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 low-stage compressor from being stopped as much as possible when a refrigerating load is reduced.SOLUTION: The refrigeration apparatus includes a liquid-refrigerant supplying channel for supplying a liquid-phase CO2 refrigerant in the CO2 refrigerant after being compressed by the high-stage compressors and cooled by the gas coolers to the evaporators, a gas-refrigerant channel for guiding a gas-phase CO2 refrigerant from the evaporators to inlets of the low-stage compressors, heat exchangers for heating the liquid-phase CO2 refrigerant with heat taken from the gas-phase CO2 refrigerant by the gas coolers, first channels connecting the liquid-refrigerant supplying channel and inlets of the heat exchangers, second channels connecting outlets of the heat exchangers and the gas-refrigerant channel, and expansion valves provided in the first channels. When the refrigeration load of the refrigeration device decreases, the expansion valve is opened, and the CO2 refrigerant heated by the heat exchangers is guided to the gas refrigerant flow path via the second flow path.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] BACKGROUND ART A refrigeration system that includes a low-stage compressor and a high-stage compressor and uses a CO2 refrigerant is known (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] In a refrigeration system equipped with a low-stage compressor and a high-stage compressor and using a CO2 refrigerant, when the refrigeration load decreases, the suction pressure of the low-stage compressor decreases. However, if the suction pressure of the low-stage compressor decreases too much, the CO2 refrigerant in the suction path of the low-stage compressor solidifies and turns into dry ice. If this dry ice is sucked into the low-stage compressor, it can damage the low-stage compressor. As a result, the low-stage compressor cannot continue to operate, and the low-stage compressor must be stopped.

[0005] Once the low-stage compressor is stopped, it takes a relatively long time to restart it, which may result in an undesirable temperature rise on the refrigeration load side until restart. Therefore, it is desirable to avoid stopping the low-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 the low-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; an evaporator to which the liquid phase CO2 refrigerant of the CO2 refrigerant cooled by the gas cooler is supplied; a liquid refrigerant supply passage for supplying the liquid phase CO refrigerant to the evaporator; a gas refrigerant flow path for guiding the gas phase CO refrigerant from the evaporator to an inlet of the low-stage compressor; a heat exchanger for heating the liquid phase CO2 refrigerant with heat removed from the gas phase CO2 refrigerant by the gas cooler; a first flow path connecting the liquid refrigerant supply flow path and an inlet of the heat exchanger; a second flow path connecting an outlet of the heat exchanger and the gas refrigerant flow path; an expansion valve provided in the first flow path; Equipped with heating the liquid phase CO refrigerant in the heat exchanger by opening the expansion valve when the 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; an evaporator to which the liquid phase CO2 refrigerant of the CO2 refrigerant cooled by the gas cooler is supplied; a liquid refrigerant supply passage for supplying the liquid phase CO refrigerant to the evaporator; a gas refrigerant flow path for guiding the gas phase CO refrigerant from the evaporator to an inlet of the low-stage compressor; a heat exchanger for heating the liquid phase CO2 refrigerant with heat removed from the gas phase CO2 refrigerant by the gas cooler; a first flow path connecting the liquid refrigerant supply flow path and an inlet of the heat exchanger; a second flow path connecting an outlet of the heat exchanger and the gas refrigerant flow path; an expansion valve provided in the first flow path; Equipped with. [Effects of the Invention]

[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 the low-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 2] 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] In the refrigeration system 1 according to some embodiments, a heat exchanger 17 is provided in the refrigerant circulation path 30 for exchanging heat between the liquid phase portion of the flash tank 13 and the refrigerant gas that has passed through, for example, an evaporator 16 as a cooling load. The heat exchanger 17 has a liquid phase side flow path provided in a liquid refrigerant supply flow path 34 that supplies the refrigerant liquid in the flash tank 13 to the evaporator 16, and a gas phase side flow path provided in a gas refrigerant flow path 35 that guides the refrigerant gas from the evaporator 16 to the inlet of the low-stage compressor 11.

[0015] 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.

[0016] 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, within the liquid refrigerant supply flow path 34 for supplying 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.

[0017] 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).

[0018] A refrigeration device 1 according to some embodiments includes a heat exchanger 18 for heating a liquid CO2 refrigerant using heat removed from a gas CO2 refrigerant in a condenser 15, a first flow path 37 connecting a liquid refrigerant supply flow path 34 to an inlet of the heat exchanger 18, a second flow path 38 connecting an outlet of the heat exchanger 18 to a gas refrigerant flow path 35, and an expansion valve 45 provided in the first flow path 37. The refrigeration device 1 shown in FIG. 1A includes an evaporating pressure control valve 46 provided in the second flow path 38, and a check valve 47 provided in the second flow path 38 downstream of the evaporating pressure control valve 46. It should be noted that the refrigeration system 1 shown in FIG. 1A does not necessarily need to be provided with the check valve 47. The refrigeration device 1 shown in FIG. 1B includes a check valve 47 provided in the second flow path .

[0019] Heat exchanger 18 is configured to be able to heat the refrigerant liquid that flows into heat exchanger 18 from first flow path 37 by utilizing heat removed from the refrigerant gas in condenser 15. That is, outside air sent to condenser 15 by blower fan 22 is heated by heat exchange with the refrigerant gas in condenser 15. Heat exchanger 18 is configured to exchange heat between this heated outside air and the refrigerant liquid that flows into heat exchanger 18 from first flow path 37.

[0020] In some embodiments of the refrigeration device 1, the upstream end 37u of the first flow path 37 is connected to the refrigerant flow path 34b in the liquid refrigerant supply flow path 34 that connects the heat exchanger 17 and the evaporator 16, but may also be connected to the refrigerant flow path 34a that connects the flash tank 13 and the heat exchanger 17. In some embodiments of the refrigeration device 1, the downstream end 38d of the second flow path 38 is connected to the refrigerant flow path 35b of the gas refrigerant flow path 35 that connects the heat exchanger 17 and the low-stage compressor 11, but may also be connected to the refrigerant flow path 35a that connects the evaporator 16 and the heat exchanger 17.

[0021] 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 The suction pressure sensor 56 detects the temperature T of the CO2 refrigerant heated by the heat exchanger 18. EXout and a temperature sensor 57 for detecting the pressure P of the CO2 refrigerant heated by the heat exchanger 18. EXout and a pressure sensor 58 for detecting the pressure.

[0022] 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.

[0023] 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.

[0024] (Issues with refrigeration equipment using CO2 refrigerant) In the refrigeration device 1 according to some embodiments, which includes a low-stage compressor 11 and a high-stage compressor 12 and uses a CO refrigerant, when the refrigeration load decreases, the suction pressure P Lin However, the suction pressure P Lin If the temperature drops too low, the CO2 refrigerant solidifies and turns into dry ice in the intake path of the low-stage compressor 11. If this dry ice is drawn into the low-stage compressor 11, it will damage the low-stage compressor 11. As a result, the low-stage compressor 11 cannot continue to operate, and the low-stage compressor 11 must be stopped. Once the low-stage compressor 11 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 low-stage compressor 11 as much as possible.

[0025] (Method for solving the problem in the refrigeration device 1) Therefore, in the refrigeration device 1 according to some embodiments, when the refrigeration load of the refrigeration device 1 decreases, the liquid phase CO refrigerant is heated in the heat exchanger 18 using the heat taken from the gas phase CO refrigerant in the condenser 15 to generate gas phase CO refrigerant, and this gas phase CO refrigerant is sucked into the low stage compressor 11, thereby increasing the suction pressure P Lin That is, the decrease in the intake temperature T Lin This suppresses the decrease in the temperature of the refrigeration load 11 and allows the low-stage compressor 11 to continue operating. This reduces undesired temperature changes on the refrigeration load side.

[0026] For example, when the refrigeration load of the refrigeration device 1 decreases, the heat exchange amount Q L Q L 1 to Q L Consider what happens if it drops to 2. In this case, for example, by heating the CO refrigerant in the heat exchanger 18, the heat exchange amount Q in the evaporator 16 is L This corresponds to the decrease in (Q L 1-Q L 2) is given to the CO2 refrigerant, and this heated CO2 refrigerant is merged with the refrigerant after heat exchange in the evaporator 16. Lin is the heat exchange amount Q in the evaporator 16 L Q L The same suction pressure P as when it was 1 Lin This means that it can be maintained at this level. In the refrigeration system 1 according to some embodiments, the suction pressure P Lin Decrease in the intake temperature T Lin We are trying to suppress the decline in productivity.

[0027] (Overview of heating of liquid CO2 refrigerant by heat exchanger 18) Specifically, in the refrigeration apparatus 1 according to some embodiments, when a condition described below for starting heating of the liquid-phase CO2 refrigerant by the heat exchanger 18 is satisfied, the processor 51 of the control device 50 opens the expansion valve 45 to supply the liquid-phase CO2 refrigerant from the flash tank 13 to the heat exchanger 18 via the first flow path 37. As a result, the gas-phase CO2 refrigerant heated and vaporized in the heat exchanger 18 is supplied to the gas refrigerant flow path 35 via the second flow path 38 and is drawn into the low-stage compressor 11 together with the gas-phase CO2 refrigerant from the evaporator 16.

[0028] In the following description, the operation mode of the refrigeration system 1 in which the liquid phase CO2 refrigerant is heated by the heat exchanger 18 as described above is also referred to as a liquid refrigerant heating mode. Note that the operation mode of the refrigeration system 1 in which the liquid phase CO2 refrigerant is not heated by the heat exchanger 18 as described above is also referred to as a normal operation mode.

[0029] (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, when the operation mode is the normal operation mode, the processor 51 controls the opening degree of the expansion valve 45 so that the expansion valve 45 of the first flow path 37 is fully closed.

[0030] (Switching from normal operation mode to liquid refrigerant heating mode) In some embodiments of the refrigeration device 1, the operation mode is switched from the normal operation mode to the liquid refrigerant heating 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.

[0031] 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.

[0032] 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 and 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.

[0033] 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 liquid refrigerant heating 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.

[0034] The intake temperature T LinThe third start condition may be that the liquid refrigerant temperature is less than a specified temperature Th1, and the operation mode may be switched from the normal operation mode to the liquid refrigerant heating 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 liquid refrigerant heating 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.

[0035] (Control content in liquid refrigerant heating mode) In the refrigeration device 1 according to some embodiments, when the operation mode is switched from the normal operation mode to the liquid refrigerant heating mode, the processor 51 opens the expansion valve 45 and controls the opening degree of the expansion valve 45 so as to supply the liquid-phase CO refrigerant from the flash tank 13 to the heat exchanger 18 via the first flow path 37. At this time, the processor 51 controls the temperature T of the CO refrigerant heated by the heat exchanger 18, which is detected by the temperature sensor 57. EXout and the pressure P of the CO refrigerant heated by the heat exchanger 18 detected by the pressure sensor 58. EXout Based on this, the opening degree of the expansion valve 45 is controlled in accordance with a program read from the memory 52. As a result, the degree of superheat of the CO2 refrigerant heated by the heat exchanger 18 is controlled to a specified degree of superheat.

[0036] In the refrigeration device 1 shown in FIG. 1A, when the operation mode is switched from the normal operation mode to the liquid refrigerant heating mode, the CO refrigerant heated in the heat exchanger 18 flows through the second flow path 38 via the evaporation pressure control valve 46 and is supplied to the gas refrigerant flow path 35. That is, in the refrigeration device 1 shown in FIG. 1A, when the operation mode is switched from the normal operation mode to the liquid refrigerant heating mode, the processor 51 controls the set pressure of the evaporation pressure control valve 46 according to the program read from the memory 52 in order to increase the evaporation temperature of the CO2 refrigerant in the heat exchanger 18 as much as possible. This allows the evaporation temperature of the CO2 refrigerant in the heat exchanger to be increased, thereby reducing frost formation in the heat exchanger.

[0037] (Switching from liquid refrigerant heating mode to normal operation mode) In some embodiments of the refrigeration device 1, the operation mode is switched from the liquid refrigerant heating 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.

[0038] 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.

[0039] 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 liquid refrigerant heating 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.

[0040] (flowchart) 2 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.

[0041] 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 liquid refrigerant heating mode.

[0042] 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. As described above, the processor 51 also controls the opening degree of the expansion valve 45 in the first flow path 37 so that the expansion valve 45 is fully closed.

[0043] 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.

[0044] 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.

[0045] 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.

[0046] 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.

[0047] 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.

[0048] 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.

[0049] 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.

[0050] 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.

[0051] 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.

[0052] 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.

[0053] 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.

[0054] 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.

[0055] 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.

[0056] 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.

[0057] 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.

[0058] 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.

[0059] 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 liquid refrigerant heating mode.

[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, 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 liquid refrigerant heating mode.

[0061] 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 liquid refrigerant heating mode.

[0062] Step S9 of operating the refrigeration device 1 in the liquid refrigerant heating mode is a step of heating the liquid phase CO2 refrigerant in the heat exchanger 18, that is, a step of operating the refrigeration device 1 in the liquid refrigerant heating mode described above. In step S9, in which the refrigeration device 1 is operated in the liquid refrigerant heating mode, the processor 51 controls the opening degree of the expansion valve 45 so as to open the expansion valve 45 and supply the liquid-phase CO2 refrigerant from the flash tank 13 to the heat exchanger 18 via the first flow path 37, as described above. At this time, the processor 51 controls the temperature T of the CO2 refrigerant heated by the heat exchanger 18, which is detected by the temperature sensor 57. EXout and the pressure P of the CO refrigerant heated by the heat exchanger 18 detected by the pressure sensor 58. EXout Based on this, the opening degree of the expansion valve 45 is controlled in accordance with a program read from the memory 52.

[0063] In the refrigeration device 1 shown in FIG. 1A, the processor 51 controls the set pressure in the evaporating pressure control valve 46 in accordance with the program read from the memory 52 as described above.

[0064] After starting the execution of step S9 in which the refrigeration device 1 is operated in the liquid refrigerant heating 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 Lin is 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.

[0065] 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 liquid refrigerant heating mode, continues operating the refrigeration device 1 in the liquid refrigerant heating 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 liquid refrigerant heating mode, continues operating the refrigeration device 1 in the liquid refrigerant heating mode, and returns to step S11 again. Furthermore, when determining in step S11 whether the above-mentioned third termination condition is satisfied, if step S11 is judged to be negative, i.e., if it is judged 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 liquid refrigerant heating mode, continues operating the refrigeration device 1 in the liquid refrigerant heating mode, and returns to step S11 again.

[0066] 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.

[0067] 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 liquid refrigerant heating mode, continues operating the refrigeration device 1 in the liquid refrigerant heating mode, and returns to step S11 again. In addition, when it is determined in step S11 whether the above-mentioned second termination condition is satisfied, if a negative judgment is made in step S13, 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 liquid refrigerant heating mode, continues operating the refrigeration device 1 in the liquid refrigerant heating 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 to operate the refrigeration device 1 in the liquid refrigerant heating mode, continues operating the refrigeration device 1 in the liquid refrigerant heating mode, and returns to step S11 again.

[0068] 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.

[0069] 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.

[0070] 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.

[0071] The contents described in each of the above embodiments can be understood, for example, as follows. (1) In a control method for 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 CO refrigerant, a high-stage compressor 12 for compressing the CO refrigerant after being compressed by the low-stage compressor 11, a gas cooler (condenser 15) for cooling the CO refrigerant compressed by the high-stage compressor 12, an evaporator 16 to which a liquid-phase CO refrigerant among the CO refrigerant after being cooled by the gas cooler (condenser 15) is supplied, and a control method for controlling the refrigeration device 1 includes a control method for controlling the refrigeration device 1 including a low-stage compressor 11 for compressing a CO refrigerant after being compressed by the low-stage compressor 11, a high-stage compressor 12 for compressing the CO refrigerant after being compressed by the low-stage compressor 11, a gas cooler (condenser 15) for cooling the CO refrigerant compressed by the high-stage compressor 12, an evaporator 16 to which a liquid-phase CO refrigerant is supplied among the CO refrigerant after being cooled by the gas cooler (condenser 15), and an evaporator 16 to which the liquid-phase CO refrigerant is supplied. The refrigeration system includes a liquid refrigerant supply passage 34 for supplying the CO refrigerant, a gas refrigerant passage 35 for guiding the gas phase CO refrigerant from the evaporator 16 to the inlet of the low-stage compressor 11, a heat exchanger 18 for heating the liquid phase CO refrigerant with heat removed from the gas phase CO refrigerant in the gas cooler (condenser 15), a first passage 37 connecting the liquid refrigerant supply passage 34 to the inlet of the heat exchanger 18, a second passage 38 connecting the outlet of the heat exchanger 18 to the gas refrigerant passage 35, and an expansion valve 45 provided in the first passage 37. A method for controlling the refrigeration system 1 according to at least one embodiment of the present disclosure includes a step of heating the liquid phase CO refrigerant in the heat exchanger 18 by opening the expansion valve 45 when the refrigeration load of the refrigeration system 1 decreases (step S9 of operating the refrigeration system 1 in a liquid refrigerant heating mode).

[0072] According to the method (1) above, when the refrigeration load decreases, the liquid-phase CO refrigerant is heated in the heat exchanger 18 to generate a gas-phase CO refrigerant, and this gas-phase CO refrigerant is sucked into the low-stage compressor 11, thereby reducing the suction pressure P Lin This can suppress a decrease in the temperature and continue the operation of the low-stage compressor 11. This can reduce undesired temperature changes on the refrigeration load side.

[0073] (2) In some embodiments, in the method (1) above, the step of heating the liquid-phase CO refrigerant (step S9 of operating the refrigeration device 1 in a liquid refrigerant heating mode) is performed by increasing 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.

[0074] According to the method (2) above, even if the refrigeration load decreases, the low-stage compressor 11 can continue to operate, so that undesired temperature changes on the refrigeration load side can be reduced.

[0075] (3) In some embodiments, in the method of (1) above, one or more high-stage compressors 12 may be provided. The step of heating the liquid-phase CO refrigerant (step S9 of operating the refrigeration device 1 in the liquid refrigerant heating mode) is performed by adjusting 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.

[0076] According to the method (3) above, even if the refrigeration load decreases, the low-stage compressor 11 can continue to operate, so that undesired temperature changes on the refrigeration load side can be reduced.

[0077] (4) In some embodiments, in any of the methods (1) to (3) above, the refrigeration device 1 is configured to maintain the temperature T of the CO refrigerant heated by the heat exchanger 18. EXout and a temperature sensor 57 for detecting the pressure P of the CO2 refrigerant heated by the heat exchanger 18. EXout In the step of heating the liquid CO2 refrigerant (step S9 of operating the refrigeration device 1 in the liquid refrigerant heating mode), the temperature T of the CO2 refrigerant detected by the temperature sensor 57 is detected. EXout and the pressure P of the CO2 refrigerant detected by the pressure sensor 58. EXout The opening degree of the expansion valve 45 may be controlled based on the above.

[0078] According to the method (4) above, the degree of superheat of the gaseous CO2 refrigerant heated by the heat exchanger 18 can be controlled.

[0079] (5) In some embodiments, in any of the methods (1) to (4) above, the refrigeration device 1 may include an evaporation pressure control valve 46 provided in the second flow path 38. In the step of heating the liquid CO2 refrigerant (step S9 of operating the refrigeration device 1 in the liquid refrigerant heating mode), the CO2 refrigerant heated in the heat exchanger 18 and circulating through the second flow path 38 may be supplied to the gas refrigerant flow path 35 via the evaporation pressure control valve 46.

[0080] According to the method (5) above, the evaporation temperature of the CO2 refrigerant in the heat exchanger 18 can be increased by increasing the evaporation pressure of the CO2 refrigerant in the heat exchanger 18, so that frosting in the heat exchanger 18 can be reduced.

[0081] (6) In some embodiments, in any of the methods (1) to (5) above, the step of heating the liquid-phase CO refrigerant (step S9 of operating the refrigeration device 1 in a liquid refrigerant heating mode) is performed by increasing the suction pressure P of the low-stage compressor 11. 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.

[0082] According to the method (6) above, when it is no longer necessary to heat the liquid phase CO2 refrigerant in the heat exchanger 18, the refrigeration device 1 can be returned to a normal operating state.

[0083] (7) The refrigeration device 1 according to at least one embodiment of the present disclosure includes a low-stage compressor 11 for compressing a CO refrigerant, a high-stage compressor 12 for compressing the CO refrigerant after being compressed by the low-stage compressor 11, a gas cooler (condenser 15) for cooling the CO refrigerant compressed by the high-stage compressor 12, an evaporator 16 to which the liquid-phase CO refrigerant of the CO refrigerant after being cooled by the gas cooler (condenser 15) is supplied, and a compressor for supplying the liquid-phase CO refrigerant to the evaporator 16. the gas refrigerant flow path 35 for guiding the gas phase CO2 refrigerant from the evaporator 16 to the inlet of the low-stage compressor 11; a heat exchanger 18 for heating the liquid phase CO2 refrigerant with heat removed from the gas phase CO2 refrigerant in the gas cooler (condenser 15); a first flow path 37 connecting the liquid refrigerant supply flow path 34 to the inlet of the heat exchanger 18; a second flow path 38 connecting the outlet of the heat exchanger 18 to the gas refrigerant flow path 35; and an expansion valve 45 provided in the first flow path 37.

[0084] According to the configuration (7) above, when the refrigeration load decreases, the liquid-phase CO refrigerant is heated in the heat exchanger 18 to generate a gas-phase CO refrigerant, and this gas-phase CO refrigerant is sucked into the low-stage compressor 11, thereby increasing the suction pressure P Lin This can suppress a decrease in the temperature and continue the operation of the low-stage compressor 11. This can reduce undesired temperature changes on the refrigeration load side. [Explanation of symbols]

[0085] 1 Refrigeration equipment 11 Low-stage compressor 12 High-stage compressor 13. Flash Tank 14 Accumulator 15 Condenser 16 Evaporator 18 Heat exchanger 22 Blower fan 37 First Channel 38 Second Channel 42 High-stage expansion valve 43 Low-stage expansion valve 45 Expansion valve 46 Evaporation pressure control valve 47 Check valve 50 Control device 53, 55 Intake temperature sensor 54, 56 Intake pressure sensor 57 Temperature Sensor 58 Pressure 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; The CO after being cooled by the gas cooler ２ Liquid CO in the refrigerant ２ an evaporator to which a refrigerant is supplied; The liquid phase CO ２ a liquid refrigerant supply flow path for supplying the refrigerant; Gas phase CO from the evaporator ２ a gas refrigerant flow path for guiding the refrigerant to an inlet of the low-stage compressor; The gas phase CO ２ The heat removed from the refrigerant is used to convert the liquid phase CO ２ a heat exchanger for heating the refrigerant; a first flow path connecting the liquid refrigerant supply flow path and an inlet of the heat exchanger; a second flow path connecting an outlet of the heat exchanger and the gas refrigerant flow path; an expansion valve provided in the first flow path; Equipped with When the refrigeration load of the refrigeration device decreases, the expansion valve is opened to release the liquid phase CO ２ heating the refrigerant; Equipped with A method for controlling a refrigeration device.

2. The liquid phase CO ２ The step of heating 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 liquid phase CO ２ The step of heating 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 The CO heated by the heat exchanger ２ a temperature sensor for detecting the temperature of the refrigerant; The CO heated by the heat exchanger ２ a pressure sensor for detecting the pressure of the refrigerant; Equipped with The liquid phase CO ２ In the step of heating the refrigerant, the CO ２ The temperature of the refrigerant and the CO detected by the pressure sensor ２ and controlling the opening degree of the expansion valve based on the pressure of the refrigerant. A method for controlling a refrigeration system according to any one of claims 1 to 3.

5. the refrigeration device includes an evaporating pressure control valve provided in the second flow path, The liquid phase CO ２ In the step of heating the refrigerant, the CO refrigerant that is heated in the heat exchanger and flows through the second flow path via the evaporation pressure control valve is ２ Supplying a refrigerant to the gas refrigerant flow path; A method for controlling a refrigeration system according to any one of claims 1 to 3.

6. The liquid phase CO ２ The step of heating 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.

7. 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; The CO after being cooled by the gas cooler ２ Liquid CO in the refrigerant ２ an evaporator to which a refrigerant is supplied; The liquid phase CO ２ a liquid refrigerant supply flow path for supplying the refrigerant; Gas phase CO from the evaporator ２ a gas refrigerant flow path for guiding the refrigerant to an inlet of the low-stage compressor; The gas phase CO ２ The heat removed from the refrigerant is used to convert the liquid phase CO ２ a heat exchanger for heating the refrigerant; a first flow path connecting the liquid refrigerant supply flow path and an inlet of the heat exchanger; a second flow path connecting an outlet of the heat exchanger and the gas refrigerant flow path; an expansion valve provided in the first flow path; Equipped with Refrigeration equipment.

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