Method for controlling refrigeration apparatus and refrigeration apparatus

Abstract

To provide a control method of a refrigerating device and the refrigerating device capable of preventing a high stage compressor from being stopped as much as possible when a refrigerating load is reduced.SOLUTION: In a method of controlling a refrigeration device according to at least one embodiment of the present invention, the refrigeration device includes a low-stage compression unit configured to compress a CO2 refrigerant, a high-stage compression unit configured to compress the CO2 refrigerant compressed by the low-stage compression unit, and a gas cooler configured to cool the CO2 refrigerant compressed by the high-stage compression unit. A control method of a refrigeration device according to at least one embodiment of the present invention includes a step of reducing a heat-exchange amount of CO2 refrigerant in a gas cooler when a refrigeration load of the refrigeration device is reduced.SELECTED DRAWING: Figure 1A

Description

[Technical Field]

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

[0002] In a refrigeration system equipped with a low-stage compressor and a high-stage compressor, the CO2 refrigerant is compressed by the high-stage compressor and cooled by a gas cooler, and the gas-phase CO2 refrigerant is sucked back into the high-stage compressor and compressed again (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2024-5797 Summary of the Invention [Problem to be solved by the invention]

[0004] When the refrigeration load decreases, it is necessary to reduce the refrigeration capacity of the refrigeration unit 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 unit may be excessive for the refrigeration load. In such a case, not only does the amount of gaseous CO2 refrigerant discharged from the low-stage compressor decrease due to a decrease in the refrigeration load, but the amount of gaseous CO2 refrigerant within the CO2 refrigerant compressed in the high-stage compressor and cooled in the gas cooler also decreases, so the amount of gaseous CO2 refrigerant that can be sucked into the high-stage compressor decreases, making it impossible for the high-stage compressor to continue operating and forcing it to 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. [Means for solving the problem]

[0007] (1) A method for controlling a refrigeration device according to at least one embodiment of the present disclosure includes: A method for controlling a refrigeration device, comprising: The refrigeration device is a low-stage compressor for compressing the CO2 refrigerant; a high-stage compressor for compressing the CO refrigerant after it has been compressed by the low-stage compressor; a gas cooler for cooling the CO refrigerant compressed by the high-stage compressor; Equipped with reducing a heat exchange amount of the CO refrigerant in the gas cooler when a refrigeration load of the refrigeration device decreases; Equipped with.

[0008] (2) A refrigeration device according to at least one embodiment of the present disclosure, a low-stage compressor for compressing the CO2 refrigerant; a high-stage compressor for compressing the CO refrigerant after it has been compressed by the low-stage compressor; a gas cooler for cooling the CO refrigerant compressed by the high-stage compressor; a control device configured to control the refrigeration device so as to reduce a heat exchange amount of the CO refrigerant in the gas cooler when a refrigeration load of the refrigeration device decreases; Equipped with. [Effects of the Invention]

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

[0010] [Figure 1A] 1 is a system diagram of a refrigeration device according to an embodiment. [Figure 1B] FIG. 10 is a system diagram of a refrigeration device according to another embodiment. [Figure 2A] 1 is an example of a Mollier diagram for a refrigeration system using CO refrigerant in summer according to some embodiments. [Figure 2B] 1 is an example of a Mollier diagram for a refrigeration system using CO refrigerant in winter according to some embodiments. [Figure 3] 10 is an example of a Mollier diagram when the heat exchange rate of the CO refrigerant in the condenser is intentionally reduced in a refrigeration device according to some embodiments. [Figure 4] 1 is a flowchart showing a processing procedure in a control method for a refrigeration device according to some embodiments. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, several embodiments of the present disclosure will be described 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 merely illustrative examples and are not intended to limit the scope of the present disclosure. For example, expressions expressing relative or absolute arrangement such as "in a certain direction," "along a certain direction," "parallel," "orthogonal," "center," "concentric," or "coaxial" not only express such an arrangement exactly, but also express a state in which there is a relative displacement with a tolerance or an angle or distance to the extent that the same function is obtained. For example, expressions such as "identical," "equal," and "homogeneous" that indicate that something is in an equal state not only indicate a state of strict equality, but also indicate a state in which there is a tolerance or a difference to the extent that the same function is obtained. For example, expressions representing shapes such as a square shape or a cylindrical shape not only represent shapes such as a square shape or a cylindrical shape in the strict geometric sense, but also represent shapes including uneven portions, chamfered portions, etc., to the extent that the same effect can be obtained. 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] FIG. 1A is a system diagram of a refrigeration apparatus according to one embodiment. FIG. 1B is a system diagram of a refrigeration apparatus according to another embodiment. A refrigeration apparatus 1 according to some embodiments is a two-stage compression, two-stage expansion type refrigeration apparatus that uses a CO2 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, but the number of low-stage compressors 11 may be one, or three or more low-stage compressors 11 may be provided in parallel. 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, but the number of high-stage compressors 12 may be one, or three or more high-stage compressors 12 may be provided in parallel.

[0013] In the refrigeration device 1 according to some embodiments, an accumulator 14 is provided in the refrigerant flow path 31 that connects the outlet of the low-stage compressor 11 and the inlet of the high-stage compressor 12. 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 inside the condenser 15 is cooled by the outside air blown by the blower fan 22.

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

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

[0016] The refrigeration apparatus 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 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 low-stage expansion valve 43 is provided in the 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 one embodiment, 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 refrigeration 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 refrigeration 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] 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 types of arithmetic processing, and a memory 52 that non-temporarily or temporarily stores various types of 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 of these. The memory 52 is implemented by a ROM, a RAM, a flash memory, or a combination of these. In the following explanation, the control contents of the control device 50 will be mainly explained in the case where the refrigeration load of the refrigeration device 1 decreases. The control contents 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, a suction 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 of the refrigerant being sucked into the high-stage compressor 12. Hin and 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, passes through the evaporator 16 and the heat exchanger 17, and is vaporized before being 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 that connects the outlet of the low-stage compressor 11 and the accumulator 14 via a 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 some embodiments, the refrigeration device 1 is configured so that gas phase refrigerant from the low stage compressor 11 and gas phase refrigerant from the flash tank 13 are supplied to the high stage compressor 12 and compressed.

[0022] 2A and 2B are Mollier diagrams illustrating an example of a Mollier diagram for a refrigeration system 1 using a CO refrigerant in summer and winter, respectively, according to some embodiments.

[0023] 2A and 2B, point n is the critical point of CO2, 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 low-stage compressor 11, point b is the state quantity of the refrigerant at the outlet of low-stage compressor 11. Point c is the state quantity of the refrigerant at the inlet of high-stage compressor 12, and point d is the state quantity of the refrigerant at the outlet of high-stage compressor 12. Point e is the state quantity of the refrigerant at the outlet of condenser 15 as a gas cooler, and point f is the state quantity of the refrigerant in a gas-liquid mixed state at the outlet of high-stage expansion valve 42. Point g is the state quantity of the liquid phase of flash tank 13, and point h is the state quantity of the gas phase after gas-liquid separation in flash tank 13. Point i is the state quantity of the refrigerant after leaving flash tank 13 and passing through heat exchanger 17, point j is the state quantity of the refrigerant at the outlet of low-stage expansion valve 43, and point k is the state quantity of the refrigerant at the outlet of evaporator 16. Point l is the state quantity of the refrigerant at the outlet of expansion valve 44.

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

[0025] 2A and 2B, on the graph line connecting points g and h, the position of point f 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 to the distance between points f and h is equal to the ratio of gas phase to liquid phase. As is clear from FIGS. 2A and 2B, the proportion of the 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] (Issues with refrigeration equipment using CO2 refrigerant) In a refrigeration device 1 equipped with a low-stage compressor 11 and a high-stage compressor 12, such as the refrigeration device 1 according to some embodiments, the CO2 refrigerant is compressed by the high-stage compressor 12 and cooled by the condenser 15, and the gas phase CO2 refrigerant is sucked back into the high-stage compressor 12 and compressed again. 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 device 1 in order to prevent 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 device 1 may become excessive for the refrigeration load. In such a case, not only does the amount of gas-phase CO2 refrigerant discharged from low-stage compressor 11 decrease due to a decrease in the refrigeration load, but the amount of gas-phase CO2 refrigerant within the CO2 refrigerant compressed by high-stage compressor 12 and cooled by condenser 15 also decreases, so the amount of gas-phase CO2 refrigerant that can be sucked into high-stage compressor 12, i.e., the proportion of gas phase CO2 refrigerant in the two-phase liquid-gas CO2 refrigerant at the outlet of high-stage expansion valve 42, decreases, and high-stage compressor 12 cannot continue to operate, and must be stopped. Once the high-stage compressor 12 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 12 as much as possible.

[0027] (Method for solving the problem in the refrigeration device 1) Therefore, in the refrigeration system 1 according to some embodiments, when the refrigeration load of the refrigeration system 1 decreases, the heat exchange rate of the CO2 refrigerant in the condenser 15 is intentionally reduced to increase the proportion of gas phase CO2 refrigerant in the two-phase liquid-gas CO2 refrigerant at the outlet of the high-stage expansion valve 42, thereby increasing 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] 3 is an example of a Mollier diagram for a winter season when the heat exchange rate of the CO2 refrigerant in the condenser 15 is intentionally reduced in the refrigeration system 1 according to some embodiments. Note that in FIG. 3, the dashed graph line indicates the case where the heat exchange rate of the CO2 refrigerant in the condenser 15 is not reduced. 3, intentionally reducing the heat exchange rate of the CO2 refrigerant in the condenser 15 eliminates the degree of subcooling of the CO2 refrigerant after it has been cooled in the condenser 15, causing the position of point e on the Mollier diagram to move to the right in the figure. As a result, point f on the graph line connecting points g and h also moves to the right in the figure, increasing the proportion of gas phase refrigerant in the two-phase liquid-gas refrigerant at the outlet of the high-stage expansion valve 42 and increasing the amount of refrigerant gas that can be drawn into the high-stage compressor 12.

[0029] In the refrigeration system 1 according to some embodiments, the rotation speed Rf of the blower fan 22 may be reduced, for example, to intentionally reduce the heat exchange rate of the CO refrigerant in the condenser 15. This makes it possible to eliminate the degree of supercooling of the CO refrigerant after it has been cooled by the condenser 15. 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] 1B, in order to intentionally reduce the heat exchange rate of the CO2 refrigerant in the condenser 15, for example, the flow control valve 45 may be opened to cause at least a portion of the CO2 refrigerant to flow into the bypass passage 33, thereby bypassing the condenser 15. This prevents a portion of the CO2 refrigerant flowing through the refrigerant passage 32b downstream of the connection position 32c with the bypass passage 33 from being cooled, thereby increasing the proportion of gas phase CO2 refrigerant in the two-phase liquid-gas CO2 refrigerant at the outlet of the high-stage expansion valve 42 and increasing the amount of refrigerant gas that can be sucked into the high-stage compressor 12. In the refrigeration device 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. 1B, when the heat exchange amount of the CO2 refrigerant in the condenser 15 is not reduced, the flow control valve 45 is fully closed. Furthermore, in the refrigeration device 1 shown in FIG. 1B, when the heat exchange amount of the CO2 refrigerant in the condenser 15 is intentionally reduced, the above-mentioned control of the rotation speed Rf of the blower fan 22 may or may not be performed at the same time.

[0032] Furthermore, when the temperature Tc of the CO2 refrigerant at the outlet of the condenser 15 is relatively high, such as in summer, even if the refrigeration load of the refrigeration device 1 decreases, the dryness of the two-phase liquid-gas CO2 refrigerant at the outlet of the high-stage expansion valve 42 is relatively high and the proportion of the gas phase is relatively large, so it is not necessary to reduce the heat exchange amount of the CO2 refrigerant in the condenser 15. In the following description, the operation mode of the refrigeration system 1 in which the heat exchange rate of the CO2 refrigerant in the condenser 15 is intentionally reduced as described above is also referred to as a heat exchange rate reduction mode. Note that the operation mode of the refrigeration system 1 in which the heat exchange rate of the CO2 refrigerant in the condenser 15 is not reduced as described above is also referred to as a normal operation mode.

[0033] (Control content 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. In the refrigeration device 1 according to some embodiments, the processor 51 determines the discharge pressure P of the high-stage compressor 12, which is determined based on the temperature Tc of the CO refrigerant after being cooled by the condenser 15. Hout 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 temperature Tc of the CO refrigerant after being cooled by the condenser 15 so as to approach the first target value Pt1. Hout Control. Here, the discharge pressure P of the high-stage compressor 12 Hout The first target value Pt1 is a value that is uniquely determined by the temperature Tc of the CO 2 refrigerant at the outlet of the condenser 15. When the refrigerant is a CO2 refrigerant, the discharge pressure P of the high-stage compressor 12 at which the COP is highest is Hout is uniquely determined by the temperature Tc of the CO2 refrigerant at the outlet of the condenser 15. Therefore, the first target value Pt1 is a value that is set in advance based on the temperature Tc of the CO2 refrigerant at the outlet of the condenser 15 so as to maximize the COP.

[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 of the bypass flow path 33 so that the flow control valve 45 is fully closed.

[0035] (Switching from normal operation mode to heat exchange volume suppression mode) In some embodiments of the refrigeration device 1, 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 below are satisfied continues for a specified time Tms1 or longer. 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 when multiple high-stage compressors 12 are installed, as in the refrigeration device 1 of some embodiments, the number of high-stage compressors 12 in operation is one, and the rotational speed RH of that one high-stage compressor 12 is equal to or less than the specified rotational speed RH1. When the number of high stage compressors 12 installed 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 the specified rotation speed RH1. In the refrigeration device 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. Linand based on a command value for the rotation speed of a drive motor (not shown) that drives high-stage compressor 12, it is determined whether or not the 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 continues for a specified time Tms1 or more. In some embodiments of the refrigeration device 1, the processor 51 switches the operating mode of the refrigeration device 1 from the normal operating 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 that "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" is satisfied, and determines that the refrigeration load has not decreased when the condition is not satisfied.

[0039] The intake temperature T Lin The third start condition may be that the temperature 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 both the second start condition and the third start condition are satisfied (instead of the first start condition) continues for a specified time Tms1 or more. In addition, 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 longer.

[0040] (Control content in heat exchange amount suppression mode) In the refrigeration apparatus 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. This eliminates the degree of supercooling of the CO2 refrigerant after being cooled in the condenser 15 as described above, thereby increasing 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 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 temperature Tc of the CO refrigerant after being cooled by the condenser 15 so that the discharge pressure P approaches a second target value Pt2 that is lower than the first target value Pt1. Hout Control. As a result, in the Mollier diagram shown in Figure 3, the position of point e in Figure 2B before the heat exchange rate of the CO2 refrigerant in the condenser 15 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, making it 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 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 reduction mode, the processor 51 controls the opening degree of the flow control valve 45 so that at least a portion of the CO2 refrigerant compressed by the high-stage compressor 12 flows into the refrigerant flow path 32b via the bypass flow path 33. This prevents a portion of the CO2 refrigerant flowing through the refrigerant flow path 32b downstream of the connection position 32c with the bypass flow path 33 from being cooled, thereby increasing the proportion of gas phase in the two-phase liquid-gas CO2 refrigerant at the outlet of the high-stage expansion valve 42 and increasing the amount of refrigerant gas that can be sucked into the high-stage compressor 12. As described above, in the refrigeration device 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 volume suppression mode to normal operation mode) In some embodiments of the refrigeration device 1, the operation mode is switched from the heat exchange amount reduction mode to the normal operation mode when any of the following conditions is met: the time Tmea that satisfies the first termination condition continues for a specified time Tme1 or more, the time Tmeb that satisfies the second termination condition continues for a specified time Tme2 or more, or the time Tmec that satisfies the third termination condition continues for a specified time Tme3 or more. Here, the first termination condition is that the suction pressure P Lin is equal to or greater than the specified pressure P1. 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 the intake temperature T Lin is equal to or higher than the specified temperature Th2. In addition, the processor 51 is configured to reduce 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 Based on this, it is determined whether the first termination condition is met. 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 rotational 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 may calculate the intake temperature T of the refrigerant drawn into the low-stage compressor 11 detected by the intake temperature sensor 53. 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 some embodiments of the refrigeration device 1, the processor 51 switches the operating mode of the refrigeration device 1 from the heat exchange amount reduction mode to the normal operating mode when it determines that any of the following conditions is met: the time Tmea that satisfies the first termination condition continues for a specified time Tme1 or more, the time Tmeb that satisfies the second termination condition continues for a specified time Tme2 or more, or the time Tmec that satisfies the third termination condition continues for a specified time Tme3 or more.

[0046] (flowchart) 4 is a flowchart showing the procedure of a process in a control method for the refrigeration device 1 according to some embodiments. A program for executing the process shown in the flowchart of FIG.

[0047] A method for controlling a 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 refrigeration device, that is, a step of operating the refrigeration device 1 in the above-described normal operation mode. 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 refrigeration device. That is, the processor 51 determines the discharge pressure P of the high-stage compressor 12, which is determined based on the temperature Tc of the CO refrigerant after being cooled by the condenser 15. Hout 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 temperature Tc of the CO refrigerant after being cooled by the condenser 15 so as to approach the first target value Pt1. Hout Control. As 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 In other words, 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, 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 Linbecomes 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, where 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 normal operation mode, continues operating the refrigeration device 1 in 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 first start condition or the third start condition described above is not satisfied, the processor 51 returns to step S1 where the refrigeration device 1 operates 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, i.e., 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 rotational speed RH of the one high-stage compressor 12 is equal to or less than the specified rotational speed RH1, i.e., whether the above-mentioned second start condition is satisfied.

[0056] 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 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 processor 51 determines whether the number of operating high-stage compressors 12 is one and the rotational speed RH of this one high-stage compressor 12 is equal to or lower than the specified rotational 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, i.e., if it is determined that both the first start condition and the third start condition are satisfied, the process proceeds to step S5, and processor 51 determines whether the number of operating high-stage compressors 12 is one and the rotational speed RH of that one high-stage compressor 12 is equal to or less than the specified rotational speed RH1, i.e., whether the second start condition described above 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 where 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 continues for a specified time Tms1 or longer.

[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 processor 51 determines whether the time Tms during which both the second start condition and the third start condition are satisfied continues 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 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 normal operation mode, continues operating the refrigeration device 1 in 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, and if step S7 is judged 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 normal operation mode, continues operating the refrigeration device 1 in 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 a heat exchange amount reduction 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 the heat exchange amount reduction mode.

[0067] 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, if step S7 is judged 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 a heat exchange amount reduction mode.

[0068] Step S9 of operating the refrigeration device 1 in the heat exchange amount reduction mode is a step of intentionally reducing the heat exchange amount of the CO2 refrigerant in the condenser 15, that is, a step of operating the refrigeration device 1 in the heat exchange amount reduction mode described above. 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, in which the refrigeration device 1 is operated in the heat exchange amount suppression mode, the processor 51 calculates the discharge pressure P Hout 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 temperature Tc of the CO refrigerant after being cooled by the condenser 15 so that the discharge pressure P approaches a second target value Pt2 that is lower than the first target value Pt1. 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 opening degree of the flow control valve 45 so that at least a portion of the CO2 refrigerant compressed by the high-stage compressor 12 flows into the refrigerant flow path 32b via the bypass flow path 33.

[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 calculates the suction pressure P Lin is 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. 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. In step S11, the processor 51 calculates the intake temperature T Linis equal to or higher than a specified temperature Th2. That is, in step S11, processor 51 may determine whether the third end condition is satisfied instead of determining whether the first or second end condition is satisfied.

[0071] If step S11 is judged negative, i.e., if it is judged 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 operating the refrigeration device 1 in the heat exchange amount reduction mode, and returns to step S11 again. Furthermore, when determining in step S11 whether the above-mentioned second termination condition is satisfied, if step S11 is judged to be negative, i.e., if it is judged that the above-mentioned second termination condition 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 operating 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 S11 is determined to be negative, i.e., if it is determined that the above-mentioned third termination condition 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 operating 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 first termination condition described above is satisfied, the process proceeds to step S13, where the processor 51 judges whether the time Tmea that satisfies the first termination condition has continued for more than the specified time Tme1. In addition, when it is determined in step S11 whether or not the above-mentioned second termination condition is satisfied, if step S11 is judged as positive, i.e., if it is judged that the above-mentioned second termination condition is satisfied, the process proceeds to step S13, and processor 51 determines whether the time Tmeb that satisfies the second termination condition has continued for more than the specified time Tme2. Furthermore, when it is determined in step S11 whether or not the above-mentioned third termination condition is satisfied, 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, and processor 51 determines whether or not the time Tmec that satisfies the third termination condition has continued for more than the specified time Tme3.

[0073] If a negative judgment is made in step S13, that is, if it is determined that the time Tmea that satisfies the first termination condition has not continued for longer than the specified time Tme1, the processor 51 returns to step S9 in which the refrigeration device 1 is operated in the heat exchange amount reduction mode, continues operating 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 second termination condition is satisfied, if step S13 is determined to be negative, that is, if it is determined that the time Tmeb that satisfies the second termination condition has not continued for longer than the specified time Tme2, the processor 51 returns to step S9 in which the refrigeration device 1 is operated in the heat exchange amount reduction mode, continues operating 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 longer 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 reduction mode, continues operating the refrigeration device 1 in the heat exchange amount reduction mode, and returns to step S11 again.

[0074] If the result of step S13 is affirmative, that is, if it is determined that the time Tmea that satisfies the first termination condition has continued for the specified time Tme1 or more, the process returns to step S1 where the refrigeration device 1 is operated in the normal operation mode. In addition, when it is determined in step S11 whether the second termination condition described above is satisfied, if step S13 is determined to be positive, that is, if it is determined that the time Tmeb that satisfies the second termination condition has continued for more than the specified time Tme2, the process returns to step S1 where the refrigeration device 1 is operated in normal operation mode. Furthermore, when it is determined in step S11 whether the above-mentioned third termination condition is satisfied, if step S13 is determined to be positive, that is, if it is determined that the time Tmec that satisfies the third termination condition has continued for more than the specified time Tme3, the process returns to step S1 where the refrigeration device 1 is operated in normal operation mode.

[0075] The specified times Tme1, Tme2, and Tme3 in step S13 described above 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 a method for controlling a 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 CO2 refrigerant, a high-stage compressor 12 for compressing the CO2 refrigerant after being compressed by the low-stage compressor 11, and a gas cooler (condenser 15) for cooling the CO2 refrigerant compressed by the high-stage compressor 12. The method for controlling a refrigeration device 1 according to at least one embodiment of the present disclosure includes a step of reducing the heat exchange amount of the CO2 refrigerant in the gas cooler (condenser 15) when the refrigeration load of the refrigeration device 1 decreases (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 heat exchange amount of the CO2 refrigerant in the gas cooler (condenser 15) is reduced, and the degree of supercooling of the CO2 refrigerant after being cooled by the gas cooler (condenser 15) is eliminated. As a result, the amount of gas-phase CO2 refrigerant in the CO2 refrigerant after being cooled by the gas cooler (condenser 15) increases, and the amount of gas-phase CO2 refrigerant that can be drawn into the high-stage compressor 12 increases. This 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) above, the step of reducing the heat exchange amount of the CO 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 It is preferable that the operation start be initiated 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 a specified pressure P1, and the second start condition, that the rotation speed RH of the 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.

[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. The step of reducing the heat exchange amount of the CO 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 of the first start condition, that is, the pressure P1 is less than the specified pressure P1, and the second start condition, that the number of high-stage compressors 12 in operation is one and the rotation speed RH of the one high-stage compressor 12 is equal to or less than the 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 may include a blower fan 22 that supplies outside air to the gas cooler (condenser 15) to cool the CO2 refrigerant compressed by the high-stage compressor 12. In the step of reducing the heat exchange amount of the CO2 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 to reduce the rotation speed Rf of the blower fan 22.

[0084] According to the method (4) above, it is possible to eliminate the degree of supercooling of the CO2 refrigerant after it has been cooled by the gas cooler (condenser 15).

[0085] (5) In some embodiments, in the methods (1) to (4) above, the refrigeration apparatus 1 may include a bypass flow path 33 connecting an inlet flow path (refrigerant flow path 32a) connected to the CO refrigerant inlet of the gas cooler (condenser 15) and an outlet flow path (refrigerant flow path 32b) connected to the CO refrigerant outlet of the gas cooler (condenser 15), and a flow control valve 45 provided in the bypass flow path 33. The flow control valve 45 may be controlled to be fully closed when the step of reducing the heat exchange rate of the CO refrigerant (step S9 of operating the refrigeration apparatus 1 in the heat exchange rate reduction mode) is not performed. In the step of reducing the heat exchange rate of the CO refrigerant (step S9 of operating the refrigeration apparatus 1 in the heat exchange rate reduction mode), the opening of the flow control valve 45 may be controlled so that the CO refrigerant compressed by the high-stage compressor 12 flows into the outlet flow path (refrigerant flow path 32b) via the bypass flow path 33.

[0086] According to the method (5) above, a part of the CO2 refrigerant flowing through the outlet flow path (refrigerant flow path 32b) downstream of the connection position 32c with the bypass flow path 33 can be prevented from being cooled.

[0087] (6) In some embodiments, in the methods (1) to (5) above, the refrigeration device 1 may include a flash tank 13 capable of receiving the CO refrigerant compressed by the high-stage compressor 12, 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, when the step of reducing the heat exchange amount of the CO refrigerant (step S9 of operating the refrigeration device 1 in a heat exchange amount reduction mode) is not performed, the discharge pressure P of the high-stage compressor 12 is reduced by controlling the opening degree of the expansion valve (high-stage expansion valve 42) based on the temperature Tc of the CO refrigerant cooled by the gas cooler (condenser 15) so as to approach a first target value Pt1 of the discharge pressure of the high-stage compressor 12, which is determined based on the temperature Tc of the CO refrigerant cooled by the gas cooler (condenser 15).Hout In the step of reducing the heat exchange amount of the CO2 refrigerant (step S9 of operating the refrigeration device 1 in the heat exchange amount suppression mode), the discharge pressure P of the high-stage compressor 12 is reduced by controlling the opening degree of the expansion valve (high-stage expansion valve 42) based on the temperature Tc of the CO2 refrigerant after being cooled by the gas cooler (condenser 15) so that the discharge pressure of the high-stage compressor 12 approaches a second target value Pt2 that is lower than the first target value Pt1. Hout may be controlled.

[0088] According to the method (6) above, it is possible to increase the amount of gas phase CO2 refrigerant in the CO2 refrigerant after it has been cooled by the gas cooler (condenser 15).

[0089] (7) In some embodiments, in the methods (1) to (6) above, the step of reducing the heat exchange amount of the CO 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, which satisfies a third termination condition, during which the temperature Tmec is equal to or higher than a specified temperature Th2, continues for a specified time Tme3 or more.

[0090] According to the method (7) above, when it is no longer necessary to perform control to intentionally reduce the heat exchange amount of the CO2 refrigerant in the condenser 15, the refrigeration device 1 can be returned to a normal operating state.

[0091] (8) A refrigeration device 1 according to at least one embodiment of the present disclosure includes a low-stage compressor 11 for compressing a CO2 refrigerant, a high-stage compressor 12 for compressing the CO2 refrigerant after it has been compressed by the low-stage compressor 11, a gas cooler (condenser 15) for cooling the CO2 refrigerant compressed by the high-stage compressor 12, and a control device 50 configured to control the refrigeration device 1 so as to reduce the heat exchange amount of the CO2 refrigerant in the gas cooler (condenser 15) when the refrigeration load of the refrigeration device 1 decreases.

[0092] According to the configuration (8) above, when the refrigeration load decreases, the heat exchange amount of the CO2 refrigerant in the gas cooler (condenser 15) is reduced, so the degree of supercooling of the CO2 refrigerant after being cooled by the gas cooler (condenser 15) is eliminated. Therefore, the amount of gas phase CO2 refrigerant in the CO2 refrigerant after being cooled by the gas cooler (condenser 15) increases, so the amount of gas phase CO2 refrigerant that can be drawn into the high-stage compressor 12 increases. This allows the high-stage compressor 12 to continue operating, reducing undesired temperature changes on the refrigeration load side.

[0093] (9) In some embodiments, the configuration of (8) above may further include a blower fan 22 that supplies outside air to the gas cooler (condenser 15) to cool the CO refrigerant compressed by the high-stage compressor 12. 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 above configuration (9), it is possible to eliminate the degree of supercooling of the CO2 refrigerant after it has been cooled by the gas cooler (condenser 15).

[0095] (10) In some embodiments, the configuration of (8) or (9) above may further include a bypass flow path 33 connecting an inlet flow path (refrigerant flow path 32a) connected to the CO refrigerant inlet of the gas cooler (condenser 15) and an outlet flow path (refrigerant flow path 32b) connected to the CO refrigerant outlet of the gas cooler (condenser 15), 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 aperture of the flow control valve 45 so that the CO refrigerant compressed by the high-stage compressor 12 flows into the outlet flow path (refrigerant flow path 32b) via the bypass flow path 33.

[0096] According to the configuration (10) above, a part of the CO2 refrigerant flowing through the outlet flow path (refrigerant flow path 32b) downstream of the connection position 32c with the bypass flow path 33 can be prevented from being cooled. [Explanation of symbols]

[0097] 1 Refrigeration equipment 11 Low-stage compressor 12 High-stage compressor 13. Flash Tank 14 Accumulator 15 Condenser 16 Evaporator 22 Blower fan 33 Bypass flow path 36 Flush gas passage 42 High-stage expansion valve 43 Low-stage expansion valve 44 Expansion valve 50 Control device 53, 55 Intake temperature sensor 54, 56 Intake pressure sensor 57 Discharge pressure sensor 58 Temperature Sensor

Claims

1. A method for controlling a refrigeration device, comprising: The refrigeration device is CO ２ a low-stage compressor for compressing a refrigerant; The CO after being compressed by the low-stage compressor ２ a high-stage compressor for compressing a refrigerant; The CO compressed by the high-stage compressor ２ a gas cooler for cooling the refrigerant; Equipped with When the refrigeration load of the refrigeration device is reduced, ２ reducing the heat exchange rate of the refrigerant; Equipped with A method for controlling a refrigeration device.

2. The CO ２ The step of reducing the heat exchange rate of the refrigerant includes: a first start condition in which the suction pressure of the low stage compressor is less than a specified pressure; a second start condition in which the rotation speed of the high-stage compressor is equal to or lower than a specified rotation speed; The event starts when both of the above conditions are met for a specified period of time or more. The method for controlling a refrigeration system according to claim 1.

3. One or more high-stage compressors are provided, The CO ２ The step of reducing the heat exchange rate of the refrigerant includes: a first start condition in which the suction pressure of the low stage compressor is less than a specified pressure; a second start condition in which the number of operating high-stage compressors is one, and the rotation speed of the one high-stage compressor is equal to or lower than a specified rotation speed; The event starts when both of the above conditions are met for a specified period of time or more. The method for controlling a refrigeration system according to claim 1.

4. The refrigeration device is configured to ２ a blower fan that supplies outside air to the gas cooler to cool the refrigerant, The CO ２ In the step of reducing the heat exchange amount of the refrigerant, the rotation speed of the blower fan is controlled to reduce the rotation speed of the blower fan. A method for controlling a refrigeration system according to any one of claims 1 to 3.

5. The refrigeration device is The CO ２ an inlet passage connected to an inlet of a refrigerant; ２ an outlet flow path connected to an outlet of the refrigerant; and a bypass flow path connecting the outlet flow path and the bypass flow path. a flow control valve provided in the bypass flow path; Equipped with The flow control valve ２ When the step of reducing the heat exchange amount of the refrigerant is not performed, the valve is controlled to be fully closed. 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 controlling the opening degree of the flow control valve so that the refrigerant flows into the outlet flow path; A method for controlling a refrigeration system according to any one of claims 1 to 3.

6. The refrigeration device is The CO after being compressed by the high-stage compressor ２ a flash tank capable of receiving a refrigerant; an expansion valve provided in a flow path connecting the gas cooler and the flash tank; Equipped with The CO 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; Equipped with The CO 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 discharge pressure of the high-stage compressor is controlled by controlling the opening degree of the expansion valve based on the temperature of the refrigerant. A method for controlling a refrigeration system according to any one of claims 1 to 3.

7. The CO ２ The step of reducing the heat exchange rate of the refrigerant includes: When the time period during which the first termination condition is satisfied, in which the suction pressure of the low-stage compressor is equal to or higher than a specified pressure, continues for equal to or longer than a specified time period, When a time period during which a second termination condition is satisfied, in which the rotation speed of the low-stage compressor is equal to or higher than a predetermined rotation speed, continues for equal to or longer than a predetermined time period, Or, When the time period during which the suction temperature of the low-stage compressor is equal to or higher than a predetermined temperature continues to satisfy a third termination condition for equal to or longer than a predetermined time period, The process ends when one of the following conditions is met: A method for controlling a refrigeration system according to any one of claims 1 to 3.

8. CO ２ a low-stage compressor for compressing a refrigerant; The CO after being compressed by the low-stage compressor ２ a high-stage compressor for compressing a refrigerant; The CO compressed by the high-stage compressor ２ a gas cooler for cooling the refrigerant; When the refrigeration load of the refrigeration device decreases, the CO ２ a control device configured to control the refrigeration device to reduce a heat exchange rate of the refrigerant; Equipped with Refrigeration equipment.

9. The CO compressed by the high-stage compressor ２ a blower fan that supplies outside air to the gas cooler to cool the refrigerant, 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.

9. The refrigeration system of claim 8.

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

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