Refrigeration apparatus control method and refrigeration apparatus

Abstract

In a refrigeration apparatus control method according to at least one embodiment of the present disclosure, a refrigeration apparatus comprises: a low-pressure stage compressor for compressing a CO2 refrigerant; a high-pressure stage compressor for compressing the CO2 refrigerant after compression by the low-pressure stage compressor; and a gas cooler for cooling the CO2 refrigerant compressed by the high-pressure stage compressor. The refrigeration apparatus control method according to at least one embodiment of the present disclosure comprises a step in which the amount of heat exchanged with the CO2 refrigerant in the gas cooler is reduced in cases when there has been a reduction in the refrigeration load on the refrigeration apparatus.

Description

Refrigeration device control method and refrigeration device

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

[0002] In a refrigeration system equipped with a low-stage compressor and a high-stage compressor, CO2 is compressed by the high-stage compressor and cooled by a gas cooler. ２ Among refrigerants, CO in gas phase ２ The refrigerant is again drawn into the high-stage compressor and compressed therein (see, for example, Patent Document 1).

[0003] Japanese Patent Application Laid-Open No. 2024-5797

[0004] When the refrigeration load decreases, it is necessary to reduce the refrigeration capacity of the refrigeration system in order to prevent an undesired temperature drop on the refrigeration load side. However, even if the rotation speed of the high-stage compressor is reduced to the lower limit of the operating range of the high-stage compressor, the refrigeration capacity of the refrigeration system may be excessive for the refrigeration load. In such a case, the gas phase CO2 discharged from the low-stage compressor due to the reduction in the refrigeration load ２ In addition to reducing the amount of refrigerant, the amount of CO after being compressed by the high-stage compressor and cooled by the gas cooler is also reduced. ２ CO in the gas phase of the refrigerant ２ The amount of refrigerant also decreases, so the amount of gaseous CO that can be sucked into the high-stage compressor ２ The amount of refrigerant decreases, making it impossible to continue operating the high-stage compressor, and the high-stage compressor must be stopped.

[0005] Once the high-stage compressor is stopped, it takes a relatively long time to restart it, which may result in an undesired temperature rise on the refrigeration load side until restart. Therefore, it is desirable to avoid stopping the high-stage compressor as much as possible.

[0006] In consideration of the above circumstances, at least one embodiment of the present disclosure aims to provide a control method for a refrigeration device and a refrigeration device that can prevent a high-stage compressor from stopping as much as possible when the refrigeration load decreases.

[0007] (1) A method for controlling a refrigeration device according to at least one embodiment of the present disclosure is a method for controlling a refrigeration device, the refrigeration device ２a low-stage compressor for compressing a refrigerant; and ２ a high-stage compressor for compressing a refrigerant; and ２ a gas cooler for cooling the refrigerant, and ２ reducing the heat exchange rate of the refrigerant.

[0008] (2) The refrigeration device according to at least one embodiment of the present disclosure is ２ a low-stage compressor for compressing a refrigerant; and ２ a high-stage compressor for compressing a refrigerant; and ２ a gas cooler for cooling the refrigerant; and a CO ２ and a control device configured to control the refrigeration device to reduce a heat exchange rate of the refrigerant.

[0009] According to at least one embodiment of the present disclosure, it is possible to provide a control method for a refrigeration device and a refrigeration device that can minimize the need to stop a high-stage compressor when the refrigeration load decreases.

[0010] FIG. 1 is a system diagram of a refrigeration device according to one embodiment; ２ 1 is an example of a Mollier diagram for a refrigeration system using a refrigerant according to some embodiments in summer. ２ 1 is an example of a Mollier diagram of a refrigeration system using a refrigerant in accordance with some embodiments in winter. ２ 10 is a flowchart illustrating a process of a control method for a refrigeration device according to some embodiments.

[0011] 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.

[0012] 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. The refrigeration device 1 according to some embodiments is a CO ２ The refrigeration apparatus 1 is a two-stage compression, two-stage expansion type refrigeration apparatus that uses a refrigerant. In some embodiments, a refrigeration apparatus 1 includes a low-stage compressor 11, a high-stage compressor 12, and a flash tank 13 in a refrigerant circuit 30. In some embodiments, two low-stage compressors 11 are provided in parallel with the refrigerant circuit 30, but one low-stage compressor 11 may be provided, or three or more low-stage compressors 11 may be provided in parallel. In some embodiments, two high-stage compressors 12 are provided in parallel with the refrigerant circuit 30, but one high-stage compressor 12 may be provided, or three or more high-stage compressors 12 may be provided in parallel.

[0013] In the refrigeration system 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 system 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, and a blower fan 22 is provided to supply outside air to the condenser 15 for cooling the refrigerant in the condenser 15. The condenser 15 is configured so that the refrigerant circulating within the condenser 15 is cooled by the outside air blown by the blower fan 22.

[0014] The refrigeration system 1 shown in Fig. 1B is provided with a bypass flow path 33 that connects a refrigerant flow path 32a, which connects the outlet of the high-stage compressor 12 to the refrigerant inlet of the condenser 15, of a refrigerant flow path 32 that connects the outlet of the high-stage compressor 12 to the inlet of the flash tank 13, and a refrigerant flow path 32b that connects the refrigerant outlet of the condenser 15 to the inlet of the flash tank 13. That is, in the refrigeration system 1 shown in Fig. 1B, the refrigerant can circulate while bypassing the condenser 15 by passing through the bypass flow path 33. The bypass flow path 33 is provided with a flow control valve 45 for controlling the flow rate of the refrigerant flowing through the bypass flow path 33.

[0015] In some embodiments, the refrigeration device 1 is provided with a heat exchanger 17 in the refrigerant circulation path 30 for exchanging heat between the liquid phase portion of the flash tank 13 and the refrigerant that has passed through, for example, an evaporator 16 as a cooling load.

[0016] The refrigeration system 1 according to some embodiments includes a flash gas flow path 36 that connects the gas phase part of the flash tank 13 to the refrigerant flow path 31a that connects the outlet of the low-stage compressor 11 to the accumulator 14, of the refrigerant flow path 31 that connects the outlet of the low-stage compressor 11 to the inlet of the high-stage compressor 12. That is, an upstream end 36u of the flash gas flow path 36 is connected to the gas phase part of the flash tank 13, and a downstream end 36d of the flash gas flow path 36 is connected to the refrigerant flow path 31a that connects the outlet of the low-stage compressor 11 to the accumulator 14.

[0017] In the refrigeration apparatus 1 according to some embodiments, a high-stage expansion valve 42 is provided in the refrigerant flow path 32b connecting the outlet of the condenser 15 and the inlet of the flash tank 13. In the refrigeration apparatus 1 according to some embodiments, a low-stage expansion valve 43 is provided in the refrigerant flow path 34b connecting the heat exchanger 17 and the evaporator 16, of the refrigerant flow path 34 for supplying the refrigerant liquid in the flash tank 13 to the evaporator 16. In the refrigeration apparatus 1 according to some embodiments, an expansion valve 44 is provided in the flash gas flow path 36.

[0018] 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).

[0019] The refrigeration device 1 according to some embodiments includes a control device 50 for controlling each part 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 explanation, the control content of the control device 50 will be mainly explained in relation to a case where the refrigeration load of the refrigeration device 1 decreases. 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 part of the refrigeration device 1. The various sensors for controlling each part of the refrigeration device 1 include, for example, an intake temperature T Ｌｉｎ and a suction temperature sensor 53 for detecting the suction pressure P of the refrigerant sucked into the low-stage compressor 11. Ｌｉｎ The suction pressure sensor 54 detects the suction temperature T Ｈｉｎand a suction temperature sensor 55 for detecting the suction pressure P of the refrigerant sucked into the high-stage compressor 12. Ｈｉｎ and a suction pressure sensor 56 for detecting the discharge pressure P of the refrigerant discharged from the high-stage compressor 12. Ｈｏｕｔ and a temperature sensor 58 for detecting the temperature Tc of the refrigerant after it has been cooled by the condenser 15. In the refrigeration device 1 shown in FIG. 1B , the temperature sensor 58 is provided in the refrigerant flow path 32b downstream of the connection position 32c with the bypass flow path 33.

[0020] 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 high-stage 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 low-stage expansion valve 43, is vaporized via the evaporator 16 and the heat exchanger 17, and is supplied to the low-stage compressor 11.

[0021] In the refrigeration apparatus 1 according to some embodiments, the gas-phase refrigerant in the flash tank 13 is supplied to a refrigerant flow path 31a connecting the outlet of the low-stage compressor 11 and the accumulator 14 via the flash gas flow path 36. That is, in the refrigeration apparatus 1 according to some embodiments, the gas-phase refrigerant in the flash tank 13 is supplied to the high-stage compressor 12 via the flash gas flow path 36 and the refrigerant flow path 31a. In the refrigeration apparatus 1 according to some embodiments, the gas-phase refrigerant from the low-stage compressor 11 and the gas-phase refrigerant from the flash tank 13 are supplied to the high-stage compressor 12 and compressed.

[0022] FIG. 2A shows CO ２ 2A and 2B are examples of Mollier diagrams for a refrigeration system 1 using a refrigerant in the summer according to some embodiments. ２2 is an example of a Mollier diagram of a refrigeration device 1 using a refrigerant according to some embodiments in winter.

[0023] In addition, in FIG. 2A and FIG. 2B, point n is CO ２ is 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 high-stage 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 low-stage 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 expansion valve 44.

[0024] In the refrigeration system 1 according to some embodiments, the flash gas passage 36 joins the refrigerant passage 31a at point b, i.e., at the refrigerant passage 31a between the low-stage compressor 11 and the accumulator 14, and therefore the specific enthalpy h of the refrigerant at point c, i.e., at the inlet of the high-stage compressor 12, is lower than that at point b. For ease of understanding, the corresponding parts in Figures 1A and 1B are also denoted by symbols a to l.

[0025] 2A and 2B, the position of point f on the graph line connecting points g and h represents the ratio of gas phase to liquid phase in the two-phase liquid-gas refrigerant at the outlet of the high-stage expansion valve 42. The ratio of the distance between points g and f and the distance between points f and h is equal to the ratio of gas phase to liquid phase. As is clear from Figures 2A and 2B, the ratio of gas phase in the two-phase liquid-gas refrigerant at the outlet of the high-stage expansion valve 42 is lower in winter than in summer.

[0026] (CO ２Problems in refrigeration devices using refrigerants) In a refrigeration device 1 including a low-stage compressor 11 and a high-stage compressor 12, as in the refrigeration device 1 according to some embodiments, CO 2 is compressed by the high-stage compressor 12 and cooled by the condenser 15. ２ Among refrigerants, CO in gas phase ２ The refrigerant is again drawn into the high-stage compressor 12 and compressed. When the refrigeration load decreases, that is, when the heat exchange amount in the evaporator 16 decreases, it is necessary to reduce the refrigeration capacity of the refrigeration system 1 in order to suppress an undesired temperature drop on the refrigeration load side. However, even if the rotation speed of the high-stage compressor 12 is reduced to the lower limit of the operating range of the high-stage compressor 12, the refrigeration capacity of the refrigeration system 1 may become excessive for the refrigeration load. In such a case, the gas-phase CO 2 discharged from the low-stage compressor 11 due to the reduction in the refrigeration load ２ In addition to the reduction in the amount of refrigerant, the amount of CO ２ CO in the gas phase of the refrigerant ２ The amount of refrigerant also decreases, so that the amount of gaseous CO that can be sucked into the high-stage compressor 12 ２ The amount of refrigerant, i.e., the amount of CO in the liquid-gas two-phase state at the outlet of the high-stage expansion valve 42 ２ The proportion of the gas phase in the refrigerant decreases, making it impossible to continue operating the high-stage compressor 12, and the high-stage compressor 12 must be stopped. Once the high-stage compressor 12 is stopped, it takes a relatively long time to restart, which may cause an undesirable temperature rise on the refrigeration load side until restart. Therefore, it is desirable to avoid stopping the high-stage compressor 12 as much as possible.

[0027] (Method for solving the problem in the refrigeration device 1) In the refrigeration device 1 according to some embodiments, when the refrigeration load of the refrigeration device 1 decreases, the CO ２ By intentionally reducing the heat exchange rate of the refrigerant, the CO ２ The proportion of the gas phase in the refrigerant is increased to increase the amount of refrigerant gas that can be sucked into the high-stage compressor 12. This allows the high-stage compressor 12 to continue operating, thereby reducing undesired temperature changes on the refrigeration load side.

[0028] FIG. 3 shows the CO condenser 15 in the refrigeration system 1 according to some embodiments. ２ 3 is an example of a Mollier diagram in the case where the heat exchange rate of the refrigerant is intentionally reduced, and shows a Mollier diagram in winter. ２ The broken line in the graph shows the case where the heat exchange amount of the refrigerant is not reduced. ２ If the heat exchange rate of the refrigerant is intentionally reduced, the CO ２ Because the degree of subcooling of the refrigerant is eliminated, the position of point e on the Mollier diagram shifts to the right in the figure. As a result, the position of point f on the graph line connecting points g and h also shifts to the right in the figure, so the proportion of gas phase refrigerant in the two-phase liquid-gas refrigerant at the outlet of the high-stage expansion valve 42 increases, and the amount of refrigerant gas that can be sucked into the high-stage compressor 12 increases.

[0029] In some embodiments of the refrigeration device 1, the CO ２ In order to intentionally reduce the heat exchange rate of the refrigerant, for example, the rotation speed Rf of the blower fan 22 may be reduced. ２ It is possible to eliminate the degree of subcooling of the refrigerant. In the refrigeration device 1 according to some embodiments, the rotation speed Rf of the blower fan 22 is controlled by the control device 50.

[0030] In the refrigeration device 1 shown in FIG. ２ In order to intentionally reduce the heat exchange rate of the refrigerant, for example, the flow control valve 45 is opened to reduce the CO ２ At least a part of the refrigerant may be made to bypass the condenser 15 by flowing through the bypass flow path 33. As a result, the CO 2 flowing through the refrigerant flow path 32b downstream of the connection position 32c with the bypass flow path 33 ２ Since a part of the refrigerant is not cooled, the CO ２ This increases the proportion of the gas phase in the refrigerant, thereby increasing the amount of refrigerant gas that can be sucked into the high-stage compressor 12. In the refrigeration system 1 shown in FIG. 1B, the opening degree of the flow control valve 45 is controlled by the control device 50.

[0031] In the refrigeration device 1 shown in FIG. ２ When the heat exchange amount of the refrigerant is not reduced, the flow control valve 45 is fully closed. ２ When the heat exchange amount of the refrigerant is intentionally reduced, the above-described control of the rotation speed Rf of the blower fan 22 may or may not be performed at the same time.

[0032] In addition, for example, in summer, the CO ２ When the refrigerant temperature Tc is relatively high, even if the refrigeration load of the refrigeration device 1 decreases, the CO ２ Since the dryness of the refrigerant is relatively high and the proportion of the gas phase is relatively large, the CO ２ In the following description, the amount of heat exchange of the refrigerant in the condenser 15 is not necessarily reduced. ２ The operation mode of the refrigeration device 1 in which the heat exchange amount of the refrigerant is intentionally reduced is also referred to as a heat exchange amount reduction mode. ２ The operation mode of the refrigeration system 1 in which the heat exchange amount of the refrigerant is not reduced is also referred to as a normal operation mode.

[0033] (Control Contents in Normal Operation Mode) In the refrigeration device 1 according to some embodiments, when the operation mode is the normal operation mode, the processor 51 of the control device 50 controls each part of the refrigeration device 1 in the same manner as a conventional two-stage compression, two-stage expansion type refrigeration device. Note that in the refrigeration device 1 according to some embodiments, the processor 51 controls the CO 2 after being cooled by the condenser 15. ２ The discharge pressure P of the high-stage compressor 12 is determined based on the refrigerant temperature Tc. Ｈｏｕｔ After being cooled by the condenser 15, the CO ２ The discharge pressure P of the high-stage compressor 12 is controlled by controlling the opening degree of the high-stage expansion valve 42 based on the refrigerant temperature Tc. Ｈｏｕｔ Here, the discharge pressure P Ｈｏｕｔ The first target value Pt1 is the CO２ This value is determined primarily by the refrigerant temperature Tc. ２ When the refrigerant is the discharge pressure P Ｈｏｕｔ is the CO at the outlet of the condenser 15 ２ Therefore, the first target value Pt1 is set to the CO 2 concentration at the outlet of the condenser 15 so as to maximize the COP. ２ This is a value that is set in advance based on the refrigerant temperature Tc.

[0034] In the refrigeration device 1 shown in FIG. 1B, when the operation mode is the normal operation mode, the processor 51 controls the opening degree of the flow control valve 45 so that the flow control valve 45 of the bypass flow path 33 is fully closed.

[0035] (Switching from normal operation mode to heat exchange amount reduction mode) In the refrigeration device 1 according to some embodiments, the operation mode is switched from the normal operation mode to the heat exchange amount reduction mode when the time Tms during which both the first start condition and the second start condition are satisfied continues for a specified time Tms1 or more. Here, the first start condition is the suction pressure P Ｌｉｎ is less than the specified pressure P1.

[0036] The second start condition is that, in a case where a plurality of high-stage compressors 12 are installed, as in the refrigeration system 1 according to some embodiments, the number of operating high-stage compressors 12 is one, and the rotation speed RH of the one high-stage compressor 12 is equal to or less than a specified rotation speed RH1. Note that, in a case where the number of installed high-stage compressors 12 in the refrigeration system 1 is one, the second start condition is that the rotation speed RH of the high-stage compressor 12 is equal to or less than a specified rotation speed RH1. In the refrigeration system 1 according to some embodiments, the rotation speed RH1 is a rotation speed RH that is preset as the lowest rotation speed RH at which the high-stage compressor 12 can operate.

[0037] In the refrigeration device 1 according to some embodiments, the processor 51 detects the suction pressure P of the refrigerant drawn into the low-stage compressor 11 by the suction pressure sensor 54. ＬｉｎBased on the command value of the rotation speed of the drive motor (not shown) that drives the high-stage compressor 12, it is determined whether the above-mentioned first start condition is satisfied, and based on the command value of the rotation speed of the drive motor (not shown) that drives the high-stage compressor 12, it is determined whether the above-mentioned second start condition is satisfied.

[0038] In the refrigeration device 1 according to some embodiments, the processor 51 determines whether the time Tms during which both the first start condition and the second start condition are satisfied has continued for a specified time Tms1 or longer. In the refrigeration device 1 according to some embodiments, the processor 51 switches the operation mode of the refrigeration device 1 from the normal operation mode to the heat exchange amount reduction mode when it determines that the time Tms during which both the first start condition and the second start condition are satisfied has continued for a specified time Tms1 or longer. That is, in the refrigeration device 1 according to some embodiments, the processor 51 determines that the refrigeration load has decreased when the condition "the time Tms during which both the first start condition and the second start condition are satisfied has continued for a specified time Tms1 or longer" is satisfied, and determines that the refrigeration load has not decreased when this condition is not satisfied.

[0039] In place of the first start condition, the suction temperature T Ｌｉｎ is less than a specified temperature Th1, and the operation mode may be switched from the normal operation mode to the heat exchange amount reduction mode when the time Tms during which the second and third start conditions are all satisfied continues for a specified time Tms1 or more. Also, the operation mode may be switched from the normal operation mode to the heat exchange amount reduction mode when the time Tms during which the first start condition, the second start condition, and the third start condition are all satisfied continues for a specified time Tms1 or more.

[0040] (Control Contents in Heat Exchange Amount Reduction Mode) In the refrigeration device 1 according to some embodiments, when the operation mode is switched from the normal operation mode to the heat exchange amount reduction mode, the processor 51 controls the rotation speed Rf of the blower fan 22 to be lower than the rotation speed Rf of the blower fan 22 in the normal operation mode. As a result, the CO 2 after being cooled by the condenser 15 as described above is reduced. ２Since the degree of subcooling of the refrigerant is eliminated, an increase in the amount of refrigerant gas that can be sucked into the high-stage compressor 12. In the normal mode, the processor 51 controls the rotation speed Rf of the blower fan 22 so that the temperature difference between the temperature of the outside air flowing into the condenser 15 and the temperature Tc of the refrigerant after being cooled in the condenser 15 is constant.

[0041] Furthermore, in the refrigeration device 1 according to some embodiments, when the operation mode is switched from the normal operation mode to the heat exchange amount reduction mode, the processor 51 Ｈｏｕｔ is adjusted so that the CO 2 after being cooled by the condenser 15 approaches a second target value Pt2 that is lower than the first target value Pt1. ２ The discharge pressure P of the high-stage compressor 12 is controlled by controlling the opening degree of the high-stage expansion valve 42 based on the refrigerant temperature Tc. Ｈｏｕｔ As a result, the CO ２ Since the position of point e in Figure 2B before the heat exchange rate of the refrigerant is intentionally reduced can be made closer to the liquid-gas two-phase region on the lower right side of the figure than line X, which is the saturated liquid line, it becomes easier to increase the proportion of gas phase in the liquid-gas two-phase refrigerant at the outlet of the high-stage expansion valve 42, and it becomes easier to increase the amount of refrigerant gas at the outlet of the high-stage expansion valve 42.

[0042] In the refrigeration device 1 shown in FIG. 1B, when the operation mode is switched from the normal operation mode to the heat exchange amount suppression mode, the processor 51 transfers the CO 2 compressed by the high-stage compressor 12 through the bypass flow path 33. ２ The opening degree of the flow control valve 45 is controlled so that at least a part of the refrigerant flows into the refrigerant flow path 32b. As a result, the CO 2 flowing through the refrigerant flow path 32b downstream of the connection position 32c with the bypass flow path 33 is reduced. ２ Since a part of the refrigerant is not cooled, the CO ２ This increases the proportion of the gas phase in the refrigerant, thereby increasing the amount of refrigerant gas that can be sucked into the high-stage compressor 12. As described above, in the refrigeration system 1 shown in FIG. 1B, the above-described control of the rotation speed Rf of the blower fan 22 may or may not be performed in the heat exchange amount reduction mode.

[0043] (Switching from heat exchange amount reduction mode to normal operation mode) In the refrigeration device 1 according to some embodiments, the operation mode is switched from the heat exchange amount reduction mode to the normal operation mode when any of the following conditions is satisfied: when a time Tmea that satisfies the first termination condition continues for a specified time Tme1 or more, when a time Tmeb that satisfies the second termination condition continues for a specified time Tme2 or more, or when a time Tmec that satisfies the third termination condition continues for a specified time Tme3 or more. Here, the first termination condition is the suction pressure P Ｌｉｎ The second termination condition is that the rotation speed RL of the low-stage compressor 11 is equal to or greater than a specified rotation speed RL1. The third termination condition is that the suction temperature T Ｌｉｎ The processor 51 detects that the suction pressure P Ｌｉｎ When the pressure rises, the rotation speed RL of the low-stage compressor 11 is controlled so as to increase.

[0044] In the refrigeration device 1 according to some embodiments, the processor 51 detects the suction pressure P of the refrigerant drawn into the low-stage compressor 11 by the suction pressure sensor 54. Ｌｉｎ Alternatively, in the refrigeration device 1 according to some embodiments, the processor 51 determines whether the second termination condition is satisfied based on a command value for the rotation speed of a drive motor (not shown) that drives the low-stage compressor 11. Alternatively, in the refrigeration device 1 according to some embodiments, the processor 51 determines whether the second termination condition is satisfied based on a command value for the rotation speed of a drive motor (not shown) that drives the low-stage compressor 11. Alternatively, in the refrigeration device 1 according to some embodiments, the processor 51 determines whether the second termination condition is satisfied based on a command value for the rotation speed of a drive motor (not shown) that drives the low-stage compressor 11. Ｌｉｎ Based on this, it is determined whether the third termination condition is met.

[0045] In the refrigeration device 1 according to some embodiments, the processor 51 determines whether the time Tmea that satisfies the first termination condition has continued for a specified time Tme1 or more, whether the time Tmeb that satisfies the second termination condition has continued for a specified time Tme2 or more, or whether the time Tmec that satisfies the third termination condition has continued for a specified time Tme3 or more. In the refrigeration device 1 according to some embodiments, the processor 51 switches the operation mode of the refrigeration device 1 from the heat exchange amount reduction mode to the normal operation mode when it determines that any of the following conditions has been met: the time Tmea that satisfies the first termination condition has continued for a specified time Tme1 or more, the time Tmeb that satisfies the second termination condition has continued for a specified time Tme2 or more, or the time Tmec that satisfies the third termination condition has continued for a specified time Tme3 or more.

[0046] 4 is a flowchart showing a processing procedure in a control method for the refrigeration device 1 according to some embodiments. A program for executing the processing shown in the flowchart of FIG. 4 is read from the memory 52 and executed by the processor 51.

[0047] A method for controlling the refrigeration device 1 according to some embodiments includes step S1 of operating the refrigeration device 1 in a normal operation mode, and step S9 of operating the refrigeration device 1 in a heat exchange amount reduction mode.

[0048] Step S1 of operating the refrigeration device 1 in the normal operation mode is a step of operating the refrigeration device 1 by controlling each part of the refrigeration device 1 in the same way as a conventional two-stage compression, two-stage expansion type refrigeration device, that is, a step of operating the refrigeration device 1 in the normal operation mode described above. In step S1 of operating the refrigeration device 1 in the normal operation mode, as described above, the processor 51 controls each part of the refrigeration device 1 in the same way as a conventional two-stage compression, two-stage expansion type refrigeration device. That is, the processor 51 controls the CO 2 after being cooled by the condenser 15. ２ The discharge pressure P of the high-stage compressor 12 is determined based on the refrigerant temperature Tc. Ｈｏｕｔ After being cooled by the condenser 15, the CO ２ The discharge pressure P of the high-stage compressor 12 is controlled by controlling the opening degree of the high-stage expansion valve 42 based on the refrigerant temperature Tc. ＨｏｕｔAs described above, the processor 51 also controls the opening degree of the flow control valve 45 of the bypass flow path 33 so that the flow control valve 45 is fully closed.

[0049] After starting the execution of step S1 in which the refrigeration device 1 is operated in the normal operation mode, in step S3, the processor 51 calculates the suction pressure P Ｌｉｎ That is, in step S3, the processor 51 determines whether the first start condition described above is satisfied.

[0050] In step S3, the processor 51 calculates the suction pressure P Ｌｉｎ is less than the specified pressure P1, the intake temperature T Ｌｉｎ In other words, in step S3, the processor 51 may determine whether the above-described third start condition is satisfied, instead of determining whether the first start condition is satisfied.

[0051] Alternatively, in step S3, the processor 51 calculates the suction pressure P Ｌｉｎ becomes less than the specified pressure P1, and the intake temperature T Ｌｉｎ In other words, in step S3, the processor 51 may determine whether both the first start condition and the third start condition are satisfied.

[0052] If step S3 is judged negative, i.e., if it is judged that the first start condition described above is not satisfied, the processor 51 returns to step S1 in which the refrigeration device 1 is operated in normal operation mode, continues operating the refrigeration device 1 in normal operation mode, and returns to step S3 again.

[0053] In addition, if, instead of determining whether the first start condition is satisfied in step S3, it is determined whether the above-mentioned third start condition is satisfied, and if a negative judgment is made in step S3, i.e., if it is determined that the above-mentioned third start condition is not satisfied, the processor 51 returns to step S1 in which the refrigeration device 1 is operated in the normal operation mode, continues operating the refrigeration device 1 in the normal operation mode, and returns to step S3 again.

[0054] Alternatively, if, instead of determining whether the first start condition is satisfied in step S3, it is determined whether both the first start condition and the third start condition are satisfied, and if a negative judgment is made in step S3, i.e., if it is determined that at least one of the above-mentioned first start condition or the third start condition is not satisfied, the processor 51 returns to step S1 in which the refrigeration device 1 is operated in normal operation mode, continues operating the refrigeration device 1 in normal operation mode, and returns to step S3 again.

[0055] If step S3 is judged to be positive, that is, if it is judged that the above-mentioned first start condition is satisfied, the process proceeds to step S5, where the processor 51 judges whether the number of operating high-stage compressors 12 is one and the rotation speed RH of the one high-stage compressor 12 is equal to or lower than the specified rotation speed RH1, that is, whether the above-mentioned second start condition is satisfied.

[0056] Note that, in step S3, instead of determining whether the first start condition is satisfied, if it is determined whether the above-mentioned third start condition is satisfied, and if step S3 is determined to be positive, i.e., if it is determined that the above-mentioned third start condition is satisfied, the process proceeds to step S5, and the processor 51 determines whether the number of operating high-stage compressors 12 is one and the rotation speed RH of the one high-stage compressor 12 is equal to or lower than the specified rotation speed RH1, i.e., whether the above-mentioned second start condition is satisfied.

[0057] Alternatively, in step S3, instead of determining whether the first start condition is satisfied, if it is determined whether both the first start condition and the third start condition are satisfied, and if step S3 is determined to be positive, that is, if it is determined that both the first start condition and the third start condition are satisfied, the process proceeds to step S5, and the processor 51 determines whether the number of operating high-stage compressors 12 is one and the rotational speed RH of the one high-stage compressor 12 is equal to or lower than the specified rotational speed RH1, that is, whether the second start condition is satisfied.

[0058] If step S5 is judged negative, i.e., if it is judged that the second start condition described above is not satisfied, the processor 51 returns to step S1 in which the refrigeration device 1 is operated in normal operation mode, continues operating the refrigeration device 1 in normal operation mode, and returns to step S3 again.

[0059] If step S5 is judged to be positive, i.e., if it is judged that the second start condition described above is satisfied, the process proceeds to step S7, where the processor 51 judges whether the time Tms during which both the first start condition and the second start condition are satisfied has continued for more than the specified time Tms1.

[0060] In addition, if, instead of determining whether the first start condition is satisfied in step S3, it is determined whether the above-mentioned third start condition is satisfied, when step S5 is judged positive, the process proceeds to step S7, and the processor 51 determines whether the time Tms during which both the second start condition and the third start condition are satisfied has continued for more than the specified time Tms1.

[0061] Alternatively, if, instead of determining whether the first start condition is satisfied in step S3, it is determined whether both the first start condition and the third start condition are satisfied, when step S5 is judged positive, the process proceeds to step S7, and the processor 51 determines whether the time Tms during which the first start condition, the second start condition, and the third start condition are all satisfied continues for more than the specified time Tms1.

[0062] If step S7 is judged negative, that is, if it is judged that the time Tms during which both the first start condition and the second start condition are satisfied has not continued for longer than the specified time Tms1, the processor 51 returns to step S1 in which the refrigeration device 1 is operated in normal operation mode, continues operating the refrigeration device 1 in normal operation mode, and returns to step S3 again.

[0063] In addition, if, instead of determining whether the first start condition is satisfied in step S3, it is determined whether the above-mentioned third start condition is satisfied, if step S7 is determined to be negative, that is, if it is determined that the time Tms during which both the second start condition and the third start condition are satisfied has not continued for longer than the specified time Tms1, the processor 51 returns to step S1 in which the refrigeration device 1 operates in the normal operation mode, continues operating the refrigeration device 1 in the normal operation mode, and returns to step S3 again.

[0064] Alternatively, if, instead of determining whether the first start condition is satisfied in step S3, it is determined whether both the first start condition and the third start condition are satisfied, if step S7 is determined to be negative, that is, if it is determined that the time Tms during which the first start condition, the second start condition, and the third start condition are all satisfied has not continued for longer than the specified time Tms1, the processor 51 returns to step S1 in which the refrigeration device 1 operates in the normal operation mode, continues operating the refrigeration device 1 in the normal operation mode, and returns to step S3 again.

[0065] If step S7 is judged to be positive, that is, if it is judged that the time Tms during which both the first start condition and the second start condition are satisfied has continued for more than the specified time Tms1, the process proceeds to step S9 in which the refrigeration device 1 is operated in the heat exchange amount suppression mode.

[0066] In addition, if, instead of determining whether the first start condition is satisfied in step S3, it is determined whether the above-mentioned third start condition is satisfied, if step S7 is determined to be positive, that is, if it is determined that the time Tms during which both the second start condition and the third start condition are satisfied has continued for more than the specified time Tms1, the process proceeds to step S9 in which the refrigeration device 1 is operated in a heat exchange amount suppression mode.

[0067] Alternatively, instead of determining whether the first start condition is satisfied in step S3, if it is determined whether both the first start condition and the third start condition are satisfied, if step S7 is determined to be positive, that is, if it is determined that the time Tms during which the first start condition, the second start condition, and the third start condition are all satisfied continues for more than the specified time Tms1, the process proceeds to step S9 in which the refrigeration device 1 is operated in the heat exchange amount reduction mode.

[0068] Step S9 of operating the refrigeration device 1 in the heat exchange amount suppression mode is ２ This is a step of intentionally reducing the heat exchange amount of the refrigerant, i.e., a step of operating the refrigeration device 1 in the heat exchange amount reduction mode. In step S9 of operating the refrigeration device 1 in the heat exchange amount reduction mode, the processor 51 controls the rotation speed Rf of the blower fan 22 to be lower than the rotation speed Rf of the blower fan 22 in the normal operation mode. In step S9 of operating the refrigeration device 1 in the heat exchange amount reduction mode, the processor 51 controls the discharge pressure P Ｈｏｕｔ is adjusted so that the CO 2 after being cooled by the condenser 15 approaches a second target value Pt2 that is lower than the first target value Pt1. ２ The discharge pressure P of the high-stage compressor 12 is controlled by controlling the opening degree of the high-stage expansion valve 42 based on the refrigerant temperature Tc. Ｈｏｕｔ Control.

[0069] In the refrigeration device 1 shown in FIG. 1B, in step S9 when the refrigeration device 1 is operated in the heat exchange amount suppression mode, the processor 51 controls the flow of CO 2 compressed by the high-stage compressor 12 through the bypass flow path 33. ２ The opening of the flow control valve 45 is controlled so that at least a portion of the refrigerant flows into the refrigerant flow path 32b.

[0070] After starting the execution of step S9 in which the refrigeration device 1 is operated in the heat exchange amount suppression mode, in step S11, the processor 51 Ｌｉｎis equal to or greater than a specified pressure P1. That is, in step S11, the processor 51 determines whether the first termination condition described above is satisfied. Note that in step S11, the processor 51 may determine whether the rotation speed RL of the low-stage compressor 11 is equal to or greater than a specified rotation speed RL1. That is, in step S11, the processor 51 may determine whether the second termination condition described above is satisfied, instead of determining whether the first termination condition described above is satisfied. Also, in step S11, the processor 51 determines whether the suction temperature T Ｌｉｎ That is, in step S11, the processor 51 may determine whether the third end condition described above is satisfied, instead of determining whether the first or second end condition described above is satisfied.

[0071] If step S11 is determined to be negative, i.e., if it is determined that the first termination condition described above is not satisfied, the processor 51 returns to step S9 in which the refrigeration device 1 is operated in the heat exchange amount reduction mode, continues operation of the refrigeration device 1 in the heat exchange amount reduction mode, and returns to step S11 again. Note that if it is determined in step S11 whether the second termination condition described above is satisfied, and if step S11 is determined to be negative, i.e., if it is determined that the second termination condition described above is not satisfied, the processor 51 returns to step S9 in which the refrigeration device 1 is operated in the heat exchange amount reduction mode, continues operation of the refrigeration device 1 in the heat exchange amount reduction mode, and returns to step S11 again. Also, if it is determined in step S11 whether the third termination condition described above is satisfied, and if step S11 is determined to be negative, i.e., if it is determined that the third termination condition described above is not satisfied, the processor 51 returns to step S9 in which the refrigeration device 1 is operated in the heat exchange amount reduction mode, continues operation of the refrigeration device 1 in the heat exchange amount reduction mode, and returns to step S11 again.

[0072] If step S11 is judged to be positive, i.e., if it is judged that the above-mentioned first termination condition is satisfied, the process proceeds to step S13, where the processor 51 determines whether the time Tmea satisfying the first termination condition has continued for a specified time Tme1 or more. Note that if it is judged in step S11 whether the above-mentioned second termination condition is satisfied, and if step S11 is judged to be positive, i.e., if it is judged that the above-mentioned second termination condition is satisfied, the process proceeds to step S13, where the processor 51 determines whether the time Tmeb satisfying the second termination condition has continued for a specified time Tme2 or more. Also, if it is judged in step S11 whether the above-mentioned third termination condition is satisfied, and if step S11 is judged to be positive, i.e., if it is judged that the above-mentioned third termination condition is satisfied, the process proceeds to step S13, where the processor 51 determines whether the time Tmec satisfying the third termination condition has continued for a specified time Tme3 or more.

[0073] If a negative determination is made in step S13, i.e., if it is determined that the time Tmea that satisfies the first termination condition has not continued for the specified time Tme1 or more, the processor 51 returns to step S9 in which the refrigeration device 1 is operated in the heat exchange amount reduction mode, continues operation of the refrigeration device 1 in the heat exchange amount reduction mode, and returns to step S11 again. Note that, if a negative determination is made in step S13 in the case where it is determined in step S11 whether or not the second termination condition described above is satisfied, i.e., if it is determined that the time Tmeb that satisfies the second termination condition has not continued for the specified time Tme2 or more, the processor 51 returns to step S9 in which the refrigeration device 1 is operated in the heat exchange amount reduction mode, continues operation of the refrigeration device 1 in the heat exchange amount reduction mode, and returns to step S11 again. Furthermore, when it is determined in step S11 whether the above-mentioned third termination condition is satisfied, if step S13 is determined to be negative, that is, if it is determined that the time Tmec that satisfies the third termination condition has not continued for more than the specified time Tme3, the processor 51 returns to step S9 in which the refrigeration device 1 is operated in the heat exchange amount suppression mode, continues operating the refrigeration device 1 in the heat exchange amount suppression mode, and returns to step S11 again.

[0074] If step S13 is judged to be YES, i.e., if it is judged that the time Tmea satisfying the first termination condition has continued for equal to or longer than the specified time Tme1, the process returns to step S1, where the refrigeration apparatus 1 is operated in the normal operation mode. Note that if it is judged in step S11 whether the second termination condition described above is satisfied, and if step S13 is judged to be YES, i.e., if it is judged that the time Tmeb satisfying the second termination condition has continued for equal to or longer than the specified time Tme2, the process returns to step S1, where the refrigeration apparatus 1 is operated in the normal operation mode. Also, if it is judged in step S11 whether the third termination condition described above is satisfied, and if step S13 is judged to be YES, i.e., if it is judged that the time Tmec satisfying the third termination condition has continued for equal to or longer than the specified time Tme3, the process returns to step S1, where the refrigeration apparatus 1 is operated in the normal operation mode.

[0075] In step S13 described above, the specified times Tme1, Tme2, and Tme3 may all be the same value, or one of them may be a different value, or all of them may be different values.

[0076] 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.

[0077] The contents described in each of the above embodiments can be understood, for example, as follows: (1) In the control method for the refrigeration device 1 according to at least one embodiment of the present disclosure, the refrigeration device 1 ２ A low-stage compressor 11 for compressing a refrigerant, and CO after being compressed by the low-stage compressor 11 ２ A high-stage compressor 12 for compressing a refrigerant, and CO compressed by the high-stage compressor 12 ２ The control method for the refrigeration device 1 according to at least one embodiment of the present disclosure is a method for controlling a CO 2 gas cooler (condenser 15) for cooling a refrigerant when the refrigeration load of the refrigeration device 1 decreases. ２ The method includes a step of reducing the heat exchange amount of the refrigerant (step S9 of operating the refrigeration device 1 in a heat exchange amount reduction mode).

[0078] According to the method (1) above, when the refrigeration load decreases, the CO ２ Since the heat exchange amount of the refrigerant is reduced, the CO ２ The degree of supercooling of the refrigerant is eliminated. Therefore, the CO ２ CO in the gas phase of the refrigerant ２ Since the amount of refrigerant increases, the amount of gaseous CO that can be sucked into the high-stage compressor 12 increases. ２ The amount of refrigerant increases, which allows the high-stage compressor 12 to continue operating, thereby reducing undesired temperature changes on the refrigeration load side.

[0079] (2) In some embodiments, in the method (1), CO ２ The step of reducing the heat exchange amount of the refrigerant (step S9 of operating the refrigeration device 1 in the heat exchange amount reduction mode) is performed by reducing the suction pressure P Ｌｉｎ The control may be started when the time Tms during which both the first start condition, that is, the pressure P1 of the high-stage compressor 12 is less than the specified pressure P1, and the second start condition, that the rotational speed RH of the high-stage compressor 12 is equal to or less than the specified rotational speed RH1, are satisfied continues for a specified time Tms1 or more.

[0080] According to the method (2) above, even if the refrigeration load decreases, the high-stage compressor 12 can continue to operate, so that undesired temperature changes on the refrigeration load side can be reduced.

[0081] (3) In some embodiments, in the method of (1) above, one or more high-stage compressors 12 may be provided. ２ The step of reducing the heat exchange amount of the refrigerant (step S9 of operating the refrigeration device 1 in the heat exchange amount reduction mode) is performed by reducing the suction pressure P Ｌｉｎ The control may be started when a time Tms during which both of the first start condition, that is, the pressure P1 is less than a specified pressure P1, and the second start condition, that the number of operating high-stage compressors 12 is one and the rotation speed RH of the one high-stage compressor 12 is equal to or less than a specified rotation speed RH1, are satisfied continues for a specified time Tms1 or more.

[0082] According to the method (3) above, even if the refrigeration load decreases, the high-stage compressor 12 can continue to operate, so that undesired temperature changes on the refrigeration load side can be reduced.

[0083] (4) In some embodiments, in the methods (1) to (3) above, the refrigeration device 1 uses CO 2 compressed by the high-stage compressor 12. ２ It is preferable that the gas cooler (condenser 15) is provided with a blower fan 22 for supplying outside air to cool the refrigerant. ２ In the step of reducing the heat exchange amount of the refrigerant (step S9 of operating the refrigeration device 1 in the heat exchange amount reduction mode), the rotation speed Rf of the blower fan 22 may be controlled so as to reduce the rotation speed Rf of the blower fan 22.

[0084] According to the method (4) above, the CO after being cooled by the gas cooler (condenser 15) ２ The degree of subcooling of the refrigerant can be eliminated.

[0085] (5) In some embodiments, in the methods (1) to (4) above, the refrigeration device 1 is configured to: ２ An inlet flow path (refrigerant flow path 32a) connected to the inlet of the refrigerant, and a CO ２ The cooling system may include an outlet flow path (coolant flow path 32b) connected to the outlet of the refrigerant, a bypass flow path 33 connecting the outlet and the refrigerant flow path 32b, and a flow control valve 45 provided in the bypass flow path 33. The flow control valve 45 is configured to control the flow of CO ２ When the step of reducing the heat exchange amount of the refrigerant (step S9 of operating the refrigeration device 1 in the heat exchange amount reduction mode) is not performed, the CO ２ In the step of reducing the heat exchange amount of the refrigerant (step S9 of operating the refrigeration device 1 in the heat exchange amount reduction mode), the CO 2 after being compressed by the high-stage compressor 12 is circulated through the bypass passage 33. ２ The opening of the flow control valve 45 may be controlled so that the refrigerant flows into the outlet flow path (refrigerant flow path 32b).

[0086] According to the method (5) above, the CO 2 flowing through the outlet flow path (refrigerant flow path 32b) downstream of the connection position 32c with the bypass flow path 33 is ２A portion of the refrigerant may not be cooled.

[0087] (6) In some embodiments, in the methods (1) to (5) above, the refrigeration device 1 uses the CO 2 compressed by the high-stage compressor 12. ２ The system may include a flash tank 13 capable of receiving a refrigerant, and an expansion valve (high-stage expansion valve 42) provided in a flow path (refrigerant flow path 32b) connecting the gas cooler (condenser 15) and the flash tank 13. In some embodiments, ２ When the step of reducing the heat exchange amount of the refrigerant (step S9 of operating the refrigeration device 1 in the heat exchange amount reduction mode) is not performed, the CO ２ The discharge pressure P of the high-stage compressor 12 is determined based on the refrigerant temperature Tc. Ｈｏｕｔ After being cooled by the gas cooler (condenser 15), the CO ２ The discharge pressure P of the high-stage compressor 12 is controlled by controlling the opening degree of the expansion valve (high-stage expansion valve 42) based on the refrigerant temperature Tc. Ｈｏｕｔ (Step S1 of operating the refrigeration device 1 in the normal operation mode). ２ In the step of reducing the heat exchange amount of the refrigerant (step S9 of operating the refrigeration device 1 in the heat exchange amount reduction mode), the discharge pressure P Ｈｏｕｔ is adjusted so that the CO 2 after being cooled by the gas cooler (condenser 15) approaches a second target value Pt2 that is lower than the first target value Pt1. ２ The discharge pressure P of the high-stage compressor 12 is controlled by controlling the opening degree of the expansion valve (high-stage expansion valve 42) based on the refrigerant temperature Tc. Ｈｏｕｔ may be controlled.

[0088] According to the method (6) above, CO after being cooled by the gas cooler (condenser 15) ２ CO in the gas phase of the refrigerant ２ The amount of refrigerant can be increased.

[0089] (7) In some embodiments, in the method of (1) to (6), CO ２The step of reducing the heat exchange amount of the refrigerant (step S9 of operating the refrigeration device 1 in the heat exchange amount reduction mode) is performed by reducing the suction pressure P Ｌｉｎ When the time Tmea that satisfies the first termination condition that the rotation speed RL of the low-stage compressor 11 becomes equal to or higher than the specified pressure P1 continues for equal to or longer than the specified time Tme1, when the time Tmeb that satisfies the second termination condition that the rotation speed RL of the low-stage compressor 11 becomes equal to or higher than the specified rotation speed RL1 continues for equal to or longer than the specified time Tme2, or when the suction temperature T Ｌｉｎ or when the time Tmec during which the temperature reaches or exceeds a predetermined temperature Th2 continues for a predetermined time Tme3 or more, satisfying a third termination condition.

[0090] According to the method (7) above, the CO ２ When it is no longer necessary to perform control for intentionally reducing the heat exchange rate of the refrigerant, the refrigeration device 1 can be returned to a normal operating state.

[0091] (8) The refrigeration device 1 according to at least one embodiment of the present disclosure is ２ A low-stage compressor 11 for compressing a refrigerant, and CO after being compressed by the low-stage compressor 11 ２ A high-stage compressor 12 for compressing a refrigerant, and CO compressed by the high-stage compressor 12 ２ A gas cooler (condenser 15) for cooling the refrigerant, and a CO ２ and a control device configured to control the refrigeration device so as to reduce the heat exchange amount of the refrigerant.

[0092] According to the configuration of (8) above, when the refrigeration load decreases, the CO ２ Since the heat exchange amount of the refrigerant is reduced, the CO ２ The degree of supercooling of the refrigerant is eliminated. Therefore, the CO ２ CO in the gas phase of the refrigerant ２ Since the amount of refrigerant increases, the amount of gaseous CO that can be sucked into the high-stage compressor 12 increases. ２The amount of refrigerant increases, which allows the high-stage compressor 12 to continue operating, thereby reducing undesired temperature changes on the refrigeration load side.

[0093] (9) In some embodiments, in the configuration of (8) above, the CO compressed by the high-stage compressor 12 ２ The refrigerant cooling system may further include a blower fan 22 that supplies outside air to the gas cooler (condenser 15) to cool the refrigerant. The control device 50 may control the rotation speed Rf of the blower fan 22 so as to reduce the rotation speed Rf of the blower fan 22 when the refrigeration load decreases.

[0094] According to the configuration of (9) above, the CO after being cooled by the gas cooler (condenser 15) ２ The degree of subcooling of the refrigerant can be eliminated.

[0095] (10) In some embodiments, in the configuration of (8) or (9), the CO ２ An inlet flow path (refrigerant flow path 32a) connected to the inlet of the refrigerant, and a CO ２ The refrigerant flow control system may include an outlet flow path (refrigerant flow path 32b) connected to the refrigerant outlet, a bypass flow path 33 connecting the outlet flow path (refrigerant flow path 32b), and a flow control valve 45 provided in the bypass flow path 33. The control device 50 may determine whether the refrigeration load has decreased. If the control device 50 determines that the refrigeration load has not decreased, the control device 50 may control the flow control valve 45 so that the flow control valve 45 is fully closed. If the control device 50 determines that the refrigeration load has decreased, the control device 50 may control the flow control valve 45 so that the CO 2 compressed by the high-stage compressor 12 is fully closed. ２ The opening of the flow control valve 45 may be controlled so that the refrigerant flows into the outlet flow path (refrigerant flow path 32b).

[0096] According to the configuration of (10) above, the CO 2 flowing through the outlet flow path (refrigerant flow path 32b) downstream of the connection position 32c with the bypass flow path 33 is ２ A portion of the refrigerant may not be cooled.

[0097] REFRIGERATION SYSTEM 11 LOW STAGE COMPRESSOR 12 HIGH STAGE COMPRESSOR 13 FLASH TANK 14 ACCUMULATOR 15 CONDENSOR 16 EVAPORATOR 22 BLADE FAN 33 BYPASS PATH 36 FLASH GAS PATH 42 HIGH STAGE EXPANSION VALVE 43 LOW STAGE EXPANSION VALVE 44 EXPANSION VALVE 50 CONTROL DEVICE 53, 55 SUCTION TEMPERATURE SENSOR 54, 56 SUCTION PRESSURE SENSOR 57 DISCHARGE PRESSURE SENSOR 58 TEMPERATURE SENSOR

Claims

1. A method for controlling a refrigeration device, wherein the refrigeration device is ２ a low-stage compressor for compressing a refrigerant; and ２ a high-stage compressor for compressing a refrigerant; and ２ a gas cooler for cooling the refrigerant, and ２ A method for controlling a refrigeration device, comprising: reducing a heat exchange amount of a refrigerant.

2. The above CO ２ 2. The control method for a refrigeration device according to claim 1, wherein the step of reducing the heat exchange amount of the refrigerant is initiated when a time period during which both of a first start condition, that is, a suction pressure of the low-stage compressor is lower than a specified pressure, and a second start condition, that is, a rotational speed of the high-stage compressor is equal to or lower than a specified rotational speed, are satisfied continues for a specified time period or more.

3. The high-stage compressor is provided at least in one unit, and ２ 2. The control method for a refrigeration device according to claim 1, wherein the step of reducing the heat exchange amount of the refrigerant is initiated when a period of time during which both of the following conditions are satisfied continues for more than a specified time: a first start condition, in which the suction pressure of the low-stage compressor is less than a specified pressure; and a second start condition, in which the number of operating high-stage compressors is one and the rotational speed of the one high-stage compressor is equal to or less than a specified rotational speed.

4. The refrigeration device is configured to refrigerate the CO 2 compressed by the high-stage compressor. ２ a blower fan that supplies outside air to the gas cooler to cool the refrigerant, ２ The method for controlling a refrigeration device according to claim 1 , wherein in the step of reducing a heat exchange amount of the refrigerant, the rotation speed of the blower fan is controlled to reduce the rotation speed of the blower fan.

5. The refrigeration device ２ an inlet passage connected to an inlet of a refrigerant; ２ an outlet flow path connected to an outlet of the refrigerant; a bypass flow path connecting the outlet flow path and the refrigerant; and a flow control valve provided in the bypass flow path, ２ When the step of reducing the heat exchange amount of the refrigerant is not performed, the CO ２ In the step of reducing the heat exchange amount of the refrigerant, the CO 2 compressed by the high-stage compressor is passed through the bypass passage. ２ The method for controlling a refrigeration device according to claim 1 , further comprising controlling an opening degree of the flow control valve so that the refrigerant flows into the outlet flow path.

6. The refrigeration device is configured to: ２ a flash tank capable of receiving a refrigerant; and an expansion valve provided in a flow path connecting the gas cooler and the flash tank, ２ When the step of reducing the heat exchange amount of the refrigerant is not performed, the CO ２ The CO 2 after being cooled by the gas cooler is cooled so as to approach a first target value of the discharge pressure of the high-stage compressor, which is determined based on the temperature of the refrigerant. ２ a step of controlling the discharge pressure of the high-stage compressor by controlling the opening degree of the expansion valve based on the temperature of the refrigerant, ２ In the step of reducing the heat exchange amount of the refrigerant, the CO 2 after being cooled by the gas cooler is reduced so that the discharge pressure of the high-stage compressor approaches a second target value which is lower than the first target value. ２ The method for controlling a refrigeration apparatus according to claim 1 , further comprising controlling an opening degree of the expansion valve based on a temperature of the refrigerant, thereby controlling a discharge pressure of the high-stage compressor.

7. The above CO ２ 4. The control method for a refrigeration device according to claim 1, wherein the step of reducing the heat exchange amount of the refrigerant is terminated when any of the following conditions is satisfied: a first termination condition, in which the suction pressure of the low-stage compressor is equal to or higher than a specified pressure, is satisfied for a specified time or more; a second termination condition, in which the rotational speed of the low-stage compressor is equal to or higher than a specified rotational speed, is satisfied for a specified time or more; or a third termination condition, in which the suction temperature of the low-stage compressor is equal to or higher than a specified temperature, is satisfied for a specified time or more.

8. CO ２ a low-stage compressor for compressing a refrigerant; and ２ a high-stage compressor for compressing a refrigerant; and ２ a gas cooler for cooling the refrigerant; and a CO ２ A refrigeration device comprising: a control device configured to control the refrigeration device to reduce a heat exchange rate of a refrigerant.

9. The CO compressed by the high-stage compressor ２ 9. The refrigeration device according to claim 8, further comprising: a blower fan that supplies outside air to the gas cooler to cool the refrigerant, wherein the control device controls the rotation speed of the blower fan so as to reduce the rotation speed of the blower fan when the refrigeration load decreases.

10. The CO of the gas cooler ２ an inlet passage connected to an inlet of a refrigerant; ２ an outlet flow path connected to a refrigerant outlet, a bypass flow path connecting the outlet and the bypass flow path; and a flow control valve provided in the bypass flow path, wherein the control device determines whether the refrigeration load has decreased, and when the control device determines that the refrigeration load has not decreased, the control device controls the flow control valve to be fully closed, and when the control device determines that the refrigeration load has decreased, the control device controls the flow control valve to be fully closed, and when the control device determines that the refrigeration load has decreased, the control device controls the flow control valve to be fully closed, ２ The refrigeration apparatus according to claim 8 or 9, wherein an opening degree of the flow control valve is controlled so that the refrigerant flows into the outlet flow path.

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