Refrigeration device and control method of refrigeration device

Abstract

A refrigeration device according to at least one embodiment of the present disclosure is provided with: a low-stage compressor for compressing a refrigerant; a high-stage compressor for compressing the refrigerant compressed by the low-stage compressor; a flash tank capable of receiving the refrigerant compressed by the high-stage compressor; and a liquid injection flow path for supplying the refrigerant liquid in the flash tank to the refrigerant that has been compressed by the low-stage compressor and discharged from the low-stage compressor.

Description

Technical Field

[0001] The present disclosure relates to a refrigeration device and a control method of the refrigeration device. Background Art

[0002] A refrigeration device is known to be configured to include a low-stage compressor and a high-stage compressor for two-stage compression. In such a refrigeration device, in order to improve the efficiency of the high-stage compressor, it is necessary to suppress the superheat of the refrigerant sucked into the high-stage compressor. Therefore, in order to suppress the superheat of the refrigerant sucked into the high-stage compressor, a structure is known in which an intercooler is provided to cool the discharged refrigerant of the low-stage compressor (for example, refer to Patent Document 1).

[0003] Prior art literature

[0004] Patent Literature

[0005] Patent Document 1: Japanese Patent Application Publication No. 2009-133585 Summary of the invention

[0006] 1. Technical issues to be resolved

[0007] However, when such an intercooler is installed, the following problems will arise, namely, it is necessary to ensure a place for installation and heat dissipation space, the cost will increase, and especially in the case of air cooling, there will be noise problems. In addition, when the outside temperature is high, it may not be possible to fully cool the refrigerant discharged from the low-stage compressor.

[0008] In view of the above situation, an object of at least one embodiment of the present invention is to efficiently suppress the superheat of the refrigerant sucked into the high-stage compressor in a refrigeration device configured to perform two-stage compression.

[0009] (II) Technical solution

[0010] (1) A refrigeration device according to at least one embodiment of the present disclosure includes:

[0011] a low-stage compressor, which is used to compress the refrigerant;

[0012] A high-stage compressor for compressing the refrigerant compressed by the low-stage compressor;

[0013] a flash tank capable of receiving the refrigerant compressed by the high stage compressor; and

[0014] The liquid injection flow path is used to supply the refrigerant liquid in the flash tank to the refrigerant compressed by the low-stage compressor and discharged from the low-stage compressor.

[0015] (2) Regarding a control method of a refrigeration device according to at least one embodiment of the present disclosure,

[0016] The refrigeration device comprises:

[0017] a low-stage compressor, which is used to compress the refrigerant;

[0018] A high-stage compressor for compressing the refrigerant compressed by the low-stage compressor;

[0019] a flash tank capable of receiving the refrigerant compressed by the high-stage compressor;

[0020] a liquid injection flow path for supplying the refrigerant liquid in the flash tank to the refrigerant compressed by the low-stage compressor; and

[0021] a first expansion valve, which is arranged in the injection flow path,

[0022] The control method comprises:

[0023] a suction temperature detection step of detecting a suction temperature of the refrigerant sucked into the high-stage compressor;

[0024] a suction pressure detection step of detecting the suction pressure of the refrigerant sucked into the high-stage compressor;

[0025] a suction superheat calculation step of calculating the suction superheat of the refrigerant sucked into the high-stage compressor based on the detected suction temperature and the detected suction pressure; and

[0026] The opening degree adjusting step adjusts the opening degree of the first expansion valve so that the calculated suction superheat degree reaches a preset target value.

[0027] (III) Beneficial effects

[0028] According to at least one embodiment of the present disclosure, in a refrigeration device configured to perform two-stage compression, the degree of superheat of the refrigerant sucked into the high-stage compressor can be efficiently suppressed. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is a system diagram of a refrigeration device according to one embodiment.

[0030] Figure 2 This is an example of a Mollier diagram of a refrigeration device according to an embodiment using CO 2 refrigerant.

[0031] Figure 3 This is a flowchart showing the flow of processing performed in the control device in order to adjust the opening degree of the first expansion valve. DETAILED DESCRIPTION

[0032] Hereinafter, some embodiments of the present disclosure will be described with reference to the accompanying drawings. However, the dimensions, materials, shapes, and relative arrangements of the components described in the embodiments or shown in the accompanying drawings do not limit the scope of the present disclosure to these, but are merely illustrative examples.

[0033] For example, expressions such as "in a certain direction", "along a certain direction", "parallel", "orthogonal", "center", "concentric" or "coaxial" that indicate relative or absolute configurations do not only indicate configurations in a strict sense, but also indicate a state of relative displacement at an angle or distance with a tolerance or a degree that can achieve the same function.

[0034] For example, expressions such as “same”, “equal”, and “homogeneous” indicating that things are equal do not only indicate a strictly equal state but also indicate a state in which there is a tolerance or a difference to the extent that the same function can be obtained.

[0035] For example, expressions indicating shapes such as a quadrilateral and a cylindrical shape not only indicate shapes such as a quadrilateral and a cylindrical shape in a strict geometric sense, but also indicate shapes including concave-convex portions, chamfered portions, and the like within a range that can obtain the same effect.

[0036] On the other hand, the expression “having,” “having,” “including,” or “having” a component is not an exclusive expression that excludes the presence of other components.

[0037] Figure 1 It is a system diagram of a refrigeration device of one embodiment. The refrigeration device 1 of one embodiment is, for example, a two-stage compression and two-stage expansion refrigeration device using CO2 refrigerant. Regarding the refrigeration device 1 of one embodiment, a low-stage compressor 11, a high-stage compressor 12 and a flash tank 13 are provided in the refrigerant circulation path 30. In the refrigeration device 1 of one embodiment, for example, two low-stage compressors 11 are provided in parallel with respect to the refrigerant circulation path 30. In the refrigeration device 1 of one embodiment, for example, two high-stage compressors 12 are provided in parallel with respect to the refrigerant circulation path 30.

[0038] In the refrigeration device 1 according to the embodiment, the accumulator 14 is provided in the refrigerant flow path 31 that connects the outlet of the low-stage compressor 11 and the inlet of the high-stage compressor 12 .

[0039] In the refrigeration device 1 of one embodiment, a condenser 15 operating as a gas cooler is provided in the refrigerant flow path 32 connecting the outlet of the high-stage compressor 12 and the inlet of the flash tank 13. In the refrigeration device 1 of one embodiment, a heat exchanger 17 is provided in the refrigerant circulation path 30, and the heat exchanger 17 is used to perform heat exchange between the liquid phase of the flash tank 13 and the refrigerant passing through the evaporator 16, for example, as a cooling load.

[0040] A refrigeration device 1 according to one embodiment includes a liquid injection flow path 35, which connects the liquid phase portion of the flash tank 13 with the refrigerant flow path 31a in the refrigerant flow path 31, wherein the refrigerant flow path 31 connects the outlet of the low-stage compressor 11 with the inlet of the high-stage compressor 12, and the refrigerant flow path 31a connects the outlet of the low-stage compressor 11 with the liquid accumulator 14.

[0041] The refrigeration device 1 of one embodiment includes a flash gas flow path 36 that connects the gas phase portion of the flash tank 13 and the refrigerant flow path 31 a that connects the outlet of the low-stage compressor 11 and the accumulator 14 .

[0042] In the refrigeration device 1 of one embodiment, a first expansion valve 41 is provided in the liquid injection flow path 35, and a second expansion valve (high-stage expansion valve) 42 is provided in the refrigerant flow path 32b, and the refrigerant flow path 32b connects the condenser 15 with the inlet of the flash tank 13. In the refrigeration device 1 of one embodiment, a third expansion valve (low-stage expansion valve) 43 is provided in the refrigerant flow path 34b in the refrigerant flow path 34, wherein the refrigerant flow path 34 is used to supply the refrigerant liquid in the flash tank 13 to the evaporator 16, and the refrigerant flow path 34b connects the heat exchanger 17 with the evaporator 16. In the refrigeration device 1 of one embodiment, a fourth expansion valve 44 is provided in the flash gas flow path 36.

[0043] In the refrigeration device 1 of one embodiment, an oil separator 21 is provided in the refrigerant flow path 32a, wherein the refrigerant flow path 32a connects the outlet of the high-stage compressor 12 with the condenser 15, and the oil separator 21 is used to separate the refrigerant gas from the refrigeration oil. In the refrigeration device 1 of one embodiment, the refrigeration oil separated by the oil separator 21 is returned to the low-stage compressor 11 and the high-stage compressor 12 via an oil tank not shown.

[0044] The refrigeration device 1 of one embodiment includes a control device 50 for controlling various parts of the refrigeration device 1. The control device 50 includes a processor 51 and a memory 53. The processor 51 performs various calculations, and the memory 53 stores various data processed by the processor 51 non-temporarily or temporarily. The processor 51 is implemented by a CPU, a GPU, an MPU, a DSP, various other calculation devices other than the above, or a combination of the above. The memory 53 is implemented by a ROM, a RAM, a flash memory, or a combination of these.

[0045] In the following description, the control contents of the control device 50 will be mainly described with respect to the opening adjustment of the first expansion valve 41. The control contents of the control device 50 will be described in detail later.

[0046] The refrigeration device 1 of one embodiment includes: various sensors for controlling various parts of the refrigeration device 1. The various sensors for controlling various parts of the refrigeration device 1 include, for example: a suction temperature sensor 55 for detecting the suction temperature Ti of the refrigerant sucked into the high-stage compressor 12; and a suction pressure sensor 57 for detecting the suction pressure Pi of the refrigerant sucked into the high-stage compressor 12.

[0047] In the refrigeration device 1 of one embodiment thus configured, the refrigerant compressed by the low-stage compressor 11 and the high-stage compressor 12 is cooled in the condenser 15. The refrigerant cooled in the condenser 15 is decompressed by the second expansion valve 42 and then sent to the flash tank 13 to be separated into a gas phase and a liquid phase.

[0048] The refrigerant liquid forming the liquid phase in the flash tank 13 flows out of the flash tank 13, exchanges heat with the refrigerant returned from the evaporator 16 in the heat exchanger 17, and heats the refrigerant. The refrigerant liquid sent from the flash tank 13 to the heat exchanger 17 flows out of the heat exchanger 17, is decompressed by the third expansion valve 43, is vaporized by the evaporator 16 and the heat exchanger 17, and is supplied to the low-stage compressor 11.

[0049] As described above, the refrigeration device 1 of the embodiment includes the liquid injection flow path 35 for supplying the refrigerant liquid in the flash tank 13 to the refrigerant compressed by and discharged from the low-stage compressor 11 .

[0050] In order to improve the efficiency of the high-stage compressor 12, it is necessary to suppress the superheat of the refrigerant sucked into the high-stage compressor 12. Therefore, it is considered to use a heat exchanger for cooling the refrigerant sucked into the high-stage compressor 12. However, when such a heat exchanger is provided, the following problems arise, namely, it is necessary to ensure a place for installation, the cost increases, etc.

[0051] After intensive research, the inventors found that by supplying the refrigerant liquid in the flash tank 13 to the refrigerant compressed by and discharged from the low-stage compressor 11, the superheat of the refrigerant sucked into the high-stage compressor 12 can be efficiently suppressed.

[0052] According to the refrigeration device 1 of one embodiment, there is no difficulty in setting a location for setting a heat exchanger for cooling the refrigerant sucked into the high-stage compressor 12, and there is no cost increase due to the installation of the heat exchanger. It can be unaffected by the external temperature conditions and can effectively suppress the superheat of the refrigerant sucked into the high-stage compressor 12. Therefore, the efficiency of the high-stage compressor 12 can be improved at a low cost.

[0053] In the refrigeration device 1 of one embodiment, the liquid injection flow path 35 may be configured to connect the liquid phase of the flash tank 13 with the refrigerant flow path 31, and the refrigerant flow path 31 is a flow path for the refrigerant compressed by the low-stage compressor 11 to flow, and connects the outlet of the low-stage compressor 11 with the inlet of the high-stage compressor 12. The downstream end 35d of the liquid injection flow path 35 may be connected to the refrigerant flow path 31.

[0054] Therefore, the refrigerant liquid in the flash tank 13 can be supplied to the refrigerant compressed by the low-stage compressor 11 with a simple structure.

[0055] In addition, the upstream end 35u of the injection channel 35 may be as follows: Figure 1 As shown, it is connected to the refrigerant flow path 34a in the refrigerant flow path 34, and can also be directly connected to the flash tank 13, wherein the refrigerant flow path 34 is used to supply the refrigerant liquid in the flash tank 13 to the evaporator 16, and the refrigerant flow path 34a connects the flash tank 13 and the heat exchanger 17.

[0056] The refrigeration device 1 according to one embodiment may include a first expansion valve 41 , and the first expansion valve 41 may be provided in the liquid injection flow path 35 .

[0057] Therefore, the refrigerant liquid in the flash tank 13 can be supplied to the refrigerant compressed by the low-stage compressor 11 with good controllability.

[0058] The refrigeration device 1 according to one embodiment may include a second expansion valve 42 provided in the refrigerant flow path 32 b that connects the condenser 15 and the flash tank 13 .

[0059] The discharge pressure of the high stage compressor 12 can thus be adjusted.

[0060] In addition, in one embodiment of the refrigeration device 1, a fourth expansion valve 44 can be provided, and the fourth expansion valve 44 is arranged in the flash gas flow path 36, and the flash gas flow path 36 connects the gas phase of the flash tank 13 with the refrigerant flow path 31a, and the refrigerant flow path 31a connects the outlet of the low-stage compressor 11 with the liquid storage tank 14.

[0061] Since the pressure in the flash tank 13 can be adjusted by the fourth expansion valve 44, the refrigerant liquid in the flash tank 13 can be stably supplied to the refrigerant compressed by the low-stage compressor 11. Therefore, the superheat of the refrigerant supplied to the high-stage compressor 12 can be stably suppressed.

[0062] In the refrigeration device 1 of one embodiment, there may be a liquid accumulator 14 as a gas-liquid separator, and the liquid accumulator 14 is provided in the refrigerant flow path 31, which is a flow path for the refrigerant compressed by the low-stage compressor 11 to flow. The liquid injection flow path 35 may be provided to connect the liquid phase of the flash tank 13 with the above-mentioned refrigerant flow path 31. The downstream end 35d of the liquid injection flow path 35 may be connected to the refrigerant flow path 31a in the above-mentioned refrigerant flow path 31, and the refrigerant flow path 31a is located between the low-stage compressor 11 and the liquid accumulator 14.

[0063] Therefore, it is possible to prevent the refrigerant liquid in the flash tank from being supplied to the higher stage compressor in a liquid state.

[0064] The refrigeration device 1 of one embodiment may include a flash gas flow path 36 for supplying the refrigerant gas in the gas phase portion in the flash tank 13 to the refrigerant compressed by the low-stage compressor 11 .

[0065] Therefore, the refrigerant gas generated in the flash tank 13 can be returned to the high stage compressor 12 .

[0066] In the refrigeration device 1 of one embodiment, the flash gas flow path 36 may be provided to connect the gas phase of the flash tank 13 with the refrigerant flow path 31. The downstream end 36d of the flash gas flow path 36 may be connected to the refrigerant flow path 31a in the refrigerant flow path 31, and the refrigerant flow path 31a is located between the low-stage compressor 11 and the accumulator 14.

[0067] Therefore, even if the refrigerant flowing through the flash gas flow path 36 contains the refrigerant liquid, it is possible to prevent the refrigerant liquid from being supplied to the higher stage compressor 12 in a liquid state.

[0068] In the refrigeration device 1 of one embodiment, the refrigerant may be a CO 2 refrigerant. The reason for this will be described below.

[0069] Figure 2 This is an example of a Mollier diagram of a refrigeration device 1 according to an embodiment using a CO 2 refrigerant.

[0070] Regarding CO2 refrigerant, Figure 2 In the Mollier diagram shown in the figure, at a constant pressure, the greater the specific enthalpy, the Figure 2Therefore, even when the suction pressure of the refrigerant sucked into the high-stage compressor 12 and the discharge pressure of the refrigerant discharged from the high-stage compressor 12 are the same, the difference between the specific enthalpy of the refrigerant sucked into the high-stage compressor 12 and the specific enthalpy of the refrigerant discharged from the high-stage compressor 12 decreases as the specific enthalpy of the refrigerant sucked into the high-stage compressor 12 decreases.

[0071] By supplying the refrigerant liquid in the flash tank 13 to the refrigerant compressed by the low-stage compressor 11, the suction amount of the refrigerant sucked into the high-stage compressor 12 is increased, but as mentioned above, the difference between the specific enthalpy of the refrigerant sucked into the high-stage compressor 12 and the specific enthalpy of the refrigerant discharged from the high-stage compressor 12 is reduced.

[0072] The inventors have conducted intensive studies and found that there is almost no difference in the power consumption of the high-stage compressor 12 between the case where the refrigerant liquid in the flash tank 13 is supplied to the refrigerant compressed by the low-stage compressor 11 and the case where such supply is not performed.

[0073] Therefore, it is possible to suppress an increase in the power consumption of the high-stage compressor 12 and to efficiently suppress the degree of superheat of the refrigerant sucked into the high-stage compressor 12 .

[0074] In addition, Figure 2 In the figure, point n is the critical point of CO2, the line X on the left side of point n is the saturated liquid line, and the line Y on the right side of point n is the saturated vapor line. Point a is the state quantity of the refrigerant at the inlet of the low-stage compressor 11, and point b is the state quantity of the refrigerant at the outlet of the low-stage compressor 11. Point c is the state quantity of the refrigerant at the inlet of the high-stage compressor 12, and point d is the state quantity of the refrigerant at the outlet of the high-stage compressor 12. Point e is the state quantity of the refrigerant at the outlet of the condenser 15 as a gas cooler, and point f is the state quantity of the refrigerant in a gas-liquid mixed state at the outlet of the second expansion valve 42. Point g is the state quantity of the liquid phase of the flash tank 13, and point h is the state quantity of the gas phase after gas-liquid separation in the flash tank 13. Point i is the state quantity of the refrigerant after it flows out of the flash tank 13 and passes through the heat exchanger 17, point j is the state quantity of the refrigerant at the outlet of the third expansion valve 43, and point k is the state quantity of the refrigerant at the outlet of the evaporator 16. Point 1 is the state amount of the refrigerant at the outlet of the fourth expansion valve 44 , and point m is the state amount of the refrigerant at the outlet of the first expansion valve 41 .

[0075] In one embodiment of the refrigeration device 1, at point b, that is, in the refrigerant flow path 31a between the low-stage compressor 11 and the liquid storage tank 14, the injection flow path 35 merges with the flash gas flow path 36. Therefore, the specific enthalpy h of the refrigerant at point c, that is, at the inlet of the high-stage compressor 12, is lower than that at point b.

[0076] In addition, for ease of understanding, Figure 1 The same parts in the figure are also marked with symbols a to m.

[0077] (Regarding the Opening Degree Adjustment of the First Expansion Valve 41)

[0078] As described above, the control device 50 of one embodiment is a control device for controlling various parts of the refrigeration device 1, and also adjusts the opening of the first expansion valve 41. The control device 50 is configured to calculate the suction superheat of the refrigerant sucked into the high-stage compressor 12 based on the suction temperature detected by the suction temperature sensor 55 and the suction pressure detected by the suction pressure sensor 57, and adjust the opening of the first expansion valve 41 so that the calculated suction superheat becomes a preset target value.

[0079] Therefore, as will be described later, the suction superheat of the refrigerant sucked into the high-stage compressor 12 can be stably suppressed.

[0080] Figure 3 41 is a flowchart showing the flow of processing performed by the control device 50 to adjust the opening degree of the first expansion valve 41. Figure 3 The program of the process shown in the flowchart is read from the memory 53 by the processor 51 and executed.

[0081] The control method of the refrigeration device 1 according to one embodiment includes a suction temperature detection step S10 , a suction pressure detection step S20 , a suction superheat degree calculation step S30 , and an opening degree adjustment step S40 .

[0082] The suction temperature detection step S10 is a step of detecting the suction temperature Ti of the refrigerant sucked into the higher stage compressor 12. In the suction temperature detection step S10, the processor 51 obtains the suction temperature Ti of the refrigerant detected by the suction temperature sensor 55.

[0083] The suction pressure detection step S20 is a step of detecting the suction pressure Pi of the refrigerant sucked into the higher stage compressor 12. In the suction pressure detection step S20, the processor 51 obtains the suction pressure Pi of the refrigerant detected by the suction pressure sensor 57.

[0084] The suction superheat calculation step S30 is a step for calculating the suction superheat of the refrigerant sucked into the high-stage compressor 12 based on the detected suction temperature Ti and the detected suction pressure Pi. In the suction superheat calculation step S30, the processor 51 calculates the suction superheat of the refrigerant sucked into the high-stage compressor 12 based on the suction temperature Ti of the refrigerant obtained in the suction temperature detection step S10 and the suction pressure Pi of the refrigerant obtained in the suction pressure detection step S20.

[0085] The opening adjustment step S40 is a step of adjusting the opening of the first expansion valve 41 so that the calculated suction superheat becomes a preset target value. In the opening adjustment step S40, the processor 51 calculates the opening of the first expansion valve 41 in such a manner that the suction superheat of the refrigerant calculated in the suction superheat calculation step S30 becomes the target value of the suction superheat that is preset and stored in the memory 53, and outputs a control signal for driving an actuator (not shown) of the first expansion valve 41 so that the opening of the first expansion valve 41 becomes the calculated opening.

[0086] The first expansion valve 41 receives the control signal and an actuator (not shown) adjusts the opening of the first expansion valve 41. Thus, the opening of the first expansion valve 41 is adjusted so that the suction superheat of the refrigerant sucked into the high-stage compressor 12 reaches the target suction superheat.

[0087] According to the control method of the refrigeration device 1 of one embodiment, it is possible to stably suppress the suction superheat of the refrigerant sucked into the high-stage compressor 12. Therefore, it is possible to stably improve the efficiency of the high-stage compressor 12.

[0088] The present disclosure is not limited to the above-described embodiments, and includes modified embodiments of the above-described embodiments and appropriate combinations of these embodiments.

[0089] The contents described in the above-mentioned embodiments can be understood, for example, as follows.

[0090] (1) A refrigeration device 1 according to at least one embodiment of the present disclosure comprises: a low-stage compressor 11 for compressing a refrigerant; a high-stage compressor 12 for compressing the refrigerant compressed by the low-stage compressor 11; a flash tank 13 capable of receiving the refrigerant compressed by the high-stage compressor 12; and a liquid injection flow path 35 for supplying the refrigerant liquid in the flash tank 13 to the refrigerant compressed by and discharged from the low-stage compressor 11.

[0091] According to the structure of (1) above, there is no difficulty in setting a location for setting a heat exchanger for cooling the refrigerant sucked into the high-stage compressor 12, and there is no cost increase due to the installation of the heat exchanger, and the superheat of the refrigerant sucked into the high-stage compressor 12 can be effectively suppressed. Therefore, the efficiency of the high-stage compressor 12 can be improved at a low cost.

[0092] (2) In some embodiments, regarding the structure of (1) above, the liquid injection flow path 35 may be configured to connect the liquid phase portion of the flash tank 13 with the flow path (refrigerant flow path 31) through which the refrigerant compressed by the low-stage compressor 11 flows. The downstream end 35d of the liquid injection flow path 35 may be connected to the above-mentioned flow path (refrigerant flow path 31).

[0093] According to the configuration of (2) above, the refrigerant liquid in the flash tank 13 can be supplied to the refrigerant compressed by the low-stage compressor 11 with a simple configuration.

[0094] (3) In some embodiments, the structure of (1) or (2) above may include a first expansion valve 41 , and the first expansion valve 41 may be provided in the liquid injection channel 35 .

[0095] According to the configuration of (3) above, the refrigerant liquid in the flash tank 13 can be stably supplied to the refrigerant compressed by the low-stage compressor 11 .

[0096] (4) In some embodiments, the structure of any one of (1) to (3) above may include: a condenser for cooling the refrigerant compressed by the high-stage compressor 12; and a second expansion valve 42 provided in a flow path (refrigerant flow path 32 b ) connecting the condenser 15 and the flash tank 13 .

[0097] According to the configuration of (4) above, the discharge pressure of the high stage compressor 12 can be adjusted.

[0098] (5) In some embodiments, regarding any of the structures of (1) to (4) above, a gas-liquid separator (liquid accumulator 14) may be provided, and the gas-liquid separator (liquid accumulator 14) may be provided in the flow path (refrigerant flow path 31) through which the refrigerant compressed by the low-stage compressor 11 flows. The liquid injection flow path 35 may be provided so as to connect the liquid phase of the flash tank 13 with the above-mentioned flow path (refrigerant flow path 31). The downstream end 35d of the liquid injection flow path 35 may be connected to the flow path (refrigerant flow path 31a) between the low-stage compressor 11 and the gas-liquid separator (liquid accumulator 14) in the above-mentioned flow path (refrigerant flow path 31).

[0099] According to the configuration of (5) above, it is possible to prevent the refrigerant liquid in the flash tank 13 from being supplied to the higher stage compressor 12 in a liquid state.

[0100] (6) In some embodiments, any one of the structures (1) to (5) above may include a flash gas flow path 36 for supplying the refrigerant gas in the flash tank 13 to the refrigerant compressed by the low-stage compressor 11 .

[0101] According to the configuration of (6) above, the refrigerant gas generated in the flash tank 13 can be returned to the high stage compressor 12. In addition, the refrigerant gas generated in the flash tank 13 can be used to suppress the superheat of the refrigerant sucked into the high stage compressor 12.

[0102] (7) In some embodiments, regarding the structure of (6), a gas-liquid separator (liquid accumulator 14) may be provided, and the gas-liquid separator (liquid accumulator 14) may be provided in the flow path (refrigerant flow path 31) through which the refrigerant compressed by the low-stage compressor 11 flows. The flash gas flow path 36 may be provided so as to connect the gas phase portion of the flash tank 13 with the above-mentioned flow path (refrigerant flow path 31). The downstream end 36d of the flash gas flow path 36 may be connected to the flow path (refrigerant flow path 31a) between the low-stage compressor 11 and the gas-liquid separator (liquid accumulator 14) in the above-mentioned flow path (refrigerant flow path 31).

[0103] According to the configuration of (7) above, even if the refrigerant flowing through the flash gas flow path 36 contains refrigerant liquid, it is possible to prevent the refrigerant liquid from being supplied to the higher stage compressor 12 in a liquid state.

[0104] (8) In some embodiments, regarding any of the structures of (1) to (7) above, the refrigerant may be a CO 2 refrigerant.

[0105] According to the configuration of (8) above, it is possible to suppress an increase in the power consumption of the high-stage compressor 12 and to efficiently suppress the degree of superheat of the refrigerant sucked into the high-stage compressor 12 .

[0106] (9) In some embodiments, the structure of any one of (1) to (8) above may include: a first expansion valve 41 disposed in the injection flow path 35; a suction temperature sensor 55 for detecting the suction temperature Ti of the refrigerant sucked into the high-stage compressor 12; a suction pressure sensor 57 for detecting the suction pressure Pi of the refrigerant sucked into the high-stage compressor 12; and a control device 50 for adjusting the opening of the first expansion valve 41. The control device 50 may be configured to calculate the suction superheat of the refrigerant sucked into the high-stage compressor 12 based on the suction temperature Ti detected by the suction temperature sensor 55 and the suction pressure Pi detected by the suction pressure sensor 57, and adjust the opening of the first expansion valve 41 so that the calculated suction superheat becomes a preset target value.

[0107] According to the configuration of (9) above, the suction superheat of the refrigerant sucked into the high-stage compressor 12 can be stably suppressed.

[0108] (10) A control method of a refrigeration device 1 according to at least one embodiment of the present disclosure is a control method of a refrigeration device 1. The refrigeration device 1 includes: a low-stage compressor 11 for compressing a refrigerant; a high-stage compressor 12 for compressing the refrigerant compressed by the low-stage compressor 11; a flash tank 13 capable of receiving the refrigerant compressed by the high-stage compressor 12; a liquid injection flow path 35 for supplying the refrigerant liquid in the flash tank 13 to the refrigerant compressed by the low-stage compressor 12; and a first expansion valve 41 provided in the liquid injection flow path 35. The control method of the refrigeration device 1 of at least one embodiment of the present disclosure comprises: an intake temperature detection step S10, detecting the intake temperature Ti of the refrigerant sucked into the high-stage compressor 12; an intake pressure detection step S20, detecting the intake pressure Pi of the refrigerant sucked into the high-stage compressor 12; an intake superheat calculation step S30, calculating the intake superheat of the refrigerant sucked into the high-stage compressor 12 based on the detected intake temperature Ti and the detected intake pressure Pi; and an opening adjustment step S40, adjusting the opening of the first expansion valve 41 so that the calculated intake superheat becomes a preset target value.

[0109] According to the method of (10) above, the suction superheat of the refrigerant sucked into the high-stage compressor 12 can be stably suppressed regardless of the outside temperature, so the efficiency of the high-stage compressor 12 can be stably improved.

[0110] Description of Reference Numerals

[0111] 1-refrigeration device; 11-low-stage compressor; 12-high-stage compressor; 13-flash tank; 14-liquid storage device; 15-condenser; 16-evaporator; 35-liquid injection flow path; 36-flash gas flow path; 41-first expansion valve; 42-second expansion valve (high-stage expansion valve); 43-third expansion valve (low-stage expansion valve); 44-fourth expansion valve; 50-control device; 55-intake temperature sensor; 57-intake temperature sensor.

Claims

1. A refrigeration device, comprising: a low-stage compressor, which is used to compress the refrigerant; A high-stage compressor for compressing the refrigerant compressed by the low-stage compressor; a flash tank capable of receiving the refrigerant compressed by the high-stage compressor; as well as The liquid injection flow path is used to supply the refrigerant liquid in the flash tank to the refrigerant compressed by the low-stage compressor and discharged from the low-stage compressor.

2. The refrigeration device according to claim 1, characterized in that: The liquid injection flow path is configured to connect the liquid phase portion of the flash tank to the flow path through which the refrigerant compressed by the low-stage compressor flows. The downstream end of the injection channel is connected to the channel.

3. The refrigeration device according to claim 1 or 2, characterized in that: A first expansion valve is provided, and the first expansion valve is provided in the liquid injection flow path.

4. The refrigeration device according to claim 1 or 2, characterized in that: have: a condenser for cooling the refrigerant compressed by the high-stage compressor; and A second expansion valve is provided in a flow path connecting the condenser and the flash tank.

5. The refrigeration device according to claim 1 or 2, characterized in that: A gas-liquid separator is provided, the gas-liquid separator being provided in a flow path through which the refrigerant compressed by the low-stage compressor flows, The liquid injection flow path is configured to connect the liquid phase of the flash tank to the flow path. The downstream end of the liquid injection flow path is connected to a flow path between the low-stage compressor and the gas-liquid separator in the flow path.

6. The refrigeration device according to claim 1 or 2, characterized in that: A flash gas flow path is provided for supplying the refrigerant gas in the flash tank to the refrigerant compressed by the low-stage compressor.

7. The refrigeration device according to claim 6, characterized in that: A gas-liquid separator is provided, the gas-liquid separator being provided in a flow path through which the refrigerant compressed by the low-stage compressor flows, The flash gas flow path is configured to connect the gas phase of the flash tank to the flow path. The downstream end of the flash gas flow path is connected to a flow path between the low-stage compressor and the gas-liquid separator in the flow path.

8. The refrigeration device according to claim 1 or 2, characterized in that: The refrigerant is CO2 refrigerant.

9. The refrigeration device according to claim 1 or 2, characterized in that: have: a first expansion valve, which is disposed in the injection flow path; a suction temperature sensor for detecting a suction temperature of the refrigerant sucked into the high-stage compressor; a suction pressure sensor for detecting a suction pressure of the refrigerant sucked into the high-stage compressor; as well as a control device for adjusting the opening of the first expansion valve, The control device is configured to calculate the suction superheat of the refrigerant sucked into the high-stage compressor based on the suction temperature detected by the suction temperature sensor and the suction pressure detected by the suction pressure sensor, and to adjust the opening degree of the first expansion valve so that the calculated suction superheat becomes a predetermined target value.

10. A method for controlling a refrigeration device, the refrigeration device comprising: a low-stage compressor, which is used to compress the refrigerant; A high-stage compressor for compressing the refrigerant compressed by the low-stage compressor; a flash tank capable of receiving the refrigerant compressed by the high-stage compressor; a liquid injection flow path for supplying the refrigerant liquid in the flash tank to the refrigerant compressed by the low-stage compressor; and a first expansion valve, which is arranged in the injection flow path, The control method comprises: a suction temperature detection step of detecting a suction temperature of the refrigerant sucked into the high-stage compressor; a suction pressure detection step of detecting the suction pressure of the refrigerant sucked into the high-stage compressor; a suction superheat calculation step, calculating the suction superheat of the refrigerant sucked into the high-stage compressor according to the detected suction temperature and the detected suction pressure; as well as The opening degree adjusting step adjusts the opening degree of the first expansion valve so that the calculated suction superheat degree reaches a preset target value.

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