Refrigeration unit, refrigeration unit control method and temperature control system

Abstract

In one embodiment of the refrigeration unit (10), when the discharge temperature of the refrigerant discharged from the compressor (11) and flowing into the condenser (12) is greater than a critical value, the liquid bypass control valve (16B) is opened, and when the discharge temperature is below the critical value, the liquid bypass control valve (16B) is closed. Furthermore, the speed of the compressor (11) in the refrigeration unit (10) is adjusted so that the evaporation pressure of the refrigerant flowing in the downstream portion of the evaporator (14) in the refrigeration circuit (10A) and the upstream portion of the compressor (11), and in the downstream portion of the connection point at the downstream end of the liquid bypass flow path (16A), becomes a predetermined target evaporation pressure.

Description

[Technical Field]

[0001] This invention relates to a refrigeration apparatus having a compressor, a condenser, an expansion valve, and an evaporator, a control method for the refrigeration apparatus, and a temperature control system having the refrigeration apparatus. [Previous Technology]

[0002] A temperature control system (e.g., JP2014-145565A) is known, which includes a refrigeration unit having a compressor, a condenser, an expansion valve and an evaporator, and a fluid circulation device for circulating fluids such as water and brine, and the fluids circulated by the fluid circulation device are cooled by the evaporator of the refrigeration unit. [Summary of the Invention]

[0003] The temperature control system described above may be relatively large because it includes a refrigeration unit and a fluid circulation unit.

[0004] However, when considering factors such as ease of transportation and reduced space requirements, it is preferable that the aforementioned system be made lightweight. For example, an accumulator (accumulator) for suppressing liquid backflow can be installed in the refrigeration unit, but since the accumulator is relatively large, this results in an overall large system size. For example, if liquid backflow can be suppressed without using such an accumulator, it would be advantageous in terms of lightweight design.

[0005] Furthermore, in refrigeration units, the compressor may burn out if the temperature of the refrigerant drawn into the compressor rises excessively. Additionally, an excessively high discharge temperature due to the excessively high temperature of the refrigerant drawn into the compressor is undesirable for the entire circuit. Therefore, a liquid bypass circuit can be used to bypass the refrigerant downstream of the condenser to the upstream side of the compressor. However, when the refrigerant is bypassed by the liquid bypass circuit, the amount of refrigerant flowing to the evaporator side decreases, potentially reducing the refrigeration capacity. In this case, the compressor speed can be increased to increase the refrigerant discharge rate. When the amount of refrigerant discharged by the compressor compensates for the reduced amount of refrigerant flowing to the evaporator side, the refrigeration unit is typically filled with a sufficient amount of refrigerant to ensure both proper bypass and refrigeration capacity.

[0006] However, as described above, using the remaining amount of refrigerant increases the overall system size. Furthermore, considering environmental load, it is desirable to avoid using excessive refrigerant. Additionally, since the liquid bypass circuit delivers the refrigerant in a gas-liquid mixed state to the upstream side of the compressor, the risk of liquid backflow may increase. Therefore, liquid bypass circuits are mostly used in conjunction with receivers. However, in this case, the entire system becomes larger.

[0007] The present invention has been made in view of the above circumstances, and its object is to provide a refrigeration apparatus, a control method for the refrigeration apparatus, and a temperature control system that can appropriately suppress liquid backflow of refrigerant in the refrigeration unit, suppress the amount of refrigerant used, appropriately suppress excessive temperature rise of the refrigerant drawn into the compressor, and perform appropriate cooling operations, even when the capacity of the receiver is suppressed or the receiver is not used. [Means for Solving the Problem]

[0008] A refrigeration apparatus according to an embodiment of the present invention comprises: a refrigeration circuit, which is sequentially connected to a compressor, a condenser, an expansion valve, and an evaporator via piping to circulate refrigerant; a liquid bypass circuit, comprising: a liquid bypass flow path, which branches off from a portion downstream of the condenser and a portion upstream of the expansion valve in the aforementioned refrigeration circuit, and is connected to a portion downstream of the evaporator and a portion upstream of the aforementioned compressor; a liquid bypass control valve, which is disposed in the aforementioned liquid bypass flow path and controls the flow of the aforementioned refrigerant in the aforementioned liquid bypass flow path; and a control device, which controls the aforementioned liquid bypass control valve and the upstream... The compressor speed is controlled; the control device performs the following control: when the discharge temperature of the refrigerant discharged from the compressor and flowing into the condenser is greater than a critical value, the liquid bypass control valve is opened; when the discharge temperature is below the critical value, the liquid bypass control valve is closed, and the compressor speed is adjusted so that the evaporation pressure of the refrigerant flowing in the downstream side of the evaporator in the refrigeration circuit and in the upstream side of the compressor, and in the downstream side of the connection position at the downstream end of the liquid bypass flow path, becomes a preset target evaporation pressure.

[0009] A control method for a refrigeration apparatus according to an embodiment of the present invention, the refrigeration apparatus comprising: a refrigeration circuit, wherein a compressor, a condenser, an expansion valve, and an evaporator are sequentially connected by piping to circulate refrigerant; and a liquid bypass circuit, comprising: a liquid bypass flow path, which branches off from a downstream portion of the condenser and an upstream portion of the expansion valve in the aforementioned refrigeration circuit, and is connected to a downstream portion of the evaporator and an upstream portion of the aforementioned compressor; and a liquid bypass control valve, which is disposed in the aforementioned liquid bypass flow path and controls the flow of the aforementioned refrigerant in the aforementioned liquid bypass flow path; the aforementioned control method comprises the following steps: The steps of operating the aforementioned refrigeration unit; and when the discharge temperature of the aforementioned refrigerant discharged from the aforementioned compressor and flowing into the aforementioned condenser is greater than a critical value, opening the aforementioned liquid bypass control valve, closing the aforementioned liquid bypass control valve when the aforementioned discharge temperature becomes below the aforementioned critical value, and adjusting the speed of the aforementioned compressor so that the evaporation pressure of the aforementioned refrigerant flowing in the downstream side of the aforementioned evaporator in the aforementioned refrigeration circuit and in the upstream side of the aforementioned compressor, and in the downstream side of the connection position at the downstream end of the aforementioned liquid bypass flow path, becomes a predetermined target evaporation pressure.

[0010] A temperature control system according to an embodiment of the present invention includes: the aforementioned refrigeration device; and a fluid circulation device that transports fluid to a temperature control object after heat exchange in the aforementioned evaporator, so that the aforementioned fluid passing through the aforementioned temperature control object undergoes heat exchange again in the aforementioned evaporator, and has a heater at a position downstream of the aforementioned temperature control object and upstream of the aforementioned evaporator.

[0011] According to the present invention, even when the capacity of the receiver is suppressed or the receiver is not used, the liquid backflow of the refrigerant in the refrigeration unit can be appropriately suppressed, the amount of refrigerant used can be suppressed, the excessive temperature rise of the refrigerant drawn into the compressor can be appropriately suppressed, and appropriate cooling action can be performed.

Implementation Method

[0013] Hereinafter, one embodiment of the present invention will be described.

[0014] FIG1 is a schematic diagram of a temperature control system 1 according to an embodiment of the present invention. The temperature control system 1 shown in FIG1 includes: a refrigeration device 10; and a fluid circulation device 20; and the refrigeration device 10 and the fluid circulation device 20 are controlled by a control device 30.

[0015] The refrigeration unit 10 controls the temperature of the fluid flowing through the fluid circulation device 20 by means of a refrigerant. The fluid circulation device 20 supplies the fluid, after being temperature-controlled by the refrigeration unit 10, to the temperature-controlled object T.

[0016] The fluid circulation device 20 is configured to circulate the fluid that has passed through the temperature control object T. Then, the temperature of the fluid returning from the temperature control object T is controlled again by the refrigeration device 10. The fluid circulating in the fluid circulation device 20 is, for example, brine, but it can also be other fluids such as water.

[0017] The control device 30, for example, sets the temperature of the fluid supplied to the temperature-controlled object T according to the user's operation, or controls each part of the refrigeration unit 10 and the fluid circulation device 20 so that the temperature of the fluid becomes the set temperature. Hereinafter, the refrigeration unit 10, the fluid circulation device 20 and the control device 30 will be described in detail.

[0018] (Refrigeration unit) The refrigeration unit 10 includes: a refrigeration circuit 10A consisting of a compressor 11, a condenser 12, an expansion valve 13 and an evaporator 14 connected in sequence by piping 15 to circulate refrigerant; a liquid bypass circuit 16 and a gas bypass circuit 17 connected to the refrigeration circuit 10A; a discharge temperature sensor 18; and an evaporation pressure sensor 19.

[0019] In the refrigeration circuit 10A, the compressor 11 compresses the refrigerant, which is in a low-temperature and low-pressure gaseous state, flowing out of the evaporator 14, and supplies it to the condenser 12 in a high-temperature and high-pressure gaseous state. The condenser 12 cools and condenses the refrigerant compressed by the compressor 11 by means of cooling water, and supplies it to the expansion valve 13 in a high-pressure liquid state at a specific cooling temperature.

[0020] The cooling water for the condenser 12 can be water or other refrigerants. Symbol 5 in the figure indicates a cooling water pipe that supplies cooling water to the condenser 12. The condenser 12 can be air-cooled.

[0021] The expansion valve 13 expands and depressurizes the refrigerant supplied from the condenser 12, setting it to a low-temperature and low-pressure gas-liquid mixture state, and supplies it to the evaporator 14. The evaporator 14 allows the refrigerant supplied from the expansion valve 13 to exchange heat with the fluid in the fluid circulation device 20. Here, the refrigerant that has exchanged heat with the fluid becomes a low-temperature and low-pressure gas state and flows out of the evaporator 14 to be compressed again by the compressor 11.

[0022] The liquid bypass circuit 16 includes: a liquid bypass flow path 16A that branches off from the downstream side of the condenser 12 and the upstream side of the expansion valve 13 in the refrigeration circuit 10A and is connected to the downstream side of the evaporator 14 and the upstream side of the compressor 11; and a liquid bypass control valve 16B provided in the liquid bypass flow path 16A for controlling the flow of refrigerant in the liquid bypass flow path 16A.

[0023] When the liquid bypass control valve 16B is opened, the refrigerant flows from the downstream side of the condenser 12 and the upstream side of the expansion valve 13 to the downstream side of the evaporator 14 and the upstream side of the compressor 11.

[0024] The gas bypass circuit 17 includes: a gas bypass flow path 17A that branches off from the downstream side of the compressor 11 and the upstream side of the condenser 12 in the refrigeration circuit 10A and is connected to the downstream side of the expansion valve 13 and the upstream side of the evaporator 14; and a gas bypass control valve 17B provided in the gas bypass flow path 17A for controlling the flow of refrigerant in the gas bypass flow path 17A.

[0025] When the gas bypass control valve 17B is opened, the refrigerant flows from the downstream side of the compressor 11 and the upstream side of the condenser 12 to the downstream side of the expansion valve 13 and the upstream side of the evaporator 14.

[0026] The discharge temperature sensor 18 detects the temperature of the refrigerant discharged from the compressor 11 and flowing into the condenser 12.

[0027] In the evaporation pressure sensor 19, the pressure of the refrigerant flowing in the downstream part of the evaporator 14 and the upstream part of the compressor 11 in the refrigeration circuit 10A, and in the downstream part of the connection position at the downstream end of the liquid bypass flow path 16A, is detected and the detected pressure is used as the evaporation pressure.

[0028] Information detected by the discharge temperature sensor 18 and information detected by the evaporation pressure sensor 19 are input to the control device 30. Details are described later. The liquid bypass control valve 16B of the liquid bypass circuit 16 is controlled by the control device 30 based on the discharge temperature detected by the discharge temperature sensor 18, and the gas bypass control valve 17B of the gas bypass circuit 17 is controlled by the control device 30 based on the evaporation pressure detected by the evaporation pressure sensor 19. Furthermore, the speed of the compressor 11 is also controlled by the control device 30 based on the evaporation pressure detected by the evaporation pressure sensor 19.

[0029] In addition, the refrigeration apparatus 10 of this embodiment does not have a liquid receiver. However, the refrigeration apparatus 10 may also have a liquid receiver.

[0030] (Fluid Circulation Device) The fluid circulation device 20 includes a main flow pipe 21 having a return port 21U and a supply port 21D, and is connected to the temperature control object T via flow path pipes connected to the return port 21U and the supply port 21D respectively. In the fluid circulation device 20, the main flow pipe 21 is connected to the evaporator 14, and the fluid flowing through the main flow pipe 21 is transported to the temperature control object T after heat exchange in the evaporator 14. Then, the fluid circulation device 20 causes the fluid that has passed through the temperature control object T to undergo heat exchange again in the evaporator 14.

[0031] In addition, the fluid circulation device 20 also includes a pump 22, a tank 23 and a heater 24 installed on the main flow piping 21, as well as first to third temperature sensors 25 to 27.

[0032] Pump 22 forms part of the main flow piping 21 and generates the driving force to make the fluid flow. Pump 22 is located upstream of the connection between the main flow piping 21 and the evaporator 14, but its location is not particularly limited.

[0033] The tank 23 and heater 24 are arranged on the upstream side of the connection between the main flow piping 21 and the evaporator 14. That is, in the fluid circulation device 20 connected to the temperature control object T, the tank 23 and heater 24 are arranged on the downstream side of the temperature control object T and on the upstream side of the evaporator 14.

[0034] Tank 23 is configured to store a certain amount of fluid and forms part of the main flow piping 21. Heater 24 is configured to heat the fluid. In this embodiment, heater 24 is disposed inside tank 23, but heater 24 may also be disposed outside tank 23. Heater 24 is electrically connected to control device 30, and heating capacity is controlled by control device 30.

[0035] Furthermore, the first temperature sensor 25 detects the temperature of the fluid flowing downstream of the connection between the main flow pipe 21 and the evaporator 14, and the second temperature sensor 26 detects the temperature of the fluid flowing upstream of the heater 24 after passing through the temperature control object T. Specifically, the second temperature sensor 26 detects the temperature of the fluid flowing upstream of the heater 24 after passing through the temperature control object T and before flowing into the tank 23.

[0036] In addition, the third temperature sensor 27 detects the temperature of the fluid flowing in the fluid circulation device 20 downstream of the heater 24 and before passing through the evaporator 14.

[0037] These first to third temperature sensors 25 to 27 are electrically connected to the control device 30, and the temperature information detected by each sensor 25 to 27 is transmitted to the control device 30.

[0038] (Control Device) The control device 30 is a controller that controls the operation of the refrigeration unit 10 and the fluid circulation unit 20, and may be, for example, a computer having a CPU, ROM, etc. In this case, various processes are executed according to the program stored in the ROM. The control device 30 may be composed of other processors or circuits (e.g., FPGA (Field Programmable Gate Alley) etc.).

[0039] Figure 2 is a block diagram showing the functional configuration of the control device 30. As shown in Figure 2, the control device 30 has a fluid circulation device control module 30A and a refrigeration device control module 35. The fluid circulation device control module 30A and the refrigeration device control module 35 can be configured in, for example, a single computer or in different computers.

[0040] "Fluid circulation device control module" First, the fluid circulation device control module 30A will be described in detail.

[0041] The fluid circulation device control module 30A includes a temperature setting unit 31, a temperature acquisition unit 32, a status determination unit 33, and a heater control unit 34. For example, each of these functional parts is implemented by executing a program.

[0042] The temperature setting unit 31 sets and maintains the temperature of the fluid supplied to the temperature control object T according to the user's operation. In addition, the temperature setting unit 31 sets and maintains the target temperature of the fluid flowing downstream of the heater 24 and the fluid before passing through the evaporator 14 according to the user's operation.

[0043] The target temperature is set within the temperature range where the refrigerant undergoes heat exchange with the fluid in the fluid circulation device 20 and flows out of the evaporator 14, becoming superheated vapor. The target temperature is appropriately set based on the freezing capacity of the refrigeration unit 10, the type of refrigerant, and the target evaporation temperature of the refrigerant (described later). When the return temperature of the fluid flowing downstream of the heater 24 and before passing through the evaporator 14 is above this target temperature, the risk of refrigerant containing liquid phase returning to the compressor 11 can be avoided, thus preventing the risk of liquid backflow.

[0044] The temperature acquisition unit 32 acquires the temperature information detected by the first to third temperature sensors 25 to 27, and sends the temperature information obtained from the first to third temperature sensors 25 to 27 to the status determination unit 33, the heater control unit 34, and the refrigeration device control module 35.

[0045] The status determination unit 33 determines the status of the fluid circulation device 20 based on the temperature information detected by the first to third temperature sensors 25 to 27.

[0046] In this embodiment, the state determination unit 33 determines whether the state of the fluid circulation device 20 has changed to no-load operation or transitional no-load operation based on the temperature information detected by the second temperature sensor 26. Specifically, the state determination unit 33 determines whether the temperature of the fluid flowing upstream of the heater 24 has become lower than a predetermined temperature after passing the temperature control target T, based on the temperature information detected by the second temperature sensor 26. If the temperature is lower than the predetermined temperature, it determines that the state of the fluid circulation device 20 has changed to no-load operation or transitional no-load operation.

[0047] No-load operation refers to the state in which the temperature control object T does not exchange heat with the fluid. No-load operation transition operation refers to the state in the middle of the transition to no-load operation, which means that the temperature control object T does not exchange more heat with the fluid than under normal conditions.

[0048] For example, when the temperature-controlled object T is a heat-generating device, when the fluid circulation device 20 is operating normally, the temperature-controlled fluid exchanges heat with the temperature-controlled object T, and the temperature becomes higher than before the heat exchange after passing through the temperature-controlled object T. On the other hand, when the temperature-controlled object T, as a device, stops and its heat generation gradually decreases, compared with the normal operation situation, the temperature-controlled object T is in a state of not exchanging heat with the fluid, and ultimately the temperature-controlled object T is in a state of not exchanging heat with the fluid.

[0049] That is, during no-load operation transition, for example when the temperature control object T of the device stops, this means that the temperature control object T is in a state of not exchanging heat with the fluid compared to normal conditions. Furthermore, no-load operation means, for example, when the temperature control object T of the device stops, the temperature control object T becomes a state of substantially not exchanging heat with the fluid.

[0050] The above-mentioned specified temperature is the basis for determining whether to switch to no-load operation or no-load operation transition operation. The above-mentioned specified temperature is, for example, a temperature above the set temperature of the fluid supplied to the temperature control object T, and is appropriately selected according to the relationship with the temperature of the temperature control object T.

[0051] Furthermore, in this embodiment, the state determination unit 33 determines whether the return temperature of the fluid flowing downstream of the heater 24 and before passing through the evaporator 14 is lower than the target temperature based on the temperature information detected by the third temperature sensor 27. If it determines that the temperature is lower, a liquid backflow risk signal is generated. When such a liquid backflow risk signal is generated, a warning can be issued, for example. In addition, the state determination unit 33 compares the temperature information detected by the first temperature sensor 25 with the set temperature to detect insufficient freezing capacity.

[0052] In addition, when the state determination unit 33 determines that the fluid circulation device 20 is in no-load operation or no-load operation transition operation, the heater control unit 34 activates the heater 24 to heat the fluid.

[0053] As described above, in this embodiment, the heater control unit 34 activates the heater 24 when the fluid circulation device 20 is in a state of no-load operation or transitional no-load operation. Thereafter, the heater control unit 34 controls the heating capacity of the heater 24.

[0054] When controlling the heating capacity of the heater 24, the control device 30 of this embodiment first calculates the heating capacity Q by the heater control unit 34 using formula (1). This heating capacity Q is the heating capacity Q used to set the temperature of the fluid passing through the evaporator 14 to the target temperature Tt. Q=m×Cp×(Tt-Ts)…(1) Here, it is assumed that the set temperature of the fluid supplied to the temperature control target T is Ts (°C), the target temperature of the fluid flowing downstream of the heater 24 of the fluid circulation device 20 and before passing through the evaporator 14 is Tt (°C), the weight flow rate of the fluid through the fluid circulation device 20 is m (kg / s), and the specific heat of the fluid is Cp (J / kg°C). The set temperature Ts and the target temperature Tt are set by the temperature setting unit 31. In addition, the weight flow rate m can be detected by a flow sensor or determined according to the state of the pump 22. Furthermore, the specific heat Cp of the fluid is pre-stored in the control device 30.

[0055] Then, the control device 30 controls the heating capacity of the heater 24 based on the heating capacity Q calculated by the heater control unit 34 using formula (1). Specifically, the heater control unit 34 controls the heating capacity of the heater 24 to be a heating capacity greater than or equal to the heating capacity Q calculated by formula (1). The heating capacity, which is such a control target value, can be predetermined based on the heating capacity Q calculated in advance by formula (1), or it can be stored in advance in the control device 30.

[0056] Furthermore, the heating capacity Q calculated by formula (1) may exceed the maximum heating capacity of heater 24. In this case, control device 30 controls heater 24 to its maximum heating capacity.

[0057] As described above, in this embodiment, the heater 24 is controlled so that its heating capacity is greater than or equal to the heating capacity Q calculated by formula (1). However, the heater 24 can also be controlled so that its heating capacity is the heating capacity Q calculated by formula (1) itself. In addition, when the heating capacity of the heater 24 is controlled to be greater than or equal to the heating capacity Q calculated by formula (1), it is desirable to set it to a value that is not too greater than the heating capacity Q (for example, less than or equal to 2Q).

[0058] The purpose of activating the heater 24 when the fluid circulation device 20 is in no-load operation or no-load transition operation is to prevent insufficient evaporation of the refrigerant on the refrigeration unit 10 side due to the fluid passing through the evaporator 14 at low temperature, thereby causing liquid backflow. Here, as the heating capacity of the heater 24 increases, the risk of liquid backflow decreases. However, if the heating capacity of the heater 24 becomes too large, adverse conditions such as compressor 11 aging may occur. Therefore, the heating capacity of the heater 24 is preferably not too large. In addition, after the control device 30 controls the heating capacity of the heater 24 to be above the heating capacity Q calculated by formula (1), the heater 24 can be adjusted if the temperature of the fluid flowing downstream of the heater 24 and before passing through the evaporator 14 is not above the target temperature Tt. That is, after controlling the heating capacity of the heater 24, the control device 30 determines whether the backflow temperature of the fluid flowing downstream of the heater 24 and before passing through the evaporator 14 is lower than the target temperature based on the temperature information detected by the third temperature sensor 27. When a liquid backflow risk signal is generated, the heater 24 can be adjusted. At this point, a warning can be issued while adjusting heater 24.

[0059] "Refrigeration Unit Control Module" Next, the refrigeration unit control module 35 will be described in detail.

[0060] The refrigeration unit control module 35 includes a fluid temperature information acquisition unit 351, a target value setting unit 352, a discharge temperature acquisition unit 353, an evaporation pressure acquisition unit 354, an expansion valve control unit 355, a compressor control unit 356, a liquid bypass control unit 357, and a gas bypass control unit 358. For example, each of these functional units is implemented by an execution program.

[0061] The fluid temperature information acquisition unit 351 acquires the set temperature set by the temperature setting unit 31 on the fluid circulation device control module 30A side, and acquires the detected temperature of the fluid detected by the first temperature sensor 25 on the fluid circulation device 20 side. The fluid temperature information acquisition unit 351 sends the acquired set temperature to the target value setting unit 352 and the expansion valve control unit 355, and sends the acquired detected temperature to the expansion valve control unit 355.

[0062] The target value setting unit 352 sets the reference speed of the compressor 11 based on the set temperature sent from the fluid temperature information acquisition unit 351, sets the target evaporation pressure corresponding to the reference speed, and sets the critical value of the discharge temperature of the refrigerant discharged from the compressor 11.

[0063] The set temperature, which is the control target value for the fluid temperature, can be set to, for example, 10°C, 0°C, -10°C, etc. The target value setting unit 352 sets, for example, the reference speed of the compressor 11 and the corresponding target evaporation pressure based on such a set temperature. This adjusts the required refrigeration capacity. The lower the set temperature, the higher the set value of the reference speed and the target evaporation pressure. In addition, in this embodiment, the critical value of the discharge temperature is set to a constant value such as 80°C and recorded in advance.

[0064] In addition, the discharge temperature acquisition unit 353 obtains the temperature of the refrigerant before it is ejected from the compressor 11 and flows into the condenser 12 from the discharge temperature sensor 18, and sends information related to the obtained refrigerant temperature to the liquid bypass control unit 357.

[0065] In addition, the evaporation pressure acquisition unit 354 acquires the evaporation pressure of the refrigerant flowing out of the evaporator 14 from the evaporation pressure sensor 19, and sends the acquired evaporation pressure-related information to the compressor control unit 356 and the gas bypass control unit 358.

[0066] As described above, the expansion valve control unit 355 obtains the set temperature set by the temperature setting unit 31 from the fluid temperature information acquisition unit 351, and obtains the detected temperature of the fluid detected by the first temperature sensor 25 on the fluid circulation device 20 side. Then, the expansion valve control unit 355 adjusts the opening of the expansion valve 13 according to the difference between these set temperatures and the detected temperatures, so that the detected temperature becomes the set temperature.

[0067] In this embodiment, the expansion valve control unit 355 adjusts the opening degree of the expansion valve 13 by means of PID control. However, the expansion valve control unit 355 does not particularly limit the control method of the expansion valve 13.

[0068] Furthermore, as described above, the compressor control unit 356 acquires information on the reference speed of the compressor 11 and the corresponding target evaporation pressure set by the target value setting unit 352, and as described above, acquires information on the evaporation pressure of the refrigerant flowing out of the evaporator 14 from the evaporation pressure acquisition unit 354. Then, the compressor control unit 356 controls the speed of the compressor 11 based on this information.

[0069] Specifically, when the refrigeration unit 10 starts operating, the compressor control unit 356 first controls the speed of the compressor 11 to the reference speed set by the target value setting unit 352. Then, after controlling the speed of the compressor 11 to the reference speed (after startup), the compressor control unit 356 continuously monitors the evaporation pressure of the refrigerant obtained from the evaporation pressure acquisition unit 354, and adjusts the speed of the compressor 11 when the evaporation pressure deviates from the target evaporation pressure.

[0070] More specifically, when the refrigerant evaporation pressure exceeds the target evaporation pressure, the compressor control unit 356 increases the speed of the compressor 11; when the refrigerant evaporation pressure is lower than the target evaporation pressure, it decreases the speed of the compressor 11, thus controlling the speed of the compressor 11 to bring the refrigerant evaporation pressure to the target evaporation pressure. In other words, the control device 30 adjusts the speed of the compressor 11 via the compressor control unit 356 to bring the refrigerant evaporation pressure to the target evaporation pressure.

[0071] In this embodiment, the compressor control unit 356 adjusts the speed of the compressor 11 using PI control to make the refrigerant evaporation pressure reach the target evaporation pressure. This prevents damage to control stability due to excessive speed fluctuations. However, the control method of the compressor control unit 356 is not particularly limited.

[0072] The compressor control unit 356 reduces the speed of the compressor 11 when the refrigerant evaporation pressure is lower than the target evaporation pressure, but the speed has a lower limit. That is, if the speed of the compressor 11 is reduced to the lower limit, the speed of the compressor 11 will not fall below the lower limit even if the refrigerant evaporation pressure is lower than the target evaporation pressure.

[0073] In addition, the liquid bypass control unit 357 obtains information about the critical value (e.g., 80°C) of the discharge temperature set by the target value setting unit 352, and simultaneously obtains information about the temperature of the refrigerant discharged from the compressor 11 and flowing into the condenser 12 from the discharge temperature sensor 18. Then, when the discharge temperature of the refrigerant based on the information from the discharge temperature sensor 18 exceeds the critical value, the liquid bypass control unit 357 opens the liquid bypass control valve 16B, and when the discharge temperature of the refrigerant is below the critical value, the liquid bypass control valve 16B closes.

[0074] That is, when the discharge temperature of the refrigerant before it is discharged from the compressor 11 and flows into the condenser 12 exceeds a critical value, the control device 30 opens the liquid bypass control valve 16B. When the discharge temperature is equal to or lower than the critical value, the liquid bypass control valve 16B is closed or remains closed.

[0075] In this embodiment, the liquid bypass control unit 357 adjusts the opening of the liquid bypass control valve 16B to below the critical value based on the difference between the discharge temperature and the critical value when the refrigerant discharge temperature exceeds a critical value. Specifically, the opening is adjusted by PID control. By using PID control in this way, the adjustment responsiveness of the discharge temperature can be improved, but the control method is not particularly limited.

[0076] In addition, as described above, the gas bypass control unit 358 obtains information on the evaporation pressure of the refrigerant flowing out of the evaporator 14 from the evaporation pressure acquisition unit 354, and controls the gas bypass control valve 17B based on the obtained evaporation pressure information.

[0077] Specifically, in the gas bypass control unit 358 of this embodiment, when the speed of the compressor 11 decreases to a lower limit and the evaporation pressure of the refrigerant is lower than the target evaporation pressure, the gas bypass control valve 17B is opened to make the evaporation pressure of the refrigerant reach or exceed the target evaporation pressure. When the gas bypass control valve 17B is open, the opening degree of the gas bypass control valve 17B is adjusted according to the difference between the evaporation pressure of the refrigerant and the target evaporation pressure; more specifically, the opening degree is adjusted by PID control. However, the control method of the gas bypass control valve 17B is not particularly limited.

[0078] (Operation when controlling the refrigeration unit) Next, an example of the operation of the control device 30 having the above configuration when controlling the refrigeration unit 10 will be described.

[0079] Figure 3A is a flowchart illustrating an example of the operation of the liquid bypass control valve 16B. Figure 3B is a flowchart illustrating an example of the operation of the compressor 11 and the gas bypass control valve 17B.

[0080] In the control device 30 of this embodiment, the control of the liquid bypass control valve 16B, the speed of the compressor 11 and the control of the gas bypass control valve 17B are performed in parallel; in other words, they are performed in different circuits.

[0081] In this embodiment, the control device 30 first starts the refrigeration unit 10 by controlling the speed of the compressor 11 to a reference speed. After this start-up, the control of the liquid bypass control valve 16B shown in FIG3A and the control of the speed of the compressor 11 and the gas bypass control valve 17B shown in FIG3B are initiated.

[0082] In the control of the liquid bypass control valve 16B shown in FIG3A, as shown in step S11, the control device 30 first monitors whether the discharge temperature of the refrigerant exceeds the critical value based on the information from the discharge temperature sensor 18.

[0083] When it is determined in step S11 that the discharge temperature exceeds the critical value (yes), in step S12, the control device 30 opens the liquid bypass control valve 16B by means of the liquid bypass control unit 357. At this time, the liquid bypass control unit 357 adjusts the opening degree of the liquid bypass control valve 16B by means of PID control, so that the discharge temperature is lower than the critical value according to the difference between the discharge temperature and the critical value.

[0084] On the other hand, if it is determined in step S11 that the discharge temperature does not exceed the critical value, i.e., below the critical value (No), the control device 30 closes the liquid bypass control valve 16B in step S13. At this time, the liquid bypass control valve 16B is closed when it is open, and remains closed when it is closed.

[0085] After the processing in steps S11 and S12, the control device 30 monitors in step S14 whether a stop command for the operation of the refrigeration unit 10 has been generated. If a stop command is generated (yes), the operation of the refrigeration unit 10 is stopped (end). On the other hand, if no stop command is generated (no), the process returns to step S11 and the discharge temperature is monitored.

[0086] On the other hand, in the control of the compressor speed 11 and the gas bypass control valve 17B shown in FIG. 3B, firstly, in step S21, the control device 30 adjusts the compressor speed 11 by means of the compressor control unit 356 so that the refrigerant evaporation pressure becomes the target evaporation pressure. When adjusting the speed, the compressor speed 11 is increased when the refrigerant evaporation pressure exceeds the target evaporation pressure, and the compressor speed 11 is decreased when the refrigerant evaporation pressure is lower than the target evaporation pressure.

[0087] After adjusting the speed in step S21 above, the control device 30 determines in step S22 whether the speed of the compressor 11 is at the lower limit. If it is not at the lower limit (No), then in step S23, the control device 30 closes the gas bypass control valve 17B. At this time, when the gas bypass control valve 17B is open, the gas bypass control valve 17B is closed, and when the gas bypass control valve 17B is closed, it remains closed.

[0088] On the other hand, when it is determined in step S22 that the compressor 11 speed is at the lower limit (yes), in step S24, the control device 30 determines whether the refrigerant evaporation pressure is lower than the target evaporation pressure. Then, when it is determined in step S24 that the refrigerant evaporation pressure is lower than the target evaporation pressure, the control device 30 performs control in step S25 to open the gas bypass control valve 17B so that the evaporation pressure matches the target evaporation pressure. This increases the evaporation pressure.

[0089] Then, after the processing in step S23, if the refrigerant evaporation pressure in step S24 is not lower than the target evaporation pressure, after the processing in step S25, and after the processing in step S25, the control device 30 monitors in step S26 whether an operation stop command for the refrigeration unit 10 has been generated. If an operation stop command has been generated (yes), the operation of the refrigeration unit 10 is stopped (end). On the other hand, if no operation stop command has been generated (no), the processing returns to step S21.

[0090] By performing the processes shown in Figures 3A and 3B as described above, in the refrigeration unit 10, the appropriate freezing capacity of the evaporator 14 can be ensured while avoiding excessive discharge temperature of the compressor 11. In addition, the risk of liquid backflow can be further suppressed.

[0091] That is, when the temperature of the fluid circulating through the fluid circulation device 20 changes (when the load changes), the difference between the detected evaporation pressure and the target evaporation pressure is used to determine whether the refrigeration capacity is excessive or insufficient, and the speed of the compressor 11 is adjusted to ensure appropriate refrigeration capacity. Specifically, when the detected evaporation pressure exceeds the target evaporation pressure, it is determined that the refrigeration capacity is insufficient, and the speed is increased. If the detected evaporation pressure is lower than the target evaporation pressure, it is determined that the refrigeration capacity is excessive, and the speed is decreased. Then, by eliminating the difference between the evaporation pressure and the target evaporation pressure, the control device 30 determines that appropriate refrigeration capacity has been ensured. In addition, excessively high discharge temperature caused by excessively high-pressure refrigerant flowing into the compressor 11, and excessively high discharge temperature caused by the increase in compression ratio due to low-pressure refrigerant flowing into the compressor 11 are suppressed. When the evaporation pressure is lower than the target evaporation pressure, the risk of liquid backflow increases, but since the evaporation pressure is controlled to the target evaporation pressure by adjusting the speed of the compressor 11, the risk of liquid backflow can also be suppressed. In this embodiment, the refrigerant flows downstream of the evaporator 14 and upstream of the compressor 11 in the refrigeration circuit 10A, and also flows downstream of the connection point at the downstream end of the liquid bypass flow path 16A. By adjusting the rotational speed of the compressor 11, the evaporation pressure of the refrigerant flowing as described above is made to reach a preset target evaporation pressure. In this configuration, when the refrigerant flows from the liquid bypass control valve 16B to the upstream side of the compressor 11, the target evaporation pressure for suppressing liquid backflow is controlled using the evaporation pressure of the refrigerant after it flows in from the liquid bypass control valve 16B as an indicator. This improves the reliability of liquid backflow suppression. Alternatively, as a variation, the refrigerant can flow downstream of the evaporator 14 and upstream of the compressor 11 in the refrigeration circuit 10A, and also flows upstream of the connection point at the downstream end of the liquid bypass flow path 16A. By adjusting the rotational speed of the compressor 11, the evaporation pressure of the refrigerant flowing as described above is made to reach a preset target evaporation pressure.

[0092] On the other hand, for example, when the discharge temperature rises because the evaporation pressure cannot be properly controlled by the aforementioned speed control due to sudden load changes, the liquid bypass control valve 16B can be used to reduce the refrigerant suction temperature of the compressor 11, thus preventing the compressor 11 from becoming too hot at the discharge temperature. However, by controlling the speed to control the evaporation pressure, the number of times the liquid bypass control valve 16B operates can be reduced. As a result, the risk of liquid backflow can be suppressed.

[0093] In this embodiment, the control of the liquid bypass control valve 16B, the speed of the compressor 11, and the control of the gas bypass control valve 17B are performed in different circuits. In this case, the responsiveness of each control can be improved. On the other hand, these controls can also be performed in a series of sequences.

[0094] (Operation when controlling the fluid circulation device) Next, FIG4 is a flowchart illustrating an example of the operation of the control device 30. Hereinafter, an example of the operation of the control device 30 (heater control unit 34) will be described with reference to FIG4.

[0095] The operation shown in Figure 4 begins when the state determination unit 33 determines that the fluid circulation device 20 is in no-load operation or no-load operation transition operation. When the operation begins, firstly, in step S101, the heater control unit 34 activates the heater 24.

[0096] Next, in step S102, the heater control unit 34 calculates the heating capacity Q for setting the temperature of the fluid passing through the evaporator 14 to the target temperature Tt according to the above formula (1).

[0097] Next, in step S103, the heater control unit 34 controls the heating capacity of the heater 24 according to the heating capacity Q calculated by formula (1). Specifically, the heater 24 is controlled to have a heating capacity of Q or higher.

[0098] Next, in step S104, the state determination unit 33 monitors whether no-load operation or no-load operation transition operation continues. Here, if no-load operation or no-load operation transition operation continues, the monitoring is repeated. On the other hand, if it is determined that no-load operation or no-load operation transition operation has ended, in step S105, the heater control unit 34 stops the heater 24 and ends the operation.

[0099] The determination of whether the operation has ended or has transitioned from no-load operation can be made by detecting the temperature information detected by the second temperature sensor 26, and determining that the temperature of the fluid flowing upstream of the heater 24 after passing the temperature control object T is above a specified temperature.

[0100] In the embodiment described above, in the control device 30 of the refrigeration unit 10, when the discharge temperature of the refrigerant discharged from the compressor 11 and flowing into the condenser 12 exceeds a critical value, the control device 30 opens the liquid bypass control valve 16B; when the discharge temperature falls below the critical value, the liquid bypass control valve 16B closes. Furthermore, the control device 30 adjusts the rotational speed of the compressor 11 to make the evaporation pressure of the refrigerant reach a preset target evaporation pressure. This refrigerant flows downstream of the evaporator 14 and upstream of the compressor 11 in the refrigeration circuit 10A, and downstream of the connection point at the downstream end of the liquid bypass flow path 16A. In the liquid bypass flow path 16A, the rotational speed of the compressor 11 is adjusted to make the evaporation pressure of the compressor 11 reach a preset target evaporation pressure.

[0101] In this case, when the temperature of the fluid circulating through the fluid circulation device 20 changes (when the load changes), the difference between the detected evaporation pressure and the target evaporation pressure is used to determine whether the refrigeration capacity is excessive or insufficient, and the speed of the compressor 11 is adjusted to ensure appropriate refrigeration capacity. Specifically, when the detected evaporation pressure exceeds the target evaporation pressure, it is determined that the refrigeration capacity is insufficient, and the speed is increased. If the detected evaporation pressure is lower than the target evaporation pressure, it is determined that the refrigeration capacity is excessive, and the speed is decreased. Then, by eliminating the difference between the evaporation pressure and the target evaporation pressure, the control device 30 determines that appropriate refrigeration capacity has been ensured. In addition, excessively high discharge temperature caused by excessively high-pressure refrigerant flowing into the compressor 11, and excessively high discharge temperature caused by the increase in compression ratio due to low-pressure refrigerant flowing into the compressor 11 are suppressed. When the evaporation pressure is lower than the target evaporation pressure, the risk of liquid backflow increases, but since the evaporation pressure is controlled to the target evaporation pressure by adjusting the speed of the compressor 11, the risk of liquid backflow can also be suppressed. For example, when the load increases, the evaporation pressure may exceed the target evaporation pressure. On the other hand, for example, when the load is reduced, the evaporation pressure may be lower than the target evaporation pressure.

[0102] On the other hand, for example, when the evaporation pressure cannot be properly controlled by the aforementioned speed control due to sudden load changes, resulting in an increase in discharge temperature, the liquid bypass control valve 16B can reduce the suction temperature of the refrigerant suction compressor 11, thus preventing the compressor 11 from becoming too hot at the discharge temperature. However, by controlling the speed to control the evaporation pressure, the number of times the liquid bypass control valve 16B operates can be reduced. As a result, the risk of liquid backflow can be suppressed.

[0103] Therefore, in this embodiment, by controlling the evaporation pressure and controlling the number of times the liquid bypass control valve 16B is operated, the risk of liquid backflow can be suppressed, the capacity of the liquid receiver can be reduced, or the liquid receiver can be omitted. This reduces the amount of refrigerant used.

[0104] Furthermore, in this embodiment, the operation of the liquid bypass control valve 16B is controlled based on the discharge temperature of the refrigerant from the compressor 11. In this case, the operation of the liquid bypass control valve 16B is less susceptible to interference, effectively suppressing frequent operation. This reduces the amount of refrigerant used. Until now, there have been circuits that use the compressor suction temperature as an indicator for liquid bypass, but in such configurations, the suction temperature is prone to change and may contain interference, thus tending to result in frequent liquid bypass. Therefore, appropriate heat exchange is required in the evaporator (to ensure refrigeration capacity) to ensure sufficient refrigerant reserves. Compared to such configurations, the configuration according to this embodiment more easily suppresses the amount of refrigerant used.

[0105] Therefore, according to this embodiment, even if the capacity of the liquid receiver is suppressed or the liquid receiver is not used, the liquid backflow of the refrigerant in the refrigeration unit 10 can be appropriately suppressed, and while suppressing the amount of refrigerant used, the excessive temperature rise of the refrigerant drawn into the compressor 11 can be appropriately suppressed, and appropriate cooling action can be performed.

[0106] Furthermore, in this embodiment, when the fluid circulation device 20 is determined to be operating without load or in a transitional state of no-load operation, the control device 30 activates the heater 24 via the heater control unit 34. In this case, the fluid circulated by the fluid circulation device 20 passes through the evaporator 14 at a low temperature, and the evaporation of the refrigerant on the refrigeration unit 10 side becomes insufficient (i.e., the evaporation pressure drops), thus preventing liquid backflow. Therefore, even when the capacity of the receiver is limited or the receiver is not used, liquid backflow of the refrigerant in the refrigeration unit 10 can be appropriately suppressed. As a result, the temperature control system 1 can be easily made more compact.

[0107] (Regarding the amount of refrigerant used) As described above, the refrigeration apparatus 10 according to this embodiment can appropriately suppress the excessive rise in temperature of the refrigerant drawn into the compressor 11 while suppressing the amount of refrigerant used, and can perform appropriate cooling operations. Specifically, when the rated freezing capacity of the refrigeration apparatus 10 is P (kW), the inventors confirmed that appropriate operation can be performed when the refrigerant loading amount (kg) is set to 0.155×P or more and 0.222×P or less. Furthermore, according to the inventors' findings, in general refrigeration apparatuses with a receiver and a receiving tank, (1.2×P) kg or more of refrigerant is used when the rated freezing capacity is P (kW). In contrast, the refrigeration apparatus 10 according to this embodiment can be said to significantly suppress the amount of refrigerant used. More specifically, in the refrigeration apparatus 10 of this embodiment with a rated freezing capacity of 4.5 (kW), appropriate operation can be performed even when the refrigerant loading amount is 0.70 kg or more and 1.0 kg or less. Specifically, the inventors manufactured and operated the refrigeration apparatus 10 of the above embodiment with a rated freezing capacity of 4.5 (kW) and a refrigerant filling amount of 0.75 kg, and confirmed that no adverse problems occurred.

[0108] The above rated freezing capacity is calculated in accordance with JIS B 8621:2011.

[0109] The embodiments of the present invention have been described above, but the present invention is not limited to the above embodiments and various modifications can be made to the above embodiments.

[0110] For example, in the fluid circulation device 20 of the above embodiment, when it is determined that the operation is under no-load or under-load transitional operation, the control device 30 activates the heater 24 via the heater control unit 34. Alternatively, when the return temperature of the fluid flowing downstream of the heater 24 and the fluid before passing through the evaporator 14 is lower than the target temperature set by the temperature setting unit 31, the control device 30 can activate the heater 24 via the heater control unit 34 to heat the fluid. That is, the heater 24 can be activated when the liquid backflow risk signal described in the above embodiment is generated.

[0111] In such a modified example, when the heater control unit 34 of the control device 30 sets the return temperature to Tb (°C), sets the target temperature to Tt (°C), sets the weight flow rate of the fluid flowing in the fluid circulation device 20 to m (kg / s), and sets the specific heat of the fluid to Cp (J / kg°C), the heating capacity Q used to set the return temperature Tb to the target temperature Tt can be calculated by the following formula (2). Q=m×Cp×(Tt-Tb)…(2)

[0112] Then, the control device 30 can control the heating capacity of the heater according to the heating capacity Q calculated by formula (2). At this time, the heater control unit 34 controls the heating capacity of the heater 24 to be a heating capacity greater than or equal to the heating capacity Q calculated by formula (2). [Simplified Explanation of the Diagram]

[0012] [Fig. 1] is a diagram showing the schematic configuration of a temperature control system according to an embodiment of the present invention. [Fig. 2] is a block diagram showing the functional configuration of the control device constituting the temperature control system shown in Fig. 1. [Fig. 3A] is a flowchart illustrating an example of the operation of the control device constituting the temperature control system shown in Fig. 1, that is, an example of the operation when controlling the liquid bypass control valve of the refrigeration unit. [Fig. 3B] is a flowchart illustrating an example of the operation of the control device constituting the temperature control system shown in Fig. 1, that is, an example of the operation when controlling the compressor speed and gas bypass control valve of the refrigeration unit. [Fig. 4] is a flowchart illustrating an example of the operation of the control device constituting the temperature control system shown in Fig. 1, that is, an example of the operation when controlling the flow circulation device.

Claims

1. A refrigeration apparatus comprising: a refrigeration circuit sequentially connected to a compressor, a condenser, an expansion valve, and an evaporator via piping to circulate refrigerant; a liquid bypass circuit comprising: a liquid bypass flow path branching from a downstream side of the condenser and an upstream side of the expansion valve in the refrigeration circuit, and connected to a downstream side of the evaporator and an upstream side of the compressor; and a liquid bypass control valve disposed in the liquid bypass flow path and controlling the flow of the refrigerant in the liquid bypass flow path; a control device controlling the rotational speed of the liquid bypass control valve and the compressor; and a gas bypass circuit comprising: a gas bypass flow path branching from a downstream side of the compressor and an upstream side of the condenser in the refrigeration circuit, and connected to a downstream side of the expansion valve and an upstream side of the evaporator; and a gas bypass control valve disposed in the gas bypass flow path and controlling the flow of the refrigerant in the gas bypass flow path; The aforementioned control device performs the following control: when the discharge temperature of the refrigerant discharged from the aforementioned compressor and flowing into the aforementioned condenser is greater than a critical value, the aforementioned liquid bypass control valve is opened; when the discharge temperature becomes below the aforementioned critical value, the aforementioned liquid bypass control valve is closed, and the speed of the aforementioned compressor is adjusted so that the evaporation pressure of the refrigerant flowing in the downstream side of the aforementioned evaporator in the aforementioned refrigeration circuit and in the upstream side of the aforementioned compressor, and in the downstream side of the connection position at the downstream end of the aforementioned liquid bypass flow path, becomes a preset target evaporation pressure; when the evaporation pressure of the aforementioned refrigerant is greater than the aforementioned target evaporation pressure, the aforementioned control device increases the speed of the aforementioned compressor; when the evaporation pressure of the aforementioned refrigerant is lower than the aforementioned target evaporation pressure, the aforementioned control device decreases the speed of the aforementioned compressor; when the speed of the aforementioned compressor decreases to a lower limit and the evaporation pressure of the aforementioned refrigerant is lower than the aforementioned target evaporation pressure, the aforementioned control device opens the aforementioned gas bypass control valve so that the evaporation pressure of the aforementioned refrigerant becomes above the aforementioned target evaporation pressure.

2. The refrigeration apparatus of claim 1, wherein the aforementioned control device adjusts the opening of the aforementioned liquid bypass control valve based on the difference between the aforementioned discharge temperature and the aforementioned critical value.

3. The refrigeration apparatus as described in claim 1, which does not include a liquid receiver.

4. The refrigeration apparatus of claim 2, wherein the aforementioned control device adjusts the opening of the aforementioned liquid bypass control valve by means of PID control based on the difference between the aforementioned discharge temperature and the aforementioned critical value, so that the discharge temperature of the aforementioned refrigerant is below the aforementioned critical value, and adjusts the speed of the aforementioned compressor by means of PI control, so that the evaporation pressure of the aforementioned refrigerant is the aforementioned target evaporation pressure.

5. The refrigeration apparatus of any one of claims 1 to 3, wherein the aforementioned control device adjusts the opening of the aforementioned gas bypass control valve based on the difference between the evaporation pressure of the aforementioned refrigerant and the aforementioned target evaporation pressure.

6. The refrigeration apparatus of any one of claims 1 to 3, wherein the rated refrigeration capacity is P (kW) and the amount of refrigerant (kg) is more than 0.155×P and less than 0.222×P.

7. The refrigeration apparatus of any one of claims 1 to 3, wherein the rated refrigeration capacity is 4.5 kW and the refrigerant filling amount is more than 0.70 kg and less than 1.0 kg.

8. A control method for a refrigeration apparatus, the refrigeration apparatus comprising: a refrigeration circuit, wherein a compressor, a condenser, an expansion valve, and an evaporator are sequentially connected via piping to circulate refrigerant; a liquid bypass circuit, comprising: a liquid bypass flow path branching from a downstream side of the condenser and an upstream side of the expansion valve in the refrigeration circuit, and connected to a downstream side of the evaporator and an upstream side of the compressor; and a liquid bypass control valve disposed in the liquid bypass flow path and controlling the flow of the refrigerant in the liquid bypass flow path; and a gas bypass circuit, comprising: a gas bypass flow path branching from a downstream side of the compressor and an upstream side of the condenser in the refrigeration circuit, and connected to a downstream side of the expansion valve and an upstream side of the evaporator; and a gas bypass control valve disposed in the gas bypass flow path and controlling the flow of the refrigerant in the gas bypass flow path; the control method comprising the step of: operating the refrigeration apparatus; When the discharge temperature of the refrigerant discharged from the compressor and flowing into the condenser is greater than a critical value, the liquid bypass control valve is opened; when the discharge temperature is below the critical value, the liquid bypass control valve is closed, and the compressor speed is adjusted so that the evaporation pressure of the refrigerant flowing in the downstream side of the evaporator in the refrigeration circuit, the upstream side of the compressor, and the downstream side of the connection at the downstream end of the liquid bypass flow path, becomes a predetermined target evaporation pressure; when the evaporation pressure of the refrigerant is greater than the target evaporation pressure, the compressor speed is increased; when the evaporation pressure of the refrigerant is lower than the target evaporation pressure, the compressor speed is decreased; when the compressor speed decreases to a lower limit and the evaporation pressure of the refrigerant is lower than the target evaporation pressure, the gas bypass control valve is opened so that the evaporation pressure of the refrigerant becomes above the target evaporation pressure.

9. A temperature control system comprising: a refrigeration apparatus as claimed in any one of claims 1 to 7; and a fluid circulation device that delivers fluid to a temperature-controlled object after heat exchange in the aforementioned evaporator, so that the fluid that has passed through the aforementioned temperature-controlled object undergoes heat exchange again in the aforementioned evaporator, and has a heater located downstream of the aforementioned temperature-controlled object and upstream of the aforementioned evaporator.

10. The temperature control system of claim 9, wherein the aforementioned control device further controls the aforementioned fluid circulation device, and when the state of the aforementioned fluid circulation device changes to no-load operation where the aforementioned fluid and the aforementioned temperature control object do not exchange heat, or transitions to no-load operation transition operation, the aforementioned heater is activated and the aforementioned fluid is heated by the aforementioned heater.

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