even if a malfunction occurs in any of the compressors. [Brief explanation of the drawings]

[0007] [Figure 1] FIG. 1 is a diagram showing a refrigeration circuit of a refrigeration system during cooling operation according to an embodiment of the present disclosure. [Figure 2] Diagram showing the refrigeration circuit around the compressor during normal operation [Figure 3] Refrigeration system block diagram [Figure 4] Refrigeration system circuit diagram showing heating operation [Figure 5] Flowchart showing compressor malfunction detection and backup operation [Figure 6] A diagram showing a refrigeration circuit that performs single-stage compression when a malfunction occurs in the high-stage compressor. [Figure 7] A diagram showing a refrigeration circuit that performs two-stage compression in the event of a malfunction in the high-stage compressor. [Figure 8] A diagram showing a refrigeration circuit that performs two-stage compression in the event of a malfunction in the high-stage compressor. [Figure 9] A diagram showing a refrigeration circuit that performs single-stage compression when a malfunction occurs in the first low-stage compressor. [Figure 10] A diagram showing a refrigeration circuit that performs two-stage compression when a malfunction occurs in the first low-stage compressor. [Figure 11] A diagram showing a refrigeration circuit that performs single-stage compression when a malfunction occurs in the second low-low compressor. [Figure 12] A diagram showing a refrigeration circuit that performs two-stage compression when a malfunction occurs in the second low-stage compressor. DETAILED DESCRIPTION OF THE INVENTION

[0008] (Findings that formed the basis of this disclosure) At the time the inventors arrived at the idea of ​​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 in a different evaporation temperature range. As a result, in this refrigeration system, for example, air conditioning of a space to be conditioned and cooling of the interior of a refrigerator can be performed simultaneously.

[0009] However, the inventors discovered a problem with such a refrigeration system: if a malfunction occurs in any of the compressors, there is a risk that the operation of the entire refrigeration system will be stopped. In order to solve this problem, the inventors came up with the subject matter of the present disclosure. Therefore, the present disclosure provides a refrigeration system that can continue to operate even if a malfunction occurs in one of the compressors.

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

[0011] (Embodiment 1) Hereinafter, the first embodiment will be described with reference to the drawings. [1-1-1. Refrigeration circuit in refrigeration system] FIG. 1 is a diagram showing a refrigeration circuit 2 of a refrigeration system 1 in a first embodiment. FIG. 1 shows the refrigeration circuit 2 of the refrigeration system 1 when performing cooling operation. For ease of explanation, in FIG. 1, a valve body in an open state is shown in white, and a valve body in a closed state and a throttling mechanism in a closed state are shown in black. For ease of explanation, in FIG. 1, pipes through which a refrigerant flows are shown in thick lines, and pipes through which a refrigerant does not flow are shown in thin lines. As shown in FIG. 1, the refrigeration system 1 includes an outdoor unit 10, an indoor unit 20, and a cooling device 30, which are connected to each other by refrigerant piping 40 to form a refrigeration circuit 2.

[0012] The indoor unit 20 air-conditions the interior of a store, which is a space to be conditioned, based on a set temperature in a store such as a convenience store or supermarket. 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 set temperature. The outdoor unit 10 functions as a so-called heat source unit. In Fig. 1, the outdoor unit 10 includes the indoor unit 20 and each part located within the dashed line, excluding the area surrounded by the dashed line indicating the cooling equipment 30. The indoor unit 20 and the cooling equipment 30 correspond to the "utilization unit" in the present disclosure.

[0013] The outdoor unit 10 includes a plurality of compressors. In this embodiment, the outdoor unit 10 includes two low-stage compressors 11, a first low-stage compressor 11A and a second low-stage compressor 11B, and a high-stage compressor 12. Each of the compressors is a rotary compressor whose compression mechanism is driven by, for example, a motor. Each of the compressors is a variable displacement compressor whose compression mechanism can change its rotation speed and whose refrigerant discharge pressure can be changed. The high-stage compressor 12 is driven to discharge the refrigerant at a higher discharge pressure than the first low-stage compressor 11A and the second low-stage compressor 11B.

[0014] An accumulator 13 is disposed between the first low-stage compressor 11A, the second low-stage compressor 11B, and the high-stage compressor 12. The refrigerant discharged from the first low-stage compressor 11A and the second low-stage compressor 11B is separated into gas and liquid by the accumulator 13, and only the gas refrigerant is sucked into the high-stage compressor 12.

[0015] An oil separator 14 is connected to the discharge side of the high-stage compressor 12 via a discharge pipe 110. An outdoor heat exchanger 15 is connected to the oil separator 14 via a refrigerant pipe 40. A first heating pipe 41 connected to the refrigerant pipe 40 between the indoor unit 20 and the accumulator 13 is connected to the refrigerant pipe 40 between the oil separator 14 and the outdoor heat exchanger 15. A first outdoor return pipe 42 is connected to the refrigerant piping 40 between the oil separator 14 and the outdoor heat exchanger 15, and is connected to the refrigeration side pipe 102 that connects the refrigeration equipment 30 to the first low-stage compressor 11A and the second low-stage compressor 11B.

[0016] A first switching mechanism 50 is provided between the oil separator 14 and the exterior heat exchanger 15. The first switching mechanism 50 includes a first cooling valve 51 that opens and closes the refrigerant piping 40 between the oil separator 14 and the outdoor heat exchanger 15, and a first heating valve 52 that is provided in the middle of the first heating piping 41 and opens and closes the first heating piping 41. The first heating piping 41 branches off from the refrigerant piping 40 between the oil separator 14 and the first cooling valve 51, and is connected to indoor piping 100 that connects the indoor unit 20 and the accumulator 13. Furthermore, the first switching mechanism 50 includes an outdoor refrigerant return valve 53 that is provided in the middle of the first outdoor return pipe 42 and opens and closes the first outdoor return pipe 42.

[0017] The outdoor heat exchanger 15 is connected to a gas-liquid separator 16 via a refrigerant pipe 40 . The gas-liquid separator 16 is connected to a refrigeration heat exchanger 31 of the refrigeration equipment 30 via a refrigerant pipe 48 and a refrigeration inlet side expansion mechanism 32 . The chilled heat exchanger 31 is connected to the low-stage compressor 11 via chilled-side piping 102. The chilled-side piping 102 is provided with a chilled-side outlet pressure adjustment mechanism 33.

[0018] A second cooling pipe 43 connected to the indoor heat exchanger 22 is connected to the refrigerant pipe 48 between the cooling heat exchanger 31 and the gas-liquid separator 16. An indoor expansion mechanism 21 is provided on the second cooling pipe 43. In the refrigerant piping 40, a second heating piping 44 connected to the second cooling piping 43 is connected between the outdoor heat exchanger 15 and the gas-liquid separator 16. The second heating piping 44 is connected in the second cooling piping 43 between the branch point with the refrigerant piping 48 and the indoor expansion mechanism 21. In the refrigerant piping 40, a second air conditioning piping 43 and a second outdoor return piping 45 connected to the branch point with the refrigerant piping 48 are connected between the outdoor heat exchanger 15 and the gas-liquid separator 16.

[0019] A second switching mechanism 54 is provided between the outdoor heat exchanger 15 and the gas-liquid separator 16. The second switching mechanism 54 includes a second cooling valve 55 that opens and closes the refrigerant pipe 40 between the outdoor heat exchanger 15 and the gas-liquid separator 16, a third cooling valve 56 that is provided in the middle of the second cooling pipe 43 and opens and closes the second cooling pipe 43, and a second heating valve 57 that is provided in the middle of the second heating pipe 44 and opens and closes the second heating pipe 44. The second switching mechanism 54 is provided in the middle of the second outdoor return pipe 45 and includes a refrigerant return expansion mechanism 58 that controls the flow rate of the second outdoor return pipe 45. The second switching mechanism 54 includes check valves 59 provided downstream of the second cooling valve 55, the third cooling valve 56, and the second heating valve 57, respectively. The outdoor heat exchanger 15 corresponds to the "heat source side heat exchanger" in the present disclosure. The indoor heat exchanger 22 corresponds to the "first use side heat exchanger" in the present disclosure, and the cooling heat exchanger 31 corresponds to the "second use side heat exchanger" in the present disclosure.

[0020] The indoor heat exchanger 22 is connected to the suction side of the high-stage compressor 12 via the indoor piping 100 and the accumulator 13. An on-off valve 23 for opening and closing the indoor piping 100 is provided in the middle of the indoor piping 100. In this embodiment, a gas refrigerant return pipe 60 is provided to send the gas refrigerant from the gas-liquid separator 16 to the inlet side of the accumulator 13. A gas refrigerant flow rate control valve 61 is provided in the middle of the gas refrigerant return pipe 60.

[0021] The cooling facility inlet side expansion mechanism 32, the cooling facility outlet side pressure adjustment mechanism 33, the indoor expansion mechanism 21, the refrigerant return expansion mechanism 58, and the gas refrigerant flow control valve 61 are each a throttling mechanism that can adjust the flow rate and pressure of the refrigerant flowing through the pipes in which they are installed.

[0022] Next, the refrigeration circuit 2 around the compressor provided in the outdoor unit 10 will be described. Fig. 2 is a diagram showing the refrigeration circuit 2 around the compressor during normal operation of the refrigeration system 1. For ease of explanation, in Fig. 2, shutoff valves in an open state are shown in white, and shutoff valves in a closed state are shown in black. For ease of explanation, in Fig. 2, pipes through which refrigerant flows are shown in thick lines, and pipes through which refrigerant does not flow are shown in thin lines. For ease of explanation, in Fig. 2, the oil return pipe 62 is shown in two-dot chain line. 2, the refrigeration circuit 2 includes an indoor piping 100 having one end connected to the indoor heat exchanger 22. The other end of the indoor piping 100 is connected to the accumulator 13.

[0023] A throttle valve 130 is provided in the middle of the indoor piping 100, at a position closer to the high-stage compressor 12 than the on-off valve 23. The throttle valve 130 is a throttling mechanism capable of adjusting the opening degree of, for example, an electric valve. The throttle valve 130 is provided in the indoor piping 100, between the on-off valve 23 and the accumulator 13. In the indoor piping 100, the flow rate and pressure of the refrigerant flowing through the indoor piping 100 are adjusted by adjusting the opening degree of the throttle valve 130.

[0024] The refrigeration circuit 2 includes a chilled-side pipe 102 having one end connected to the chilled-side heat exchanger 31. The other end of the chilled-side pipe 102 is connected to low-stage compressors 11A and 11B via a pair of suction pipes 104. That is, the refrigeration circuit 2 branches into each of the suction pipes 104 at the other end of the chilled-side pipe 102.

[0025] The other end of suction piping 104 is connected to the suction sides of low-stage compressors 11A, 11B. Each suction piping 104 is provided with a suction-side shutoff valve 134 and a switching shutoff valve 132. In suction piping 104, suction-side shutoff valve 134 is provided at a position closer to each of low-stage compressors 11A, 11B than switching shutoff valve 132.

[0026] One end of a discharge pipe 108 is connected to the discharge side of each of the low-stage compressors 11A, 11B. The other end of each of the discharge pipes 108 is connected to the indoor side pipe 100, between the throttle valve 130 and the accumulator 13. A discharge-side shutoff valve 138 and a switching shutoff valve 142 are provided in the discharge pipe 108. The discharge-side shutoff valve 138 is provided at a position closer to each of the low-stage compressors 11A, 11B than the switching shutoff valve 142.

[0027] A check valve 160 is provided in the discharge piping 108 between the discharge-side shutoff valve 138 and the switching shutoff valve 142. This prevents the refrigeration system 1 from having the refrigerant flowing out of the indoor heat exchanger 22 and flowing through the indoor piping 100 flowing into the discharge sides of the low-stage compressors 11A and 11B via the discharge piping 108.

[0028] In the refrigeration system 1, by adjusting the opening degree of the throttle valve 130, the pressure of the refrigerant that flows out of the indoor heat exchanger 22 and flows through the indoor piping 100 may be reduced to the same level as the pressure of the refrigerant that flows into the indoor piping 100 via the discharge piping 108. This prevents the refrigerant that flows out of the indoor heat exchanger 22 and flows through the indoor piping 100 from flowing into the discharge sides of the low-stage compressors 11A, 11B via the discharge piping 108. In this case, the check valve 160 may be omitted.

[0029] The accumulator 13 and the high-stage compressor 12 are connected by a suction pipe 114. One end of the suction pipe 114 is connected to the suction side of the high-stage compressor 12. A suction-side shutoff valve 144 is provided in the suction pipe 114.

[0030] One end of a discharge pipe 110 is connected to the discharge side of the high-stage compressor 12. The other end of the discharge pipe 110 is connected to the oil separator 14. A discharge-side shutoff valve 148 and a switching shutoff valve 146 are provided in the discharge pipe 110. The discharge-side shutoff valve 148 is provided at a position closer to the high-stage compressor 12 than the switching shutoff valve 146.

[0031] 1 and 2, in the refrigeration circuit 2, the first low-stage compressor 11A and the second low-stage compressor 11B are arranged on the suction side of the high-stage compressor 12. In the refrigeration circuit 2, the first low-stage compressor 11A and the second low-stage compressor 11B are arranged in parallel with each other. The high-stage compressor 12, the first low-stage compressor 11A, and the second low-stage compressor 11B are connected in series in the refrigeration circuit 2.

[0032] Each suction pipe 104 is provided with a suction side connection pipe 106. One end of the suction side connection pipe 106 is connected to the suction pipe 104 between the suction side shutoff valve 134 and the switching shutoff valve 132. The suction side connection pipes 106 join at the other end and are then connected to the suction pipe 114. The other end of the suction side connection pipe 106 is connected to the suction pipe 114 between the accumulator 13 and the suction side shutoff valve 144. A connecting pipe shutoff valve 136 is provided in the middle of each of the suction side connecting pipes 106 .

[0033] Each of the discharge pipes 108 is provided with a discharge-side connecting pipe 112. One end of the discharge-side connecting pipe 112 is connected to the discharge pipe 108 between the discharge-side shutoff valve 138 and the switching shutoff valve 142. The discharge-side connecting pipes 112 are joined at the other end and then connected to the discharge pipe 110. The other end of the discharge-side connecting pipe 112 is connected to the discharge pipe 110 between the switching shutoff valve 146 and the oil separator 14. A connecting pipe shutoff valve 140 is provided in each of the discharge side connecting pipes 112 at a midpoint.

[0034] A connecting pipe 116 is provided in the indoor side piping 100. One end of the connecting pipe 116 is connected in the indoor side piping 100 between the connection points with the discharge pipes 108 and the accumulator 13. The other end of the connecting pipe 116 is connected in the discharge piping 110 between the discharge side shutoff valve 148 and the switching shutoff valve 146. A connecting pipe shutoff valve 150 is provided midway through the connecting pipe 116 .

[0035] The accumulator 13 is provided with a connection pipe 118. One end of the connection pipe 118 is connected to the accumulator 13. The other end of the connection pipe 118 is connected to the discharge pipe 110, between the switching shutoff valve 146 and the oil separator 14. A connecting pipe shutoff valve 152 is provided midway through the connecting pipe 118 .

[0036] The suction side shut-off valves 134, 144, the discharge side shut-off valves 138, 148, the switching shut-off valves 132, 142, and the connecting pipe shut-off valves 136, 140, 150, 152 are opening and closing devices that can switch between an open state in which the refrigerant flows and a closed state in which the flow of the refrigerant is blocked in the refrigerant piping in which they are installed. The suction side shutoff valves 134, 144 correspond to the "suction side opening and closing device" in this disclosure, and the discharge side shutoff valves 138, 148 correspond to the "discharge side opening and closing device" in this disclosure.

[0037] An oil return pipe 62 that supplies oil to the first low-stage compressor 11A, the second low-stage compressor 11B, and the high-stage compressor 12 is connected to the oil separator 14. The oil return pipe 62 extends from the oil separator 14, branches off midway, and is connected to the first low-stage compressor 11A, the second low-stage compressor 11B, and the high-stage compressor 12, respectively.

[0038] Oil shutoff valves 69 are provided in the oil return pipe 62 at locations located between the midpoint and each of the first low-stage compressor 11A, the second low-stage compressor 11B, and the high-stage compressor 12. The oil shutoff valves 69 are opening / closing devices that can switch between an open state in which oil flows through the oil return pipe 62 and a closed state in which the flow of oil in the oil return pipe 62 is blocked at the location where the oil shutoff valves 69 are provided. In the refrigeration system 1, if a malfunction occurs in any of the first low-stage compressor 11A, the second low-stage compressor 11B, and the high-stage compressor 12 and operation stops, the oil shut-off valve 69 provided in the oil return pipe 62 connected to that compressor is shut off to prevent oil or refrigerant from being supplied to that compressor. The oil shutoff valve 69 corresponds to the "oil return pipe opening / closing device" of the present disclosure.

[0039] [1-1-2. Configuration related to refrigeration system control] FIG. 3 is a block diagram of the refrigeration system 1. 3, the refrigeration system 1 includes a space temperature sensor 27. The space temperature sensor 27 is disposed in the space to be conditioned of the indoor unit 20, and detects the temperature of the space to be conditioned. The refrigeration system 1 includes an internal temperature sensor 37. The internal temperature sensor 37 is disposed inside the refrigerator showcase or freezer showcase included in the refrigeration equipment 30, and detects the internal temperature.

[0040] 2 and 3, each of the discharge pipes 108 and the discharge pipe 110 is provided with a refrigerant temperature sensor 17. The refrigerant temperature sensor 17 detects the temperature of the refrigerant discharged from each of the high-stage compressor 12, the first low-stage compressor 11A, and the second low-stage compressor 11B.

[0041] The high-stage compressor 12, the first low-stage compressor 11A, and the second low-stage compressor 11B are each provided with a current sensor 19. The current sensor 19 detects the value of a current input to each of the high-stage compressor 12, the first low-stage compressor 11A, and the second low-stage compressor 11B. The current sensor 19 may be any of various detectors equipped with a current detection circuit.

[0042] As shown in Fig. 3, the outdoor unit 10 is provided with an operation panel 96. The operation panel 96 includes, for example, a display unit such as a monitor and controls such as switches, and is provided in a position where it can be operated by a worker repairing the compressor. In this embodiment, the operation panel 96 is capable of transmitting a predetermined signal when a worker operates the operation panel 96. The signal is transmitted when the worker operates the operation panel 96 after repair of the malfunctioning compressor has been completed. In other words, the operation panel 96 functions as an operation unit for the outdoor unit 10.

[0043] The operation panel 96 is not limited to being provided in the outdoor unit 10, but may be provided in any location in the refrigeration system 1, such as the indoor unit 20 or the cooling equipment 30. For example, the operation panel 96 may be a terminal device that includes communication hardware conforming to a predetermined communication standard and is capable of communicating with the control unit 91. For example, the operation panel 96 may include a touch panel.

[0044] 3, 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 through the outdoor heat exchanger 15, the indoor heat exchanger 22, and the cooling equipment 31, respectively, to promote heat exchange between the air and the refrigerant in each of these heat exchangers.

[0045] The outdoor unit 10 has a control device 90 and an outdoor unit I / F 95. The control device 90 has a control unit 91 and a storage unit 93.

[0046] The control unit 91 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 93. The control unit 91 may be configured with a single processor or multiple processors. A DSP (Digital Signal Processor) or the like may be used as the control unit 91. Furthermore, a control circuit such as an LSI (Large Scale Integration), an ASIC (Application Specific Integrated Circuit), or an FPGA (Field-Programming Gate Array) may be used as the control unit 91.

[0047] The control unit 91 is capable of receiving various signals from each unit provided in the outdoor unit 10, the indoor unit 20, and the cooling equipment 30 via the outdoor unit I / F 95. The control unit 91 is connected via the outdoor unit I / F 95 to each part of the outdoor unit 10, such as the memory unit 93 and the low-stage compressor 11, the indoor unit 20, and the cooling equipment 30, either by wire or wirelessly, and controls each part.

[0048] The control unit 91 reads a computer program stored in the storage unit 93 and operates in accordance with the read computer program, thereby functioning as an operation control unit 91a and a determination unit 91b.

[0049] The operation control unit 91a controls various devices such as the low-stage compressor 11, the high-stage compressor 12, and the opening and closing device of the outdoor unit 10. The operation control unit 91a transmits control signals to the indoor unit 20 and the cooling equipment 30 via the outdoor unit I / F 95, and causes the refrigeration system 1 to operate in coordination with each other.

[0050] The operation control unit 91a can change the rotation speed of the compression mechanism provided in each compressor and can change the discharge pressure of the refrigerant. The operation control unit 91a can, for example, drive the first low-stage compressor 11A and the second low-stage compressor 11B so that the refrigerant discharge pressure is approximately the same as that of the high-stage compressor 12. Furthermore, for example, the operation control unit 91a can drive the high-stage compressor 12 so that the refrigerant discharge pressure is approximately the same as that of each of the first low-stage compressor 11A and the second low-stage compressor 11B.

[0051] The operation control unit 91a can adjust the opening degree of the throttle valve 130 and can switch the oil cutoff valve 69 between an open state and a closed state. The operation control unit 91a can switch each of the suction side cutoff valves 134, 144, the discharge side cutoff valves 138, 148, the switching cutoff valves 132, 142, and the connecting pipe cutoff valves 136, 140, 150, 152 between an open state and a closed state. The operation control unit 91a corresponds to the "drive control unit" of the present disclosure.

[0052] The determination unit 91b compares the detection values ​​of the refrigerant temperature sensors 17 and the current sensors 19 with data such as a reference temperature and a reference current value included in the setting data 93a stored in the storage unit 93. If any of the detection values ​​of the refrigerant temperature sensors 17 and the current sensors 19 is equal to or greater than the reference temperature or reference current value, the determination unit 91b determines that a malfunction has occurred in one of the high-stage compressor 12, the first low-stage compressor 11A, or the second low-stage compressor 11B. Then, the determination unit 91b identifies the compressor having the sensor that detected the detection value equal to or greater than the reference value.

[0053] When a compressor equipped with a sensor that detected a detection value equal to or greater than the reference value is identified, the judgment unit 91b calculates the temperature difference between the detection value of the space temperature sensor 27 and the set temperature of the indoor unit 20, and the temperature difference between the detection value of the internal temperature sensor 37 and the set temperature of the cooling equipment 30, and compares these temperature differences.

[0054] If the temperature difference between the detection value of the space temperature sensor 27 and the set temperature of the indoor unit 20 is larger than the temperature difference between the detection value of the in-cabinet temperature sensor 37 and the set temperature of the cooling equipment 30, the determination unit 91b determines that the indoor unit 20 has a greater load than the cooling equipment 30. If the temperature difference between the detection value of the in-cabinet temperature sensor 37 and the set temperature of the cooling equipment 30 is larger than the temperature difference between the detection value of the space temperature sensor 27 and the set temperature of the indoor unit 20, the determination unit 91b determines that the cooling equipment 30 has a greater load than the indoor unit 20. The determination unit 91b corresponds to the "drive detection unit" and the "load detection unit" of the present disclosure.

[0055] When a malfunction occurs in any of the compressors and the determination unit 91b determines the difference in load between the cooling equipment 30 and the indoor unit 20, the operation control unit 91a stops the operation of all compressors. Next, the operation control unit 91a closes the shutoff valves provided on the suction side and discharge side of the compressor where the malfunction occurred. This allows the refrigeration system 1 to separate the malfunctioning compressor from the refrigeration circuit 2.

[0056] Next, the operation control unit 91a opens or closes each of the switching shutoff valves 132, 142 and the connecting pipe shutoff valves 136, 140, 150, 152 depending on the compressor in which the malfunction has occurred and the difference in load between the cooling equipment 30 and the indoor unit 20. In this way, the operation control unit 91a can connect multiple compressors in which no malfunction has occurred in the refrigeration circuit 2 in series or in parallel with each other. Thereafter, the operation control unit 91a restarts the operation of each of the compressors that are not experiencing any malfunction.

[0057] If a malfunction occurs in either the first low-stage compressor 11A or the second low-stage compressor 11B and the judgment unit 91b judges that the load on the cooling equipment 30 is equal to or greater than the load on the indoor unit 20, the operation control unit 91a drives the high-stage compressor 12 so that the discharge pressure of the refrigerant becomes approximately the same as that of the low-stage compressor 11 when operation is resumed.

[0058] If a malfunction occurs in either the first low-stage compressor 11A or the second low-stage compressor 11B and the determination unit 91b determines that the indoor unit 20 is under a greater load than the cooling equipment 30, the operation control unit 91a drives each of the compressors that are not malfunctioning when operation is resumed so that the refrigerant discharge pressure is approximately the same as before operation was stopped.

[0059] If a malfunction occurs in the high-stage compressor 12 and the judgment unit 91b judges that the indoor unit 20 is under a greater load than the cooling equipment 30, the operation control unit 91a drives one of the low-stage compressors 11 so that the discharge pressure of the refrigerant becomes approximately the same as that of the high-stage compressor 12 when operation is resumed.

[0060] The operation control unit 91a may switch the operation of either the first low-stage compressor 11A or the second low-stage compressor 11B when operation is resumed, based on the load on the first low-stage compressor 11A and the second low-stage compressor 11B. For example, the operation control unit 91a may acquire the cumulative operating time and cumulative rotation speed of the first low-stage compressor 11A and the second low-stage compressor 11B. The operation control unit 91a may drive the low-stage compressor 11 with a shorter operating time or a lower rotation speed so that the refrigerant discharge pressure becomes approximately the same as that of the high-stage compressor 12. In other words, the operation control unit 91a may switch the operation of the low-stage compressor 11 with a lighter load so that the discharge pressure becomes approximately the same as that of the high-stage compressor 12. In the refrigeration system 1, the determination unit 91b may determine the low-stage compressor 11 with a lighter load.

[0061] The determining unit 91b can determine that the repair of each compressor has been completed when it receives a predetermined signal, which is transmitted, for example, when a worker repairing the compressor operates the operation panel 96.

[0062] The storage unit 93 includes a memory device such as a random access memory (RAM) or a read-only memory (ROM), 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 93 also stores computer programs, databases, tables, and the like used for various operations of the refrigeration system 1. These computer programs, etc. may be installed into the storage unit 93 from a computer-readable portable recording medium using a known setup program, etc. The portable recording medium may be, for example, a compact disc read-only memory (CD-ROM), a digital versatile disc read-only memory (DVD-ROM), a universal serial bus (USB) memory, or a semiconductor storage device including an SSD (Solid State Drive). The computer programs, etc. may be installed from a predetermined server, etc. The storage unit 93 may also include a volatile storage area and may constitute a work area for the control unit 91.

[0063] Setting data 93a is stored in the storage unit 93. The setting data 93a includes data on the set temperature of the indoor unit 20 and data on the set temperature of the cooling equipment 30. The setting data 93a includes data on a reference temperature of the refrigerant discharged from each compressor and a reference current value input to each compressor. The reference temperature corresponds to, for example, the refrigerant temperature discharged from a compressor in an oil shortage state. The reference current value corresponds to, for example, a current value that causes a so-called overcurrent.

[0064] The outdoor unit I / F 95 has communication hardware such as a communication interface circuit and a connector that enables the outdoor unit 10 to communicate with each device in accordance with a predetermined communication protocol via a cable, etc. The outdoor unit I / F 95 sends data received from each device to the control device 90, and also sends data received from the control device 90 to each device.

[0065] The indoor unit 20 has an indoor unit control device 80 and an indoor unit I / F 85. The indoor unit control device 80 has an indoor unit control section 81 and an indoor unit storage section 83.

[0066] The indoor unit control unit 81 is a processor such as a CPU or MPU, similar to the control unit 91. The indoor unit control unit 81 operates in accordance with a computer program stored in the indoor unit storage unit 83, thereby controlling various devices such as the blower 28 mounted in the indoor unit 20. The indoor unit control unit 81 also receives output signals from various sensors mounted in the indoor unit 20, such as the space temperature sensor 27. The indoor unit storage unit 83, like the storage unit 93, has storage devices such as RAM and ROM, and stores computer programs and the like used for various operations of the indoor unit 20.

[0067] The indoor unit I / F 85 has communication hardware such as a communication interface circuit and connectors for the indoor unit 20 to communicate with each device. The indoor unit I / F 85 sends data received from the space temperature sensor 27 and each device to the indoor unit control device 80, and also sends data received from the indoor unit control device 80 to each device.

[0068] The refrigeration equipment 30 has a refrigeration equipment control device 70 and a refrigeration equipment I / F 75. The refrigeration equipment control device 70 has a refrigeration equipment control unit 71 and a refrigeration equipment storage unit 73.

[0069] The refrigeration equipment control unit 71 is a processor such as a CPU or an MPU, similar to the control unit 91. The refrigeration equipment control unit 71 operates in accordance with a computer program stored in the refrigeration equipment storage unit 73 to control various devices such as the blower 38 mounted in the refrigeration equipment 30. The refrigeration equipment control unit 71 also receives output signals from various sensors mounted in the refrigeration equipment 30, such as the internal temperature sensor 37. The refrigeration equipment storage unit 73, like the storage unit 93, has storage devices such as RAM and ROM, and stores computer programs and the like used for various operations of the refrigeration equipment 30.

[0070] The refrigeration equipment I / F 75 has communication hardware such as a communication interface circuit and a connector for the refrigeration equipment 30 to communicate with each device. The refrigeration equipment I / F 75 sends data received from the inside temperature sensor 37 and each device to the refrigeration equipment control device 70, and also sends data received from the refrigeration equipment control device 70 to each device.

[0071] The operation control unit 91a and the determination unit 91b are not limited to being included in the control unit 91, and may also be included in the indoor unit control unit 81 or the refrigeration equipment control unit 71. For example, the operation control unit 91a and the determination unit 91b may be included in a processor provided in another location in the refrigeration system 1. For example, the operation control unit 91a and the determination unit 91b may also be included 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.

[0072] [1-2-1. Refrigeration system operation] First, the cooling operation will be described. 1, when the refrigeration system 1 performs cooling operation, the operation control unit 91a opens the first cooling valve 51 and also opens the second cooling valve 55 and the third cooling valve 56. In addition, the operation control unit 91a closes the first heating valve 52, the second heating valve 57, the outdoor refrigerant return valve 53, and the refrigerant return expansion mechanism 58. In this state, by driving the low-stage compressor 11 and each high-stage compressor 12, the refrigerant compressed by each low-stage compressor 11 is sent to the high-stage compressor 12, where it is further compressed and discharged toward the oil separator 14.

[0073] The refrigerant that has passed through the oil separator 14 passes through the first cooling valve 51 and is sent to the outdoor heat exchanger 15, where it exchanges heat with outside air. The refrigerant after heat exchange is sent to the gas-liquid separator 16 via the second cooling valve 55 and sent to the indoor heat exchanger 22 via the third cooling valve 56 . In the indoor heat exchanger 22, the refrigerant exchanges heat with the indoor air to cool the indoor air. The refrigerant that has exchanged heat with the indoor air is returned to the high-stage compressor 12 via the accumulator 13.

[0074] On the other hand, a portion of the refrigerant from the gas-liquid separator 16 is sent to the refrigeration heat exchanger 31 via the refrigeration inlet side expansion mechanism 32, where it undergoes heat exchange to cool the refrigeration equipment 30. The refrigerant that has undergone heat exchange in the refrigeration heat exchanger 31 is returned to each of the low-stage compressors 11 via the refrigeration outlet side pressure adjustment mechanism 33.

[0075] Next, the operation when performing heating operation will be described. FIG. 4 is a circuit diagram of the refrigeration system 1 showing the operation of the heating mode. In FIG. 4, the flow of the refrigerant is indicated by arrows. For ease of explanation, in FIG. 4, the valve body in the open state is shown in white, and the valve body in the closed state and the throttling mechanism in the closed state are shown in black. For ease of explanation, in FIG. 4, the pipes through which the refrigerant flows are shown in thick lines, and the pipes through which the refrigerant does not flow are shown in thin lines. As shown in FIG. 4, when performing heating operation, the operation control unit 91a opens the first heating valve 52 and the second heating valve 57, and closes the on-off valve 23, the first cooling valve 51, the second cooling valve 55, the third cooling valve 56, the outdoor refrigerant return valve 53, and the refrigerant return expansion mechanism 58.

[0076] In this state, by driving each of the low-stage compressors 11 and the high-stage compressor 12, the refrigerant compressed by each of the low-stage compressors 11 is sent to the high-stage compressor 12, where it is further compressed and discharged toward the oil separator 14. The refrigerant that has passed through the oil separator 14 passes through the first heating valve 52 and is sent to the indoor heat exchanger 22, where it exchanges heat with indoor air to heat the indoor air.

[0077] The refrigerant that has undergone heat exchange in the indoor heat exchanger 22 is sent to the gas-liquid separator 16 via the second heating valve 57, and then sent to the refrigeration heat exchanger 31 via the refrigeration inlet side expansion mechanism 32, where it undergoes heat exchange and cools the refrigeration equipment 30. The refrigerant that has exchanged heat in the chiller heat exchanger 31 is returned to the low-stage compressor 11 via the chiller outlet pressure adjustment mechanism 33 . That is, when the refrigeration system 1 of the present disclosure performs heating operation, the outdoor heat exchanger 15 is not used, and the indoor heat exchanger 22 functions as a gas cooler or a radiator.

[0078] [1-2-2. Operation of the refrigeration system around the compressor] Next, the operation of the refrigeration system 1 around the compressor will be described. 2, when no malfunction occurs in any of the compressors in the refrigeration system 1, the operation control unit 91a opens the suction side shutoff valves 134, 144, the discharge side shutoff valves 138, 148, the switching shutoff valve 146, and the oil shutoff valve 69. Furthermore, the operation control unit 91a closes the connecting pipe shutoff valves 136, 140, 150, 152, and opens the switching shutoff valves 132, 142.

[0079] In the refrigeration circuit 2 in this state, in the refrigeration system 1, the refrigerant flowing out from the cooling equipment 30 is compressed by each of the low-stage compressors 11. Also, in the refrigeration system 1, the refrigerant flowing out from the indoor unit 20 is compressed by the high-stage compressor 12 together with the refrigerant compressed by each of the low-stage compressors 11. As a result, in the refrigeration system 1, the refrigerant flowing out from each of the heat exchangers with different evaporation temperatures is compressed in two stages, making it possible to operate each of the indoor unit 20 and the cooling equipment 30. Hereinafter, in the refrigeration system 1, a state in which no malfunction occurs in any of the compressors will be referred to as a normal state.

[0080] [1-2-3. Operation of the refrigeration system when a compressor malfunctions] Next, the operation of the refrigeration system 1 when a malfunction occurs in any of the compressors will be described. FIG. 5 is a flowchart showing the operation of the refrigeration system 1. 5, determination unit 91b acquires the detection values ​​of each refrigerant temperature sensor 17 and each current sensor 19, and compares the detection values ​​with data such as a reference temperature and a reference current value included in setting data 93a stored in memory unit 93 (step SA1). If the detection values ​​are all lower than the reference temperature and reference current value included in setting data 93a stored in memory unit 93 (step SA1: NO), determination unit 91b acquires the detection values ​​of each refrigerant temperature sensor 17 and each current sensor 19 again.

[0081] If any of the detected values ​​is equal to or greater than the reference temperature or reference current value contained in the setting data 93a stored in the memory unit 93 (step SA1: YES), the judgment unit 91b judges whether the compressor in which the detected value is equal to or greater than the reference value is the high-stage compressor 12 (step SA2). If the compressor in which a detected value equal to or greater than the reference value is detected is the high-stage compressor 12 (step SA2: YES), the determination unit 91b determines whether the load of the cooling equipment 30 is equal to or greater than the load of the indoor unit 20 (step SA3).

[0082] Fig. 6 is a diagram showing the refrigeration circuit 2 when a malfunction occurs in the high-stage compressor 12. In Fig. 6, the malfunctioning high-stage compressor 12 is shown in black. In the following drawings in this disclosure, the malfunctioning compressor is shown in black. If the load of the cooling equipment 30 is equal to or greater than the indoor unit 20 (step SA3: YES), the operation control unit 91a stops the operation of all compressors (step SA4). Next, as shown in Fig. 6, the operation control unit 91a closes the suction-side shutoff valve 144, the discharge-side shutoff valve 148, and the switching shutoff valve 146, and opens the connecting pipe shutoff valve 152. Furthermore, the operation control unit 91a closes the oil shutoff valve 69 provided in the oil return pipe 62 connected to the high-stage compressor 12. Other opening and closing devices around the compressors provided in the outdoor unit 10 remain in the same state as in the normal state (step SA5). As a result, the high-stage compressor 12 is disconnected from the refrigeration circuit 2, and the first low-stage compressor 11A and the second low-stage compressor 11B are connected in parallel.

[0083] Next, the operation control unit 91a resumes the operation of the compressors other than the compressor determined to have a malfunction (step SA6), as shown in Fig. 5. This enables the refrigeration system 1 to perform single-stage compression of the refrigerant.

[0084] After resuming operation of the high-stage compressor 12, the operation control unit 91a determines whether or not a predetermined signal has been received by operating the operation panel 96, i.e., whether or not repairs have been completed for the compressor that was determined to have a malfunction (step SA7). When the operation control unit 91a receives the predetermined signal, that is, when it determines that the repair of the compressor determined to have malfunctioned has been completed, the operation control unit 91a stops the operation of all compressors (step SA8). Next, the operation control unit 91a returns each shutoff valve to the open / close state before step SA5, i.e., the state shown in Figure 2 (step SA9). Thereafter, the operation control section 91a restarts the operations of all the compressors (step SA10). That is, the operation control section 91a causes the refrigeration system 1 to perform normal operation.

[0085] FIG. 7 is a diagram showing the refrigeration circuit 2 when a malfunction occurs in the high-stage compressor 12. In step SA3, if the load of the cooling equipment 30 is smaller than that of the indoor unit 20 (step SA3: NO), the operation control unit 91a stops the operation of all compressors (step SA11). Next, the operation control unit 91a closes the suction side shutoff valve 144, the discharge side shutoff valve 148, and the switching shutoff valve 146, as shown in FIG. The operation control unit 91a closes the switching shutoff valve 132 provided in the intake piping 104 connected to the first low-stage compressor 11A and the switching shutoff valve 142 provided in the discharge piping 108 connected to the first low-stage compressor 11A. The operation control unit 91a opens a connecting pipe shutoff valve 140 provided in a discharge side connecting pipe 112 branching off from a discharge pipe 108 connected to the first low stage compressor 11A. The operation control unit 91a opens a connecting pipe shutoff valve 136 provided in a suction side connecting pipe 106 branching off from a suction pipe 104 connected to the first low stage compressor 11A. Furthermore, the operation control unit 91a closes the oil shutoff valve 69 provided in the oil return pipe 62 connected to the high-stage compressor 12. Other opening and closing devices around the compressor provided in the outdoor unit 10 are in the same state as in the normal state (step SA12). As a result, the high-stage compressor 12 is disconnected from the refrigeration circuit 2, and the first low-stage compressor 11A and the second low-stage compressor 11B are connected in series.

[0086] Next, as shown in Fig. 5, the operation control unit 91a resumes operation of the compressors other than the compressor determined to have a malfunction (step SA13). In this case, the operation control unit 91a drives the first low-stage compressor 11A as a high-stage compressor. This enables the refrigeration system 1 to perform two-stage compression of the refrigerant. Next, the operation control unit 91a performs steps SA7 to SA10.

[0087] FIG. 8 is a diagram showing the refrigeration circuit 2 when a malfunction occurs in the high-stage compressor 12. In step SA13, the operation control unit 91a may drive the second low-stage compressor 11B as the high-stage compressor. In this case, in step SA13, the operation control unit 91a closes the suction-side shutoff valve 144, the discharge-side shutoff valve 148, and the switching shutoff valve 146, as shown in FIG. The operation control unit 91a closes the switching shutoff valve 132 provided in the suction pipe 104 connected to the second low-stage compressor 11B and the switching shutoff valve 142 provided in the discharge pipe 108 connected to the second low-stage compressor 11B. The operation control unit 91a opens the connecting pipe shutoff valve 140 provided in the discharge side connecting pipe 112 branching off from the discharge pipe 108 connected to the second low stage compressor 11B.

[0088] 5, if the compressor in which a detected value equal to or greater than the reference value is detected is not the high-stage compressor 12 in step SA2 (step SA2: NO), the determination unit 91b determines whether or not the compressor in which a detected value equal to or greater than the reference value is the first low-stage compressor 11A (step SA14). If the compressor in which a detected value equal to or greater than the reference value is the first low-stage compressor 11A (step SA14: YES), the determination unit 91b determines whether or not the load of the cooling equipment 30 is equal to or greater than the load of the indoor unit 20 (step SA15). If the load of the cooling equipment 30 is equal to or greater than the load of the indoor unit 20 (step SA15: YES), the operation control section 91a stops the operation of all compressors (step SA16).

[0089] FIG. 9 is a diagram showing the refrigeration circuit 2 when a malfunction occurs in the first low stage compressor 11A. Next, as shown in Figure 9, the operation control unit 91a closes the suction side shutoff valve 134 provided in the suction piping 104 connected to the first low-stage compressor 11A, and the discharge side shutoff valve 138 and the switching shutoff valve 142 provided in the discharge piping 108 connected to the first low-stage compressor 11A. The operation control unit 91a opens the connecting pipe shutoff valve 136 provided in the suction side connecting pipe 106 branching off from the suction pipe 104 connected to the first low stage compressor 11A. The operation control unit 91a opens the connecting pipe cutoff valves 150 and 152 and closes the switching cutoff valve 146. Furthermore, the operation control unit 91a closes the oil shutoff valve 69 provided in the oil return pipe 62 connected to the first low-stage compressor 11A (step SA17). As a result, the first low-stage compressor 11A is disconnected from the refrigeration circuit 2, and the second low-stage compressor 11B and the high-stage compressor 12 are connected in parallel.

[0090] Next, as shown in Fig. 5, the operation control unit 91a resumes operation of the compressors other than the compressor determined to have a malfunction (step SA18). In this case, the operation control unit 91a drives the high-stage compressor 12 as a low-stage compressor. This enables the refrigeration system 1 to perform single-stage compression of the refrigerant. Next, the operation control unit 91a performs steps SA7 to SA10.

[0091] FIG. 10 is a diagram showing the refrigeration circuit 2 when a malfunction occurs in the first low stage compressor 11A. In step SA15, if the load of the cooling equipment 30 is smaller than that of the indoor unit 20 (step SA15: NO), the operation control section 91a stops the operation of all compressors (step SA19). Next, the operation control unit 91a closes the suction-side shutoff valve 134 and the switching shutoff valve 132 provided in the suction piping 104 connected to the first low-stage compressor 11A, as shown in Fig. 10. The operation control unit 91a closes the switching shutoff valve 142 provided in the discharge piping 108 connected to the first low-stage compressor 11A. Furthermore, the operation control unit 91a closes the oil shutoff valve 69 provided in the oil return pipe 62 connected to the first low-stage compressor 11A (step SA20). As a result, the first low-stage compressor 11A is separated from the refrigeration circuit 2, and the high-stage compressor 12 and the second low-stage compressor 11B are connected in series.

[0092] Next, the operation control unit 91a resumes operation of the compressors other than the compressor determined to have a malfunction (step SA21), as shown in Fig. 5. This enables the refrigeration system 1 to perform two-stage compression of the refrigerant. Next, the operation control unit 91a performs steps SA7 to SA10.

[0093] In step SA14, if the compressor in which a detected value equal to or greater than the reference value is detected is not the first low-stage compressor 11A (step SA14: NO), the determination unit 91b determines whether the compressor in which a detected value equal to or greater than the reference value is detected is the second low-stage compressor 11B (step SA22).If the compressor in which a detected value equal to or greater than the reference value is detected is the second low-stage compressor 11B (step SA22: YES), the determination unit 91b determines whether the load of the cooling equipment 30 is equal to or greater than the load of the indoor unit 20 (step SA23). If the load of the cooling equipment 30 is equal to or greater than the load of the indoor unit 20 (step SA23: YES), the operation control section 91a stops the operation of all compressors (step SA24).

[0094] FIG. 11 is a diagram showing the refrigeration circuit 2 when a malfunction occurs in the second low stage compressor 11B. 11, the operation control unit 91a closes the suction side shutoff valve 134 provided in the suction piping 104 connected to the second low-stage compressor 11B, and the discharge side shutoff valve 138 and the switching shutoff valve 142 provided in the discharge piping 108 connected to the second low-stage compressor 11B. The operation control unit 91a opens the connecting pipe shutoff valve 136 and the connecting pipe shutoff valves 150 and 152 provided in the suction side connecting piping 106 branching from the suction piping 104 connected to the second low-stage compressor 11B, and closes the switching shutoff valve 146. Furthermore, the operation control unit 91a closes the oil shutoff valve 69 provided in the oil return pipe 62 connected to the second low-stage compressor 11B (step SA25). As a result, the second low-stage compressor 11B is separated from the refrigeration circuit 2, and the high-stage compressor 12 and the first low-stage compressor 11A are connected in parallel.

[0095] Next, as shown in Fig. 5, the operation control unit 91a resumes operation of the compressors other than the compressor determined to have a malfunction (step SA26). In this case, the operation control unit 91a drives the high-stage compressor 12 as a low-stage compressor. This enables the refrigeration system 1 to perform single-stage compression of the refrigerant. Next, the operation control unit 91a performs steps SA7 to SA10.

[0096] FIG. 12 is a diagram showing the refrigeration circuit 2 when a malfunction occurs in the second low stage compressor 11B. At step SA23, if the load of the cooling equipment 30 is smaller than that of the indoor unit 20 (step SA23: NO), the operation control unit 91a stops the operation of all compressors (step SA27). Next, as shown in Fig. 12, the operation control unit 91a closes the suction side shutoff valve 134 and the switching shutoff valve 132 provided in the suction piping 104 connected to the second low-stage compressor 11B, and the discharge side shutoff valve 138 and the switching shutoff valve 142 provided in the discharge piping 108 connected to the second low-stage compressor 11B. Furthermore, the operation control unit 91a closes the oil shutoff valve 69 provided in the oil return pipe 62 connected to the second low-stage compressor 11B (step SA28). As a result, the second low-stage compressor 11B is separated from the refrigeration circuit 2, and the high-stage compressor 12 and the first low-stage compressor 11A are connected in series.

[0097] Next, as shown in FIG. 5, the operation control unit 91a resumes the operation of the compressors other than the compressor determined to have a malfunction (step SA29). This allows the refrigeration system 1 to perform two-stage compression of the refrigerant. Next, the operation control unit 91a performs steps SA7 to SA10.

[0098] As described above, the refrigeration system 1 is provided with the throttle valve 130, which is capable of adjusting the opening degree of the indoor piping 100, in the indoor piping 100 that connects the outdoor unit 10 and the indoor unit 20. When the determination unit 91b detects an abnormality in the driving state of the low-stage compressor 11, the operation control unit 91a may open and close the throttle valve 130 so that the pressure of the refrigerant flowing from the indoor unit 20 to the outdoor unit 10 approaches the pressure of the refrigerant flowing from the cooling equipment 30 to the outdoor unit 10. This allows the refrigeration system 1 to continue operation by prioritizing air conditioning-related operations even if a malfunction occurs in the low-stage compressor 11. Therefore, even if a malfunction occurs in the low-stage compressor 11, the refrigeration system 1 can continue operation while suppressing a decrease in the performance of the indoor unit 20.

[0099] As in this embodiment, when the judgment unit 91b detects an abnormality in the driving state of the high-stage compressor 12, the operation control unit 91a may open and close the throttle valve 130 so that the pressure of the refrigerant flowing from the indoor unit 20 to the outdoor unit 10 approaches the pressure of the refrigerant flowing from the cooling equipment 30 to the outdoor unit 10. As a result, the refrigeration system 1 can continue to operate using single-stage compression even if a malfunction occurs in the high-stage compressor 12. Therefore, even if a malfunction occurs in the high-stage compressor 12, the refrigeration system 1 can continue to operate while suppressing a decrease in the performance of the indoor unit 20.

[0100] When a malfunction occurs in any of the compressors shown in FIG. 5, the refrigeration system 1 can operate in any operating state, such as heating operation, cooling operation, or fan operation.

[0101] [1-3. Effects, etc.] As described above, in this embodiment, the refrigeration system 1 includes a refrigeration circuit 2 provided with the outdoor heat exchanger 15, the indoor heat exchanger 22, the chilled heat exchanger 31, a plurality of low-stage compressors 11, and the high-stage compressor 12 located on the discharge side of the low-stage compressor 11. The low-stage compressor 11 and the high-stage compressor 12 are each provided with discharge pipes 108, 110 that are connected to the discharge side, and suction pipes 104, 114 that are connected to the suction side. The discharge pipes 108, 110 are each provided with discharge-side shutoff valves 138, 148 that can open and close the discharge pipes 108, 110, and the suction pipes 104, 114 are each provided with suction-side shutoff valves 134, 144 that can open and close the suction pipes 104, 114. The suction pipe 104 provided in each of the low-stage compressors 11 is provided with a suction-side connecting pipe 106 that connects the upstream side of the suction-side shutoff valve 134 to the upstream side of the suction pipe 114 provided in the high-stage compressor 12, the suction pipe 114 being provided in the high-stage compressor 12. The discharge pipe 108 provided in the low-stage compressor 11 is provided with a discharge-side connecting pipe 112 that connects the downstream side of the discharge-side shutoff valve 138 to the downstream side of the discharge-side shutoff valve 148 of the discharge pipe 110 provided in the high-stage compressor 12. This allows the refrigeration system 1 to separate the malfunctioning compressor from the refrigeration circuit 2. Therefore, the refrigeration system 1 can continue to operate while the malfunctioning compressor is being repaired.

[0102] As in the present embodiment, the refrigeration system 1 includes an operation control unit 91a and a determination unit 91b capable of detecting the operating state of each of the compressors. When the determination unit 91b detects an abnormality in the operating state of at least one of the compressors, the operation control unit 91a may close discharge-side shutoff valves 138, 148 provided in the discharge pipes 108, 110 of the compressor for which the abnormality has been detected, and suction-side shutoff valves 134, 144 provided in the suction pipes 104, 114 of the compressor for which the abnormality has been detected. This allows the refrigeration system 1 to separate the malfunctioning compressor from the refrigeration circuit 2. Therefore, the refrigeration system 1 can continue to operate while the malfunctioning compressor is being repaired.

[0103] As in this embodiment, when the determination unit 91b detects an abnormality in the driving state of the low-stage compressor 11, the operation control unit 91a may drive the high-stage compressor 12 as the low-stage compressor 11. As a result, the refrigeration system 1 can perform single-stage compression using two compressors connected in parallel even if a malfunction occurs in the low-stage compressor 11. Therefore, even if a malfunction occurs in the low-stage compressor 11, the refrigeration system 1 can continue to operate while suppressing a decrease in the performance of the refrigeration equipment 30.

[0104] As in this embodiment, when the judgment unit 91b detects an abnormality in the driving state of the high-stage compressor 12, the operation control unit 91a may drive one of the low-stage compressors 11 as the high-stage compressor 12. As a result, the refrigeration system 1 can perform two-stage compression using two compressors connected in series even if a malfunction occurs in the high-stage compressor 12. Therefore, even if a malfunction occurs in the high-stage compressor 12, the refrigeration system 1 can continue to operate while suppressing a decrease in the performance of the indoor unit 20 and the cooling equipment 30.

[0105] As in the present embodiment, the refrigeration system 1 includes an accumulator 13. The accumulator 13 is connected to a discharge pipe 108 extending from the discharge side of each of the low-stage compressors 11 and a suction pipe 114 extending from the suction side of the high-stage compressor 12. The refrigeration system 1 may also be provided with a connection pipe 118 that connects the accumulator 13 to a downstream side of the switching shutoff valve 146 of the discharge pipe 110 provided in the high-stage compressor 12. This allows the refrigeration system 1 to separate the malfunctioning compressor from the refrigeration circuit 2 and perform single-stage compression using another compressor. Therefore, the refrigeration system 1 can continue to operate while the malfunctioning compressor is being repaired.

[0106] As in the present embodiment, the refrigeration system 1 includes a determination unit 91b that can detect the loads of each of the cooling equipment 30 and the indoor units 20. When the determination unit 91b detects an abnormality in the driving state of at least one of the compressors, the operation control unit 91a may determine to drive compressors other than the compressor in which the abnormality was detected, based on the detection result of the determination unit 91b. As a result, even if a malfunction occurs in the low-stage compressor 11, the refrigeration system 1 can change the operation of the compressors according to the loads of the cooling equipment 30 and the indoor units 20. Therefore, the refrigeration system 1 can continue operation by prioritizing the utilization unit with a greater load, either the cooling equipment 30 or the indoor units 20.

[0107] As in the present embodiment, an oil return pipe 62 that supplies oil is connected to the low-stage compressor 11 and the high-stage compressor 12, and an oil shut-off valve 69 that can open and close the oil return pipe 62 is provided in the oil return pipe 62. In the refrigeration system 1, when the determination unit 91b detects an abnormality in the driving state of either the low-stage compressor 11 or the high-stage compressor 12, the oil shut-off valve 69 may be closed. As a result, in the refrigeration system 1, if a malfunction occurs in the low-stage compressor 11 or the high-stage compressor 12 and operation stops, the oil shut-off valve 69 can be shut off. Therefore, in the refrigeration system 1, if a malfunction occurs in the low-stage compressor 11 or the high-stage compressor 12, the supply of oil or refrigerant to the low-stage compressor 11 or the high-stage compressor 12 is suppressed.

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

[0109] In the embodiment described above, the determination unit 91b determines the loads on the indoor unit 20 and the cooling equipment 30 by comparing the temperature difference between the detection value of the space temperature sensor 27 and the set temperature of the indoor unit 20 with the temperature difference between the detection value of the inside temperature sensor 37 and the set temperature of the cooling equipment 30. However, this is not limiting, and in the refrigeration system 1, the determination unit 91b may determine the loads on the indoor unit 20 and the cooling equipment 30 based on other detection values.

[0110] For example, the judgment unit 91b may compare the temperature difference between the outside air temperature and the set temperature of the indoor unit 20 with the temperature difference between the temperature of the cool air blown out of the cooling equipment and the set temperature of the cooling equipment 30 to judge the load on the indoor unit 20 and the cooling equipment 30. For example, sensors may be provided to detect the pressure of the refrigerant flowing from each of the indoor unit 20 and the cooling equipment 30 into the outdoor unit 10, and the load on the indoor unit 20 and the cooling equipment 30 may be determined by the judgment unit 91b comparing the detected values ​​of the sensors.

[0111] In the above-described embodiment, the refrigeration system 1 includes one indoor heat exchanger 22 and one cooling-use heat exchanger 31. However, the present invention is not limited to this, and the refrigeration system 1 may include another cooling-use heat exchanger 31 instead of the indoor heat exchanger 22. That is, the refrigeration system 1 may omit the indoor unit 20 and include multiple cooling devices 30. In this case, the evaporating temperature ranges of the plurality of refrigeration heat exchangers 31 are different from one another. Of the plurality of refrigeration heat exchangers 31, the refrigeration heat exchanger 31 with a higher evaporating temperature range is connected to the inlet side of the high-stage compressor 12, and the refrigeration heat exchanger 31 with a lower evaporating temperature range is connected to the inlet side of the low-stage compressor 11.

[0112] For example, if the refrigeration system 1 includes a chiller 30 set to the freezing temperature range and a chiller 30 set to the refrigeration temperature range, the chiller heat exchanger 31 in the chiller 30 set to the refrigeration temperature range is connected to the inlet side of the high-stage compressor 12. On the other hand, the chiller heat exchanger 31 in the chiller 30 set to the freezing temperature range is connected to the inlet side of the low-stage compressor 11.

[0113] 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 to the high-stage compressor 12. Similarly, a plurality of use-side heat exchangers connected to the inlet side of the low-stage compressor 11 may be provided in parallel to the low-stage compressor 11. In this case, at least one of the refrigeration heat exchangers 31 provided in parallel may have an evaporation temperature range different from that of the other refrigeration heat exchangers 31.

[0114] Furthermore, for example, the control device 90 and the operation panel 96 may be provided integrally with an operation terminal such as a remote control provided in the indoor unit 20 or the cooling equipment 30. The remote control is a terminal that operates the temperature settings of the indoor unit 20 or the cooling equipment 30, starts the indoor unit 20 or the cooling equipment 30, etc.

[0115] Furthermore, for example, the control device 90 may be a communication terminal such as a smartphone or tablet on which an app or program that transmits predetermined signals to the outdoor unit 10 and each part of the refrigeration system 1 is installed. In this case, the control device 90 may be capable of communicating with the outdoor unit 10 and each part of the refrigeration system 1 via a network consisting of a public line network, a dedicated line, other communication lines, and various communication facilities. The specific form of this network is not limited. The communication network may include at least one of a wireless communication circuit and a wired communication circuit. In this case, the operation panel 96 may be provided integrally with the control device 90.

[0116] Furthermore, for example, the control device 90 may be a server device on which an application or program is installed that transmits predetermined signals to the outdoor unit 10 and each part of the refrigeration system 1. The server device may be capable of communicating with the outdoor unit 10 and each part of the refrigeration system 1 via the above-mentioned network.

[0117] In the above-described embodiment, when a malfunction occurs in the high-stage compressor 12, the refrigeration system 1 is capable of performing single-stage compression of the refrigerant by configuring the circuit as shown in Fig. 6. However, this is not limiting, and for example, when the indoor unit 20 is not in use, the refrigeration system 1 may perform single-stage compression of the refrigerant by stopping the operation of the high-stage compressor 12 and configuring the circuit as shown in Fig. 6.

[0118] For example, when the refrigeration system 1 is equipped with a cooling device 30 set to a freezing temperature range and the indoor unit 20 is not used, the refrigeration system 1 may perform two-stage compression of the refrigerant by stopping the operation of the high-stage compressor 12 and configuring a circuit as shown in Figures 7 and 8.

[0119] Furthermore, for example, when the load on the refrigeration equipment 30 is small, the refrigeration system 1 may perform single-stage or two-stage compression of the refrigerant by stopping the operation of either the low-stage compressor 11A or 11B and using any of the circuits shown in Figures 9 to 12. In this case, the control device 90 may acquire the operation time of each of the low-stage compressors 11A, 11B, and stop the compressor with the longer operation time preferentially.

[0120] The components shown in FIG. 3 are merely examples, and the specific implementation form 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 as 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.

[0121] The step units of the operation shown in Figure 5 are divided according to the main processing content to make it easier to understand the operation of each part of the refrigeration system 1, and the operation is not limited by the way the processing units are divided or the names of the processing units. The operation may be divided into more step units depending on the processing content. Furthermore, one step unit may be divided so that it includes more processing. Furthermore, the order of the steps may be changed as appropriate within the scope that does not interfere with the purpose of this disclosure.

[0122] 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.

[0123] (Addendum) The above description of the embodiments discloses the following techniques.

[0124] (Technology 1) A refrigeration circuit is provided with a plurality of compressors, a heat source side heat exchanger, and a plurality of user side heat exchangers, wherein 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 plurality of compressors are composed of a plurality of low stage compressors and at least one high stage compressor provided on the discharge side of the plurality of low stage compressors, and each of the low stage compressors and the high stage compressors is provided with a discharge pipe which is a pipe connected to the discharge side, and a suction pipe which is a pipe connected to the suction side, and each of the discharge pipes is provided with a discharge side opening and closing device capable of opening and closing the discharge pipe is provided, each of the suction pipes is provided with a suction side opening and closing device capable of opening and closing the suction pipe, the suction pipe provided in the low-stage compressor is provided with a suction side connecting pipe that connects the downstream side of the suction side opening and closing device to the downstream side of the suction side opening and closing device of the suction pipe provided in the high-stage compressor, and the discharge pipe provided in the low-stage compressor is provided with a discharge side connecting pipe that connects the downstream side of the discharge side opening and closing device to the downstream side of the discharge side opening and closing device of the discharge pipe provided in the high-stage compressor. This allows the refrigeration system to isolate the failed compressor from the refrigeration circuit, allowing the refrigeration system to continue operating while the failed compressor is repaired.

[0125] (Technology 2) A refrigeration system according to Technology 1, comprising a drive control unit that controls the drive of the compressors and a drive detection unit that can detect the drive state of each of the compressors, wherein when the drive detection unit detects an abnormality in the drive state of at least one of the compressors, the drive control unit closes the suction side opening / closing device provided in the suction piping of the compressor in which the abnormality has been detected and the discharge side opening / closing device provided in the discharge piping of the compressor in which the abnormality has been detected. This allows the refrigeration system to isolate the failed compressor from the refrigeration circuit, allowing the refrigeration system to continue operating while the failed compressor is repaired.

[0126] (Technology 3) A refrigeration system according to Technology 2, wherein when the drive detection unit detects an abnormality in the drive state of any of the low-stage compressors, the drive control unit drives the high-stage compressor as a low-stage compressor. This allows the refrigeration system to compress the refrigerant flowing from the user-side heat exchanger using the parallel low-stage compressor even if a malfunction occurs in the low-stage compressor, so the refrigeration system can continue to operate while suppressing a decrease in the performance of the user-side heat exchanger even if a malfunction occurs in the low-stage compressor.

[0127] (Technology 4) A refrigeration system according to Technology 2 or Technology 3, wherein when the drive detection unit detects an abnormality in the drive state of the high-stage compressor, the drive control unit drives the low-stage compressor as a high-stage compressor. As a result, even if a malfunction occurs in the high-stage compressor, the refrigeration system can compress the refrigerant flowing from the user-side heat exchanger using the series-connected low-stage compressor and high-stage compressor. Therefore, even if a malfunction occurs in the high-stage compressor, the refrigeration system can continue to operate while suppressing a decrease in the performance of the user-side heat exchanger.

[0128] (Technology 5) A refrigeration system according to any one of Technologies 2 to 4, comprising a first usage unit including the first usage-side heat exchanger, a second usage unit including the second usage-side heat exchanger, and a load detection unit capable of detecting the loads of the first usage unit and the second usage unit, wherein when the drive detection unit detects an abnormality in the drive state of at least one of the compressors, the drive control unit determines to drive the compressors other than the compressor in which the abnormality has been detected, based on the detection result of the load detection unit. As a result, even if a malfunction occurs in one of the compressors, the refrigeration system can change the operation of the compressors depending on the load of each of the cooling equipment and the indoor units, so the refrigeration system can continue to operate by prioritizing the utilization unit with the greater load between the cooling equipment and the indoor units.

[0129] (Technology 6) A refrigeration system according to any one of Technology 1 to Technology 5, comprising: an accumulator to which the discharge piping connected to each of the low-stage compressors and the suction piping connected to the high-stage compressor are connected; and a connecting piping that connects the accumulator to a downstream side of the discharge side opening and closing device of the discharge piping provided in the high-stage compressor. This allows the refrigeration system to disconnect the failed compressor from the refrigeration circuit and perform single-stage compression with another compressor, allowing the refrigeration system to continue operating while the failed compressor is repaired.

[0130] (Technology 7) A refrigeration system according to any one of Technology 1 to Technology 6, wherein an oil return pipe for supplying oil is connected to at least one of the compressors, and the oil return pipe is provided with an oil return pipe opening and closing device that can open and close the oil return pipe. This allows the oil shutoff valve to be shut off if a malfunction occurs in any of the compressors in the refrigeration system and operation stops, thereby preventing oil and refrigerant from being supplied to the compressor in the event of a malfunction in the refrigeration system. [Industrial Applicability]

[0131] The present disclosure is applicable to a refrigeration system including a plurality of compressors connected in series in a refrigerant circuit, specifically to a refrigeration system including a refrigeration circuit in which a refrigeration and cooling system and an air conditioning system are provided. [Explanation of symbols]

[0132] 1. Refrigeration system 2 Refrigeration circuit 10 Outdoor units (excluding indoor units and cooling equipment) 11 Low-stage compressor 11A First low stage compressor 11B Second low stage compressor 12 High-stage compressor 13 Accumulator 14 Oil separator 15 Outdoor heat exchanger (heat source side heat exchanger) 16 Gas-liquid separator 17 Refrigerant temperature sensor 18, 28, 38 blowers 19 Current Sensor 20 Indoor unit (utilization unit) 21 Indoor expansion mechanism 22 Indoor heat exchanger (1st user side heat exchanger) 23 On-off valve 27 Space temperature sensor 30 Refrigeration equipment (utilization unit) 31 Refrigeration heat exchanger (second user side heat exchanger) 32 Inlet expansion mechanism for refrigeration 33 Refrigeration outlet pressure adjustment mechanism 37 Internal temperature sensor 40 Refrigerant piping 41 First heating pipe 42 First outdoor return pipe 43 Second cooling pipe 44 Second heating pipe 45 Second outdoor return pipe 48 Refrigerant piping 50 First switching mechanism 51 First cooling valve 52 First heating valve 53 Outdoor refrigerant return valve 54 Second switching mechanism 55 Second cooling valve 56 Third cooling valve 57 Second heating valve 58 Refrigerant return expansion mechanism 59 Check valve 60 Gas refrigerant return pipe 61 Gas refrigerant flow control valve 62 Oil return pipe 69 Oil shutoff valve (oil return pipe opening and closing device) 70 Refrigeration equipment control device 71 Refrigeration equipment control unit 73 Refrigeration equipment storage section 75 Refrigeration equipment I / F 80 Indoor unit control device 81 Indoor unit control unit 83 Indoor unit storage section 85 Indoor unit I / F 90 Control device 91 Control Unit 91a Operation control unit (drive control unit) 91b Determination unit (drive detection unit, load detection unit) 93 Memory section 93a Setting data 95 Outdoor unit I / F 96 Operation Panel 100 Indoor piping 102 Cold side piping 104, 114 Intake piping 106 Suction side connecting pipe 108, 110 Discharge piping 112 Discharge side connecting pipe 116, 118 Connection piping 130 Throttle valve 132, 142, 146 Switching shutoff valve 134, 144 Suction side shutoff valve (suction side opening and closing device) 136, 140, 150, 152 Connecting pipe shutoff valve 138, 148 Discharge side shutoff valve (discharge side opening and closing device)

Claims

1. A plurality of compressors; a heat source side heat exchanger; A plurality of utilization side heat exchangers; a refrigeration circuit provided with The plurality of use-side heat exchangers include a first utilization-side heat exchanger; a second use-side heat exchanger having a refrigerant evaporation temperature lower than that of the first use-side heat exchanger; It consists of The plurality of compressors include: a plurality of low stage compressors; at least one high-stage compressor provided on the discharge side of the plurality of low-stage compressors; It consists of Each of the low-stage compressor and the high-stage compressor has a discharge pipe that is a pipe connected to the discharge side; an intake pipe which is a pipe connected to the intake side; is established, Each of the discharge pipes is provided with a discharge-side opening / closing device that can open and close the discharge pipe, Each of the suction pipes is provided with a suction side opening and closing device that can open and close the suction pipe, the suction piping provided in the low-stage compressor is provided with a suction-side connecting piping that connects a side upstream of the suction-side opening and closing device to a side upstream of the suction-side opening and closing device of the suction piping provided in the high-stage compressor, The discharge piping provided in the low-stage compressor is provided with a discharge-side connecting piping that connects a downstream side of the discharge-side opening and closing device with a downstream side of the discharge piping provided in the high-stage compressor. Refrigeration system.

2. a drive control unit that controls the drive of the compressor; a drive detection unit capable of detecting the drive state of each of the compressors; Equipped with When the drive detection unit detects an abnormality in the drive state of at least one of the compressors, The drive control unit the suction side opening and closing device provided in the suction pipe of the compressor in which an abnormality has been detected; the discharge side opening and closing device provided in the discharge pipe of the compressor in which an abnormality has been detected; Close The refrigeration system of claim 1 .

3. When the drive detection unit detects an abnormality in the drive state of the low-stage compressor, The drive control unit drives the high-stage compressor as a low-stage compressor.

3. The refrigeration system of claim 2.

4. When the drive detection unit detects an abnormality in the drive state of the high-stage compressor, The drive control unit drives the low-stage compressor as a high-stage compressor.

4. The refrigeration system according to claim 2 or claim 3.

5. a first utilization unit including the first utilization-side heat exchanger; a second usage unit including the second usage-side heat exchanger; a load detection unit capable of detecting a load on each of the first usage unit and the second usage unit; Equipped with When the drive detection unit detects an abnormality in the drive state of at least one of the compressors, The drive control unit determines to drive the compressors other than the compressor in which an abnormality is detected based on the detection result of the load detection unit.

4. The refrigeration system according to claim 2 or claim 3.

6. an accumulator to which the discharge pipes connected to the low-stage compressors and the suction pipes connected to the high-stage compressors are connected; a connecting pipe that connects the accumulator to a downstream side of the discharge pipe provided in the high-stage compressor relative to the discharge-side opening and closing device; will be established 4. A refrigeration system according to any one of claims 1 to 3.

7. an oil return pipe for supplying oil is connected to at least one of the compressors; The oil return pipe is provided with an oil return pipe opening and closing device that can open and close the oil return pipe.

4. A refrigeration system according to any one of claims 1 to 3.

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