Multi-stage compression refrigeration unit

Abstract

To provide a refrigeration device capable of operating stably over a wide range of operation conditions while improving efficiency of a refrigeration cycle due to increase of the number of compression stages.SOLUTION: A refrigeration device comprises: a compression unit including a multi-stage compression mechanism, where a stage number N is 3 or more; a first heat exchanger that radiates the heat of a refrigerant discharged from the compression unit to outside air; a decompression unit including a plurality of decompression mechanisms provided to each of the multiple stages; a second heat exchanger that causes the refrigerant having passed through the decompression unit to absorb heat from a heat load; a plurality of gas-liquid separators provided between the decompression mechanisms; a plurality of intermediate-pressure injection flow paths that corresponds to the plurality of gas-liquid separators, and supplies a gas-phase refrigerant from the corresponding gas-liquid separators between the compression mechanisms; and a valve provided in at least one of the plurality of intermediate-pressure injection flow paths. Upon operating the valve, the effective number of stages through which the refrigerant circulates is changed.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to a refrigeration device that compresses a refrigerant in multiple stages. [Background technology]

[0002] Patent Document 1 discloses a refrigeration device equipped with a two-stage compression mechanism. The refrigeration device includes an electric compressor equipped with a low-stage compression mechanism and a high-stage compression mechanism in a sealed housing, a radiator, a high-pressure expansion valve, a gas-liquid separator, a low-pressure expansion valve, an evaporator, and a gas injection pipe. The gas refrigerant introduced from the gas-liquid separator into the housing of the electric compressor is sucked into the high-stage compression mechanism together with the refrigerant discharged from the low-stage compression mechanism into the housing by the gas injection pipe. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2017-44420 A Summary of the Invention [Problem to be solved by the invention]

[0004] In order to reduce the global warming potential (GWP) and improve the coefficient of performance (COP), refrigerants with low GWP are being adopted, and the development and commercialization of refrigeration equipment including two-stage compression mechanisms is progressing. CO as a refrigerant 2When a refrigerant containing is used, in order to suppress the high refrigerant discharge temperature associated with high-pressure operation to an allowable limit, it is effective to introduce a gas refrigerant at an intermediate pressure between the high pressure set in the radiator and the low pressure set in the evaporator from the gas-liquid separator between the low-stage compression mechanism and the high-stage compression mechanism (intermediate-pressure gas injection). With this configuration, the discharge temperature can be suppressed by injecting a gas refrigerant with a lower temperature than the refrigerant discharged from the low-stage compression mechanism. In addition, by supplying liquid refrigerant from the gas-liquid separator to the low-pressure expansion valve, the enthalpy obtained by the evaporator is increased compared to the case of single-stage compression, so that the refrigeration capacity can be increased and the COP can be improved.

[0005] In a refrigeration system using a low GWP refrigerant, it is desirable to realize a refrigeration system with an increased COP while suppressing the discharge temperature from the compressor by further increasing the number of stages of the compression mechanism. However, according to experimental research by the inventor of the present disclosure, a refrigeration system with an increased number of stages of the compression mechanism, for example, to "4", does not operate stably depending on the operating conditions such as the outside air temperature. Such a refrigeration system includes N compression mechanisms, N expansion valves, N-1 gas-liquid separators, and N-1 gas injection pipes.

[0006] In view of the above, an object of the present disclosure is to provide a refrigeration apparatus that can operate stably over a wide range of operating conditions while improving the efficiency of the refrigeration cycle by increasing the number of compression stages. [Means for solving the problem]

[0007] The present disclosure relates to a refrigeration device that circulates a refrigerant through a refrigeration cycle, the refrigeration device including a compression section having three or more stages including a compression mechanism having multiple stages connected in series and each compressing a refrigerant, a first heat exchanger that dissipates heat to outside air from the refrigerant compressed by the compression section from a low stage to a high stage over multiple steps and discharged from the compression section, a pressure reduction section including multiple pressure reduction mechanisms provided for each of the multiple stages and reducing the pressure of the refrigerant that has passed through the first heat exchanger over multiple steps, a second heat exchanger that absorbs heat from a heat load from the refrigerant that has passed through the pressure reduction section, a plurality of gas-liquid separators provided between the pressure reduction mechanisms, a plurality of intermediate pressure injection flow paths corresponding to the plurality of gas-liquid separators, respectively, and supplying gas-phase refrigerant from the corresponding gas-liquid separator between the compression mechanisms, and a valve provided in at least one of the plurality of intermediate pressure injection flow paths. The refrigeration device is configured such that the number of effective stages through which the refrigerant circulates can be changed by operating the valve. In the present invention, the valve provided in the intermediate pressure injection passage can be opened and closed during operation of the refrigeration system according to the operating conditions for the purpose of stable operation of the refrigeration system, and can also be closed for other purposes, such as to prevent the movement of the refrigerant when the refrigeration system is stopped. Effect of the Invention

[0008] According to the refrigeration device of the present disclosure, the number of effective stages through which the refrigerant circulates can be varied by switching between opening and closing a valve provided in at least one of the multiple intermediate pressure injection flow paths. Therefore, while the COP is improved by using a refrigeration cycle with the maximum number of stages, if the operating state becomes unstable when the refrigeration device is operated with the maximum number of stages, the valve can be closed during operation to reduce the number of effective stages from the maximum number of stages, thereby enabling the refrigeration device to operate stably. According to the present disclosure, a cycle that is suitable for each of the refrigerant states under various operating conditions can be easily realized by changing the number of effective stages by opening and closing the valves, so that a multi-stage compression refrigeration system that can operate stably over a wide range of operating conditions can be provided. [Brief description of the drawings]

[0009] [Figure 1] 1 is a diagram showing a circuit configuration of a refrigeration device according to a first embodiment. [Diagram 2] FIG. 2 is a Moliere diagram of the refrigeration unit shown in FIG. 1 in a normal operation mode. [Diagram 3] FIG. 2 is a Moliere diagram of the refrigeration unit shown in FIG. 1 in a high outdoor temperature mode. [Figure 4] FIG. 4 is a diagram showing a circuit configuration of a refrigeration device according to a modified example of the first embodiment. [Diagram 5] FIG. 6 is a diagram showing a circuit configuration of a refrigeration device according to a second embodiment. [Figure 6] FIG. 6 is a Moliere diagram of the refrigeration unit shown in FIG. 5 in a low outdoor air temperature mode. [Figure 7] FIG. 13 is a diagram showing a circuit configuration of a refrigeration device according to a modified example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, an embodiment of the present disclosure will be described with reference to the accompanying drawings. [First embodiment] (Basic elements of the refrigeration cycle) A multi-stage compression refrigeration device 1 shown in FIG. 1 circulates a refrigerant through a refrigeration cycle, thereby cooling an appropriate heat load (for example, air and stored items inside a device housing) using outside air as a heat source. The refrigeration device 1 includes, as basic elements forming a refrigeration cycle, a compression section 10 that compresses a refrigerant, a radiator E1 (first heat exchanger) that radiates heat from the refrigerant to the outside air, a pressure reduction section 20 that reduces the pressure of the refrigerant, and a heat absorber E2 (second heat exchanger) that absorbs heat from a thermal load into the refrigerant. The refrigerant compressed by the compression section 10 flows through the radiator E1, the pressure reduction section 20, and the heat absorber E2 in this order, and is sucked into the compression section 10.

[0011] The refrigerant circuit of the refrigeration device 1 of this embodiment includes carbon dioxide (CO 2 The refrigerant is at least partially composed of CO. 2or CO 2 This corresponds to a mixed refrigerant in which, for example, R32 refrigerant is mixed in a ratio of about 10 to 20%. The GWP of carbon dioxide is "1". The critical temperature of carbon dioxide is lower than the critical temperature of other refrigerants, for example, HFC (Hydro Fluoro Carbon). Therefore, in the normal operation mode of the refrigeration device 1, the refrigerant of this embodiment is compressed to a critical pressure P C The refrigerant is compressed to a pressure exceeding 1000 psi, and is operated at a higher set pressure on the high pressure side H than when other refrigerants are used.

[0012] (Multiple-stage compression and decompression mechanisms) The compression section 10 includes a plurality of compression mechanisms 11-14 connected in series. The first stage compression mechanism 11, the second stage compression mechanism 12, the third stage compression mechanism 13, and the fourth stage compression mechanism 14 sequentially compress the refrigerant over a plurality of steps from the low pressure side L to the high pressure side H. The number of stages N of the compression section 10 is 3 or more, and as an example, the number of stages N is "4". The first to fourth stages are indicated by the symbols n1, n2, n3, and n4.

[0013] As described later, the number of stages N is changed depending on the operation mode of the refrigeration system 1. Fig. 2 is a Moliere diagram showing the relationship between the pressure and specific enthalpy of the refrigerant assumed in the normal operation mode. Symbols such as r1, r2, ... shown in Fig. 2 correspond to the same symbols shown in Fig. 1.

[0014] The refrigeration device 1 of this embodiment includes two electric compressors 101, 102, a control device 15 capable of controlling the operation of the electric motors and expansion valves of the electric compressors 101, 102, and an intermediate cooling heat exchanger 16 provided between the electric compressors 101, 102. The first electric compressor 101 includes a first stage compression mechanism 11 and a second stage compression mechanism 12 connected in series, a housing 101A that houses the compression mechanisms 11, 12, and an electric motor 101B that drives the compression mechanisms 11, 12 to rotate. The second electric compressor 102 includes a third stage compression mechanism 13 and a fourth stage compression mechanism 14 connected in series, a housing 102A that houses the compression mechanisms 13, 14, and an electric motor 102B that drives the compression mechanisms 13, 14 to rotate.

[0015] A multi-stage compression refrigeration device 1 with N stages is realized by combining two electric compressors 101, 102 each having a multi-stage compression mechanism driven by the same electric motor. Therefore, the control device 15 only needs to control the rotation speed of each of the two electric motors 101B, 102B. This makes it easier to control the refrigeration device 1 compared to a case in which the compression mechanisms 11-14 of each stage are driven by their respective corresponding electric motors. Also, the refrigeration device 1 can be made smaller and lighter in weight compared to a case in which the compression section 10 is made up of four compressors each having a compression mechanism, an electric motor, and a housing.

[0016] The intermediate cooling heat exchanger 16 cools the refrigerant discharged from the second stage compression mechanism 12 by dissipating heat to the outside air, and supplies the refrigerant to the suction portion of the third stage compression mechanism 13 (from operating point r4 to r5 in FIG. 2).

[0017] The first stage compression mechanism 11 includes, for example, a piston rotor and Yo The second stage compression mechanism 12 corresponds to a rotary type compression mechanism including a cylinder and a compressor. The third stage compression mechanism 13 corresponds to the same. The second stage compression mechanism 12 corresponds to a scroll type compression mechanism including a pair of scroll members. The fourth stage compression mechanism 14 corresponds to the same.

[0018] Corresponding to the compression section 10 being composed of multiple compression mechanisms 11-14, the decompression section 20 includes decompression mechanisms 21-24, the number of which is the same as the number N of compression stages provided for each stage (n1, n2, n3, n4). Each of the decompression mechanisms 21-24 may be an expansion valve, a capillary tube, or the like. The fourth stage decompression mechanism 24, the third stage decompression mechanism 23, the second stage decompression mechanism 22, and the first stage decompression mechanism 21, in this order, sequentially reduce the pressure of the refrigerant that has passed through the radiator E1 over multiple steps.

[0019] 2, the refrigerant pressure increases stepwise as the refrigerant is compressed by the compression mechanisms 11-14 in multiple stages n1, n2, n3, and n4, and the discharge temperature of the refrigerant increases accordingly. The temperature of the refrigerant is reduced by the action of the intermediate cooling heat exchanger 16 which dissipates heat of the refrigerant to the outside air (see arrow A1 in FIG. 2), which can contribute to suppressing the discharge temperature of the compression section 10 as a whole.

[0020] The pressure between the suction pressure to the first stage n1 and the discharge pressure from the second stage n2 is called the first intermediate pressure P 1 Similarly, the pressure between the suction pressure to the second stage n2 and the discharge pressure from the third stage n3 is called the second intermediate pressure P 2 The pressure between the suction pressure to the third stage n3 and the discharge pressure from the fourth stage n4 is called the third intermediate pressure P 3 It is called. 1 <P 2 <P 3 The relationship holds. Set pressure P of radiator E1 on high pressure side H H and the set pressure P of the heat sink E2 on the low pressure side L L and intermediate pressure (P 1 ,P 2 ,P 3 The refrigerant circulates through the refrigerant circuit of the refrigeration device 1 while changing its pressure and enthalpy with a phase change based on the pressure ratio of each stage n1, n2, n3, n4 determined from the above.

[0021] (Medium pressure gas injection) The refrigeration system 1 performs gas injection to supply intermediate-pressure gas refrigerant obtained by gas-liquid separation of the refrigerant between the stages of the first- to fourth-stage pressure reduction mechanisms 21-24 to between the first- to fourth-stage compression mechanisms 11-14. To this end, the refrigeration system 1 includes N-1 gas-liquid separators 31-33 provided between the first- to fourth-stage pressure reduction mechanisms 21-24, respectively, and N-1 intermediate-pressure injection flow paths 41-43 corresponding to the gas-liquid separators 31-33, respectively.

[0022] In the normal operation mode, the pressures (r12, r13, r14) of the refrigerant discharged from the fourth-stage compression mechanism 14 and passing through the radiator E1 and the fourth-stage pressure reduction mechanism 24, i.e., the third intermediate pressure P 3 is the critical pressure P C Stay below. The third intermediate pressure gas-liquid separator 33 (receiver) receives the refrigerant from the fourth stage pressure reducing mechanism 24 into the inside of the storage tank 33A and separates the refrigerant into a gas phase and a liquid phase. This corresponds to a state change from r12 to r13 and r14 as shown in FIG. 2. The refrigerant is separated into a gas phase and a liquid phase based on the density difference inside the storage tank 33A. A third intermediate pressure injection flow path 43 is connected to the gas phase region 33B above the liquid level.

[0023] The third intermediate pressure injection flow path 43 is a gas phase region 33B. 3 The gas refrigerant is supplied to the suction section of the fourth stage compression mechanism 14 (from r13 to r8). The temperature of the gas refrigerant supplied to the fourth stage compression mechanism 14 by the third intermediate pressure injection passage 43 is lower than the temperature of the refrigerant discharged from the third stage compression mechanism 13. Therefore, the temperature of the refrigerant supplied by the third intermediate pressure injection passage 43 and the refrigerant discharged from the third stage compression mechanism 13 as a whole to be sucked into the fourth stage compression mechanism 14 decreases (from r7 to r8). As a result, the temperature of the refrigerant discharged from the fourth stage compression mechanism 14 also decreases, so that the intermediate pressure gas injection contributes to reducing the discharge temperature.

[0024] On the other hand, the third intermediate pressure P stored in the storage tank 33A 3 The liquid refrigerant flows out of the storage tank 33A and is depressurized by the third-stage depressurization mechanism 23 (from r14 to r15). By supplying the liquid refrigerant to the depressurization mechanisms 21 to 23 including the depressurization mechanism 23, the COP can be improved due to an increase in enthalpy corresponding to the evaporation process in the heat absorber E2 (see arrow A2 in FIG. 2 for the third-stage depressurization mechanism 23).

[0025] The reduction in discharge temperature and the increase in efficiency due to the expansion of enthalpy mentioned above are achieved by the third intermediate pressure P 3, second intermediate pressure P 2 , and the first intermediate pressure P 1 The effect of reducing the discharge temperature and improving the efficiency can be increased by increasing the number of stages N to five stages, six stages, or not limited to four stages as in this embodiment.

[0026] Second intermediate pressure P 2 and the first intermediate pressure P 1 For each gas injection, the third intermediate pressure P 3 This is similar to gas injection. The refrigerant that has passed through the third stage pressure reducing mechanism 23 is received by the second intermediate pressure gas-liquid separator 32, and separated into a gas phase and a liquid phase in the same manner as in the third intermediate pressure gas-liquid separator 33. This corresponds to a state change from r15 to r16 and r17.

[0027] A second intermediate pressure injection passage 42 is connected to the gas phase region of the second intermediate pressure gas-liquid separator 32. The second intermediate pressure injection passage 42 injects the second intermediate pressure P 2 When the gas refrigerant is supplied to the suction section of the third stage compression mechanism 13 (from r16 to r6), the temperature of the refrigerant flowing out of the intermediate cooling heat exchanger 16 and being suctioned into the third stage compression mechanism 13 decreases (from r5 to r6). 2 In addition to the injection action of r4, the action of the intermediate cooling heat exchanger 16 (from r4 to r5) also reduces the suction temperature to the third stage compression mechanism 13, so that the discharge temperature can be further reduced. The second intermediate pressure P flowing out from the second intermediate pressure gas-liquid separator 32 2 This liquid refrigerant is decompressed by the second stage decompression mechanism 22 (from r17 to r18).

[0028] The refrigerant that has passed through the second stage pressure reducing mechanism 22 is received in the first intermediate pressure gas-liquid separator 31 and separated into a gas phase and a liquid phase. This corresponds to a state change from r18 to r19 and r20. The first intermediate pressure P 1When this gas refrigerant is supplied to the suction portion of the second stage compression mechanism 12 (from r18 to r3), the temperature of the refrigerant to be sucked into the second stage compression mechanism 12 decreases (from r2 to r3). The first intermediate pressure P flowing out from the first intermediate pressure gas-liquid separator 31 1 The liquid refrigerant is decompressed by the first-stage decompression mechanism 21 (from r20 to r21). The refrigerant that has passed through the first-stage decompression mechanism 21 is evaporated by absorbing heat from the thermal load by the heat absorber E2, and is sucked into the first-stage compression mechanism 11 (from r21 to r22, r1).

[0029] When the refrigeration unit 1 is operated in a normal operation mode set by the control device 15, compression, expansion, and intermediate pressure injection are performed for the number N of stages provided in the refrigeration unit 1, thereby enabling the refrigeration unit 1 to be operated stably while using a refrigerant with a low GWP, improving the COP, and maintaining the discharge temperature below the allowable limit. However, for example, if the outside air temperature is excessively high relative to the range of outside air temperatures assumed in normal operation mode, operating the refrigeration device 1 at the maximum number of stages N may result in an unstable operating state, and it may not be possible to circulate the refrigerant. CO discharged from the compression section 10 after multiple compression stages 2 The temperature of the refrigerant reaches the critical pressure P C Even if it is permitted to exceed the third intermediate pressure P 3 (r12, r13, r14) is the critical pressure P C If the pressure exceeds this limit, the refrigerant will not condense in the third intermediate pressure gas-liquid separator 33, and gas-liquid separation will not be possible, and the behavior of the refrigerant in the supercritical state will be unstable, making it difficult to perform stable control. It is difficult to predict the pressure, temperature, flow rate, etc. of the supercritical fluid and stabilize the operating state.

[0030] Therefore, in order to operate the refrigeration system 1 stably over a wide range of operating conditions, including operating conditions where the outside air temperature is excessively high or other operating conditions, the refrigeration system 1 is equipped with a valve (V3) provided in at least one of the intermediate pressure injection passages 41-43 selected at random. The refrigeration system 1 of the present embodiment includes a third intermediate pressure valve V3 provided in the third intermediate pressure injection flow passage 43 on the highest pressure side H. The third intermediate pressure valve V3 is a solenoid valve, and is switched between open and closed based on a command issued from the control device 15.

[0031] In the normal operation mode, the refrigeration device 1 supplies the first to third intermediate pressures P through the first to third intermediate pressure injection passages 41 to 43 with the third intermediate pressure valve V3 open. 1 ,P 2 ,P 3 The injection is performed while changing the pressure and enthalpy of the refrigerant as shown in FIG. 2. At this time, the effective number of stages N A is “4”, which corresponds to the total number N of stages provided in the refrigeration device 1.

[0032] (High outdoor temperature mode) When the outdoor air temperature is so high that the refrigerant exceeds the critical pressure, the control device 15 switches the operation mode of the refrigeration device 1 to a high outdoor air temperature mode in which the third intermediate pressure valve V3 is closed and intermediate pressure injection is performed only through the first intermediate pressure injection flow path 41 and the second intermediate pressure injection flow path 42. In the high outdoor air temperature mode, the refrigerant that is still in a supercritical state even after passing through the fourth stage pressure reducing mechanism 24 passes through the inside of the storage tank 33A of the third intermediate pressure gas-liquid separator 33, is reduced in pressure by the third stage pressure reducing mechanism 23, and then flows into the second intermediate pressure gas-liquid separator 32 (from r12, r13, r14 to r15). At this time, no liquid refrigerant is stored in the storage tank 33A (corresponding to the internal state of the storage tank 33A shown in FIG. 4).

[0033] When the third intermediate pressure valve V3 is closed, no refrigerant flows through the third intermediate pressure injection flow passage 43, so that the third stage n3 and the fourth stage n4 in the normal operation mode are combined into one stage in the compression and expansion process, and the number of effective stages N is reduced to "3". As shown in FIG. 3, the state of the refrigerant in the high outdoor air temperature mode, the refrigeration device 1 is operated by a three-stage compression and three-stage expansion cycle of n1 to n3. As the pressure of the refrigerant in a supercritical state is reduced by the third stage pressure reducing mechanism 23 (from r12, r13, r14 to r15), the second intermediate pressure P 2 is the critical pressure P C Therefore, the refrigeration device 1 operates stably.

[0034] In the normal operation mode, the control device 15 uses, for example, map data or the like showing the correspondence between the outside air temperature and the set pressure of the high-pressure side H, and the outside air temperature detected by the temperature sensor 17, to determine whether the high-pressure side H pressure on the map data corresponding to the detection result of the outside air temperature is greater than the critical pressure P C A first threshold pressure T 1 (Fig. 3). It is judged whether the high pressure side H pressure on the map data corresponding to the detection result of the outside air temperature is larger than the first threshold pressure T 1 , the controller 15 closes the third intermediate pressure valve V3 and transitions from the normal operation mode to the high outside air temperature mode. Even in the high outside temperature mode, the outside temperature is continuously monitored. For example, when the high pressure side H pressure on the map data corresponding to the detection result of the outside temperature exceeds the first threshold pressure T 1 A second threshold pressure T 2 , the controller 15 opens the third intermediate pressure valve V3 to return from the high outside air temperature mode to the normal operation mode.

[0035] According to the refrigeration system 1 of the first embodiment described above, by switching the valve V3 provided in at least one of the intermediate pressure injection passages 41 to 43 between open and closed, the effective number of stages N through which the refrigerant circulates is increased. ATherefore, in the normal operation mode, the COP is improved by the refrigeration cycle with the maximum number of stages N, while the intermediate pressure on the high pressure side H reaches the critical pressure P C When the outside air temperature rises to exceed the effective number of stages N, the valve V3 provided in the intermediate pressure injection flow path 43 of the high pressure side H is closed to reduce the effective number of stages N. A By reducing the amount of heat generated, the refrigeration device 1 can be operated stably. In other words, according to this embodiment, even though the refrigerant is compressed to a supercritical state, difficult control based on prediction of the behavior of the refrigerant in the supercritical state is not required, and the effective number of stages N by opening and closing the valve V3 is reduced. A By changing the above, it is possible to easily realize a cycle that is suitable for each of the refrigerant states under various operating conditions. Therefore, it is possible to provide a multi-stage compression refrigeration system 1 that can be stably operated over a wide range of operating conditions.

[0036] The refrigeration system 1 may include valves provided in the other intermediate pressure injection flow paths 42, 41, in addition to the valve V3 provided in the third intermediate pressure injection flow path 43. For example, as shown in Fig. 4, the second intermediate pressure injection flow path 42 may also be provided with a valve V2 that can be opened and closed by the control device 15. In the high outside air temperature mode shown in Fig. 4, of the intermediate pressure valves V2 and V3, only the third intermediate pressure valve V3 shown in black is closed.

[0037] Second Embodiment Next, a second embodiment will be described with reference to Figures 5 and 6. Below, differences from the first embodiment will be mainly described. Components similar to those in the first embodiment are given the same reference numerals. 5 is provided with a first intermediate pressure valve V1 in the first intermediate pressure injection passage 41 to accommodate operating conditions different from those of the refrigeration system 1 of the first embodiment. The refrigeration system 1-2 is also provided with a third intermediate pressure valve V3 provided in the third intermediate pressure injection passage 43, similar to the refrigeration system 1 of the first embodiment. Except for being provided with the first intermediate pressure valve V1, the refrigeration system 1-2 of the second embodiment is configured similarly to the refrigeration system 1 of the first embodiment.

[0038] The refrigeration system 1-2 is provided with the third intermediate pressure valve V1 like the refrigeration system 1, so that only the third intermediate pressure valve V3 is closed among the intermediate pressure valves V1 and V3 to obtain the effective stage number N A By decreasing to "3", the high outside temperature mode described above can be implemented.

[0039] Contrary to the high outside temperature mode, when the outside temperature is low, the set pressure P H and the set pressure P of the low pressure side L L The pressure ratio between the gas-liquid separators 31-33 and the compression mechanisms 12-14 is reduced. Since the pressure ratio is allocated to each stage, when the system is operated with the maximum number of stages N as in the normal operation mode, the pressure ratio of each stage n1, n2, n3, and n4 is reduced. When the outside air temperature is so low that the pressure ratio of each stage is insufficient for the pressure ratio required to transport the refrigerant from the gas-liquid separators 31-33 to the compression mechanisms 12-14, respectively, the refrigerant cannot be circulated to each stage. In this case, the control device 15 switches the operation mode of the refrigeration device 1-2 from the normal operation mode to the low outdoor temperature mode (low pressure ratio operation mode) by closing both the first intermediate pressure valve V1 and the third intermediate pressure valve V3. In the low outdoor temperature mode, intermediate pressure injection is performed only through the second intermediate pressure injection passage 42.

[0040] FIG. 6 shows the state of the refrigerant in the low outdoor temperature mode. The first intermediate pressure valve V1 and the third intermediate pressure valve V3 are closed, so that the number of effective stages N A is reduced to "2", and the refrigeration unit 1-2 is operated by a two-stage compression / two-stage expansion cycle. The effective number of stages N is ABy the amount of the reduction, a pressure sufficient for transporting the refrigerant from each of the gas-liquid separators 31-33 to the compression mechanisms 12-14 is ensured at each stage, so that the refrigeration system 1 operates stably.

[0041] In the normal operation mode, the control device 15 uses, for example, map data or the like showing the correspondence between the outside air temperature and the pressure ratio of each stage and the outside air temperature detected by the temperature sensor 17, and calculates that the pressure ratio of each stage on the map data corresponding to the detection result of the outside air temperature is the first pressure ratio R 1 It is judged whether the pressure ratio of each stage on the map data corresponding to the detected outside air temperature is larger or smaller than the first pressure ratio R 1 , the control device 15 closes the first intermediate pressure valve V1 and the third intermediate pressure valve V3, and transitions from the normal operation mode to the low outside air temperature mode. The outside air temperature is continuously monitored. For example, the pressure ratio of each stage on the map data corresponding to the detected outside air temperature is the second pressure ratio R 2 (R 1 <R 2 ), the controller 15 opens the intermediate pressure valves V1 and V3 and returns from the low outside air temperature mode to the normal operation mode.

[0042] According to the refrigeration system 1-2 of the second embodiment described above, by closing at least the third intermediate pressure valve V3 among the intermediate pressure valves V1 and V3 provided on each of the high pressure side H and the low pressure side L, the number of effective stages N is reduced by 4. A In this way, the refrigeration apparatus 1-2 can be stably operated over a wider range of operating conditions than the refrigeration apparatus 1 of the first embodiment.

[0043] Effective number of stages N AFrom the viewpoint of reducing the amount of heat generated by the intermediate pressure valves V1 and V3, only one of the intermediate pressure valves V1 and V3 of the second embodiment can be closed in the low outdoor air temperature mode. For example, this is the case when only the third intermediate pressure valve V3 is closed and a pressure ratio sufficient for performing intermediate pressure injection through the first intermediate pressure injection flow path 41 and the second intermediate pressure injection flow path 42 is ensured in each of the stages n1, n2, and n3. While detecting the outdoor air temperature, the refrigeration device 1-2 can be operated at the most stable stage number among a state in which all of the intermediate pressure valves V1 to V3 are open (four stages), a state in which only the intermediate pressure valve V3 is closed (three stages), and a state in which both the intermediate pressure valves V1 and V3 are closed (two stages). Alternatively, only the first intermediate pressure valve V1 may be closed to ensure a pressure ratio in each stage n2, n3, and n4 sufficient for intermediate pressure injection through the third intermediate pressure injection flow path 43 and the second intermediate pressure injection flow path 42. In the latter case, the third intermediate pressure P 3 is the critical pressure P C If the refrigeration apparatus 1-2 is not used in an environment where the outside air temperature is so high as to exceed 100° C., the intermediate pressure valve V3 need not be provided in the third intermediate pressure injection flow passage 43.

[0044] In the second embodiment, it is not prevented from providing an opening and closing valve in the second intermediate pressure injection passage 42. However, in the second embodiment, since the two-stage compression / two-stage expansion cycle is maintained by constantly performing intermediate pressure injection through the second intermediate pressure injection passage 42 in all operating modes including the low outside air temperature mode, the cost of the device can be reduced by not providing an intermediate pressure valve in the second intermediate pressure injection passage 42.

[0045] Even if the total number N of stages is more than "4", for example, "5" or "6", the refrigeration apparatus can be operated with the number N of stages reduced, as in the second embodiment. For example, when the number of stages N is "5", the refrigeration device is provided with an intermediate pressure valve provided in at least one of the fourth intermediate pressure injection flow path and the third intermediate pressure injection flow path of the high pressure side H, and an intermediate pressure valve provided in at least one of the fourth intermediate pressure injection flow path and the third intermediate pressure injection flow path of the high pressure side H. In this case, if the refrigeration system is equipped with the fourth intermediate pressure valve V4, the third intermediate pressure valve V3, the second intermediate pressure valve V2, and the first intermediate pressure valve V1, in the low outdoor air temperature mode, for example, it is possible to close the first intermediate pressure valve V1, the third intermediate pressure valve V3, and the fourth intermediate pressure valve V4 to operate in a two-stage cycle, or close the first intermediate pressure valve V1 and the fourth intermediate pressure valve V4 to operate in a three-stage cycle. A can be changed to "2" or "3".

[0046] [Modifications] Although not shown in the figure, it is also possible to provide an intermediate pressure valve for each of the first to third intermediate pressure injection flow paths 41 to 43, that is, for all of the intermediate pressure injection flow paths 41 to 43. In that case, by closing all of the three intermediate pressure valves V1, V2, and V3 provided in the refrigeration device, the effective number of stages N A It is possible to reduce it to "1". In addition, one or two of the three intermediate pressure valves V1, V2, and V3 provided in the refrigeration unit are always open, and only the remaining intermediate pressure valve is opened and closed, allowing the refrigeration unit to respond to various required operating conditions. In this case, even the valves that are always open can be closed according to the operating mode depending on the operating conditions such as the refrigerant used in the refrigeration unit and the outside air temperature range suitable for the area where the refrigeration unit is used. In other words, the same refrigerant circuit can be deployed in multiple products with different refrigerants, operating ambient temperatures, or applications.

[0047] 7 does not include a multi-stage electric compressor (101, 102 in FIG. 1). Each of the compression mechanisms 11 to 13 included in the refrigeration device 1-3 is configured as a single-stage compressor together with an electric motor 10M and a housing 10H. The refrigeration device 1-3 is equipped with a second intermediate pressure valve V2 in the second intermediate pressure injection flow path 42 on the high pressure side H of the first and second intermediate pressure injection flow paths 41, 42, and a first intermediate pressure valve V1 in the first intermediate pressure injection flow path 41 on the low pressure side L.

[0048] When the outside air temperature is high and intermediate pressure injection is performed using both the first and second intermediate pressure injection paths 41 and 42, the second intermediate pressure P 2 is the critical pressure P C If the pressure exceeds 100 MPa, the second intermediate pressure valve V2 on the highest pressure side H should be closed to operate the refrigeration system 1-3 in a two-stage compression / two-stage expansion cycle. In addition, if the pressure ratio of each stage is insufficient when intermediate pressure injection is performed using both the first and second intermediate pressure injection passages 41, 42 due to low outside air temperature, or for other reasons, it is preferable to operate the refrigeration system 1-3 in a two-stage compression / two-stage expansion cycle or a one-stage compression / expansion cycle by closing either one or both of the intermediate pressure valves V1, V2.

[0049] Although the refrigeration device 1-3 does not include an intermediate cooling heat exchanger 16 (FIG. 1), an intermediate cooling heat exchanger 16 can be provided at least either between the compression mechanisms 11 and 12 and between the compression mechanisms 12 and 13 in order to reduce the discharge temperature. In the above-described refrigeration systems 1 and 1-2, the intermediate cooling heat exchanger 16 may be provided as needed.

[0050] In addition to the above, it is possible to select and discard the configurations given in the above embodiment, or to change them to other configurations as appropriate. For example, in each of the above embodiments, a liquid level sensor can be provided in the gas-liquid separators 31-33 to protect the compression mechanisms 11-14. If the liquid level sensor detects that an excessive amount of liquid refrigerant is stored in the storage tank, the control device 15 can close the intermediate pressure valve of the corresponding intermediate pressure injection flow path. This can prevent damage to the compression mechanisms due to the inflow of liquid refrigerant.

[0051] [Additional Notes] The refrigeration apparatus described above can be understood as follows. [1] A refrigeration device 1, 1-2, 1-3 that circulates a refrigerant by a refrigeration cycle includes a compression section 10 having a number of stages N of 3 or more, compression mechanisms 11-14 that are connected in series and compress the refrigerant, a first heat exchanger (E1) that radiates heat to the outside air from the refrigerant that has been compressed by the compression section 10 from a low stage to a high stage over a plurality of steps and discharged from the compression section 10, and a pressure reduction section 2 that includes a plurality of pressure reduction mechanisms 21-24 provided to each of the plurality of stages and reduces the pressure of the refrigerant that has passed through the first heat exchanger (E1) over a plurality of steps. The refrigerant circulation system includes a first heat exchanger (E2) that absorbs heat from a heat load through the pressure reduction unit 20, a plurality of gas-liquid separators (31-33) provided between the pressure reduction mechanisms (21-24), a plurality of intermediate pressure injection flow paths (41-43) that correspond to the plurality of gas-liquid separators (31-33) respectively and supply gas-phase refrigerant from the corresponding gas-liquid separators (31-33) between the compression mechanisms (11-14), and valves (V1, V2, V3) provided in at least one of the plurality of intermediate pressure injection flow paths (41-43). By operating the valves (V1, V2, V3), the effective number of stages N through which the refrigerant circulates is increased. A is variably configured. [2] The valve V3 is provided in the intermediate-pressure injection flow path 41-43 having the highest pressure among the multiple intermediate-pressure injection flow paths 41-43. [3] The refrigerant contains at least a portion of carbon dioxide. [4] The number of stages N is 4 or more, and the valves V1, V2, and V3 are provided in at least one of the high-pressure side intermediate pressure injection flow paths 41-43 and at least one of the low-pressure side intermediate pressure injection flow paths 41-43 among the multiple intermediate pressure injection flow paths 41-43. [5] The refrigeration devices 1, 1-2, and 1-3 are equipped with an intermediate cooling heat exchanger 16 that exchanges heat with outside air for the refrigerant discharged from a low-pressure side compression mechanism serving as any one of the compression mechanisms 11 to 14, and causes the refrigerant to flow into a high-pressure side compression mechanism serving as a compression mechanism connected in series with the low-pressure side compression mechanism. [6] The compression section 10 includes a multi-stage electric compressor 101, 102 having a plurality of compression mechanisms 11, 12 (or 13, 14) connected in series, a housing (101A, etc.) that accommodates the plurality of compression mechanisms 11, 12 (or 13, 14), and an electric motor (101B, etc.) that drives the plurality of compression mechanisms 11, 12 (or 13, 14). [7] The refrigeration units 1, 1-2, and 1-3 are provided with a control device 15 that generates commands to operate the valves V1, V2, and V3. The control device 15 generates commands in response to the outside air temperature, thereby increasing the number of effective stages N. A Change the value. [Explanation of symbols]

[0052] 1,1-2,1-3 Refrigeration equipment 10 Compression section 10H Housing 10M electric motor 11 First stage compression mechanism 12 Second stage compression mechanism 13 Third stage compression mechanism 14 Fourth stage compression mechanism 15 Control device 16 Intercooled heat exchanger (intermediate heat exchanger) 17 Temperature Sensor 20 Pressure reduction section 21 First stage pressure reduction mechanism 22 Second stage pressure reduction mechanism 23 Third stage pressure reduction mechanism 24 Fourth stage pressure reduction mechanism 31 First intermediate pressure gas-liquid separator 32 Second intermediate pressure gas-liquid separator 33 3rd intermediate pressure gas-liquid separator 33A Storage tank 33B Gas Phase Region 41 First intermediate pressure injection passage 42 Second intermediate pressure injection passage 43 3rd intermediate pressure injection channel 101 First electric compressor (multiple-stage electric compressor) 101A Housing 101B Electric motor 102 Second electric compressor (multiple-stage electric compressor) 102A Housing 102B Electric motor E1 radiator (1st heat exchanger) E2 heat absorber (second heat exchanger) H High pressure side L Low pressure side N number of stages N A Effective number of stages P 1 First intermediate pressure P 2 Second intermediate pressure P 3 3rd intermediate pressure P C Critical Pressure P H ,P L Set pressure R 1 ,R 2 Pressure Ratio T 1 First Threshold Pressure T 2 Second Threshold Pressure V1 First intermediate pressure valve V2 Second intermediate pressure valve V3 3rd intermediate pressure valve n1~n4 steps r1~r22 Operating points

Claims

1. A refrigeration system that circulates a refrigerant through a supercritical refrigeration cycle, a compression unit including a plurality of compression mechanisms connected in series to compress the refrigerant, the number of stages being three or more; a first heat exchanger that dissipates heat of the refrigerant, which has been compressed in a plurality of steps from a low stage to a high stage by the compression unit and discharged from the compression unit, to outside air; a pressure reducing unit including a plurality of pressure reducing mechanisms provided for each of the plurality of stages, and reducing the pressure of the refrigerant passing through the first heat exchanger over a plurality of steps; a second heat exchanger that absorbs heat from a thermal load through the refrigerant that has passed through the pressure reducing section; A plurality of gas-liquid separators provided between the pressure reducing mechanisms, respectively; a plurality of intermediate pressure injection flow paths corresponding to the plurality of gas-liquid separators, respectively, for supplying the refrigerant in a gas phase from the corresponding gas-liquid separators to between the compression mechanisms; a valve provided in at least one of the plurality of intermediate pressure injection flow paths, wherein the number of effective stages through which the refrigerant circulates is variable.

2. The valve is provided in the intermediate pressure injection flow path having the highest pressure among the plurality of intermediate pressure injection flow paths, 2. The refrigeration system of claim 1, wherein the valve is open in a normal operation mode and is closed in a high outdoor air temperature mode in which the outdoor air temperature is higher than that in the normal operation mode.

3. When the pressure in the highest intermediate pressure injection flow path is greater than a first threshold pressure set lower than a critical pressure on map data showing the correspondence between outside air temperature and set pressure, the normal operation mode is switched to the high outside air temperature mode.

3. The refrigeration system of claim 2.

4. The refrigerant contains at least a portion of carbon dioxide. The refrigeration apparatus according to any one of claims 1 to 3.

5. The number of stages is 4 or more, The valve is provided in at least one of the intermediate pressure injection flow paths on a high pressure side and at least one of the intermediate pressure injection flow paths on a low pressure side among the plurality of intermediate pressure injection flow paths.

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

6. an intermediate heat exchanger that exchanges heat between the refrigerant discharged from a low-stage compression mechanism serving as any one of the compression mechanisms and the outside air and causes the refrigerant to flow into a high-stage compression mechanism serving as the compression mechanism that is connected in series with the low-stage compression mechanism; 6. A refrigeration system according to any one of claims 1 to 5.

7. The compression section includes: The compressor includes a multi-stage electric compressor including a multi-stage compression mechanism connected in series, a housing that accommodates the multi-stage compression mechanism, and an electric motor that drives the multi-stage compression mechanism.

7. A refrigeration system according to any one of claims 1 to 6.

8. a controller that generates a command to operate the valve; The control device generates the command in response to the outside air temperature to change the number of effective stages.

8. A refrigeration device according to any one of claims 1 to 7.

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