JP7299395B1 - refrigeration equipment - Google Patents

Abstract

A refrigeration system including a low temperature refrigeration cycle and a high temperature refrigeration cycle efficiently cools a low temperature refrigerant with a simple configuration even when a low temperature compressor is stopped. A refrigeration system (1) includes a low-order refrigeration cycle (10) that circulates carbon dioxide as a low-order refrigerant and cools an object to be cooled in a low-order evaporator (14), and a high-order refrigeration cycle (10) that circulates a high-order refrigerant. A cascade condenser 5 having a cycle 20, a low-level condenser 5a and a high-level evaporator 5b, performing heat exchange between the low-level refrigerant and the high-level refrigerant, and capable of storing the liquefied low-level refrigerant; A pressure sensor 15a for measuring the suction pressure of the low-order compressor 11 in the refrigerating cycle 10, and a pressure sensor 15a in the cascade capacitor 5 by closing the electromagnetic valve 15 when cooling of the object to be cooled in the low-order refrigerating cycle 10 becomes unnecessary. A controller 30 recovers and stores the liquefied low-concentration refrigerant, and stops the low-concentration compressor 11 when the suction pressure measured by the pressure sensor 15a becomes equal to or lower than the lower limit value. [Selection drawing] Fig. 1

Description

TECHNICAL FIELD The present invention relates to a refrigeration system, and more particularly to a refrigeration system including a low-order refrigeration cycle and a high-order refrigeration cycle.

A refrigeration system is known in which a low-order refrigeration cycle and a high-order refrigeration cycle are thermally connected by a cascade condenser. For example, Patent Literature 1 discloses such a refrigeration system that employs carbon dioxide (CO2) as a refrigerant in a low-level refrigeration cycle. CO2 used as a low-concentration refrigerant has a GWP (global warming potential) of 1 and is excellent in environmental friendliness. However, since the saturation pressure of CO2 is very high, cooling is required to suppress the pressure rise.

The refrigeration system of Patent Document 1 includes a low-order compressor, a low-order condenser, a low-order expansion valve, a low-order evaporator, a low-order liquid receiver, and arranged between the low-order liquid receiver and the low-order expansion valve. and a check valve positioned between the low-pressure compressor and the low-pressure condenser. In the refrigeration system, when the low-pressure compressor is stopped, the low-pressure refrigerant is collected between the solenoid valve and the check valve by closing the solenoid valve, and the low pressure of the low-pressure refrigeration cycle is below a predetermined value. When it becomes, the low energy compressor is stopped. As a result, even when the low-level compressor is stopped, the low-level refrigerant is recovered to the low-level liquid receiver, and the low-level liquid receiver is cooled, thereby efficiently cooling the low-level refrigerant and accompanying low temperature. This is intended to suppress the pressure rise of the original refrigerant.

Japanese Patent No. 5323023

The refrigerating apparatus of Patent Document 1 is provided with a low-concentration liquid receiver for storing low-concentration refrigerant. A low-level liquid receiver is, for example, a large tank, and is easily affected by heat from the outside. Therefore, an additional configuration may be required to cool the low-level liquid receiver, which may complicate the configuration of the refrigeration system.

An object of the present invention is to efficiently cool a low temperature refrigerant with a simple configuration in a refrigeration system including a low temperature refrigeration cycle and a high temperature refrigeration cycle even when a low temperature compressor is stopped.

The present invention provides a low-level compressor, a low-level condenser, a low-level expansion valve, a low-level evaporator, a solenoid valve disposed between the low-level condenser and the low-level expansion valve, and the low-level compression a low-level refrigeration cycle that has a check valve arranged between the machine and the low-level condenser, circulates carbon dioxide as a low-level refrigerant, and cools an object with the low-level evaporator; , a high-level refrigeration cycle having a high-level compressor, a high-level condenser, a high-level expansion valve, and a high-level evaporator, and circulating a high-level refrigerant, and the low-level condenser and the high-level evaporator a cascade condenser capable of performing heat exchange between the low-level refrigerant and the high-level refrigerant and storing the liquefied low-level refrigerant; and measuring the suction pressure of the low-level compressor in the low-level refrigeration cycle. a pressure sensor, and by closing the solenoid valve when cooling of the object in the low-level refrigeration cycle becomes unnecessary, recovering and storing the liquefied low-level refrigerant in the cascade condenser; a control device that stops the low-level compressor when the measured suction pressure becomes equal to or lower than the lower limit; The intermediate refrigerant cycle for circulating the original refrigerant is further provided, the cascade condenser further includes the intermediate evaporator, performs heat exchange between the low refrigerant and the intermediate refrigerant, and the intermediate compressor , to provide a refrigeration system having a smaller capacity than the high-pressure compressor ;

According to this configuration, the low-level refrigerant can be recovered and stored in the cascade condenser before stopping the low-level compressor. The low temperature refrigerant in the cascade condenser is cooled by heat exchange with the high temperature refrigerant. As a result, even when the low temperature compressor is stopped, the low temperature refrigerant can be efficiently cooled at one location (cascade condenser). In particular, since there is no need to additionally provide a low-level liquid receiver for separately storing the low-level refrigerant and a configuration for cooling the low-level liquid receiver, the configuration can be realized with a very simple configuration. In addition, since the high-level refrigeration cycle or the middle-level refrigeration cycle can be selected according to the cooling demand of the object to be cooled, the operating efficiency of the refrigeration system can be improved. That is, when the cooling demand of the object to be cooled is high, the high-order refrigeration cycle can be used, and when the cooling demand of the object to be cooled is low, the middle-order refrigeration cycle can be used. Here, the "capacity" is a performance value of the compressor determined by design from the maximum motor output, maximum discharge pressure, maximum discharge amount, or the like. For simplicity, the maximum motor output, maximum discharge pressure, or maximum discharge amount may be used as the "capacity" of the compressor.

A design pressure may be specified for the cascade condenser, the high-pressure compressor may be controllable in rotation speed, and the control device may control the pressure in the cascade condenser after the low-pressure compressor stops. The rotation speed of the high-pressure compressor may be controlled so that the pressure of the low-pressure refrigerant is lower than the design pressure within a certain range. For example, the design pressure may be 0.3 MPaA or more and 0.4 MPaA or less, and the certain range may be 0.05 MPaA or more and 0.1 MPaA or less.

According to this configuration, the cascade condenser can be used safely by making the pressure of the low-concentration refrigerant in the cascade condenser lower than the design pressure. In addition, by operating the high-pressure compressor so that the value obtained by subtracting the pressure of the low-pressure refrigerant in the cascade condenser from the design pressure is less than a certain range, excessive cooling or insufficient cooling of the low-pressure refrigerant can be prevented. The above power consumption can be prevented and the desired cooling capacity can be achieved. For example, when the design pressure is 0.3 MPaA, the pressure of the low-concentration refrigerant in the cascade condenser may be 0.20-0.25 MPaA.

After stopping the low-level compressor and when the rotation speed of the high-level compressor reaches a permissible minimum value, the control device stops the high-level compressor and starts the middle-level compressor. good too.

According to this configuration, the high-level refrigerating cycle or the middle-level refrigerating cycle can be automatically selected according to the cooling demand of the object to be cooled, so that the operating efficiency of the refrigeration system can be improved. That is, the high-level refrigerating cycle is used in normal operation, and can be switched to the middle-level refrigerating cycle as the cooling demand for the object to be cooled decreases.

The cascade condenser may be a shell and plate heat exchanger.

According to this configuration, a high-performance and compact cascade capacitor can be realized.

According to the present invention, in a refrigeration system including a low temperature refrigeration cycle and a high temperature refrigeration cycle, the low temperature refrigerant can be efficiently cooled with a simple configuration even when the low temperature compressor is stopped.

1 is a refrigerant circuit diagram of a refrigeration system according to a first embodiment of the present invention; FIG. 1 is a perspective view showing an example of a cascade capacitor in the first embodiment; FIG. 4 is a flowchart showing control in the first embodiment; FIG. 4 is a flow chart showing details of low-level refrigeration cycle stop operation of FIG. 3 ; FIG. FIG. 4 is a perspective view showing another example of the cascade capacitor in the first embodiment; The refrigerant circuit diagram of the refrigerating device which concerns on 2nd Embodiment. The perspective view which shows an example of the cascade capacitor in 2nd Embodiment. 8 is a flowchart showing control in the second embodiment;

Embodiments of the present invention will be described below with reference to the accompanying drawings.

(First embodiment)
Referring to FIG. 1 , a refrigeration system 1 according to the first embodiment includes a low temperature refrigeration cycle 10 , a high temperature refrigeration cycle 20 and a control device 30 . The low-order refrigerating cycle 10 and the high-order refrigerating cycle 20 are thermally connected by the cascade condenser 5 . That is, the refrigerating device 1 is a dual refrigerating device.

The low-concentration refrigeration cycle 10 uses CO2 (carbon dioxide) as a low-concentration refrigerant. The low-level refrigeration cycle 10 includes a low-level compressor 11, an oil recovery device 12, a check valve 16, a low-level condenser 5a, a solenoid valve 15, a low-level expansion valve 13, and a low-level evaporator 14. and in that order.

The high-order refrigeration cycle 20 uses, for example, HFO (hydrofluoroolefin), HFC (hydrofluorocarbon), or NH3 (ammonia) as a high-order refrigerant. In this embodiment, R1234yf, which is a type of HFO, is used as the high-level refrigerant. The high-level refrigeration cycle 20 includes a high-level compressor 21, an oil recovery device 22, a high-level condenser 23, a high-level expansion valve 24, and a high-level evaporator 5b in this order.

The cascade condenser 5 has a low temperature condenser 5a and a high temperature evaporator 5b, and is configured to perform heat exchange between the low temperature refrigerant and the high temperature refrigerant and to store the liquefied low temperature refrigerant. . The details of the structure of the cascade capacitor 5 will be described later.

First, the low-order refrigerating cycle 10 will be described.

The low-concentration compressor 11 is of a screw type and compresses the low-concentration refrigerant. The low-order compressor 11 has a low-order motor 11a serving as a drive source, and an inverter 11b is electrically connected to the low-order motor 11a. Therefore, the current flowing through the low-order compressor 11 can be adjusted by the inverter 11b, and thus the rotation speed of the low-order compressor 11 can be adjusted. A rated current value, which is the maximum current value at which performance is guaranteed, is set for the low-level motor 11a. The current flowing through the low-level motor 11a via the inverter 11b is constantly measured and transmitted to the control device 30, and in particular the magnitude relationship with the rated current is monitored.

The low-concentration compressor 11 sucks the low-concentration refrigerant from the suction port 11c, compresses it inside, and discharges it from the discharge port 11d. In this embodiment, the low-concentration compressor 11 is an oil-fed type, and the discharged low-concentration refrigerant contains oil. The discharged low-level refrigerant and oil are sent to the oil recovery device 12 . Oil is recovered in the oil recovery device 12 . The recovered oil is supplied to the low energy compressor 11 and recycled. The low-level refrigerant from which the oil is separated by the oil collector 12 passes through the check valve 16 and is sent to the low-level condenser 5 a of the cascade condenser 5 . The check valve 16 is a valve for preventing backflow of the low-concentration refrigerant. It should be noted that the low-level compressor 11 is not limited to the lubricating type, and may be of the non-lubricating type.

In the low-level condenser 5a of the cascade condenser 5, the low-level refrigerant is cooled and condensed. The low-level refrigerant condensed in the low-level condenser 5 a passes through the solenoid valve 15 and the low-level expansion valve 13 and is sent to the low-level evaporator 14 .

The solenoid valve 15 is an open/close valve whose opening/closing is controlled by the control device 30 . The solenoid valve 15 is arranged between the low-order condenser 5 a and the low-order expansion valve 13 .

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

The low-level evaporator 14 evaporates the low-level refrigerant, and the evaporated low-level refrigerant is sent to the low-level compressor 11 . The low-level evaporator 14 has a function of cooling an object C (schematically shown in FIG. 1) through heat exchange with a low-level refrigerant.

The low-order refrigeration cycle 10 is provided with a pressure sensor 15a for measuring the suction pressure of the low-order refrigerant in the low-order compressor 11 and a pressure sensor 15b for measuring the pressure of the low-order refrigerant in the low-order condenser 5a. . The pressure values measured by pressure sensors 15 a and 15 b are transmitted to control device 30 .

Next, the high-level refrigeration cycle 20 will be described.

In this embodiment, the high-level compressor 21 is of a screw type and compresses the high-level refrigerant. The high-level compressor 21 has a high-level motor 21a serving as a drive source, and an inverter 21b is electrically connected to the high-level motor 21a. Therefore, the high-level compressor 21 can adjust the rotation speed by the inverter 21b. A rated current value, which is a maximum current value at which performance is guaranteed, is set for the high-level motor 21a. The current flowing through the high-level motor 21a via the inverter 21b is constantly measured and transmitted to the control device 30, and in particular the magnitude relationship with the rated current is monitored. Note that the high-level compressor 21 may be of a scroll type or a reciprocating type, for example.

The high-level compressor 21 sucks the high-level refrigerant from the suction port 21c, compresses it inside, and discharges it from the discharge port 21d. In this embodiment, the high-level compressor 21 is of an oil-fed type, and the discharged high-level refrigerant contains oil. The discharged high -grade refrigerant and oil are sent to the oil recovery device 22 . Oil is recovered in the oil recovery device 22 . The collected oil is supplied to the high-pressure compressor 21 and recycled. The high-level refrigerant from which the oil is separated by the oil recovery device 22 is sent to the high-level condenser 23 . In addition, the high-level compressor 21 is not limited to the lubricating type, and may be a non-lubricating type.

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

In the high-level evaporator 5b of the cascade condenser 5, the high-level refrigerant is heated and evaporated. The high-level refrigerant evaporated in the high-level evaporator 5 b is sent to the high-level compressor 21 .

Referring to FIG. 2, in this embodiment, cascade condenser 5 is a shell-and-plate heat exchanger.

In this embodiment, the cascade capacitor 5 has a cylindrical casing 5d. The casing 5d includes a low-level refrigerant inlet 5e for introducing the low-level refrigerant, a low-level refrigerant outlet 5f for leading out the low-level refrigerant, a high-level refrigerant inlet 5g for introducing the high-level refrigerant, and a high-level refrigerant for leading out the high-level refrigerant. and a source refrigerant outlet 5h. In the illustrated example, the low-concentration refrigerant inlet 5e is arranged at the upper portion of the casing 5d, and the low-concentration refrigerant outlet 5f is arranged at the lower portion of the casing 5d. The high-concentration refrigerant inlet 5g is arranged at the lower portion of the side surface of the casing 5d, and the high-concentration refrigerant outlet 5h is arranged at the upper portion of the same side surface of the casing 5d.

The cascade capacitor 5 has a plurality of disk-shaped plates 5i inside a casing 5d. A plurality of plates 5i are arranged concentrically and adjacent to each other. A groove is formed in the surface of each of the plurality of plates 5i, and the groove constitutes a channel through which the coolant passes. A through hole 5j is provided in each of the plurality of plates 5i. The through holes 5j of the plurality of plates 5i are aligned and constitute a flow path for the coolant.

The high-level refrigerant is introduced from the high-level refrigerant inlet 5g, flows through the through hole 5j and between the plurality of plates 5i, and is discharged from the high-level refrigerant outlet 5h (see thin arrow A). The low-level refrigerant is introduced from the low-level refrigerant inlet 5e, flows between and outside the plurality of plates 5i, and is discharged from the low-level refrigerant outlet 5f (see thick arrow B). The high-concentration refrigerant and the low-concentration refrigerant flow in channels adjacent to each other via a plurality of plates 5i so as not to mix. Therefore, in the cascade condenser 5, heat is exchanged between the high-level refrigerant and the low-level refrigerant, the high-level refrigerant is heated, and the low-level refrigerant is cooled.

Next, the control device 30 will be explained.

The control device 30 performs arithmetic processing and overall control in the refrigeration system 1 . The control device 30 includes, for example, a CPU (Central Processing Unit) or MPU (Micro Processing Unit) that cooperates with software to realize a predetermined function. The control device 30 may be configured with a hardware circuit such as a dedicated electronic circuit or a reconfigurable electronic circuit designed to achieve a predetermined function, or may be configured with various semiconductor integrated circuits. good. Examples of various semiconductor integrated circuits include CPUs, MPUs, microcomputers, DSPs (Digital Signal Processors), FPGAs (Field Programmable Gate Arrays), and ASICs (Application Specific Integrated Circuits). 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 can be configured by, 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 having equivalent functions.

The control device 30 reads stored data and programs and performs various arithmetic processing, thereby realizing a predetermined function. The program executed by the control device 30 may be provided externally using a communication unit or the like that performs communication according to a predetermined communication standard, or may be stored in a portable recording medium.

The control device 30 can receive a cooling demand for the object to be cooled C (see FIG. 1). The cooling demand is automatically or manually input to the controller 30 . When the cooling demand of the object C to be cooled is high, the cooling load of the refrigeration system 1 is high, and the control device 30 increases the rotation speed of the low-order compressor 11 . When the cooling demand of the object C to be cooled is small, the cooling load of the refrigerating device 1 becomes low, and the control device 30 reduces the rotational speed of the low-order compressor 11 .

The control device 30 closes the electromagnetic valve 15 when cooling of the object C to be cooled in the low-level refrigeration cycle 10 becomes unnecessary (when the cooling demand becomes zero). When the electromagnetic valve 15 is closed, the piping on the upstream side of the electromagnetic valve 15 is gradually filled with the low-concentration refrigerant. Then, when the pipe from the electromagnetic valve 15 to the cascade condenser 5 is filled with the low-concentration refrigerant, the inside of the casing 5d of the cascade condenser 5 is gradually filled with the low-concentration refrigerant from below. By closing the electromagnetic valve 15 in this way, the liquefied low-level refrigerant can be recovered and stored in the cascade condenser 5 . In the cascade condenser 5, the flow paths of the high-concentration refrigerant and the low-concentration refrigerant are separated from each other. can.

The solenoid valve 15 may be arranged at the low-concentration refrigerant outlet 5f or near the low-concentration refrigerant outlet 5f. The amount of original refrigerant may be reduced. As a result, a large amount of low-concentration refrigerant can be recovered in the cascade condenser 5 . The cascade condenser 5 may have a volume capable of storing substantially all of the low-concentration refrigerant.

As the low-level refrigerant is stored in the cascade condenser 5 as described above, the suction pressure of the low-level compressor 11 decreases. The reduction in suction pressure is detected by the pressure sensor 15a. When all of the low-concentration refrigerant is collected in the cascade condenser 5, the suction pressure becomes zero (vacuum state), which may cause adverse effects. Therefore, the pressure at which the suction pressure is greater than zero and most of the low-concentration refrigerant is recovered in the cascade condenser 5 is confirmed in advance, and the pressure is set in the controller 30 as the lower limit. The control device 30 stops the low-pressure compressor 11 when the suction pressure measured by the pressure sensor 15a becomes equal to or lower than the lower limit value. As a result, in the low-concentration refrigeration cycle 10, a pump-down operation is performed in which most of the low-concentration refrigerant can be recovered and stored in the cascade condenser 5 while avoiding a vacuum state.

Control by the control device 30 will be described with reference to FIG. 3 as well.

When the operation of the refrigeration system 1 is started, the control device 30 activates the high-level compressor 21 (step S3-1), activates the low-level compressor 11 (step S3-2), and cools the object C to be cooled. normal operation is performed (step S3-3). The normal operation is an operation for cooling the object C to be cooled. After that, the control device 30 receives the cooling demand for the object to be cooled C as described above, and determines whether or not the cooling demand is zero (step S3-4). If the cooling demand for the object to be cooled C is not zero (N: step S3-4), normal operation is continued (step S3-3). When the cooling demand for the object to be cooled C becomes zero (Y: step S3-4), the following low-order refrigeration cycle stop operation is executed (step S3-5).

With reference to FIG. 4, the details of the above-described low refrigeration cycle stop operation will be described.

In the low temperature refrigerating cycle stop operation, the solenoid valve 15 is closed (step S4-1). As a result, the pump-down operation for collecting and storing the low-concentration refrigerant in the cascade condenser 5 is performed as described above. Then, the pump-down operation of the low-pressure compressor 11 is continued until the suction pressure P1 measured by the pressure sensor 15a reaches the lower limit Pm for preventing a vacuum state as described above, and the suction pressure P1 is lowered to the lower limit Pm or less. After reducing the pressure, the low-pressure compressor 11 is stopped (step S4-2).

Next, it is determined whether or not the pressure P2 of the low-concentration refrigerant 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 of 0.3 MPaA or more and 0.4 MPaA or less. If the pressure P2 is not less than the design pressure Ps (N: step S4-3), it is determined whether or not 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). If the current I is less than the rated current Ir (Y: step S4-4), the rotation speed of the high-level compressor 21 is increased (step S4-5). When the rotation speed of the high-order compressor 21 is increased, the cooling capacity of the high-order refrigeration cycle 20 is increased, the temperature of the low-order refrigerant in the cascade condenser 5 is lowered, and the pressure P2 is lowered. Therefore, the pressure P2 of the low-concentration refrigerant can be adjusted so that the pressure P2 is less than the design pressure Ps. Also, if the current I is not less than the rated current Ir (N: step S4-4), the rotation speed of the high-level compressor 21 is reduced to operate at the rated current Ir or less (step S4-6).

If the pressure P2 is less than the design pressure Ps (Y: step S4-3), it is determined whether the value obtained by subtracting the pressure P2 from the design pressure Ps (Ps-P2) is less than a certain range ΔP (step S4-7). For example, the certain range ΔP can be greater than or equal to 0.05 MPaA and less than or equal to 0.1 MPaA. If the value obtained by subtracting the pressure P2 from the design pressure Ps (Ps-P2) is less than a certain range ΔP (Y: step S4-7), the rotational speed of the high-level compressor 21 is maintained (step S4-8 ). That is, the cooling capacity of the high-order evaporator 5b of the high-order refrigeration cycle 20 is maintained, that is, the cooling of the low-order refrigerant in the cascade condenser 5 is maintained. Further, when the value obtained by subtracting the pressure P2 from the design pressure Ps (Ps-P2) is not less than the certain range ΔP (N: step S4-7), the rotational speed of the high-level compressor 21 is reduced (step S4- 6). When the rotational speed of the high-order compressor 21 is reduced, the cooling capacity of the high-order refrigeration cycle 20 is lowered, the temperature of the low-order refrigerant in the cascade condenser 5 rises, and the pressure P2 of the low-order refrigerant rises. Therefore, the pressure P2 of the low-concentration refrigerant can be adjusted so that the value obtained by subtracting the pressure P2 from the design pressure Ps (Ps−P2) is less than the certain range ΔP.

Thus, in the present embodiment, after the low-pressure compressor 11 is stopped, the control device 30 controls the high-pressure refrigerant so that the pressure P2 of the low-pressure refrigerant in the cascade condenser 5 becomes lower than the design pressure Ps within a certain range ΔP. It controls the rotational speed of the compressor 21 . For example, when the design pressure Ps is 0.3 MPaA, the pressure P2 of the low-level refrigerant in the cascade condenser 5 may be controlled within the range of 0.20-0.25 MPaA.

According to the refrigerating apparatus 1 according to this embodiment, the following effects are obtained.

Low-level refrigerant can be recovered and stored in the cascade condenser 5 before the low-level compressor 11 is stopped. The low temperature refrigerant in the cascade condenser 5 is cooled by heat exchange with the high temperature refrigerant. As a result, even when the low temperature compressor 11 is stopped, the low temperature refrigerant can be efficiently cooled at one location (the cascade condenser 5). In particular, since there is no need to additionally provide a low-level liquid receiver for separately storing the low-level refrigerant and a configuration for cooling the low-level liquid receiver, the configuration can be realized with a very simple configuration.

Also, the cascade condenser 5 can be used safely by making the pressure P2 of the low-concentration refrigerant smaller than the design pressure Ps. By operating the high-level compressor 21 so that the value obtained by subtracting the pressure P2 from the design pressure Ps (Ps-P2) is less than a certain range ΔP, excessive cooling or insufficient cooling of the low-level refrigerant can be prevented. The above power consumption can be prevented and the desired cooling capacity can be achieved.

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

Referring to FIG. 5, as a variant, 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.

In the illustrated example, the low-concentration refrigerant inlet 5e is arranged at the upper portion of the casing 5d, and the low-concentration refrigerant outlet 5f is arranged at the lower portion of the casing 5d. The high-concentration refrigerant inlet 5g is arranged on the side surface of the casing 5d, and the high-concentration refrigerant outlet 5h is arranged on the opposite side surface. Moreover, in this modification, the cascade capacitor 5 has a plurality of tubes 5k inside the casing 5d. The plurality of tubes 5k extends substantially horizontally from the high-level refrigerant inlet 5g to the high-level refrigerant outlet 5h.

The high-level refrigerant is introduced from the high-level refrigerant inlet 5g, flows inside the plurality of tubes 5k, and is discharged from the high-level refrigerant outlet 5h (see thin arrow A). The low-level refrigerant is introduced from the low-level refrigerant inlet 5e, flows outside the plurality of tubes 5k, and is discharged from the low-level refrigerant outlet 5f (see thick arrow B). Also in this modification, the low-level refrigerant can be stored in the casing 5d without mixing the high-level refrigerant and the low-level refrigerant, and the flow paths of the high-level refrigerant and the low-level refrigerant are separated. Therefore, in the cascade condenser 5, heat is exchanged between the high-level refrigerant and the low-level refrigerant, the high-level refrigerant is heated, and the low-level refrigerant is cooled.

As shown in the above embodiments and modifications, the form of the cascade condenser 5 is not particularly limited, and various forms of heat exchangers capable of storing the low-concentration refrigerant can be used for the cascade condenser 5 .

(Second embodiment)
A refrigerating apparatus 1 according to the second embodiment shown in FIG. 6 is different from the first embodiment in that it additionally includes an intermediate refrigerating cycle 40 . Except for this part, it is substantially the same as the first embodiment. Therefore, the description of the parts shown in the first embodiment may be omitted.

A refrigerating apparatus 1 according to this embodiment includes a low-level refrigerating cycle 10 , a high-level refrigerating cycle 20 , and a middle-level refrigerating cycle 40 . The low refrigeration cycle 10 , the high refrigeration cycle 20 and the middle refrigeration cycle 40 are thermally connected by the cascade capacitor 5 .

In the intermediate refrigeration cycle 40, for example, HFO (hydrofluoroolefin), HFC (hydrofluorocarbon), or NH3 (ammonia) is used as the intermediate refrigerant. In this embodiment, R1234yf, which is a type of HFO, is used as the intermediate refrigerant. Therefore, the mid-level refrigerant is of the same type (the same in this embodiment) as the high-level refrigerant. Further, the intermediate refrigeration cycle 40 includes a intermediate compressor 41, an oil recovery device 42, an intermediate condenser 43, an intermediate expansion valve 44, and an intermediate evaporator 5c in this order.

The cascade condenser 5 has a low temperature condenser 5a, a high temperature evaporator 5b, and a middle temperature evaporator 5c, and performs heat exchange between the low temperature refrigerant and the high temperature refrigerant and between the low temperature refrigerant and the middle temperature refrigerant. It is configured to be able to store the liquefied low-concentration refrigerant while performing heat exchange between them. The details of the structure of the cascade capacitor 5 will be described later.

In this embodiment, the intermediate compressor 41 is of a screw type and compresses intermediate refrigerant. The intermediate compressor 41 has an intermediate motor 41a serving as a drive source, and an inverter 41b is electrically connected to the intermediate motor 41a. Therefore, the intermediate compressor 41 can adjust the rotation speed by the inverter 41b. A rated current value, which is a maximum current value at which performance is guaranteed, is set for the intermediate motor 41a. The current flowing through the intermediate motor 41a via the inverter 41b is constantly measured and transmitted to the control device 30, and in particular the magnitude relationship with the rated current is monitored. Note that the intermediate compressor 41 may be of a scroll type or a reciprocating type, for example.

In the middle source compressor 41, the middle source refrigerant is sucked from the suction port 41c, internally compressed, and discharged from the discharge port 41d. In this embodiment, the intermediate compressor 41 is an oil-fed type, and the discharged intermediate refrigerant contains oil. The discharged intermediate refrigerant and oil are sent to the oil recovery device 42 . Oil is recovered in the oil recovery device 42 . The recovered oil is supplied to the intermediate compressor 41 and recycled. The intermediate refrigerant from which the oil is separated by the oil collector 42 is sent to the intermediate condenser 43 . Note that the intermediate compressor 41 is not limited to the lubricating type, and may be of the non-lubricating type.

The middle-range compressor 41 has a smaller capacity than the high-range compressor 21 . Here, the "capacity" is a performance value of the compressor determined by design from the maximum motor output, maximum discharge pressure, maximum discharge amount, or the like. For simplicity, the maximum motor output, maximum discharge pressure, or maximum discharge amount may be used as the "capacity" of the compressor.

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

In the intermediate evaporator 5c of the cascade condenser 5, the intermediate refrigerant is heated and evaporated. The intermediate refrigerant evaporated in the intermediate evaporator 5 c is sent to the intermediate compressor 41 .

Referring to FIG. 7, in this embodiment, cascade condenser 5 is a shell-and-tube heat exchanger.

In this embodiment, the cascade condenser 5 has a plurality of tubes 5k, 5l inside a casing 5d. The plurality of tubes 5k extends substantially horizontally from the high-level refrigerant inlet 5g to the high-level refrigerant outlet 5h, and the plurality of tubes 5l extends horizontally from the medium-level refrigerant inlet 5m to the medium-level refrigerant outlet 5n.

The high-level refrigerant is introduced from the high-level refrigerant inlet 5g, flows inside the plurality of tubes 5k, and is discharged from the high-level refrigerant outlet 5h (see thin arrow A). The low-level refrigerant is introduced from the low-level refrigerant inlet 5e, flows through the outsides of the plurality of tubes 5k and 5l, and is discharged from the low-level refrigerant outlet 5f (see thick arrow B). The intermediate refrigerant is introduced from the intermediate refrigerant inlet 5m, flows inside the plurality of tubes 5l, and is discharged from the intermediate refrigerant outlet 5n (see thin arrow C). Therefore, in the cascade condenser 5, heat exchange is performed between the high-level refrigerant and the low-level refrigerant, and heat exchange is performed between the intermediate-level refrigerant and the low-level refrigerant. Specifically, the high temperature refrigerant is heated and the low temperature refrigerant is cooled. In addition, the intermediate refrigerant is heated and the low refrigerant is cooled.

Also in this embodiment, when the solenoid valve 15 is closed, the low-concentration refrigerant gradually accumulates in the pipe upstream of the solenoid valve 15 . Then, when the pipe from the solenoid valve 15 to the cascade condenser 5 is filled with the low-concentration refrigerant, the inside of the cascade condenser 5 is gradually filled with the low-concentration refrigerant from below. By closing the electromagnetic valve 15 in this way, the liquefied low-level refrigerant can be recovered and stored in the cascade condenser 5 . In the cascade condenser 5, the flow paths of the high-concentration refrigerant and the low-concentration refrigerant are separated from each other. can. Similarly, since the flow paths of the medium-level refrigerant and the low-level refrigerant are separated from each other in the cascade condenser 5, the medium-level refrigerant can flow through the cascade condenser 5 even when the low-level refrigerant is stored in the cascade condenser 5. can be done.

The solenoid valve 15 may be arranged at the low-concentration refrigerant outlet 5f or near the low-concentration refrigerant outlet 5f. The amount of original refrigerant may be reduced. As a result, a large amount of low-concentration refrigerant can be recovered in the cascade condenser 5 . At this time, the cascade condenser 5 may have a volume capable of storing substantially all of the low-concentration refrigerant.

In the refrigeration system 1 of the present embodiment, the intermediate refrigeration cycle 40 is used when the cooling capacity of the refrigeration system 1 becomes excessive with respect to the cooling demand if the high refrigeration cycle 20 is used. Therefore, in this embodiment, the details of the low-order refrigerating cycle stop operation (step S3-5) in FIG. 3 are different from those in the first embodiment.

With reference to FIG. 8, the details of the low-order refrigeration cycle stop operation in this embodiment will be described.

In the low temperature refrigerating cycle stop operation in this embodiment, the electromagnetic valve 15 is closed (step S8-1). Then, the operation of the low-level compressor 11 is continued until the suction pressure P1 measured by the pressure sensor 15a reaches the lower limit value Pm, and the low-level compressor 11 is stopped after reducing the pressure until the suction pressure P1 becomes equal to or lower than the lower limit value Pm. (step S8-2). That is, as in the first embodiment, a pump-down operation is performed to collect and store the low-concentration refrigerant in the cascade condenser 5 .

Next, it is determined whether or not the pressure P2 of the low-concentration refrigerant 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 of 0.3 MPaA or more and 0.4 MPaA or less. If the pressure P2 is not less than the design pressure Ps (N: step S8-3), it is determined whether or not the current I1 flowing through the low-level motor 11a is less than the rated current Ir of the low-level motor 11a (step S8 -4). If the current I1 is less than the rated current Ir (Y: step S8-4), the rotational speed of the high-level compressor 21 is increased (step S8-5). If the current I1 is not less than the rated current Ir (N: step S8-4), the rotation speed of the high-order compressor 21 is reduced (step S8-6).

Further, when the pressure P2 is less than the design pressure Ps (Y: step S8-3), the controller 30 determines whether the value obtained by subtracting the pressure P2 from the design pressure Ps (Ps-P2) is less than a certain range ΔP. It is determined whether or not (step S8-7). For example, the certain range ΔP can be greater than or equal to 0.05 MPaA and less than or equal to 0.1 MPaA. If the value obtained by subtracting the pressure P2 from the design pressure Ps (Ps-P2) is less than the certain range ΔP (Y: step S8-7), the rotational speed of the high-level compressor 21 is maintained (step S8-8 ). If the value obtained by subtracting the pressure P2 from the design pressure Ps (Ps-P2) is not less than a certain range ΔP (N: step S8-7), the rotational speed of the high-level compressor 21 is reduced (step S8-6), It is determined whether or not the rotation speed R of the high-level compressor 21 matches the allowable minimum value Rm (step S8-9). The permissible minimum value Rm is the lower limit value of the rotational speed adjustment permissible range of the high-level compressor 21 . If the rotation speed R of the high-level compressor 21 matches the allowable minimum value Rm (Y: step S8-9), the high-level compressor 21 is stopped and the middle-level compressor 41 is started (step S8- 10). If the rotation speed R of the high-level compressor 21 does not match the allowable minimum value Rm (N: step S8-9), no special processing is executed.

Thus, in the present embodiment, the control device 30 stops the high-level compressor 21 after the low-level compressor 11 is stopped and when the rotation speed R of the high-level compressor 21 reaches the allowable minimum value Rm. and the intermediate compressor 41 is started. That is, the thermal connection destination of the low-order refrigeration cycle 10 is switched from the high-order refrigeration cycle 20 to the middle-order refrigeration cycle 40 .

According to the refrigeration system 1 of the present embodiment, the high-level refrigeration cycle 20 or the middle-level refrigeration cycle 40 can be selected according to the cooling demand of the object C to be cooled, so that the operating efficiency of the refrigeration system 1 can be improved. That is, when the cooling demand of the object C to be cooled is high, the high-level refrigeration cycle 20 can be used, and when the cooling demand of the object C to be cooled is low, the middle-level refrigeration cycle 40 can be used.

Further, since the high-level refrigerating cycle 20 or the middle-level refrigerating cycle 40 can be automatically selected according to the cooling demand of the object C to be cooled, the operating efficiency of the refrigeration system 1 can be improved. That is, the high-level refrigerating cycle 20 is used in normal operation, and the middle-level refrigerating cycle 40 can be used as the cooling demand for the object C to be cooled decreases.

In the present embodiment, it has been described that the middle-level compressor 41 is started when the low-level compressor 11 is stopped. For example, when the low-level compressor 11 and the high-level compressor 21 are activated and the performance of the high-level compressor 21 becomes insufficient, or when the low-level compressor 11 and the high-level compressor 21 are activated In some cases, the intermediate compressor 41 may be started when the cooling demand for the object to be cooled C is low. According to this configuration, the operating efficiency of the refrigeration system 1 can be improved.

As described above, specific embodiments and modifications thereof of the present invention have been described, but the present invention is not limited to the above embodiments, and various changes can be made within the scope of the present invention.

1 refrigerating device 5 cascade condenser 5a low-level condenser 5b high-level evaporator 5c middle-level evaporator 5d casing 5e low-level refrigerant inlet 5f low-level refrigerant outlet 5g high-level refrigerant inlet 5h high-level refrigerant outlet 5i plate 5j through hole 5k, 5l tube 5m intermediate refrigerant inlet 5n intermediate refrigerant outlet 10 low-level refrigeration cycle 11 low-level compressor 11a low-level motor 11b inverter 11c suction port 11d discharge port 12 oil recovery device 13 low-level expansion valve 14 low-level evaporator
15 Solenoid valve
15a, 15b pressure sensor 20 high-level refrigerating cycle 21 high-level compressor 21a high-level motor 21b inverter 21c suction port 21d outlet 22 oil collector 23 high-level condenser 24 high-level expansion valve 30 control device 40 middle-level refrigerating cycle 41 Intermediate compressor 41a Intermediate motor 41b Inverter 41c Suction port 41d Discharge port 42 Oil recovery device 43 Intermediate condenser 44 Intermediate expansion valve

Claims (5)

a low-level compressor, a low-level condenser, a low-level expansion valve, a low-level evaporator, an electromagnetic valve disposed between the low-level condenser and the low-level expansion valve, and a low-level compressor and the low-level expansion valve. a low-level refrigeration cycle having a check valve arranged between the primary condenser and circulating carbon dioxide as a low-level refrigerant to cool an object to be cooled in the low-level evaporator;
a high-level refrigeration cycle having a high-level compressor, a high-level condenser, a high-level expansion valve, and a high-level evaporator and circulating a high-level refrigerant;
a cascade condenser having the low-level condenser and the high-level evaporator, performing heat exchange between the low-level refrigerant and the high-level refrigerant and capable of storing the liquefied low-level refrigerant;
a pressure sensor that measures the suction pressure of the low-order compressor in the low-order refrigeration cycle;
When the object to be cooled in the low-level refrigeration cycle no longer needs to be cooled, the low-level refrigerant liquefied in the cascade condenser is collected and stored by closing the solenoid valve, and the pressure sensor measures the a control device that stops the low-pressure compressor when the suction pressure becomes equal to or lower than the lower limit ;
further comprising a central refrigeration cycle having a central compressor, a central condenser, a central expansion valve, and a central evaporator, and circulating the central refrigerant,
The cascade condenser further has the intermediate evaporator, performs heat exchange between the low-level refrigerant and the intermediate-level refrigerant,
The refrigeration system , wherein the medium-level compressor has a smaller capacity than the high-level compressor . A design pressure is specified for the cascade capacitor,
The high-level compressor is controllable in rotational speed,
The control device controls the rotation speed of the high-order compressor so that the pressure of the low-order refrigerant in the cascade condenser becomes lower than the design pressure within a certain range after the low-order compressor is stopped. Refrigeration apparatus according to claim 1 . The design pressure is a value of 0.3 MPaA or more and 0.4 MPaA or less,
3. The refrigeration system according to claim 2, wherein said certain range is 0.05 MPaA or more and 0.1 MPaA or less. After stopping the low-level compressor and when the rotation speed of the high-level compressor reaches an allowable minimum value, the control device stops the high-level compressor and starts the middle-level compressor. 4. The refrigeration system according to any one of claims 1 to 3 . 4. The refrigeration system according to any one of claims 1 to 3, wherein said cascade condenser is a shell and plate heat exchanger.

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