Refrigeration device

Abstract

A refrigeration device (1) is provided with: a low-stage refrigeration cycle (10) that circulates carbon dioxide as a low-stage cooling medium and cools an object to be cooled by means of a low-stage evaporator (14); a high-stage refrigeration cycle (20) that circulates a high-stage cooling medium; a cascade condenser (5) that has a low-stage condenser (5a) and a high-stage evaporator (5b), exchanges heat between the low-stage cooling medium and the high-stage cooling medium, and is capable of storing the liquefied low-stage cooling medium; a pressure sensor (15a) that measures the suction pressure of the low-stage compressor (11) in the low-stage refrigeration cycle (10); and a control device (30) that closes the solenoid valve (15) when the cooling of the object to be cooled in the low-stage refrigeration cycle (10) is not required, thereby recovering and storing the liquefied low-stage cooling medium in the cascade condenser (5), and stops the low-stage compressor (11) when the suction pressure measured by the pressure sensor (15a) becomes equal to or less than a lower limit value.

Description

Technical Field

[0001] The present invention relates to a refrigeration device, in particular to a refrigeration device comprising a low-level refrigeration cycle and a high-level refrigeration cycle. Background Art

[0002] It is known that a refrigeration device is provided that thermally connects a low-stage refrigeration cycle and a high-stage refrigeration cycle by means of a cascade condenser. For example, in Patent Document 1, as such a refrigeration device, a device that uses carbon dioxide (CO2) as a cooling medium for a low-stage refrigeration cycle is disclosed. The global warming potential (GWP) of CO2 used as a low-stage cooling medium is 1, and it is excellent in environmental friendliness. However, since the saturation pressure of CO2 is very high, cooling is required to suppress the pressure rise.

[0003] The refrigeration device of Patent Document 1 is equipped with a low-stage compressor, a low-stage condenser, a low-stage expansion valve, a low-stage evaporator, a low-stage liquid accumulator, a solenoid valve arranged between the low-stage liquid accumulator and the low-stage expansion valve, and a one-way valve arranged between the low-stage compressor and the low-stage condenser. In this refrigeration device, when the low-stage compressor is stopped, the solenoid valve is closed so that the low-stage cooling medium is collected between the solenoid valve and the one-way valve, and when the low-pressure of the low-stage refrigeration cycle drops below a predetermined value, the low-stage compressor is stopped. Thus, even if the low-stage compressor is in a stopped state, the low-stage cooling medium can be efficiently cooled and the pressure rise of the low-stage cooling medium can be suppressed by recovering the low-stage cooling medium into the low-stage liquid accumulator and cooling the low-stage liquid accumulator.

[0004] Patent document 1: Japanese Patent No. 5323023.

[0005] In the refrigeration device of Patent Document 1, a low-level liquid accumulator for storing a low-level cooling medium is provided. The low-level liquid accumulator is, for example, a large tank and is easily affected by heat from the outside. Therefore, an additional structure for cooling the low-level liquid accumulator is sometimes required, and the structure of the refrigeration device may become complicated. Summary of the invention

[0006] An object of the present invention is to efficiently cool a low-stage refrigerant in a refrigeration device including a low-stage refrigeration cycle and a high-stage refrigeration cycle, even when a low-stage compressor is stopped, using a simple structure.

[0007] The present invention provides a refrigeration device, characterized in that it comprises: a low-stage refrigeration cycle, which comprises a low-stage compressor, a low-stage condenser, a low-stage expansion valve, a low-stage evaporator, a solenoid valve arranged between the low-stage condenser and the low-stage expansion valve, and a one-way valve arranged between the low-stage compressor and the low-stage condenser, wherein carbon dioxide is used as a low-stage cooling medium and circulated, and an object is cooled by means of the low-stage evaporator; a high-stage refrigeration cycle, which comprises a high-stage compressor, a high-stage condenser, a high-stage expansion valve and a high-stage evaporator, and circulates the high-stage cooling medium; a cascade condenser, which comprises The aforementioned low-stage condenser and the aforementioned high-stage evaporator are provided for performing heat exchange between the aforementioned low-stage cooling medium and the aforementioned high-stage cooling medium and for storing the aforementioned low-stage cooling medium after liquefaction; a pressure sensor for measuring the suction pressure of the aforementioned low-stage compressor in the aforementioned low-stage refrigeration cycle; a control device for closing the aforementioned solenoid valve when cooling of the aforementioned object in the aforementioned low-stage refrigeration cycle is not required, thereby recovering and storing the liquefied aforementioned low-stage cooling medium in the aforementioned cascade condenser, and stopping the aforementioned low-stage compressor when the aforementioned suction pressure measured by the aforementioned pressure sensor becomes below a lower limit value.

[0008] According to this structure, before stopping the low-stage compressor, the low-stage cooling medium can be recovered and stored in the cascade condenser. The low-stage cooling medium in the cascade condenser is cooled by heat exchange with the high-stage cooling medium. Thus, even in a state where the low-stage compressor is stopped, the low-stage cooling medium can be efficiently cooled in one place (cascade condenser). In particular, since there is no need to additionally set up a low-stage liquid reservoir for separately storing the low-stage cooling medium and a structure for cooling the low-stage liquid reservoir, it can be achieved with a very simple structure.

[0009] The cascade condenser may be provided with a design pressure, the high-stage compressor may be capable of controlling the rotation speed, and the control device may control the rotation speed of the high-stage compressor after the low-stage compressor stops, so that the pressure of the low-stage cooling medium in the cascade condenser is lower than the design pressure by a certain range. For example, the design pressure may be a value greater than 0.3 MPaA and less than 0.4 MPaA, and the certain range may be greater than 0.05 MPaA and less than 0.1 MPaA.

[0010] According to this structure, by making the pressure of the low-level cooling medium in the cascade condenser lower than the design pressure, the cascade condenser can be used safely. In addition, by operating the high-level compressor in a manner that the value obtained by subtracting the pressure of the low-level cooling medium in the cascade condenser from the design pressure is less than a certain range, overcooling or insufficient cooling of the low-level cooling medium can be prevented, unnecessary power consumption can be avoided, and the desired cooling capacity can be achieved. For example, when the design pressure is 0.3 MPaA, the pressure of the low-level cooling medium in the cascade condenser can be set to 0.20-0.25 MPaA.

[0011] The aforementioned refrigeration device may also be equipped with an intermediate refrigeration cycle, the aforementioned intermediate refrigeration cycle having an intermediate compressor, an intermediate condenser, an intermediate expansion valve and an intermediate evaporator, so that the intermediate cooling medium circulates, the aforementioned cascade condenser may also have the aforementioned intermediate evaporator, to perform heat exchange between the aforementioned low-level cooling medium and the aforementioned intermediate cooling medium, and the aforementioned intermediate compressor has a smaller capacity than the aforementioned high-level compressor.

[0012] According to this structure, a high-level refrigeration cycle or an intermediate refrigeration cycle can be selected according to the cooling demand of the cooling object, thereby improving the operating efficiency of the refrigeration device. That is, when the cooling demand of the cooling object is high, the high-level refrigeration cycle can be used, and when the cooling demand of the cooling object is low, the intermediate refrigeration cycle can be used. Here, "capacity" refers to the performance value of the compressor specified in the design by the maximum motor output, maximum discharge pressure or maximum discharge volume. In simple terms, the maximum motor output, maximum discharge pressure or maximum discharge volume can also be used as the "capacity" of the compressor.

[0013] The control device may stop the high-stage compressor and start the middle-stage compressor after the low-stage compressor stops and when the rotation speed of the high-stage compressor reaches an allowable minimum value.

[0014] According to this structure, the high-stage refrigeration cycle or the intermediate-stage refrigeration cycle can be automatically selected according to the cooling demand of the cooling object, thereby improving the operating efficiency of the refrigeration device. That is, the high-stage refrigeration cycle can be used in normal operation, and the intermediate-stage refrigeration cycle can be switched to use as the cooling demand of the cooling object decreases.

[0015] The aforementioned cascade condenser may also be a shell and plate heat exchanger.

[0016] According to this configuration, a high-performance and compact cascade condenser can be realized.

[0017] Effects of the Invention

[0018] According to the present invention, in a refrigeration device including a low-stage refrigeration cycle and a high-stage refrigeration cycle, the low-stage refrigerant can be efficiently cooled with a simple structure even when the low-stage compressor is stopped. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is a cooling medium circuit diagram of the refrigeration device according to the first embodiment of the present invention.

[0020] Figure 2 It is a perspective view showing an example of the cascade condenser according to the first embodiment.

[0021] Figure 3 This is a flowchart showing control in the first embodiment.

[0022] Figure 4 Yes means Figure 3 Flow chart showing details of the low-stage refrigeration cycle shutdown.

[0023] Figure 5 It is a perspective view showing another example of the cascade condenser according to the first embodiment.

[0024] Figure 6 This is a refrigerant circuit diagram of a refrigeration device according to a second embodiment.

[0025] Figure 7 It is a perspective view showing an example of a cascade condenser according to the second embodiment.

[0026] Figure 8 This is a flowchart showing control according to the second embodiment. DETAILED DESCRIPTION

[0027] Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[0028] (First embodiment)

[0029] Reference Figure 1 The refrigeration device 1 of the first embodiment includes a low-stage refrigeration cycle 10, a high-stage refrigeration cycle 20, and a control device 30. The low-stage refrigeration cycle 10 and the high-stage refrigeration cycle 20 are thermally connected via a cascade condenser 5. That is, the refrigeration device 1 is a two-stage refrigeration device.

[0030] In the low-stage refrigeration cycle 10, CO2 (carbon dioxide) is used as the low-stage cooling medium. The low-stage refrigeration cycle 10 includes a low-stage compressor 11, an oil recovery device 12, a non-return valve 16, a low-stage condenser 5a, a solenoid valve 15, a low-stage expansion valve 13 and a low-stage evaporator 14 in sequence.

[0031] In the advanced refrigeration cycle 20, for example, HFO (hydrofluoroolefin), HFC (hydrofluorocarbon) or NH3 (ammonia) is used as the advanced cooling medium. In the present embodiment, R1234yf, which is a kind of HFO, is used as the advanced cooling medium. The advanced refrigeration cycle 20 includes an advanced compressor 21, an oil recovery device 22, an advanced condenser 23, an advanced expansion valve 24 and an advanced evaporator 5b in sequence.

[0032] The cascade condenser 5 includes a low-stage condenser 5a and a high-stage evaporator 5b, and is configured to perform heat exchange between the low-stage cooling medium and the high-stage cooling medium and to store the liquefied low-stage cooling medium. The structure of the cascade condenser 5 will be described in detail later.

[0033] First, the low-stage refrigeration cycle 10 will be described.

[0034] The low-stage compressor 11 is a screw type, which compresses the low-stage cooling medium. The low-stage compressor 11 has a low-stage motor 11a as a driving source, and the low-stage motor 11a is electrically connected to the converter 11b. Therefore, the current flowing through the low-stage compressor 11 can be adjusted by means of the converter 11b, thereby adjusting the rotation speed of the low-stage compressor 11. A maximum current value, i.e., a rated current value, is set for the low-stage motor 11a to ensure performance. The current flowing to the low-stage motor 11a via the converter 11b is continuously measured and transmitted to the control device 30, and in particular, its magnitude relationship with the rated current is monitored.

[0035] The low-stage compressor 11 sucks in the low-stage cooling medium from the suction port 11c, compresses it internally, and discharges it from the discharge port 11d. In the present embodiment, the low-stage compressor 11 is of the oil supply type, and the discharged low-stage cooling medium contains oil. The discharged low-stage cooling medium and oil are sent to the oil recovery device 12. In the oil recovery device 12, the oil is recovered. The recovered oil is supplied to the low-stage compressor 11 and recycled. The low-stage cooling medium after the oil is separated in the oil recovery device 12 is sent to the low-stage condenser 5a of the cascade condenser 5 through the one-way valve 16. The one-way valve 16 is a valve for preventing the backflow of the low-stage cooling medium. In addition, the low-stage compressor 11 is not limited to the oil supply type, and can also be an oil-free type.

[0036] The low-stage cooling medium is cooled and condensed in the low-stage condenser 5a of the cascade condenser 5. The low-stage cooling medium condensed in the low-stage condenser 5a is sent to the low-stage evaporator 14 through the solenoid valve 15 and the low-stage expansion valve 13.

[0037] The solenoid valve 15 is an on-off valve whose opening and closing is controlled by the control device 30. The solenoid valve 15 is provided between the low-stage condenser 5a and the low-stage expansion valve 13.

[0038] The low-stage expansion valve 13 is a pressure regulating valve. The low-stage refrigerant expands as it passes through the low-stage expansion valve 13 , and the expanded low-stage refrigerant is sent to the low-stage evaporator 14 .

[0039] In the low-stage evaporator 14, the low-stage cooling medium evaporates, and the evaporated low-stage cooling medium is sent to the low-stage compressor 11. The low-stage evaporator 14 has a function of cooling the object C (in the low-stage compressor 11) by heat exchange with the low-stage cooling medium. Figure 1 The cooling function is schematically shown in FIG.

[0040] In the low-stage refrigeration cycle 10, a pressure sensor 15a for measuring the suction pressure of the low-stage cooling medium in the low-stage compressor 11 and a pressure sensor 15b for measuring the pressure of the low-stage cooling medium at the low-stage condenser 5a are provided. The pressure values ​​measured by the pressure sensors 15a and 15b are transmitted to the control device 30.

[0041] Next, the high-stage refrigeration cycle 20 will be described.

[0042] In the present embodiment, the high-level compressor 21 is a screw type, which compresses the high-level cooling medium. The high-level compressor 21 has a high-level motor 21a as a driving source, and the high-level motor 21a is electrically connected to the converter 21b. Therefore, the high-level compressor 21 can adjust the rotation speed with the help of the converter 21b. A maximum current value, i.e., a rated current value, is set for the high-level motor 21a to ensure performance. The current flowing to the high-level motor 21a via the converter 21b is continuously measured and transmitted to the control device 30, and in particular, its relationship with the rated current is monitored. In addition, the high-level compressor 21 may also be, for example, a scroll type or a reciprocating type.

[0043] In the high-stage compressor 21, the high-stage cooling medium is sucked in from the suction port 21c, compressed inside, and discharged from the discharge port 21d. In the present embodiment, the high-stage compressor 21 is of the oil supply type, and the discharged high-stage cooling medium contains oil. The discharged high-stage cooling medium and oil are sent to the oil recovery device 22. In the oil recovery device 22, the oil is recovered. The recovered oil is supplied to the high-stage compressor 21 and recycled. The high-stage cooling medium after the oil is separated in the oil recovery device 22 is sent to the high-stage condenser 23. In addition, the high-stage compressor 21 is not limited to the oil supply type, and can also be an oil-free type.

[0044] In the high-stage condenser 23, the high-stage refrigerant is cooled and condensed by heat exchange with the low-temperature cooling water W. The high-stage refrigerant condensed in the high-stage condenser 23 is expanded by passing through the high-stage expansion valve 24 and is sent to the high-stage evaporator 5b of the cascade condenser 5. The high-stage expansion valve 24 is a pressure regulating valve.

[0045] The high-stage refrigerant is heated and evaporated in the high-stage evaporator 5 b of the cascade condenser 5 . The high-stage refrigerant evaporated in the high-stage evaporator 5 b is sent to the high-stage compressor 21 .

[0046] Reference Figure 2 In this embodiment, the cascade condenser 5 is a shell and plate heat exchanger.

[0047] In the present embodiment, the cascade condenser 5 has a cylindrical shell 5d. The shell 5d has a low-level cooling medium inlet 5e for introducing a low-level cooling medium, a low-level cooling medium outlet 5f for exporting the low-level cooling medium, a high-level cooling medium inlet 5g for introducing a high-level cooling medium, and a high-level cooling medium outlet 5h for exporting the high-level cooling medium. In the illustrated example, the low-level cooling medium inlet 5e is arranged at the upper part of the shell 5d, and the low-level cooling medium outlet 5f is arranged at the lower part of the shell 5d. The high-level cooling medium inlet 5g is arranged at the lower part of the side of the shell 5d, and the high-level cooling medium outlet 5h is arranged at the upper part of the same side of the shell 5d.

[0048] The cascade condenser 5 has a plurality of disc-shaped plates 5i in a housing 5d. The plurality of plates 5i are arranged concentrically and adjacent to each other. A groove is formed on the surface of each of the plurality of plates 5i, and a flow path for the cooling medium to pass through is formed by the groove. In addition, a through hole 5j is provided on each of the plurality of plates 5i. The through holes 5j of the plurality of plates 5i are aligned and arranged to form a flow path for the cooling medium.

[0049] The high-level cooling medium is introduced from the high-level cooling medium inlet 5g, flows through the through hole 5j and between the plurality of plates 5i, and is led out from the high-level cooling medium outlet 5h (see thin arrow A). The low-level cooling medium is introduced from the low-level cooling medium inlet 5e, flows through between and outside the plurality of plates 5i, and is led out from the low-level cooling medium outlet 5f (see thick arrow B). The high-level cooling medium and the low-level cooling medium flow in adjacent flow paths through the plurality of plates 5i in a non-mixed manner. Therefore, in the cascade condenser 5, heat exchange is performed between the high-level cooling medium and the low-level cooling medium, the high-level cooling medium is heated, and the low-level cooling medium is cooled.

[0050] Next, the control device 30 will be described.

[0051] The control device 30 performs calculation processing and overall control in the refrigeration device 1. The control device 30 includes, for example, a CPU (central processing unit) or an MPU (microprocessor) that works in conjunction with software to achieve a predetermined function. The control device 30 may also be composed of hardware circuits such as dedicated electronic circuits or reconfigurable electronic circuits designed to achieve a predetermined function, or may be composed of various semiconductor integrated circuits. As various semiconductor integrated circuits, for example, in addition to CPUs and MPUs, microcomputers, DSPs (digital signal processors), FPGAs (field programmable gate arrays), and ASICs (application-specific integrated circuits) are also included. In addition, the control device 30 may also include storage devices such as RAM (random access memory) and ROM (read-only memory). Specifically, the control device 30 may be composed of, for example, an information processing device such as a desktop computer, a notebook computer, a workstation, or a tablet terminal, or a printed circuit board with equivalent functions.

[0052] The control device 30 reads the stored data and programs and performs various calculations to realize predetermined functions. The programs executed by the control device 30 may be provided from the outside by using a communication unit that communicates in accordance with a predetermined communication standard, or may be stored in a portable storage medium.

[0053] The control device 30 can receive the cooling object C (refer to Figure 1 ) of the cooling demand. The cooling demand is automatically or manually input to the control device 30. When the cooling demand of the cooling object C is large, the cooling load of the refrigeration device 1 increases, and the control device 30 increases the rotation speed of the low-stage compressor 11. When the cooling demand of the cooling object C is small, the cooling load of the refrigeration device 1 decreases, and the control device 30 reduces the rotation speed of the low-stage compressor 11.

[0054] When cooling of the cooling object C in the low-stage refrigeration cycle 10 is not required (when the cooling demand becomes zero), the control device 30 closes the solenoid valve 15. When the solenoid valve 15 is closed, the piping on the upstream side of the solenoid valve 15 is gradually filled with the low-stage cooling medium. And, when the piping from the solenoid valve 15 to the cascade condenser 5 is filled with the low-stage cooling medium, the inside of the shell 5d of the cascade condenser 5 is gradually filled with the low-stage cooling medium from the bottom. In this way, by closing the solenoid valve 15, the liquefied low-stage cooling medium can be recovered and stored in the cascade condenser 5. In addition, since the flow paths of the high-stage cooling medium and the low-stage cooling medium in the cascade condenser 5 are spaced from each other, the high-stage cooling medium can flow in the cascade condenser 5 even when the low-stage cooling medium is stored in the cascade condenser 5.

[0055] The solenoid valve 15 may also be disposed at or near the low-level cooling medium outlet 5f, and the amount of low-level cooling medium stored in the pipe outside the cascade condenser 5 may be reduced by shortening the pipe distance from the solenoid valve 15 to the cascade condenser 5. Thus, more low-level cooling medium can be recovered into the cascade condenser 5. The cascade condenser 5 may also have a volume capable of storing almost all of the low-level cooling medium.

[0056] As the low-level cooling medium is accumulated in the cascade condenser 5 as described above, the suction pressure of the low-level compressor 11 decreases. The decrease in the suction pressure is detected by the pressure sensor 15a. If all the low-level cooling medium is recovered in the cascade condenser 5, the suction pressure becomes zero (vacuum state), which may have adverse effects. Therefore, it is confirmed in advance that the suction pressure is greater than zero and the pressure when most of the low-level cooling medium is recovered in the cascade condenser 5 is set as the lower limit value in the control device 30. When the suction pressure measured by the pressure sensor 15a becomes below the lower limit value, the control device 30 stops the low-level compressor 11. Thus, in the low-level refrigeration cycle 10, it is possible to perform an evacuation operation in which most of the low-level cooling medium is recovered and accumulated in the cascade condenser 5 while avoiding the vacuum state.

[0057] Refer to Figure 3 The control performed by the control device 30 will be described.

[0058] When the control device 30 starts the operation of the refrigeration device 1, it starts the high-stage compressor 21 (step S3-1), starts the low-stage compressor 11 (step S3-2), and performs normal operation to cool the cooling object C (step S3-3). Normal operation refers to the operation of cooling the cooling object C. Afterwards, the control device 30 receives the cooling demand of the cooling object C as described above, and determines whether the cooling demand is zero (step S3-4). When the cooling demand of the cooling object C is not zero (no: step S3-4), normal operation (step S3-3) continues. When the cooling demand of the cooling object C becomes zero (yes: step S3-4), the following low-stage refrigeration cycle stop operation (step S3-5) is executed.

[0059] Reference Figure 4 The details of stopping the operation of the above-mentioned low-stage refrigeration cycle are described.

[0060] During the low-stage refrigeration cycle stop operation, the electromagnetic valve 15 is closed (step S4-1). Thus, as described above, the evacuation operation for recovering and storing the low-stage cooling medium in the cascade condenser 5 is performed. Then, the evacuation operation of the low-stage compressor 11 is continued until the suction pressure P1 measured by the pressure sensor 15a becomes the lower limit value Pm set to prevent the vacuum state as described above, and after the suction pressure P1 is reduced to below the lower limit value Pm, the low-stage compressor 11 is stopped (step S4-2).

[0061] Next, it is determined whether the pressure P2 of the low-level cooling medium in the cascade condenser 5 measured by the pressure sensor 15b is less than the design pressure Ps of the cascade condenser 5 (step S4-3). For example, the design pressure Ps can be a value greater than 0.3 MPaA and less than 0.4 MPaA. When the pressure P2 is not less than the design pressure Ps (no: step S4-3), it is determined whether the current I flowing through the high-level motor 21a is less than the rated current Ir of the high-level motor 21a (step S4-4). When the current I is less than the rated current Ir (yes: step S4-4), the speed of the high-level compressor 21 is increased (step S4-5). If the speed of the high-level compressor 21 increases, the cooling capacity of the high-level refrigeration cycle 20 increases, the temperature of the low-level cooling medium in the cascade condenser 5 decreases, and the pressure P2 decreases. Therefore, the pressure P2 of the low-level cooling medium can be adjusted so that the pressure P2 is less than the design pressure Ps. Furthermore, when the current I is not less than the rated current Ir (No: step S4-4), the rotation speed of the high-stage compressor 21 is reduced (step S4-6) in order to operate below the rated current Ir.

[0062] When the pressure P2 is less than the design pressure Ps (yes: step S4-3), determine whether the value (Ps-P2) obtained by subtracting the pressure P2 from the design pressure Ps is less than a certain range ΔP (step S4-7). For example, the certain range ΔP can be greater than 0.05MPaA and less than 0.1MPaA. When the value (Ps-P2) obtained by subtracting the pressure P2 from the design pressure Ps is less than a certain range ΔP (yes: step S4-7), maintain the rotation speed of the high-stage compressor 21 (step S4-8). That is, maintain the cooling capacity of the high-stage refrigeration cycle 20 at the high-stage evaporator 5b, that is, maintain the cooling of the low-stage cooling medium in the cascade condenser 5. In addition, when the value (Ps-P2) obtained by subtracting the pressure P2 from the design pressure Ps is not less than a certain range ΔP (no: step S4-7), reduce the rotation speed of the high-stage compressor 21 (step S4-6). If the rotation speed of the high-stage compressor 21 decreases, the cooling capacity of the high-stage refrigeration cycle 20 decreases, the temperature of the low-stage cooling medium in the cascade condenser 5 increases, and the pressure P2 of the low-stage cooling medium increases. Therefore, the pressure P2 of the low-stage cooling medium can be adjusted so that the value (Ps-P2) obtained by subtracting the pressure P2 from the design pressure Ps is less than a certain range ΔP.

[0063] Thus, in this embodiment, after stopping the low-stage compressor 11, the control device 30 controls the rotation speed of the high-stage compressor 21 so that the pressure P2 of the low-stage cooling medium in the cascade condenser 5 is smaller than the design pressure Ps within a certain range ΔP. For example, when the design pressure Ps is 0.3 MPaA, the pressure P2 of the low-stage cooling medium in the cascade condenser 5 can be controlled within the range of 0.20 to 0.25 MPaA.

[0064] According to the refrigeration device 1 of this embodiment, the following effects are obtained.

[0065] Before stopping the low-stage compressor 11, the low-stage cooling medium can be recovered and stored in the cascade condenser 5. The low-stage cooling medium in the cascade condenser 5 is cooled by heat exchange with the high-stage cooling medium. Thus, even in the stopped state of the low-stage compressor 11, the low-stage cooling medium can be efficiently cooled in one place (the cascade condenser 5). In particular, since there is no need to additionally set up a low-stage liquid reservoir for separately storing the low-stage cooling medium and a structure for cooling the low-stage liquid reservoir, it can be achieved with a very simple structure.

[0066] Furthermore, by making the pressure P2 of the low-stage cooling medium lower than the design pressure Ps, the cascade condenser 5 can be safely used. By operating the high-stage compressor 21 in such a manner that the value (Ps-P2) obtained by subtracting the pressure P2 from the design pressure Ps is lower than a certain range ΔP, overcooling or insufficient cooling of the low-stage cooling medium can be prevented, unnecessary power consumption can be prevented, and the desired cooling capacity can be achieved.

[0067] Furthermore, since the cascade condenser 5 is a shell-and-plate heat exchanger, a high-performance and compact cascade condenser can be realized.

[0068] Reference Figure 5 As a modification, the cascade condenser 5 may be a shell and tube heat exchanger. The shell and tube heat exchanger is obtained by replacing the plurality of plates 5i of the shell and plate heat exchanger with a plurality of tubes 5k.

[0069] In the illustrated example, the low-stage cooling medium inlet 5e is arranged at the upper part of the shell 5d, and the low-stage cooling medium outlet 5f is arranged at the lower part of the shell 5d. The high-stage cooling medium inlet 5g is arranged at the side of the shell 5d, and the high-stage cooling medium outlet 5h is arranged at the opposite side. In addition, in this modified example, the cascade condenser 5 has a plurality of tubes 5k in the shell 5d. The plurality of tubes 5k extend substantially horizontally from the high-stage cooling medium inlet 5g to the high-stage cooling medium outlet 5h.

[0070] The high-level cooling medium is introduced from the high-level cooling medium inlet 5g, flows through the inner side of the plurality of tubes 5k, and is led out from the high-level cooling medium outlet 5h (see thin arrow A). The low-level cooling medium is introduced from the low-level cooling medium inlet 5e, flows through the outer side of the plurality of tubes 5k, and is led out from the low-level cooling medium outlet 5f (see thick arrow B). In this modified example, the low-level cooling medium can also be stored in the shell 5d in a manner that the high-level cooling medium and the low-level cooling medium are not mixed, and the flow paths of the high-level cooling medium and the low-level cooling medium are separated. Therefore, in the cascade condenser 5, heat exchange is performed between the high-level cooling medium and the low-level cooling medium, the high-level cooling medium is heated, and the low-level cooling medium is cooled.

[0071] As shown in the above-mentioned embodiment and modification examples, the form of the cascade condenser 5 is not particularly limited, and various forms of heat exchangers capable of storing a low-level cooling medium can be used as the cascade condenser 5 .

[0072] (Second embodiment)

[0073] Figure 6 The refrigeration device 1 of the second embodiment shown is different from the first embodiment in that an intermediate refrigeration cycle 40 is additionally provided. Except for the parts related to this, it is substantially the same as the first embodiment. Therefore, the description of the parts already shown in the first embodiment may be omitted.

[0074] The refrigeration device 1 of the present embodiment includes a low-stage refrigeration cycle 10 , a high-stage refrigeration cycle 20 , and an intermediate-stage refrigeration cycle 40 . The low-stage refrigeration cycle 10 , the high-stage refrigeration cycle 20 , and the intermediate-stage refrigeration cycle 40 are thermally connected via a cascade condenser 5 .

[0075] In the intermediate refrigeration cycle 40, for example, HFO (hydrofluoroolefin), HFC (hydrofluorocarbon) or NH3 (ammonia) is used as the intermediate cooling medium. In the present embodiment, R1234yf, which is a kind of HFO, is used as the intermediate cooling medium. Therefore, the intermediate cooling medium is of the same type as the high-level cooling medium (the same in the present embodiment). In addition, the intermediate refrigeration cycle 40 includes an intermediate compressor 41, an oil recovery device 42, an intermediate condenser 43, an intermediate expansion valve 44, and an intermediate evaporator 5c in sequence.

[0076] The cascade condenser 5 is configured to include a low-level condenser 5a, a high-level evaporator 5b, and an intermediate-level evaporator 5c, and performs heat exchange between the low-level cooling medium and the high-level cooling medium, and between the low-level cooling medium and the intermediate cooling medium, and can store liquefied low-level cooling medium. The structure of the cascade condenser 5 will be described in detail later.

[0077] In the present embodiment, the intermediate compressor 41 is of a screw type, which compresses the intermediate cooling medium. The intermediate compressor 41 has an intermediate motor 41a as a driving source, and the converter 41b is electrically connected to the intermediate motor 41a. Therefore, the intermediate compressor 41 can adjust the rotation speed with the aid of the converter 41b. The maximum current value, i.e., the rated current value, which guarantees the performance is set on the intermediate motor 41a. The current flowing to the intermediate motor 41a via the converter 41b is continuously measured and transmitted to the control device 30, and its magnitude relationship with the rated current is particularly monitored. In addition, the intermediate compressor 41 may also be, for example, a scroll type or a reciprocating type.

[0078] In the intermediate compressor 41, the intermediate cooling medium is sucked in from the suction port 41c, compressed inside, and discharged from the discharge port 41d. In the present embodiment, the intermediate compressor 41 is of the oil supply type, and the discharged intermediate cooling medium contains oil. The discharged intermediate cooling medium and oil are sent to the oil recovery device 42. In the oil recovery device 42, the oil is recovered. The recovered oil is supplied to the intermediate compressor 41 and recycled. The intermediate cooling medium from which the oil is separated in the oil recovery device 42 is sent to the intermediate condenser 43. In addition, the intermediate compressor 41 is not limited to the oil supply type, and can also be an oil-free type.

[0079] The intermediate compressor 41 has a smaller capacity than the high-stage compressor 21. Here, "capacity" refers to the compressor performance value specified in the design by the maximum motor output, maximum discharge pressure or maximum discharge volume. In simple terms, the maximum motor output, maximum discharge pressure or maximum discharge volume can also be regarded as the "capacity" of the compressor.

[0080] In the intermediate condenser 43, the intermediate cooling medium is cooled and condensed by heat exchange with the low-temperature cooling water W. The intermediate cooling medium condensed in the intermediate condenser 43 is expanded by the intermediate expansion valve 44 and sent to the intermediate evaporator 5c of the cascade condenser 5. The intermediate expansion valve 44 is a pressure regulating valve.

[0081] The intermediate cooling medium is heated and evaporated in the intermediate evaporator 5 c of the cascade condenser 5 . The intermediate cooling medium evaporated in the intermediate evaporator 5 c is sent to the intermediate compressor 41 .

[0082] Reference Figure 7 In this embodiment, the cascade condenser 5 is a shell and tube heat exchanger.

[0083] In this embodiment, the cascade condenser 5 has a plurality of tubes 5k and 51 in a shell 5d. The plurality of tubes 5k extend substantially horizontally from the high-stage coolant inlet 5g to the high-stage coolant outlet 5h, and the plurality of tubes 51 extend horizontally from the intermediate coolant inlet 5m to the intermediate coolant outlet 5n.

[0084] The high-level cooling medium is introduced from the high-level cooling medium inlet 5g, flows through the inner sides of the plurality of tubes 5k, and is led out from the high-level cooling medium outlet 5h (refer to the thin arrow A). The low-level cooling medium is introduced from the low-level cooling medium inlet 5e, flows through the outer sides of the plurality of tubes 5k and 5l, and is led out from the low-level cooling medium outlet 5f (refer to the thick arrow B). The intermediate cooling medium is introduced from the intermediate cooling medium inlet 5m, flows through the inner sides of the plurality of tubes 5l, and is led out from the intermediate cooling medium outlet 5n (refer to the thin arrow C). Therefore, in the cascade condenser 5, heat exchange is performed between the high-level cooling medium and the low-level cooling medium, and heat exchange is performed between the intermediate cooling medium and the low-level cooling medium. Specifically, the high-level cooling medium is heated, and the low-level cooling medium is cooled. In addition, the intermediate cooling medium is heated, and the low-level cooling medium is cooled.

[0085] In the present embodiment, when the electromagnetic valve 15 is closed, the low-level cooling medium gradually accumulates in the piping on the upstream side of the electromagnetic valve 15. Furthermore, when the piping from the electromagnetic valve 15 to the cascade condenser 5 is filled with the low-level cooling medium, the interior of the cascade condenser 5 is gradually filled with the low-level cooling medium from the bottom. In this way, by closing the electromagnetic valve 15, the liquefied low-level cooling medium can be recovered and stored in the cascade condenser 5. In addition, since the flow paths of the high-level cooling medium and the low-level cooling medium are spaced apart from each other in the cascade condenser 5, the high-level cooling medium can flow in the cascade condenser 5 even when the low-level cooling medium is stored in the cascade condenser 5. Similarly, since the flow paths of the intermediate cooling medium and the low-level cooling medium are spaced apart from each other in the cascade condenser 5, the intermediate cooling medium can flow in the cascade condenser 5 even when the low-level cooling medium is stored in the cascade condenser 5.

[0086] The solenoid valve 15 may be disposed at or near the low-level cooling medium outlet 5f, and the amount of low-level cooling medium stored in the piping outside the cascade condenser 5 may be reduced by shortening the piping distance from the solenoid valve 15 to the cascade condenser 5. Thus, more low-level cooling medium can be recovered into the cascade condenser 5. In this case, the cascade condenser 5 may have a volume capable of storing almost all of the low-level cooling medium.

[0087] In the refrigeration device 1 of the present embodiment, if the high-stage refrigeration cycle 20 is used, when the cooling capacity of the refrigeration device 1 becomes excessive relative to the cooling demand, the intermediate-stage refrigeration cycle 40 is used. Figure 3 The details of the low-stage refrigeration cycle stop operation (step S3-5) are different from those in the first embodiment.

[0088] Reference Figure 8 The details of the low-stage refrigeration cycle stop operation in this embodiment will be described.

[0089] In the low-stage refrigeration cycle stop operation of the present embodiment, the electromagnetic valve 15 is closed (step S8-1). Then, the low-stage compressor 11 is continuously operated until the suction pressure P1 measured by the pressure sensor 15a becomes the lower limit value Pm. After the suction pressure P1 is reduced to below the lower limit value Pm, the low-stage compressor 11 is stopped (step S8-2). That is, similar to the first embodiment, an evacuation operation for recovering and storing the low-stage cooling medium in the cascade condenser 5 is performed.

[0090] Next, determine whether the pressure P2 of the low-stage cooling medium in the cascade condenser 5 measured by the pressure sensor 15b is less than the design pressure Ps of the cascade condenser 5 (step S8-3). For example, the design pressure Ps can be a value greater than 0.3MPaA and less than 0.4MPaA. When the pressure P2 is not less than the design pressure Ps (no: step S8-3), determine whether the current I1 flowing to the low-stage motor 11a is less than the rated current Ir of the low-stage motor 11a (step S8-4). When the current I1 is less than the rated current Ir (yes: step S8-4), the rotation speed of the high-stage compressor 21 increases (step S8-5). When the current I1 is not less than the rated current Ir (no: step S8-4), the rotation speed of the high-stage compressor 21 is reduced (step S8-6).

[0091] In addition, when the pressure P2 is less than the design pressure Ps (yes: step S8-3), the control device 30 determines whether the value (Ps-P2) obtained by subtracting the pressure P2 from the design pressure Ps is less than a certain range ΔP (step S8-7). For example, the certain range ΔP can be greater than 0.05MPaA and less than 0.1MPaA. When the value (Ps-P2) obtained by subtracting the pressure P2 from the design pressure Ps is less than the certain range ΔP (yes: step S8-7), the rotation speed of the high-stage compressor 21 is maintained (step S8-8). When the value (Ps-P2) obtained by subtracting the pressure P2 from the design pressure Ps is not less than the certain range ΔP (no: step S8-7), the rotation speed of the high-stage compressor 21 is reduced (step S8-6), and it is determined whether the rotation speed R of the high-stage compressor 21 is consistent with the allowable minimum value Rm (step S8-9). The allowable minimum value Rm is the lower limit of the allowable range of the rotation speed adjustment of the high-stage compressor 21. When the rotation speed R of the high-stage compressor 21 is consistent with the allowable minimum value Rm (yes: step S8-9), the high-stage compressor 21 is stopped and the intermediate compressor 41 is started (step S8-10). When the rotation speed R of the high-stage compressor 21 is inconsistent with the allowable minimum value Rm (no: step S8-9), no special processing is performed.

[0092] Thus, in this embodiment, the control device 30 stops the high-stage compressor 21 and starts the intermediate-stage compressor 41 if the rotation speed R of the high-stage compressor 21 reaches the allowable minimum value Rm after the low-stage compressor 11 is stopped. That is, the thermal connection object of the low-stage refrigeration cycle 10 is switched from the high-stage refrigeration cycle 20 to the intermediate refrigeration cycle 40.

[0093] According to the refrigeration device 1 of this embodiment, since the high-stage refrigeration cycle 20 or the intermediate refrigeration cycle 40 can be selected according to the cooling demand of the cooling object C, the operation efficiency of the refrigeration device 1 can be improved. That is, when the cooling demand of the cooling object C is high, the high-stage refrigeration cycle 20 can be used, and when the cooling demand of the cooling object C is low, the intermediate refrigeration cycle 40 can be used.

[0094] Furthermore, since the high-stage refrigeration cycle 20 or the intermediate refrigeration cycle 40 can be automatically selected according to the cooling demand of the cooling object C, the operation efficiency of the refrigeration device 1 can be improved. That is, the high-stage refrigeration cycle 20 can be used in normal operation, and the intermediate refrigeration cycle 40 can be switched to use as the cooling demand of the cooling object C decreases.

[0095] In this embodiment, the case where the intermediate compressor 41 is started when the low-stage compressor 11 is stopped is described. For example, when the capacity of the high-stage compressor 21 becomes insufficient when the low-stage compressor 11 and the high-stage compressor 21 are started, or when the cooling demand of the cooling object C is low when the low-stage compressor 11 and the high-stage compressor 21 are started, the intermediate compressor 41 may be started. According to this structure, the operating efficiency of the refrigeration device 1 can be improved.

[0096] In summary, although the specific embodiments and modifications of the present invention have been described above, the present invention is not limited to the above-described embodiments and can be implemented with various modifications within the scope of the present invention.

[0097] The contents of the present invention are summarized as follows.

[0098] (Method 1)

[0099] A refrigeration device, comprising:

[0100] A low-stage refrigeration cycle, comprising a low-stage compressor, a low-stage condenser, a low-stage expansion valve, a low-stage evaporator, a solenoid valve disposed between the low-stage condenser and the low-stage expansion valve, and a one-way valve disposed between the low-stage compressor and the low-stage condenser, wherein carbon dioxide is circulated as a low-stage cooling medium, and a cooling object is cooled by means of the low-stage evaporator;

[0101] Advanced refrigeration cycle, with advanced compressor, advanced condenser, advanced expansion valve and advanced evaporator, so that advanced cooling medium circulates;

[0102] A cascade condenser, comprising the aforementioned low-stage condenser and the aforementioned high-stage evaporator, performs heat exchange between the aforementioned low-stage cooling medium and the aforementioned high-stage cooling medium, and can store the aforementioned low-stage cooling medium after liquefaction;

[0103] a pressure sensor for measuring the suction pressure of the aforementioned low-stage compressor in the aforementioned low-stage refrigeration cycle;

[0104] The control device closes the solenoid valve when cooling of the cooling object in the low-stage refrigeration cycle is not required, thereby recovering and storing the liquefied low-stage cooling medium in the cascade condenser, and stops the low-stage compressor when the suction pressure measured by the pressure sensor becomes below a lower limit value.

[0105] (Method 2)

[0106] The refrigeration device as described in method 1,

[0107] The aforementioned cascade condenser is specified with a design pressure.

[0108] The aforementioned advanced compressor can control the speed,

[0109] After the low-stage compressor stops, the control device controls the rotation speed of the high-stage compressor so that the pressure of the low-stage cooling medium in the cascade condenser is lower than the design pressure within a certain range.

[0110] (Method 3)

[0111] The refrigeration device as described in method 2,

[0112] The above-mentioned design pressure is a value not less than 0.3MPaA and not more than 0.4MPaA.

[0113] The aforementioned certain range is 0.05 MPaA or more and 0.1 MPaA or less.

[0114] (Method 4)

[0115] A refrigeration device as described in any one of methods 1 to 3,

[0116] The intermediate refrigeration cycle is provided, wherein the intermediate refrigeration cycle has an intermediate compressor, an intermediate condenser, an intermediate expansion valve and an intermediate evaporator, so that the intermediate cooling medium circulates.

[0117] The cascade condenser further comprises the intermediate evaporator for performing heat exchange between the low-level cooling medium and the intermediate cooling medium.

[0118] The aforementioned mid-level compressor has a smaller capacity than the aforementioned high-level compressor.

[0119] (Method 5)

[0120] The refrigeration device as described in mode 4,

[0121] After the low-stage compressor stops, and if the rotation speed of the high-stage compressor reaches a minimum allowable value, the control device stops the high-stage compressor and starts the middle-stage compressor.

[0122] (Method 6)

[0123] A refrigeration device as described in any one of methods 1 to 5,

[0124] The aforementioned cascade condenser is a shell and plate heat exchanger.

[0125] This application claims priority based on Japanese Patent Application No. 2022-143973, filed on September 9, 2022. The entire disclosure of Japanese Patent Application No. 2022-143973 is incorporated herein by reference.

[0126] Description of Reference Numerals

[0127] 1 Refrigeration unit

[0128] 5 Cascade condenser

[0129] 5a Low-stage condenser

[0130] 5b Advanced Evaporator

[0131] 5c Intermediate Evaporator

[0132] 5d housing

[0133] 5e Low-level cooling medium inlet

[0134] 5f Low-level cooling medium outlet

[0135] 5g Advanced Cooling Medium Inlet

[0136] 5h high-grade cooling medium outlet

[0137] 5i Board

[0138] 5j Through hole

[0139] 5k, 5l tube

[0140] 5m Intermediate cooling medium inlet

[0141] 5n Intermediate cooling medium outlet

[0142] 10 Low-stage refrigeration cycle

[0143] 11 Low-level compressor

[0144] 11a Low-level motor

[0145] 11b Converter

[0146] 11c Inlet

[0147] 11d Exhaust port

[0148] 12 Oil recovery device

[0149] 13 Low-stage expansion valve

[0150] 14 Low-level evaporator

[0151] 15 Solenoid valve

[0152] 15a, 15b pressure sensor

[0153] 20 Advanced Refrigeration Cycle

[0154] 21 Advanced Compressor

[0155] 21a Advanced Motor

[0156] 21b Converter

[0157] 21c Inlet

[0158] 21d Exhaust port

[0159] 22 Oil recovery device

[0160] 23 Advanced Condenser

[0161] 24 Advanced Expansion Valve

[0162] 30 Control device

[0163] 40 Intermediate Refrigeration Cycle

[0164] 41 Intermediate compressor

[0165] 41a Intermediate Motor

[0166] 41b Converter

[0167] 41c Inlet

[0168] 41d Exhaust port

[0169] 42 Oil recovery device

[0170] 43 Intermediate Condenser

[0171] 44 Intermediate expansion valve.

Claims

1. A refrigeration device, comprising: A low-stage refrigeration cycle, comprising a low-stage compressor, a low-stage condenser, a low-stage expansion valve, a low-stage evaporator, a solenoid valve disposed between the low-stage condenser and the low-stage expansion valve, and a one-way valve disposed between the low-stage compressor and the low-stage condenser, wherein carbon dioxide is circulated using carbon dioxide as a low-stage cooling medium, and a cooling object is cooled by means of the low-stage evaporator; Advanced refrigeration cycle, with advanced compressor, advanced condenser, advanced expansion valve and advanced evaporator, so that advanced cooling medium circulates; A cascade condenser, comprising the aforementioned low-stage condenser and the aforementioned high-stage evaporator, performs heat exchange between the aforementioned low-stage cooling medium and the aforementioned high-stage cooling medium, and can store the aforementioned low-stage cooling medium after liquefaction; a pressure sensor for measuring the suction pressure of the aforementioned low-stage compressor in the aforementioned low-stage refrigeration cycle; The control device closes the solenoid valve when cooling of the cooling object in the low-stage refrigeration cycle is not required, thereby recovering and storing the liquefied low-stage cooling medium in the cascade condenser, and stops the low-stage compressor when the suction pressure measured by the pressure sensor becomes below a lower limit value.

2. The refrigeration device according to claim 1, characterized in that: The aforementioned cascade condenser is specified with a design pressure. The aforementioned advanced compressor can control the speed, The control device controls the rotation speed of the high-stage compressor so that after the low-stage compressor stops, the pressure of the low-stage cooling medium in the cascade condenser is lower than the design pressure within a certain range.

3. The refrigeration device according to claim 2, characterized in that: The above-mentioned design pressure is a value not less than 0.3MPaA and not more than 0.4MPaA. The aforementioned certain range is 0.05 MPaA or more and 0.1 MPaA or less.

4. The refrigeration device according to any one of claims 1 to 3, characterized in that: The intermediate refrigeration cycle is provided, wherein the intermediate refrigeration cycle has an intermediate compressor, an intermediate condenser, an intermediate expansion valve and an intermediate evaporator, so that the intermediate cooling medium circulates. The cascade condenser further comprises the intermediate evaporator for performing heat exchange between the low-level cooling medium and the intermediate cooling medium. The aforementioned mid-level compressor has a smaller capacity than the aforementioned high-level compressor.

5. The refrigeration device according to claim 4, characterized in that: The control device is configured to stop the high-stage compressor and start the intermediate-stage compressor after the low-stage compressor stops and when the rotation speed of the high-stage compressor reaches the minimum allowable value.

6. The refrigeration device according to any one of claims 1 to 3, characterized in that: The aforementioned cascade condenser is a shell and plate heat exchanger.

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