Refrigeration apparatus and control method for refrigeration apparatus

Abstract

A refrigeration apparatus according to at least one embodiment of the present disclosure comprises: a low-pressure stage compressor for compressing a refrigerant; a high-pressure stage compressor for compressing the refrigerant that has been compressed by the low-pressure stage compressor; a flash tank capable of receiving the refrigerant that has been compressed by the high-pressure stage compressor; a liquid injection flow path for supplying the liquid refrigerant in the flash tank to the refrigerant that has been compressed by the low-pressure stage compressor and discharged from the low-pressure stage compressor; and a heat exchanger for heating brine using the refrigerant that has been compressed by the low-pressure stage compressor and discharged from the low-pressure stage compressor.

Description

Refrigeration device and method for controlling the same

[0001] The present disclosure relates to a refrigeration device and a method for controlling a refrigeration device.

[0002] BACKGROUND ART A refrigeration system including a low-stage compressor and a high-stage compressor is known (see, for example, Patent Document 1).

[0003] JP 2024-5797 A

[0004] In such a refrigeration system, in order to increase the efficiency of the high-stage compressor, it is necessary to suppress the degree of superheat of the refrigerant sucked into the high-stage compressor.

[0005] In view of the above circumstances, at least one embodiment of the present disclosure has an object to improve the efficiency of a high-stage compressor at low cost in a refrigeration device including a low-stage compressor and a high-stage compressor.

[0006] (1) A refrigeration device according to at least one embodiment of the present disclosure includes: a low-stage compressor for compressing a refrigerant; a high-stage compressor for compressing the refrigerant after it has been compressed by the low-stage compressor; a flash tank capable of receiving the refrigerant after it has been compressed by the high-stage compressor; a liquid injection flow path for supplying refrigerant liquid in the flash tank to the refrigerant after it has been compressed by the low-stage compressor and discharged from the low-stage compressor; and a heat exchanger for heating brine with the refrigerant after it has been compressed by the low-stage compressor and discharged from the low-stage compressor.

[0007] (2) A control method for a refrigeration device according to at least one embodiment of the present disclosure is a control method for a refrigeration device, the refrigeration device comprising: a low-stage compressor for compressing a refrigerant; a high-stage compressor for compressing the refrigerant after being compressed by the low-stage compressor; a flash tank capable of receiving the refrigerant after being compressed by the high-stage compressor; a liquid injection flow path for supplying refrigerant liquid in the flash tank to the refrigerant after being compressed by the low-stage compressor; a heat exchanger for heating brine with the refrigerant after being compressed by the low-stage compressor and discharged from the low-stage compressor; and a first expansion valve provided in the liquid injection flow path, the control method comprising: an intake temperature detection step for detecting an intake temperature of the refrigerant sucked into the high-stage compressor; an intake pressure detection step for detecting an intake pressure of the refrigerant sucked into the high-stage compressor; and an intake superheat calculation step for calculating an intake superheat of the refrigerant sucked into the high-stage compressor based on the detected intake temperature and the detected suction pressure. and an opening degree adjusting step of adjusting the opening degree of the first expansion valve so that the calculated degree of suction superheat becomes a preset target value.

[0008] According to at least one embodiment of the present disclosure, in a refrigeration system including a low-stage compressor and a high-stage compressor, the efficiency of the high-stage compressor can be improved at low cost.

[0009] FIG. 1 is a system diagram of a refrigeration device according to one embodiment; FIG. 2 is a system diagram of a refrigeration device according to another embodiment; FIG. 3 is a system diagram of a refrigeration device according to yet another embodiment; and FIG. 4 is a system diagram of a refrigeration device according to yet another embodiment. ２ 1 is a flowchart showing a process performed by a control device for adjusting the opening degree of a first expansion valve according to some embodiments of the present invention;

[0010] Several embodiments of the present disclosure will be described below with reference to the accompanying drawings. However, the dimensions, materials, shapes, relative arrangements, etc. of components described as embodiments or shown in the drawings are not intended to limit the scope of the present disclosure and are merely illustrative examples. For example, expressions expressing relative or absolute arrangements, such as "in a certain direction," "along a certain direction," "parallel," "orthogonal," "center," "concentric," or "coaxial," not only strictly express such arrangements, but also express relative displacements with a tolerance or angle or distance to the extent that the same function is achieved. For example, expressions expressing the equality of things, such as "same," "equal," and "homogeneous," not only express strict equality, but also express tolerance or differences to the extent that the same function is achieved. For example, expressions expressing shapes such as a square or cylindrical shape not only express shapes such as a square or cylindrical shape in the strict geometric sense, but also express shapes including concave and convex portions, chamfered portions, etc., to the extent that the same effect is achieved. On the other hand, the expressions "comprise," "include," "have," "includes," or "have" of one element are not exclusive expressions that exclude the presence of other elements.

[0011] FIG. 1A is a system diagram of a refrigeration device according to one embodiment. FIG. 1B is a system diagram of a refrigeration device according to another embodiment. FIG. 1C is a system diagram of a refrigeration device according to yet another embodiment. FIG. 1D is a system diagram of a refrigeration device according to yet another embodiment. The refrigeration device 1 according to some embodiments is configured to refrigerate a refrigerant such as CO ２ The refrigeration apparatus 1 is a two-stage compression, two-stage expansion type refrigeration apparatus that uses a refrigerant. In the refrigeration apparatus 1 according to some embodiments, a low-stage compressor 11, a high-stage compressor 12, and a flash tank 13 are provided in a refrigerant circuit 30. In the refrigeration apparatus 1 according to some embodiments, for example, two low-stage compressors 11 are provided in parallel with the refrigerant circuit 30. In the refrigeration apparatus 1 according to some embodiments, for example, two high-stage compressors 12 are provided in parallel with the refrigerant circuit 30.

[0012] In the refrigeration apparatus 1 according to some embodiments, an accumulator 14 is provided in a refrigerant flow path 31 connecting the outlet of the low-stage compressor 11 and the inlet of the high-stage compressor 12. In the refrigeration apparatus 1 according to some embodiments, a condenser 15 operating as a gas cooler is provided in a refrigerant flow path 32 connecting the outlet of the high-stage compressor 12 and the inlet of the flash tank 13. In the refrigeration apparatus 1 according to some embodiments, a heat exchanger 17 is provided in the refrigerant circulation path 30 for exchanging heat between the liquid phase portion of the flash tank 13 and refrigerant that has passed through, for example, an evaporator 16 as a cooling load.

[0013] The refrigeration device 1 according to some embodiments includes a refrigerant flow path 31a that connects the outlet of the low-stage compressor 11 and the inlet of the high-stage compressor 12, the refrigerant flow path 31a connecting the outlet of the low-stage compressor 11 and the accumulator 14, and a liquid injection flow path 35 that connects the liquid phase part of the flash tank 13. The refrigeration device 1 according to some embodiments includes a flash gas flow path 36 that connects the gas phase part of the flash tank 13 and the refrigerant flow path 31a that connects the outlet of the low-stage compressor 11 and the accumulator 14.

[0014] In the refrigeration apparatus 1 according to some embodiments, 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 a refrigerant flow path 32b that connects the outlet of the condenser 15 and the inlet of the flash tank 13. In the refrigeration apparatus 1 according to some embodiments, a third expansion valve (low-stage expansion valve) 43 is provided in a refrigerant flow path 34b that connects the heat exchanger 17 and the evaporator 16, of the refrigerant flow path 34 that supplies the refrigerant liquid in the flash tank 13 to the evaporator 16. In the refrigeration apparatus 1 according to some embodiments, a fourth expansion valve 44 is provided in the flash gas flow path 36.

[0015] In the refrigeration device 1 according to some embodiments, an oil separator 21 for separating refrigerant gas and refrigerating machine oil is provided in the refrigerant flow path 32a connecting the outlet of the high-stage compressor 12 and the inlet of the condenser 15. In the refrigeration device 1 according to some embodiments, the refrigerating machine oil separated in the oil separator 21 is returned to the low-stage compressor 11 and the high-stage compressor 12 via an oil tank (not shown).

[0016] The refrigeration system 1 according to some embodiments includes a defrosting device 60 for defrosting the evaporator 16. The defrosting device 60 according to some embodiments includes a brine coil 61 for heating the evaporator 16 with brine, a brine tank 62 for storing the brine, a heat exchanger 63 for heating the brine with the refrigerant compressed by the low-stage compressor 11 and discharged from the low-stage compressor 11, and a supply pump 64 for supplying the brine to the brine coil 61.

[0017] In the refrigeration system 1 shown in Figures 1A, 1B, and 1C, the heat exchanger 63 is a heat exchanger configured to exchange heat between the refrigerant discharged from the low-stage compressor 11 and brine supplied from the brine tank 62 by a circulation pump 65. In the refrigeration system 1 shown in Figures 1A, 1B, and 1C, the brine supplied to the heat exchanger 63 by the circulation pump 65 is heated by heat exchange with the refrigerant discharged from the low-stage compressor 11 in the heat exchanger 63, and is returned to the brine tank 62. In the refrigeration system 1 shown in Figure 1D, the heat exchanger 63 is a pipe 63a provided in the brine tank 62 for heating the brine, and the refrigerant discharged from the low-stage compressor 11 flows through the pipe 63a, thereby performing heat exchange between the refrigerant and the brine in the brine tank 62.

[0018] In some embodiments of the refrigeration device 1, the refrigerant side flow path 63b in the heat exchanger 63 is connected in series to the refrigerant flow path 31a connecting the outlet of the low-stage compressor 11 and the accumulator 14, upstream of the connection position between the downstream end 35d of the liquid injection flow path 35 and the refrigerant flow path 31a (the outlet side of the low-stage compressor 11).

[0019] 1B and 1D , a flow path switching valve 66 is provided in the refrigerant flow path 31a upstream of the connection position between the downstream end 35d of the liquid injection flow path 35 and the refrigerant flow path 31a (on the outlet side of the low-stage compressor 11). The flow path switching valve 66 is a switching valve, for example a three-way valve, that switches whether the refrigerant discharged from the low-stage compressor 11 is supplied to the refrigerant-side flow path 63b in the heat exchanger 63 or is supplied to the downstream side of the refrigerant flow path 31a, bypassing the refrigerant-side flow path 63b in the heat exchanger 63.

[0020] The refrigeration device 1 according to some embodiments has a brine flow path 70 that connects the brine tank 62 and the brine coil 61. The brine flow path 70 has a supply flow path 71 for supplying the brine in the brine tank 62 to the brine coil 61, and a return flow path 72 for returning the brine discharged from the brine coil 61 to the brine tank 62. That is, the downstream end of the supply flow path 71 is connected to the brine inlet 61 a of the brine coil 61, and the upstream end of the return flow path 72 is connected to the brine outlet 61 b ​​of the brine coil 61.

[0021] In the refrigeration device 1 according to some embodiments, the supply flow path 71 is provided with the supply pump 64 described above.

[0022] In the refrigeration system 1 shown in FIG. 1C , the brine flow path 70 has a bypass flow path 73 that connects the return flow path 72 and the supply flow path 71 upstream of the supply pump 64. In the refrigeration system 1 shown in FIG. 1C , the supply flow path 71 is provided with a bypass valve 74 for controlling the amount of brine flowing through the bypass flow path 73. The bypass valve 74 is provided midway through the return flow path 72 and is also connected to the bypass flow path 73. The bypass valve 74 is configured to be able to adjust the ratio of the flow rate of brine flowing from the upstream side (brine coil 61 side) of the return flow path 72 to the downstream side (brine tank 62 side) of the return flow path 72 and the flow rate of brine flowing into the bypass flow path 73. The operation of the bypass valve 74 will be described later.

[0023] A refrigeration device 1 according to some embodiments includes a control device 50 for controlling each component of the refrigeration device 1. The control device 50 includes a processor 51 that executes various arithmetic processes and a memory 52 that non-temporarily or temporarily stores various data processed by the processor 51. The processor 51 is implemented by a CPU, a GPU, an MPU, a DSP, various other arithmetic devices, or a combination thereof. The memory 52 is implemented by a ROM, a RAM, a flash memory, or a combination thereof. In the following description, the control content of the control device 50 will be mainly described with respect to adjusting the opening degree of the first expansion valve 41. The control content of the control device 50 will be described in detail later. The refrigeration device 1 according to some embodiments includes various sensors for controlling each component of the refrigeration device 1. The various sensors for controlling each part of the refrigeration device 1 include, for example, an intake temperature sensor 55 for detecting an intake temperature Ti of the refrigerant sucked into the high-stage compressor 12, an intake pressure sensor 56 for detecting an intake pressure Pi of the refrigerant sucked into the high-stage compressor 12, and a temperature sensor 53 for detecting a temperature Tbt of the brine in the brine tank 62. In the refrigeration device 1 shown in FIG. 1C , the various sensors for controlling each part of the refrigeration device 1 include, for example, a temperature sensor 54 for detecting a temperature Tbd of the brine flowing into the brine coil 61.

[0024] (Overview of Refrigerant Flow) In the refrigeration system 1 according to some embodiments configured as described above, the refrigerant compressed in 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 reduced in pressure through the second expansion valve 42 and then sent to the flash tank 13, where it is separated into a gas phase and a liquid phase. The refrigerant liquid forming the liquid phase in the flash tank 13 leaves the flash tank 13 and exchanges heat with the gas phase refrigerant returning from the evaporator 16 in the heat exchanger 17 to heat the gas phase refrigerant, and the refrigerant liquid itself is cooled in the heat exchanger 17. The refrigerant liquid sent from the flash tank 13 to the heat exchanger 17 leaves the heat exchanger 17, is reduced in pressure through the third expansion valve 43, is vaporized via the evaporator 16 and the heat exchanger 17, and is supplied to the low-stage compressor 11.

[0025] (Regarding the flow of refrigerant after being discharged from the low-stage compressor 11 and temperature control of brine) In the refrigeration system 1 shown in FIGS. 1A and 1C, the refrigerant compressed by the low-stage compressor 11 is supplied to the accumulator 14 via the refrigerant-side flow path 63b in the heat exchanger 63.

[0026] In the refrigeration device 1 shown in FIGS. 1A and 1C, the processor 51 of the control device 50 controls the on / off of the circulation pump 65 based on the temperature Tbt of the brine in the brine tank 62 detected by the temperature sensor 53.

[0027] That is, when the temperature Tbt of the brine in the brine tank 62 detected by the temperature sensor 53 falls below a specified temperature Tbt1, for example, the processor 51 starts operation of the circulation pump 65. As a result, the brine in the brine tank 62 is supplied to the heat exchanger 63, where it exchanges heat with the refrigerant discharged from the low-stage compressor 11, and is then heated and returned to the brine tank 62.

[0028] When the temperature Tbt of the brine in the brine tank 62 detected by the temperature sensor 53 exceeds a specified temperature Tbt2 that is higher than the above-mentioned specified temperature Tbt1, for example, the processor 51 stops the circulation pump 65. As a result, the brine in the brine tank 62 is no longer supplied to the heat exchanger 63, and the temperature Tbt of the brine in the brine tank 62 stops increasing.

[0029] In the refrigeration system 1 shown in Figures 1B and 1D, the refrigerant compressed by the low-stage compressor 11 is supplied to the refrigerant-side flow path 63b of the heat exchanger 63 via the flow path switching valve 66, or is supplied to the accumulator 14 by bypassing the refrigerant-side flow path 63b of the heat exchanger 63. That is, in the refrigeration system 1 shown in Figures 1B and 1D, when the brine in the brine tank 62 is heated, the flow path switching valve 66 is switched to supply the refrigerant after being discharged from the low-stage compressor 11 to the refrigerant-side flow path 63b of the heat exchanger 63. In the refrigeration system 1 shown in Figures 1B and 1D, when it is not necessary to heat the brine in the brine tank 62, the flow path switching valve 66 is switched to supply the refrigerant after being discharged from the low-stage compressor 11 to the downstream side of the refrigerant flow path 31a by bypassing the refrigerant-side flow path 63b of the heat exchanger 63.

[0030] That is, when the temperature Tbt of the brine in the brine tank 62 detected by the temperature sensor 53 falls below, for example, a specified temperature Tbt1, the processor 51 controls the flow path switching valve 66 to supply the refrigerant discharged from the low-stage compressor 11 to the refrigerant-side flow path 63b in the heat exchanger 63. As a result, the refrigerant discharged from the low-stage compressor 11 is supplied to the refrigerant-side flow path 63b in the heat exchanger 63. In the refrigeration system 1 shown in FIG. 1B , when the temperature Tbt of the brine in the brine tank 62 detected by the temperature sensor 53 falls below, for example, a specified temperature Tbt1, the processor 51 starts operation of the circulation pump 65. As a result, the brine in the brine tank 62 is supplied to the heat exchanger 63, where it exchanges heat with the refrigerant discharged from the low-stage compressor 11, and is then heated and returned to the brine tank 62. In the refrigeration system 1 shown in FIG. 1D , when the flow path switching valve 66 is switched and the refrigerant discharged from the low-stage compressor 11 is supplied to the refrigerant-side flow path 63 b in the heat exchanger 63 as described above, the refrigerant discharged from the low-stage compressor 11 flows through the piping 63 a for heating the brine provided in the brine tank 62, and the brine in the brine tank 62 is heated by the refrigerant discharged from the low-stage compressor 11.

[0031] 1B and 1D , when the temperature Tbt of the brine in the brine tank 62 detected by the temperature sensor 53 exceeds a specified temperature Tbt2 that is higher than the specified temperature Tbt1, for example, the processor 51 controls the flow path switching valve 66 so that the refrigerant discharged from the low-stage compressor 11 bypasses the refrigerant-side flow path 63b in the heat exchanger 63 and is supplied to the downstream side of the refrigerant flow path 31a. This stops the heat exchange between the refrigerant discharged from the low-stage compressor 11 and the brine in the heat exchanger 63. Furthermore, in the refrigeration system 1 shown in FIG. 1B , when the temperature Tbt of the brine in the brine tank 62 detected by the temperature sensor 53 exceeds a specified temperature Tbt2 that is higher than the specified temperature Tbt1, for example, the processor 51 stops the circulation pump 65.

[0032] In some embodiments of the refrigeration system 1, the components of the defrosting device 60 are controlled as described above, thereby maintaining the temperature Tbt of the brine in the brine tank 62 between the specified temperature Tbt1 and the specified temperature Tbt2. If the temperature Tbt of the brine in the brine tank 62 is higher than the temperature suitable for defrosting, steam may be generated during defrosting, which may lead to undesirable phenomena such as refreezing of the evaporator 16 or the freezer compartment in which the evaporator 16 is installed. Therefore, in the refrigeration systems 1 shown in FIGS. 1A, 1B, and 1D, the temperature Tbt of the brine in the brine tank 62 is maintained at a temperature suitable for defrosting. Note that in the refrigeration system 1 shown in FIG. 1C, the temperature Tbt of the brine in the brine tank 62 is maintained at a temperature higher than the temperature suitable for defrosting. The reason for this will be explained later.

[0033] (Regarding Refrigerant Flow from the Flash Tank 13) As described above, the refrigeration system 1 according to some embodiments includes a liquid injection flow path 35 for supplying refrigerant liquid from the flash tank 13 to the refrigerant compressed by the low-stage compressor 11 and discharged therefrom. To increase the efficiency of the high-stage compressor 12, it is necessary to suppress the degree of superheat of the refrigerant drawn into the high-stage compressor 12. Therefore, it is conceivable to use a heat exchanger for cooling the refrigerant drawn into the high-stage compressor 12. However, providing such a heat exchanger presents challenges, such as the need to secure an installation space and increased costs. After extensive research, the inventors discovered that supplying refrigerant liquid from the flash tank 13 to the refrigerant compressed by the low-stage compressor 11 and discharged therefrom can efficiently suppress the degree of superheat of the refrigerant drawn into the high-stage compressor 12. According to the refrigeration system 1 according to some embodiments, there is no need for an installation space for a heat exchanger for cooling the refrigerant drawn into the high-stage compressor 12, and the cost of providing the heat exchanger is not required, and the degree of superheat of the refrigerant drawn into the high-stage compressor 12 can be efficiently suppressed regardless of the temperature conditions of the outside air. This makes it possible to improve the efficiency of the high-stage compressor 12 at low cost.

[0034] According to the refrigeration system 1 of some embodiments, the temperature of the refrigerant drawn into the high-stage compressor 12 can be lowered by heating the brine, and therefore the degree of superheat of the refrigerant drawn into the high-stage compressor 12 can be efficiently suppressed even if the amount of refrigerant liquid in the flash tank 13 that is supplied to the refrigerant discharged from the low-stage compressor 11 is reduced. This allows the amount of refrigerant liquid that can be used for refrigeration to be increased by the amount of the reduced supply amount, thereby improving the COP.

[0035] In the refrigeration system 1 according to some embodiments, the liquid injection flow path 35 may be provided to communicate between the liquid phase portion of the flash tank 13 and a refrigerant flow path 31, which is a flow path through which the refrigerant compressed by the low-stage compressor 11 flows and connects the outlet of the low-stage compressor 11 to 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. This allows the refrigerant liquid in the flash tank 13 to be supplied to the refrigerant compressed by the low-stage compressor 11 with a simple configuration. Note that the upstream end 35u of the liquid injection flow path 35 may be connected to a refrigerant flow path 34a connecting the flash tank 13 and the heat exchanger 17, among the refrigerant flow paths 34 for supplying the refrigerant liquid in the flash tank 13 to the evaporator 16, as shown in FIGS. 1A to 1D , or may be directly connected to the flash tank 13.

[0036] When the liquid injection flow path 35 is connected to the refrigerant flow path 31 (refrigerant flow path 31a) upstream of the heat exchanger 63, the refrigerant whose temperature has been lowered by the refrigerant liquid from the liquid injection flow path 35 is supplied to the heat exchanger 63, thereby reducing the temperature difference between the refrigerant supplied to the heat exchanger 63 and the brine, and reducing the heat exchange efficiency in the heat exchanger 63. In some embodiments, the downstream end 35d of the liquid injection flow path 35 is connected to the refrigerant flow path 31 (refrigerant flow path 31a) downstream of the heat exchanger 63. This allows for a larger temperature difference between the refrigerant supplied to the heat exchanger 63 and the brine than when the liquid injection flow path 35 is connected to the refrigerant flow path 31 (refrigerant flow path 31a) upstream of the heat exchanger 63, thereby improving the heat exchange efficiency in the heat exchanger 63. As a result, more heat from the refrigerant after being compressed by the low-stage compressor 11 can be transferred to the brine, thereby lowering the temperature of the refrigerant sucked into the high-stage compressor 12, thereby reducing the amount of refrigerant liquid in the flash tank 13 that is supplied to the refrigerant after being discharged from the low-stage compressor 11.

[0037] The refrigeration system 1 according to some embodiments may include a first expansion valve 41 provided in the liquid injection flow path 35. This allows the refrigerant liquid in the flash tank 13 to be supplied to the refrigerant compressed by the low-stage compressor 11 with good controllability.

[0038] The refrigeration system 1 according to some embodiments may include a second expansion valve 42 provided in the refrigerant flow path 32b, which is a flow path connecting the condenser 15 and the flash tank 13. This allows the discharge pressure of the high-stage compressor 12 to be adjusted. Furthermore, the refrigeration system 1 according to some embodiments may include a fourth expansion valve 44 provided in the flash gas flow path 36, which connects the gas phase portion of the flash tank 13 with the refrigerant flow path 31a, which connects the outlet of the low-stage compressor 11 with the accumulator 14. The fourth expansion valve 44 allows the pressure in the flash tank 13 to be adjusted, thereby stably supplying the refrigerant liquid in the flash tank 13 to the refrigerant compressed by the low-stage compressor 11. This allows the degree of superheat of the refrigerant supplied to the high-stage compressor 12 to be stably suppressed.

[0039] The refrigeration system 1 according to some embodiments may include an accumulator 14 as a gas-liquid separator provided in a refrigerant flow path 31, which is a path through which the refrigerant flows after being compressed by the low-stage compressor 11. A liquid injection flow path 35 may be provided to communicate between a liquid phase portion of the flash tank 13 and the refrigerant flow path 31. A downstream end 35d of the liquid injection flow path 35 may be connected to a refrigerant flow path 31a between the low-stage compressor 11 and the accumulator 14 in the refrigerant flow path 31. This prevents the refrigerant liquid in the flash tank from being supplied to the high-stage compressor 12 in liquid form.

[0040] The refrigeration system 1 according to some embodiments may include a flash gas flow path 36 for supplying refrigerant gas from the gas phase in the flash tank 13 to the refrigerant compressed by the low-stage compressor 11. This allows the refrigerant gas generated in the flash tank 13 to be returned to the high-stage compressor 12.

[0041] In the refrigeration system 1 according to some embodiments, the flash gas passage 36 may be provided to communicate between the gas phase part of the flash tank 13 and the refrigerant passage 31. The upstream end 36u of the flash gas passage 36 may be connected to the gas phase part of the flash tank 13, and the downstream end 36d of the flash gas passage 36 may be connected to the refrigerant passage 31a between the low-stage compressor 11 and the accumulator 14, within the refrigerant passage 31. This prevents the refrigerant liquid from being supplied in liquid form to the high-stage compressor 12, even if the refrigerant flowing through the flash gas passage 36 contains refrigerant liquid.

[0042] In some embodiments of the refrigeration system 1, the refrigerant is CO ２ The reason for this will be explained below. ２ 1 is an example of a Mollier diagram for a refrigeration system 1 according to some embodiments that uses a refrigerant CO ２ In the Mollier diagram shown in Fig. 2, the larger the specific enthalpy at a certain pressure, the smaller the slope of the isentropic curve Ei, shown by the multiple thin solid lines in Fig. 2. Therefore, even if the suction pressure of the refrigerant drawn into the high-stage compressor 12 is the same and the discharge pressure of the refrigerant discharged from the high-stage compressor 12 is the same, the smaller the specific enthalpy of the refrigerant drawn into the high-stage compressor 12, the smaller the difference between the specific enthalpy of the refrigerant drawn into the high-stage compressor 12 and the specific enthalpy of the refrigerant discharged from the high-stage compressor 12. By supplying the refrigerant liquid in the flash tank 13 to the refrigerant compressed by the low-stage compressor 11, the amount of refrigerant drawn into the high-stage compressor 12 increases, but as described above, the difference between the specific enthalpy of the refrigerant drawn into the high-stage compressor 12 and the specific enthalpy of the refrigerant discharged from the high-stage compressor 12 becomes smaller. As a result of extensive research by the inventors, it was found that there is almost no difference in the power consumption of the high-stage compressor 12 between when the refrigerant liquid in the flash tank 13 is supplied to the refrigerant compressed by the low-stage compressor 11 and when it is not supplied. This makes it possible to efficiently suppress the degree of superheat of the refrigerant drawn into the high-stage compressor 12 while suppressing an increase in the power consumption of the high-stage compressor 12.

[0043] In FIG. 2, point n is CO ２is the critical point of the refrigerant system, and line X to the left of point n is the saturated liquid line, and line Y to the right 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, 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 serving 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 leaving the flash tank 13 and passing 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 l is the state quantity of the refrigerant at the outlet of the fourth expansion valve 44 , and point m is the state quantity of the refrigerant at the outlet of the first expansion valve 41 .

[0044] In the refrigeration system 1 according to some embodiments, the liquid injection flow path 35 and the flash gas flow path 36 merge at point b, i.e., at the refrigerant flow path 31a between the low-stage compressor 11 and the accumulator 14. This causes the specific enthalpy h of the refrigerant at point c, i.e., at the inlet of the high-stage compressor 12, to be lower than that at point b. In addition, in the refrigeration system 1 according to some embodiments, the temperature of the refrigerant drawn into the high-stage compressor 12 can be lowered by discharging heat to the outside by heating the brine. Furthermore, in the refrigeration system 1 according to some embodiments, the amount of refrigerant liquid in the flash tank 13 supplied to the refrigerant discharged from the low-stage compressor 11 can be reduced or eliminated by discharging heat to the outside by heating the brine. Therefore, the line connecting point m and point l in the Mollier diagram of FIG. 2 can be eliminated. For ease of understanding, the corresponding portions in FIGS. 1A to 1D are also labeled a to m.

[0045] (Regarding Adjustment of Opening Degree of First Expansion Valve 41) As described above, the control device 50 according to some embodiments is a control device for controlling each part of the refrigeration system 1, and also adjusts the opening degree 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 56, and adjust the opening degree of the first expansion valve 41 so that the calculated suction superheat becomes a preset target value. This makes it possible to stably suppress the suction superheat of the refrigerant sucked into the high-stage compressor 12, as will be described later.

[0046] (Regarding the flow of brine during defrosting) In the refrigeration device 1 according to some embodiments, the processor 51 controls the on / off of the supply pump 64. That is, when defrosting the evaporator 16, the processor 51 starts the operation of the supply pump 64. As a result, the brine in the brine tank 62 is supplied to the brine coil 61, and the evaporator 16 is defrosted. The brine whose temperature has been reduced by defrosting is returned to the brine tank 62 via the return flow path 72. When defrosting of the evaporator 16 is to be ended, the processor 51 stops the supply pump 64. As a result, the supply of brine to the brine coil 61 is stopped, and defrosting is ended.

[0047] (Regarding the Flow of Brine During Defrosting in the Refrigeration System 1 Shown in FIG. 1C) In the refrigeration system 1 shown in FIG. 1C, as described above, the temperature Tbt of the brine in the brine tank 62 is maintained at a temperature higher than the temperature suitable for defrosting. Therefore, in the refrigeration system 1 shown in FIG. 1C, brine at a temperature higher than the temperature suitable for defrosting is supplied to the brine coil 61. However, because the temperature of the brine drops due to defrosting, brine at a temperature lower than the temperature Tbt of the brine in the brine tank 62 flows through the return flow path 72. Therefore, in the refrigeration system 1 shown in FIG. 1C, the aperture of the bypass valve 74 is controlled so that a portion of the brine flowing through the return flow path 72 and having a temperature lower than the temperature Tbt of the brine in the brine tank 62 is returned to the supply flow path 71 via the bypass flow path 73. As a result, the temperature of the brine flowing through the supply flow path 71 downstream of the connection position 75 between the supply flow path 71 and the bypass flow path 73 becomes lower than the temperature Tbt of the brine in the brine tank 62. By utilizing this, the temperature of the brine supplied to the brine coil 61 can be adjusted to a temperature suitable for defrosting.

[0048] 1C , the processor 51 controls the opening degree of the bypass valve 74 so that the temperature Tbd of the brine flowing into the brine coil 61, detected by the temperature sensor 54, becomes a temperature suitable for defrosting. As a result, the bypass valve 74 adjusts the ratio of the flow rate of the brine flowing from the upstream side (brine coil 61 side) of the return flow path 72 to the downstream side (brine tank 62 side) of the return flow path 72 (brine coil 61 side) and the flow rate of the brine flowing into the bypass flow path 73, thereby adjusting the temperature Tbd of the brine flowing into the brine coil 61 to a temperature suitable for defrosting.

[0049] As described above, if the temperature of the brine in the brine tank 62 is higher than the temperature suitable for Tbt defrosting, steam may be generated during defrosting, potentially causing undesirable phenomena such as refreezing of the evaporator 16 or the freezing chamber in which the evaporator 16 is installed. According to the refrigeration system 1 shown in FIG. 1C , by opening the bypass valve 74, the brine whose temperature has been reduced by defrosting flows from the return flow path 72 into the supply flow path 71, thereby lowering the temperature (temperature Tbd) of the brine supplied to the brine coil 61. Therefore, the temperature Tbt of the brine in the brine tank 62 can be set to a temperature higher than the temperature suitable for defrosting. Therefore, by raising the temperature of the brine in the brine tank 62, the temperature of the refrigerant after passing through the refrigerant-side flow path 63b in the heat exchanger 63 can be further lowered, thereby further reducing the amount of refrigerant liquid in the flash tank 13 supplied to the refrigerant discharged from the low-stage compressor 11. This further increases the amount of refrigerant liquid available for refrigeration, thereby further improving the COP.

[0050] 3 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. A program for executing the processing shown in the flowchart of FIG. 3 is read from the memory 52 and executed by the processor 51.

[0051] The control method for the refrigeration device 1 according to some embodiments 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.

[0052] The suction temperature detection step S10 is a step of detecting the suction temperature Ti of the refrigerant suctioned into the high-stage compressor 12. In the suction temperature detection step S10, the processor 51 acquires the suction temperature Ti of the refrigerant detected by the suction temperature sensor 55. The suction pressure detection step S20 is a step of detecting the suction pressure Pi of the refrigerant suctioned into the high-stage compressor 12. In the suction pressure detection step S20, the processor 51 acquires the suction pressure Pi of the refrigerant detected by the suction pressure sensor 56.

[0053] The suction superheat calculation step S30 is a step of 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 acquired in the suction temperature detection step S10 and the suction pressure Pi of the refrigerant acquired in the suction pressure detection step S20.

[0054] The opening degree adjusting step S40 is a step of adjusting the opening degree of the first expansion valve 41 so that the calculated suction superheat degree becomes a preset target value. In the opening degree adjusting step S40, the processor 51 calculates the opening degree of the first expansion valve 41 so that the suction superheat degree of the refrigerant calculated in the suction superheat degree calculating step S30 becomes a preset target value of the suction superheat degree stored in the memory 52, and outputs a control signal for driving an actuator (not shown) of the first expansion valve 41 so that the calculated opening degree is achieved. In the first expansion valve 41, upon receiving the control signal, the actuator (not shown) adjusts the opening degree of the first expansion valve 41. As a result, the opening degree of the first expansion valve 41 is adjusted so that the suction superheat degree of the refrigerant drawn into the high-stage compressor 12 becomes the target value of the suction superheat degree. According to the control method for the refrigeration system 1 according to some embodiments, the suction superheat degree of the refrigerant drawn into the high-stage compressor 12 can be stably suppressed. As a result, the efficiency of the high-stage compressor 12 can be stably improved.

[0055] Furthermore, according to the control method for the refrigeration system 1 according to some embodiments, the temperature of the refrigerant drawn into the high-stage compressor 12 can be lowered by heating the brine, so that the degree of superheat of the refrigerant drawn into the high-stage compressor 12 can be efficiently suppressed even if the amount of refrigerant liquid in the flash tank 13 that is supplied to the refrigerant discharged from the low-stage compressor 11 is reduced. This allows the amount of refrigerant liquid that can be used for refrigeration to be increased by the amount of the reduced supply amount, thereby improving the COP.

[0056] The present disclosure is not limited to the above-described embodiments, but also includes modifications to the above-described embodiments and appropriate combinations of these modifications.

[0057] The contents described in each of the above embodiments can be understood as follows, for example. (1) A refrigeration device 1 according to at least one embodiment of the present disclosure includes a low-stage compressor 11 for compressing a refrigerant, a high-stage compressor 12 for compressing the refrigerant after being compressed by the low-stage compressor 11, a flash tank 13 that can receive the refrigerant after being compressed by the high-stage compressor 12, a liquid injection flow path 35 for supplying refrigerant liquid in the flash tank 13 to the refrigerant after being compressed by the low-stage compressor 11 and discharged from the low-stage compressor 11, and a heat exchanger 63 for heating brine with the refrigerant after being compressed by the low-stage compressor 11 and discharged from the low-stage compressor 11.

[0058] According to the above configuration (1), by supplying the refrigerant liquid in the flash tank 13 to the refrigerant compressed by and discharged from the low-stage compressor 11, the degree of superheat of the refrigerant drawn into the high-stage compressor 12 can be efficiently suppressed. This makes it possible to improve the efficiency of the high-stage compressor 12 at low cost. Furthermore, according to the above configuration (1), the temperature of the refrigerant drawn into the high-stage compressor 12 can be lowered by heating the brine, so that the degree of superheat of the refrigerant drawn into the high-stage compressor 12 can be efficiently suppressed even if the amount of refrigerant liquid in the flash tank 13 supplied to the refrigerant discharged from the low-stage compressor 11 is reduced. This makes it possible to increase the amount of refrigerant liquid available for refrigeration by the amount of the supply reduced, thereby improving the COP.

[0059] (2) In some embodiments, in the configuration described in (1) above, the liquid injection flow path 35 may be provided to communicate between the liquid phase portion of the flash tank 13 and a low-stage compressor discharge flow path (refrigerant flow path 31) through which the refrigerant compressed by the low-stage compressor 11 flows. The heat exchanger 63 may be provided in the low-stage compressor discharge flow path (refrigerant flow path 31). The downstream end 35d of the liquid injection flow path 35 may be connected to the low-stage compressor discharge flow path (refrigerant flow path 31) downstream of the heat exchanger 63.

[0060] When the liquid injection passage 35 is connected to the low-stage compressor discharge passage (refrigerant passage 31) upstream of the heat exchanger 63, the refrigerant whose temperature has been reduced by the refrigerant liquid from the liquid injection passage 35 is supplied to the heat exchanger 63, thereby reducing the temperature difference between the refrigerant supplied to the heat exchanger 63 and the brine, and reducing the heat exchange efficiency in the heat exchanger 63. According to the configuration (2) above, the temperature difference between the refrigerant supplied to the heat exchanger 63 and the brine can be made larger than when the liquid injection passage 35 is connected to the low-stage compressor discharge passage (refrigerant passage 31) upstream of the heat exchanger 63, thereby improving the heat exchange efficiency in the heat exchanger 63.

[0061] (3) In some embodiments, in the configuration described in (1) or (2) above, the brine may be used to defrost the refrigerant liquid in the evaporator 16. The refrigeration device 1 according to at least one embodiment of the present disclosure may include: a storage tank (brine tank 62) for storing brine heated by heat exchange in the heat exchanger 63; a supply flow path 71 for supplying the brine in the storage tank (brine tank 62) to the evaporator 16 (brine coil 61); a return flow path 72 for returning the brine discharged from the evaporator 16 (brine coil 61) to the storage tank (brine tank 62); a supply pump 64 provided in the supply flow path 71 for supplying the brine to the evaporator 16 (brine coil 61); a bypass flow path 73 connecting the return flow path 72 to the supply flow path 71 upstream of the supply pump 64; and a bypass valve 74 for controlling the amount of brine flowing through the bypass flow path 73.

[0062] If the temperature of the brine in the storage tank (brine tank 62) is higher than the temperature suitable for defrosting, steam is generated during defrosting, which may lead to undesirable phenomena such as refreezing of the evaporator 16 or the freezing chamber in which the evaporator 16 is installed. According to the configuration (3) above, by opening the bypass valve 74, the brine whose temperature has been reduced by defrosting flows from the return flow path 72 into the supply flow path 71, thereby lowering the temperature of the brine supplied to the evaporator 16 (brine coil 61). Therefore, the temperature of the brine in the storage tank (brine tank 62) can be set to a temperature higher than the temperature suitable for defrosting. Therefore, by raising the temperature of the brine in the storage tank (brine tank 62), the amount of refrigerant liquid in the flash tank 13 supplied to the refrigerant discharged from the low-stage compressor 11 can be further reduced. This further increases the amount of refrigerant liquid available for refrigeration, thereby further improving the COP.

[0063] (4) In some embodiments, in any of the configurations (1) to (3) above, the refrigerant is CO ２ It may also be a refrigerant.

[0064] According to the above configuration (4), the degree of superheat of the refrigerant drawn into the high-stage compressor 12 can be efficiently suppressed while suppressing an increase in the power consumption of the high-stage compressor 12 .

[0065] (5) In the control method for the refrigeration device 1 according to at least one embodiment of the present disclosure, the refrigeration device 1 includes a low-stage compressor 11 for compressing a refrigerant, a high-stage compressor 12 for compressing the refrigerant after being compressed by the low-stage compressor 11, a flash tank 13 capable of receiving the refrigerant after being compressed by the high-stage compressor 12, a liquid injection flow path 35 for supplying refrigerant liquid in the flash tank 13 to the refrigerant after being compressed by the low-stage compressor 11, a heat exchanger 63 for heating brine with the refrigerant after being compressed by the low-stage compressor 11 and discharged from the low-stage compressor 11, and a first expansion valve 41 provided in the liquid injection flow path 35. A control method for the refrigeration device 1 according to at least one embodiment of the present disclosure includes an intake temperature detection step S10 for detecting an intake temperature Ti of the refrigerant sucked into the high-stage compressor 12, an intake pressure detection step S20 for detecting an intake pressure Pi of the refrigerant sucked into the high-stage compressor 12, an intake superheat calculation step S30 for calculating an intake superheat of the refrigerant sucked into the high-stage compressor 12 based on the detected intake temperature Ti and the detected suction pressure Pi, and an opening adjustment step S40 for adjusting the opening of the first expansion valve 41 so that the calculated intake superheat becomes a predetermined target value.

[0066] According to the method (5) above, the degree of suction superheat of the refrigerant drawn into the high-stage compressor 12 can be stably suppressed. This makes it possible to stably improve the efficiency of the high-stage compressor 12. Furthermore, according to the method (5) above, the temperature of the refrigerant drawn into the high-stage compressor 12 can be lowered by heating the brine, so that the degree of superheat of the refrigerant drawn into the high-stage compressor 12 can be efficiently suppressed even if the amount of refrigerant liquid in the flash tank 13 that is supplied to the refrigerant after being discharged from the low-stage compressor 11 is reduced. This makes it possible to increase the amount of refrigerant liquid that can be used for refrigeration by the amount of the reduced supply amount, thereby improving the COP.

[0067] REFRIGERATION SYSTEM 11 LOW STAGE COMPRESSOR 12 HIGH STAGE COMPRESSOR 13 FLASH TANK 14 ACCUMULATOR 15 CONDENSOR 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 53 TEMPERATURE SENSOR 54 TEMPERATURE SENSOR 55 SUCTION TEMPERATURE SENSOR 56 SUCTION PRESSURE SENSOR 60 DEFROST DEVICE 61 BRINE COIL 62 BRINE TANK 63 HEAT EXCHANGER 70 BRINE FLOW PATH 71 SUPPLY FLOW PATH 72 RETURN FLOW PATH 73 BYPASS FLOW PATH 74 BYPASS VALVE

Claims

1. A refrigeration system comprising: a low-stage compressor for compressing a refrigerant; a high-stage compressor for compressing the refrigerant after it has been compressed by the low-stage compressor; a flash tank capable of receiving the refrigerant after it has been compressed by the high-stage compressor; a liquid injection flow path for supplying refrigerant liquid in the flash tank to the refrigerant after it has been compressed by the low-stage compressor and discharged from the low-stage compressor; and a heat exchanger for heating brine with the refrigerant after it has been compressed by the low-stage compressor and discharged from the low-stage compressor.

2. The refrigeration system of claim 1, wherein the liquid injection flow path is arranged to communicate between the liquid phase portion of the flash tank and a low-stage compressor discharge flow path through which the refrigerant flows after being compressed by the low-stage compressor, the heat exchanger is arranged in the low-stage compressor discharge flow path, and the downstream end of the liquid injection flow path is connected to the low-stage compressor discharge flow path downstream of the heat exchanger.

3. A refrigeration system as claimed in claim 1 or 2, wherein the brine is used for defrosting the refrigerant liquid in the evaporator, and the refrigeration system comprises: a storage tank for storing the brine heated by heat exchange in the heat exchanger; a supply flow path for supplying the brine in the storage tank to the evaporator; a return flow path for returning the brine discharged from the evaporator to the storage tank; a supply pump provided in the supply flow path for supplying the brine to the evaporator; a bypass flow path connecting the return flow path to the supply flow path upstream of the supply pump; and a bypass valve for controlling the amount of brine circulating in the bypass flow path.

4. The refrigerant is CO ２ The refrigeration device according to claim 1 or 2, wherein the refrigerant is a refrigerant.

5. A control method for a refrigeration device, comprising: a low-stage compressor for compressing a refrigerant; a high-stage compressor for compressing the refrigerant after being compressed by the low-stage compressor; a flash tank capable of receiving the refrigerant after being compressed by the high-stage compressor; a liquid injection flow path for supplying refrigerant liquid in the flash tank to the refrigerant after being compressed by the low-stage compressor; a heat exchanger for heating brine with the refrigerant after being compressed by the low-stage compressor and discharged from the low-stage compressor; and a first expansion valve provided in the liquid injection flow path, wherein the method comprises: an intake temperature detection step for detecting an intake temperature of the refrigerant sucked into the high-stage compressor; an intake pressure detection step for detecting an intake pressure of the refrigerant sucked into the high-stage compressor; an intake superheat calculation step for calculating an intake superheat of the refrigerant sucked into the high-stage compressor based on the detected intake temperature and the detected suction pressure; and an opening adjustment step for adjusting an opening of the first expansion valve so that the calculated intake superheat becomes a predetermined target value. A method for controlling a refrigeration device comprising:

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