Control method for refrigeration device and refrigeration device

Abstract

A refrigeration device according to the present invention comprises a liquid refrigerant supply passage for supplying liquid-phase CO2 refrigerant of CO2 refrigerant that has been compressed at a high-stage compressor and cooled at a gas cooler to an evaporator, a gas refrigerant passage for leading gas-phase CO2 refrigerant from the evaporator to an inlet of a low-stage compressor, a heat exchanger for heating liquid-phase CO2 refrigerant with heat taken from gas-phase CO2 refrigerant at the gas cooler, a first passage that connects the liquid refrigerant supply passage and an inlet of the heat exchanger, a second passage that connects an outlet of the heat exchanger and the gas refrigerant passage, and an expansion valve that is provided on the first passage. When the refrigeration load of the refrigeration device has fallen, the expansion valve is opened, and CO2 refrigerant that has been heated at the heat exchanger is led to the gas refrigerant passage via the second passage.

Description

Refrigeration device control method and refrigeration device

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

[0002] A low-stage compressor and a high-stage compressor are provided, ２ 2. Description of the Related Art Refrigeration devices using a refrigerant are known (see, for example, Patent Document 1).

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

[0004] A low-stage compressor and a high-stage compressor are provided, ２ In a refrigeration system using a 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, CO ２ The refrigerant solidifies and turns into dry ice. If this dry ice is sucked into the low-stage compressor, it will cause damage to the compressor. Therefore, to prevent damage to the low-stage compressor, the low-stage compressor must be stopped, and operation of the low-stage compressor cannot be continued.

[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.

[0007] (1) A method for controlling a refrigeration device according to at least one embodiment of the present disclosure is a method for controlling a refrigeration device, the refrigeration device ２ a low-stage compressor for compressing a refrigerant; and ２ a high-stage compressor for compressing a refrigerant; and ２ a gas cooler for cooling the refrigerant; and ２ Liquid CO in the refrigerant２ an evaporator to which a refrigerant is supplied; ２ a liquid refrigerant supply passage for supplying a refrigerant; and ２ a gas refrigerant passage for guiding the refrigerant to an inlet of the low-stage compressor; ２ The heat removed from the refrigerant is used to convert the liquid phase CO ２ a heat exchanger for heating a 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; and an expansion valve provided in the first flow path, wherein when the refrigeration load of the refrigeration device decreases, the expansion valve is opened to produce the liquid phase CO 2 in the heat exchanger. ２ heating the refrigerant.

[0008] (2) The refrigeration device according to at least one embodiment of the present disclosure is ２ a low-stage compressor for compressing a refrigerant; and ２ a high-stage compressor for compressing a refrigerant; and ２ a gas cooler for cooling the refrigerant; and ２ Liquid CO in the refrigerant ２ an evaporator to which a refrigerant is supplied; ２ a liquid refrigerant supply passage for supplying a refrigerant; and ２ a gas refrigerant passage for guiding the refrigerant to an inlet of the low-stage compressor; ２ The heat removed from the refrigerant is used to convert the liquid phase CO ２ The refrigerant cooling system comprises: a heat exchanger for heating a 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; and an expansion valve provided in the first flow path.

[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 low-stage compressor when the refrigeration load decreases.

[0010] Fig. 1 is a system diagram of a refrigeration device according to one embodiment Fig. 2 is a system diagram of a refrigeration device according to another embodiment Fig. 3 is a flowchart showing a processing procedure in a control method for a refrigeration device according to some embodiments.

[0011] Several embodiments of the present disclosure will be described below with reference to the accompanying drawings. However, the dimensions, materials, shapes, relative arrangements, etc. of components described as embodiments or shown in the drawings are not intended to limit the scope of the present disclosure and are merely illustrative examples. For example, expressions expressing relative or absolute arrangements, such as "in a certain direction," "along a certain direction," "parallel," "orthogonal," "center," "concentric," or "coaxial," not only strictly express such arrangements, but also express relative displacements with a tolerance or angle or distance to the extent that the same function is achieved. For example, expressions expressing the equality of things, such as "same," "equal," and "homogeneous," not only express strict equality, but also express tolerance or differences to the extent that the same function is achieved. For example, expressions expressing shapes such as a square or cylindrical shape not only express shapes such as a square or cylindrical shape in the strict geometric sense, but also express shapes including concave and convex portions, chamfered portions, etc., to the extent that the same effect is achieved. On the other hand, the expressions "comprise," "include," "have," "includes," or "have" of one element are not exclusive expressions that exclude the presence of other elements.

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

[0013] In the refrigeration system 1 according to some embodiments, an accumulator 14 is provided in a refrigerant flow path 31 connecting the outlet of the low-stage compressor 11 and the inlet of the high-stage compressor 12. In the refrigeration system 1 according to some embodiments, a condenser 15 operating as a gas cooler is provided in a refrigerant flow path 32 connecting the outlet of the high-stage compressor 12 and the inlet of the flash tank 13, and a blower fan 22 is provided to supply outside air to the condenser 15 for cooling the refrigerant in the condenser 15. The condenser 15 is configured so that the refrigerant circulating within the condenser 15 is cooled by the outside air blown by the blower fan 22.

[0014] 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 system 1 according to some embodiments includes a flash gas flow path 36 that connects the gas phase part of the flash tank 13 to the refrigerant flow path 31a that connects the outlet of the low-stage compressor 11 to the accumulator 14, of the refrigerant flow path 31 that connects the outlet of the low-stage compressor 11 to the inlet of the high-stage compressor 12. That is, an upstream end 36u of the flash gas flow path 36 is connected to the gas phase part of the flash tank 13, and a downstream end 36d of the flash gas flow path 36 is connected to the refrigerant flow path 31a that connects the outlet of the low-stage compressor 11 to the accumulator 14.

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

[0018] The refrigeration device 1 according to some embodiments converts gas phase CO 2 into CO 3 in the condenser 15. ２ The heat removed from the refrigerant converts the CO into liquid phase. ２The refrigeration system 1 shown in FIG. 1A includes a heat exchanger 18 for heating the refrigerant, a first flow path 37 connecting the liquid refrigerant supply flow path 34 and the inlet of the heat exchanger 18, a second flow path 38 connecting the outlet of the heat exchanger 18 and the gas refrigerant flow path 35, and an expansion valve 45 provided in the first flow path 37. The refrigeration system 1 shown in FIG. 1A includes an evaporation 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 evaporation pressure control valve 46. Note that the refrigeration system 1 shown in FIG. 1A does not necessarily include the check valve 47. The refrigeration system 1 shown in FIG. 1B includes the check valve 47 provided in the second flow path 38.

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

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

[0021] The refrigeration device 1 according to some embodiments includes a control device 50 for controlling each part of the refrigeration device 1. The control device 50 includes a processor 51 that executes various arithmetic processes, and a memory 52 that non-temporarily or temporarily stores various data processed by the processor 51. The processor 51 is implemented by a CPU, a GPU, an MPU, a DSP, various other arithmetic devices, or a combination thereof. The memory 52 is implemented by a ROM, a RAM, a flash memory, or a combination thereof. In the following explanation, the control content of the control device 50 will be mainly explained in relation to a case where the refrigeration load of the refrigeration device 1 decreases. The control content of the control device 50 will be described in detail later. The refrigeration device 1 according to some embodiments includes various sensors for controlling each part of the refrigeration device 1. The various sensors for controlling each part of the refrigeration device 1 include, for example, an intake temperature T Ｌｉｎ and a suction temperature sensor 53 for detecting the suction pressure P of the refrigerant sucked into the low-stage compressor 11. Ｌｉｎ The suction pressure sensor 54 detects the suction temperature T 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 CO heated by the heat exchanger 18. ２ Refrigerant temperature T ＥＸｏｕｔ and a temperature sensor 57 for detecting CO heated by the heat exchanger 18. ２ Refrigerant pressure P 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, is vaporized via the evaporator 16 and the heat exchanger 17, and is 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 connecting the outlet of the low-stage compressor 11 and the accumulator 14 via the flash gas flow path 36. That is, in the refrigeration apparatus 1 according to some embodiments, the gas-phase refrigerant in the flash tank 13 is supplied to the high-stage compressor 12 via the flash gas flow path 36 and the refrigerant flow path 31a. In the refrigeration apparatus 1 according to some embodiments, the gas-phase refrigerant from the low-stage compressor 11 and the gas-phase refrigerant from the flash tank 13 are supplied to the high-stage compressor 12 and compressed.

[0024] (CO ２ Problems in refrigeration devices using a refrigerant) As in the refrigeration device 1 according to some embodiments, a refrigeration device using a low-stage compressor 11 and a high-stage compressor 12 is provided. ２ In the refrigeration system 1 using the refrigerant, when the refrigeration load decreases, the suction pressure P Ｌｉｎ However, the suction pressure P Ｌｉｎ If the temperature drops too much, the CO ２The refrigerant solidifies and becomes dry ice. If this dry ice is sucked into the low-stage compressor 11, it will cause damage to the low-stage compressor 11. Therefore, in order to prevent damage to the low-stage compressor 11, the low-stage compressor 11 must be stopped, and operation of the low-stage compressor 11 cannot be continued. Once the low-stage compressor 11 is stopped, it takes a relatively long time to restart, which may cause an undesirable temperature rise on the refrigeration load side until restart. Therefore, it is desirable to avoid stopping the low-stage compressor 11 as much as possible.

[0025] (Method for solving the problem in the refrigeration device 1) In the refrigeration device 1 according to some embodiments, when the refrigeration load of the refrigeration device 1 decreases, the condenser 15 condenses gas-phase CO ２ The heat removed from the refrigerant converts the CO ２ The refrigerant is heated in a heat exchanger 18 to produce gaseous CO ２ The refrigerant is generated and the gas phase CO ２ By drawing the refrigerant into the low-stage compressor 11, the suction pressure P Ｌｉｎ That is, the decrease in the intake temperature T Ｌｉｎ This suppresses the decrease in the temperature of the low-stage compressor 11, thereby allowing the low-stage compressor 11 to continue operating. This makes it possible to reduce 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 GaQ Ｌ 1 to Q Ｌ In this case, for example, the heat exchanger 18 ２ By heating the refrigerant, the heat exchange amount Q in the evaporator 16 Ｌ This corresponds to the decrease in (Q Ｌ 1-Q Ｌ 2) CO ２ This heated CO ２ If the refrigerant and the refrigerant after heat exchange in the evaporator 16 are combined, the suction pressure P Ｌｉｎ is the heat exchange amount Q in the evaporator 16 Ｌ GaQ Ｌ The same suction pressure P as when ＬｉｎIn 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] (Liquid phase CO by heat exchanger 18 ２ Overview of refrigerant heating) Specifically, in the refrigeration device 1 according to some embodiments, the liquid phase CO ２ When the conditions for starting heating of the refrigerant, which will be described later, are met, the processor 51 of the control device 50 opens the expansion valve 45 to allow the liquid CO 2 from the flash tank 13 to flow through the first flow path 37. ２ The refrigerant is supplied to the heat exchanger 18. As a result, the refrigerant is heated in the heat exchanger 18 and vaporized into gaseous CO ２ The refrigerant is supplied to the gas refrigerant flow path 35 via the second flow path 38, and the gas phase CO ２ The refrigerant is sucked into the low-stage compressor 11 together with the refrigerant.

[0028] In the following description, the liquid phase CO ２ The operation mode of the refrigeration system 1 in which the refrigerant is heated is also referred to as a liquid refrigerant heating mode. ２ The operation mode of the refrigeration system 1 in which the refrigerant is not heated is also referred to as a normal operation mode.

[0029] (Control Contents in Normal Operation Mode) In the refrigeration device 1 according to some embodiments, when the operation mode is the normal operation mode, the processor 51 of the control device 50 controls each part of the refrigeration device 1 in the same manner as a conventional two-stage compression, two-stage expansion 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 of the first flow path 37 so that the expansion valve 45 is fully closed.

[0030] (Switching from normal operation mode to liquid refrigerant heating mode) In the refrigeration device 1 according to some embodiments, 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 and second start conditions below are satisfied continues for a specified time Tms1 or more. Here, the first start condition is the suction pressure P Ｌｉｎ is less than the specified pressure P1.

[0031] The second start condition is that, in a case where a plurality of high-stage compressors 12 are installed, as in the refrigeration system 1 according to some embodiments, the number of operating high-stage compressors 12 is one, and the rotation speed RH of the one high-stage compressor 12 is equal to or less than a specified rotation speed RH1. Note that, in a case where the number of installed high-stage compressors 12 in the refrigeration system 1 is one, the second start condition is that the rotation speed RH of the high-stage compressor 12 is equal to or less than a specified rotation speed RH1. In the refrigeration system 1 according to some embodiments, the rotation speed RH1 is a rotation speed RH that is preset as the lowest rotation speed RH at which the high-stage compressor 12 can operate.

[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 Based on the command value of the rotation speed of the drive motor (not shown) that drives the high-stage compressor 12, it is determined whether the above-mentioned first start condition is satisfied, and based on the command value of the rotation speed of the drive motor (not shown) that drives the high-stage compressor 12, it is determined whether the above-mentioned second start condition is satisfied.

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

[0034] In place of the first start condition, the suction temperature T Ｌｉｎ is less than a specified temperature Th1, and the operation mode may be switched from the normal operation mode to the liquid refrigerant heating mode when the time Tms during which the second and third start conditions are all satisfied continues for a specified time Tms1 or longer. Alternatively, 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, second, and third start conditions are all satisfied continues for a specified time Tms1 or longer.

[0035] (Control Contents 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 to allow the liquid-phase CO 2 from the flash tank 13 to flow through the first flow path 37. ２ The processor 51 controls the opening degree of the expansion valve 45 so as to supply the refrigerant to the heat exchanger 18. At this time, the processor 51 controls the CO 2 heated by the heat exchanger 18 detected by the temperature sensor 57. ２ Refrigerant temperature T ＥＸｏｕｔ and CO heated by the heat exchanger 18 detected by the pressure sensor 58. ２ Refrigerant pressure P 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 CO heated by the heat exchanger 18 is２ The degree of superheat of the refrigerant 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 2 heated by the heat exchanger 18 ２ The refrigerant 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 CO ２ In order to increase the evaporation temperature of the refrigerant, the processor 51 controls the set pressure of the evaporation pressure control valve 46 in accordance with a program read from the memory 52. ​​This reduces the CO ２ Since the evaporation temperature of the refrigerant can be increased, frosting in the heat exchanger 18 can be reduced.

[0037] (Switching from Liquid Refrigerant Heating Mode to Normal Operation Mode) In the refrigeration device 1 according to some embodiments, the operation mode is switched from the liquid refrigerant heating mode to the normal operation mode when any of the following conditions is satisfied: a time Tmea that satisfies the first termination condition continues for a specified time Tme1 or more, a time Tmeb that satisfies the second termination condition continues for a specified time Tme2 or more, or a time Tmec that satisfies the third termination condition continues for a specified time Tme3 or more. Here, the first termination condition is the suction pressure P Ｌｉｎ The second termination condition is that the rotation speed RL of the low-stage compressor 11 is equal to or greater than a specified rotation speed RL1. The third termination condition is that the suction temperature T Ｌｉｎ The processor 51 detects that the suction pressure P Ｌｉｎ When the pressure rises, the rotation speed RL of the low-stage compressor 11 is controlled so as to increase.

[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. ＬｉｎAlternatively, in the refrigeration device 1 according to some embodiments, the processor 51 determines whether the second termination condition is satisfied based on a command value for the rotation speed of a drive motor (not shown) that drives the low-stage compressor 11. Alternatively, in the refrigeration device 1 according to some embodiments, the processor 51 determines whether the second termination condition is satisfied based on a command value for the rotation speed of a drive motor (not shown) that drives the low-stage compressor 11. Alternatively, in the refrigeration device 1 according to some embodiments, the processor 51 determines whether the second termination condition is satisfied based on a command value for the rotation speed of a drive motor (not shown) that drives the low-stage compressor 11. Ｌｉｎ Based on this, it is determined whether the third termination condition is met.

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

[0040] 2 is a flowchart showing a processing procedure in a control method for the refrigeration device 1 according to some embodiments. A program for executing the processing shown in the flowchart of FIG. 2 is read from the memory 52 and executed by the processor 51.

[0041] A method for controlling the refrigeration device 1 according to some embodiments includes step S1 of operating the refrigeration device 1 in a normal operation mode, and step S9 of operating the refrigeration device 1 in a liquid refrigerant heating mode.

[0042] Step S1 of operating the refrigeration apparatus 1 in the normal operation mode is a step of operating the refrigeration apparatus 1 by controlling each part of the refrigeration apparatus 1 in the same manner as a conventional two-stage compression, two-stage expansion refrigeration apparatus, that is, a step of operating the refrigeration apparatus 1 in the above-described normal operation mode. In step S1 of operating the refrigeration apparatus 1 in the normal operation mode, as described above, the processor 51 controls each part of the refrigeration apparatus 1 in the same manner as a conventional two-stage compression, two-stage expansion refrigeration apparatus. Also, as described above, the processor 51 controls the aperture of the expansion valve 45 of 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 That is, 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, the 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 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.

[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 the normal operation mode, continues operating the refrigeration device 1 in the 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 above-mentioned first start condition or the third start condition is not satisfied, the processor 51 returns to step S1 in which the refrigeration device 1 is operated in normal operation mode, continues operating the refrigeration device 1 in normal operation mode, and returns to step S3 again.

[0049] If step S3 is judged to be positive, that is, if it is judged that the above-mentioned first start condition is satisfied, the process proceeds to step S5, where the processor 51 judges whether the number of operating high-stage compressors 12 is one and the rotation speed RH of the one high-stage compressor 12 is equal to or lower than the specified rotation speed RH1, that is, whether the above-mentioned second start condition is satisfied.

[0050] Note that, in step S3, instead of determining whether the first start condition is satisfied, if it is determined whether the above-mentioned third start condition is satisfied, and if step S3 is determined to be positive, i.e., if it is determined that the above-mentioned third start condition is satisfied, the process proceeds to step S5, and the processor 51 determines whether the number of operating high-stage compressors 12 is one and the rotation speed RH of the one high-stage compressor 12 is equal to or lower than the specified rotation speed RH1, i.e., whether the above-mentioned second start condition is satisfied.

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

[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 in which the refrigeration device 1 is operated in normal operation mode, continues operating the refrigeration device 1 in normal operation mode, and returns to step S3 again.

[0053] If step S5 is judged to be positive, i.e., if it is judged that the second start condition described above is satisfied, the process proceeds to step S7, where the processor 51 judges whether the time Tms during which both the first start condition and the second start condition are satisfied has continued for more than the specified time Tms1.

[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 the processor 51 determines whether the time Tms during which both the second start condition and the third start condition are satisfied has continued for more than the specified time Tms1.

[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 the processor 51 determines whether the time Tms during which the first start condition, the second start condition, and the third start condition are all satisfied continues for more than the specified time Tms1.

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

[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 the 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 longer 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, instead of determining whether the first start condition is satisfied in step S3, if it is determined whether both the first start condition and the third start condition are satisfied, if step S7 is 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 to convert the liquid phase CO ２ This is a step of heating the refrigerant, that is, a step of operating the refrigeration device 1 in the liquid refrigerant heating mode. In step S9 of operating the refrigeration device 1 in the liquid refrigerant heating mode, as described above, the processor 51 opens the expansion valve 45 to allow the liquid-phase CO 2 from the flash tank 13 to flow through the first flow path 37. ２ The processor 51 controls the opening degree of the expansion valve 45 so as to supply the refrigerant to the heat exchanger 18. At this time, the processor 51 controls the CO 2 heated by the heat exchanger 18 detected by the temperature sensor 57. ２ Refrigerant temperature T ＥＸｏｕｔ and CO heated by the heat exchanger 18 detected by the pressure sensor 58. ２ Refrigerant pressure P 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. Note that in step S11, the processor 51 may determine whether the rotation speed RL of the low-stage compressor 11 is equal to or greater than a specified rotation speed RL1. That is, in step S11, the processor 51 may determine whether the second termination condition described above is satisfied, instead of determining whether the first termination condition described above is satisfied. Also, in step S11, the processor 51 determines whether the suction temperature T Ｌｉｎ That is, in step S11, the processor 51 may determine whether the third end condition is satisfied, instead of determining whether the first or second end condition is satisfied.

[0065] If a negative determination is made in step S11, i.e., if it is determined that the first termination condition described above is not satisfied, the processor 51 returns to step S9 to operate the refrigeration device 1 in the liquid refrigerant heating mode, continues operation of the refrigeration device 1 in the liquid refrigerant heating mode, and returns to step S11 again. Note that, if a negative determination is made in step S11 when it is determined whether the second termination condition described above is satisfied, i.e., if it is determined that the second termination condition described above is not satisfied, the processor 51 returns to step S9 to operate the refrigeration device 1 in the liquid refrigerant heating mode, continues operation of the refrigeration device 1 in the liquid refrigerant heating mode, and returns to step S11 again. Note that, if a negative determination is made in step S11 when it is determined whether the third termination condition described above is satisfied, i.e., if it is determined that the third termination condition described above is not satisfied, the processor 51 returns to step S9 to operate the refrigeration device 1 in the liquid refrigerant heating mode, continues operation of 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 above-mentioned first termination condition is satisfied, the process proceeds to step S13, where the processor 51 determines whether the time Tmea satisfying the first termination condition has continued for a specified time Tme1 or more. Note that if it is judged in step S11 whether the above-mentioned second termination condition is satisfied, and if step S11 is judged to be positive, i.e., if it is judged that the above-mentioned second termination condition is satisfied, the process proceeds to step S13, where the processor 51 determines whether the time Tmeb satisfying the second termination condition has continued for a specified time Tme2 or more. Also, if it is judged in step S11 whether the above-mentioned third termination condition is satisfied, and if step S11 is judged to be positive, i.e., if it is judged that the above-mentioned third termination condition is satisfied, the process proceeds to step S13, where the processor 51 determines whether the time Tmec satisfying the third termination condition has continued for a specified time Tme3 or more.

[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 the specified time Tme1 or more, the processor 51 returns to step S9 to operate the refrigeration device 1 in the liquid refrigerant heating mode, continues operation of the refrigeration device 1 in the liquid refrigerant heating mode, and returns to step S11 again. Note that, if a negative judgment is made in step S13 when it is determined in step S11 whether or not the second termination condition is satisfied, that is, if it is determined that the time Tmeb that satisfies the second termination condition has not continued for the specified time Tme2 or more, the processor 51 returns to step S9 to operate the refrigeration device 1 in the liquid refrigerant heating mode, continues operation of 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 a negative judgment is made in step S13, 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 liquid refrigerant heating mode, continues operating the refrigeration device 1 in the liquid refrigerant heating mode, and returns to step S11 again.

[0068] If step S13 is judged to be positive, i.e., if it is judged that the time Tmea satisfying the first termination condition has continued for equal to or longer than the specified time Tme1, the process returns to step S1, where the refrigeration apparatus 1 is operated in the normal operation mode. Note that if it is judged in step S11 whether the second termination condition described above is satisfied, and if step S13 is judged to be positive, i.e., if it is judged that the time Tmeb satisfying the second termination condition has continued for equal to or longer than the specified time Tme2, the process returns to step S1, where the refrigeration apparatus 1 is operated in the normal operation mode. Also, if it is judged in step S11 whether the third termination condition described above is satisfied, and if step S13 is judged to be positive, i.e., if it is judged that the time Tmec satisfying the third termination condition has continued for equal to or longer than the specified time Tme3, the process returns to step S1, where the refrigeration apparatus 1 is operated in the normal operation mode.

[0069] In step S13 described above, the specified times Tme1, Tme2, and Tme3 may all be the same value, or one of them may be a different value, or all of them may be different values.

[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 the control method for the refrigeration device 1 according to at least one embodiment of the present disclosure, the refrigeration device 1 ２ A low-stage compressor 11 for compressing a refrigerant, and CO after being compressed by the low-stage compressor 11 ２ A high-stage compressor 12 for compressing a refrigerant, and CO compressed by the high-stage compressor 12 ２ A gas cooler (condenser 15) for cooling the refrigerant, and CO after being cooled by the gas cooler (condenser 15). ２ Liquid CO in the refrigerant ２ An evaporator 16 to which a refrigerant is supplied, and a liquid phase CO ２ A liquid refrigerant supply passage 34 for supplying refrigerant, and a gas phase CO ２A gas refrigerant flow path 35 for guiding the refrigerant to the inlet of the low-stage compressor 11, and a gas cooler (condenser 15) for converting the gas phase CO ２ The heat removed from the refrigerant converts the CO into liquid phase. ２ The refrigeration system includes a heat exchanger 18 for heating a refrigerant, a first flow path 37 connecting a liquid refrigerant supply flow path 34 and an inlet of the heat exchanger 18, a second flow path 38 connecting an outlet of the heat exchanger 18 and a gas refrigerant flow path 35, and an expansion valve 45 provided in the first flow path 37. A control method for the refrigeration system 1 according to at least one embodiment of the present disclosure includes a step of opening the expansion valve 45 when the refrigeration load of the refrigeration system 1 decreases, thereby expanding the liquid-phase CO 2 in the heat exchanger 18. ２ The method includes a step of heating the refrigerant (step S9 of operating the refrigeration device 1 in a liquid refrigerant heating mode).

[0072] According to the method (1) above, when the refrigeration load is reduced, the liquid phase CO ２ The refrigerant is heated in a heat exchanger 18 to produce gaseous CO ２ The refrigerant is generated and the gas phase CO ２ By drawing the refrigerant into the low-stage compressor 11, the suction pressure P Ｌｉｎ This can suppress a decrease in the temperature of the low-stage compressor 11 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), liquid phase CO ２ The step of heating the 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 the first start condition, that is, the pressure P1 of the high-stage compressor 12 is less than the specified pressure P1, and the second start condition, that the rotational speed RH of the high-stage compressor 12 is equal to or less than the specified rotational speed RH1, are satisfied continues for a specified time Tms1 or more.

[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. ２The step of heating the 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 a time Tms during which both of the first start condition, that is, the pressure P1 is less than a specified pressure P1, and the second start condition, that the number of operating high-stage compressors 12 is one and the rotation speed RH of the one high-stage compressor 12 is equal to or less than a specified rotation speed RH1, are satisfied continues for a specified time Tms1 or more.

[0076] According to the method (3) above, the low-stage compressor 11 can continue to operate even when the refrigeration load is reduced, 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 uses CO 2 heated by the heat exchanger 18. ２ Refrigerant temperature T ＥＸｏｕｔ and a temperature sensor 57 for detecting CO heated by the heat exchanger 18. ２ Refrigerant pressure P ＥＸｏｕｔ and a pressure sensor 58 for detecting the liquid phase CO. ２ In the step of heating the refrigerant (step S9 of operating the refrigeration device 1 in the liquid refrigerant heating mode), the CO ２ Refrigerant temperature T ＥＸｏｕｔ and CO detected by the pressure sensor 58 ２ Refrigerant pressure P ＥＸｏｕｔ The opening degree of the expansion valve 45 may be controlled based on the above.

[0078] According to the method (4) above, the gas phase CO heated by the heat exchanger 18 is ２ The degree of superheat of the refrigerant 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. ２ In the step of heating the refrigerant (step S9 of operating the refrigeration device 1 in the liquid refrigerant heating mode), the CO 2 that is heated in the heat exchanger 18 and flows through the second flow path 38 via the evaporation pressure control valve 46 is ２ The refrigerant may be supplied to the gas refrigerant flow path 35 .

[0080] According to the method (5) above, the CO ２ Increasing the evaporation pressure of the refrigerant reduces the CO ２ Since the evaporation temperature of the refrigerant can be increased, frosting in the heat exchanger 18 can be reduced.

[0081] (6) In some embodiments, in any of the methods (1) to (5) above, liquid phase CO ２ The step of heating the refrigerant (step S9 of operating the refrigeration device 1 in the liquid refrigerant heating mode) is performed by adjusting the suction pressure P Ｌｉｎ When the time Tmea that satisfies the first termination condition that the rotation speed RL of the low-stage compressor 11 becomes equal to or higher than the specified pressure P1 continues for equal to or longer than the specified time Tme1, when the time Tmeb that satisfies the second termination condition that the rotation speed RL of the low-stage compressor 11 becomes equal to or higher than the specified rotation speed RL1 continues for equal to or longer than the specified time Tme2, or when the suction temperature T Ｌｉｎ or when the time Tmec during which the temperature reaches or exceeds a predetermined temperature Th2 continues for a predetermined time Tme3 or more, satisfying a third termination condition.

[0082] According to the method (6) above, liquid phase CO ２ When it is no longer necessary to heat the refrigerant in the heat exchanger 18, the refrigeration system 1 can be returned to normal operating conditions.

[0083] (7) The refrigeration device 1 according to at least one embodiment of the present disclosure is ２ A low-stage compressor 11 for compressing a refrigerant, and CO after being compressed by the low-stage compressor 11 ２ A high-stage compressor 12 for compressing a refrigerant, and CO compressed by the high-stage compressor 12 ２ A gas cooler (condenser 15) for cooling the refrigerant, and CO after being cooled by the gas cooler (condenser 15). ２ Liquid CO in the refrigerant ２ An evaporator 16 to which a refrigerant is supplied, and a liquid phase CO ２ A liquid refrigerant supply passage 34 for supplying refrigerant, and a gas phase CO ２ A gas refrigerant flow path 35 for guiding the refrigerant to the inlet of the low-stage compressor 11, and a gas cooler (condenser 15) for converting the gas phase CO ２The heat removed from the refrigerant converts the CO into liquid phase. ２ The refrigerant-heating device includes a heat exchanger (18) for heating the refrigerant, a first flow path (37) connecting a liquid refrigerant supply flow path (34) and an inlet of the heat exchanger (18), a second flow path (38) connecting an outlet of the heat exchanger (18) and a 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 ２ The refrigerant is heated in a heat exchanger 18 to produce gaseous CO ２ The refrigerant is generated and the gas phase CO ２ By drawing the refrigerant into the low-stage compressor 11, the suction pressure P Ｌｉｎ This can suppress a decrease in the temperature of the low-stage compressor 11 and continue the operation of the low-stage compressor 11. This can reduce undesired temperature changes on the refrigeration load side.

[0085] REFRIGERATION SYSTEM 11 LOW-STAGE COMPRESSOR 12 HIGH-STAGE COMPRESSOR 13 FLASH TANK 14 ACCUMULATOR 15 CONDENSOR 16 EVAPORATOR 18 HEAT EXCHANGER 22 BLADE FAN 37 FIRST FLOW PATH 38 SECOND FLOW PATH 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 SUCTION TEMPERATURE SENSOR 54, 56 SUCTION PRESSURE SENSOR 57 TEMPERATURE SENSOR 58 PRESSURE SENSOR

Claims

1. A method for controlling a refrigeration device, wherein the refrigeration device is ２ a low-stage compressor for compressing a refrigerant; and ２ a high-stage compressor for compressing a refrigerant; and ２ a gas cooler for cooling the refrigerant; and ２ Liquid CO in the refrigerant ２ an evaporator to which a refrigerant is supplied; ２ a liquid refrigerant supply passage for supplying a refrigerant; and ２ a gas refrigerant passage for guiding the refrigerant to an inlet of the low-stage compressor; ２ The heat removed from the refrigerant is used to convert the liquid phase CO ２ a heat exchanger for heating a 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; and an expansion valve provided in the first flow path, wherein when the refrigeration load of the refrigeration device decreases, the expansion valve is opened to produce the liquid phase CO 2 in the heat exchanger. ２ A method for controlling a refrigeration device, comprising: heating a refrigerant.

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

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

4. The refrigeration device ２ a temperature sensor for detecting the temperature of the refrigerant; ２ a pressure sensor for detecting the pressure of the refrigerant; and 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 The method for controlling a refrigeration device according to claim 1 , further comprising controlling an opening degree of the expansion valve based on a pressure of the refrigerant.

5. The refrigeration device includes an evaporation pressure control valve provided in the second flow path, and 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 The method for controlling a refrigeration device according to claim 1 , further comprising the step of supplying a refrigerant to the gas refrigerant flow path.

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

7. CO ２ a low-stage compressor for compressing a refrigerant; and ２ a high-stage compressor for compressing a refrigerant; and ２ a gas cooler for cooling the refrigerant; and ２ Liquid CO in the refrigerant ２ an evaporator to which a refrigerant is supplied; ２ a liquid refrigerant supply passage for supplying a refrigerant; and ２ a gas refrigerant passage for guiding the refrigerant to an inlet of the low-stage compressor; ２ The heat removed from the refrigerant is used to convert the liquid phase CO ２ A refrigeration device comprising: a heat exchanger for heating a 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; and an expansion valve provided in the first flow path.

Images