JP2024039427A - Refrigeration equipment - Google Patents

Abstract

The present invention provides a refrigeration system including a low-base refrigerating cycle and a high-base refrigerating cycle, which efficiently cools a low-base refrigerant with a simple configuration even when a low-base compressor is stopped. [Solution] A refrigeration device 1 includes a low-source refrigeration cycle 10 that uses and circulates carbon dioxide as a low-source refrigerant and cools objects to be cooled in a low-source evaporator 14, and a high-source refrigeration cycle that circulates a high-source refrigerant. A cascade condenser 5 which has a cycle 20, a low-base condenser 5a and a high-base evaporator 5b, performs heat exchange between the low-base refrigerant and the high-base refrigerant, and can store the liquefied low-base refrigerant; In the refrigeration cycle 10, there is a pressure sensor 15a that measures the suction pressure of the low source compressor 11, and a pressure sensor 15a that measures the suction pressure of the low source compressor 11, and a pressure sensor 15a that measures the suction pressure of the low source compressor 11. The control device 30 collects and stores the liquefied low-base refrigerant and stops the low-base compressor 11 when the suction pressure measured by the pressure sensor 15a becomes equal to or lower than the lower limit value. [Selection diagram] Figure 1

Description

The present invention relates to a refrigeration system, and particularly to a refrigeration system including a low-base refrigeration cycle and a high-base refrigeration cycle.

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

The refrigeration system of Patent Document 1 includes a low-base compressor, a low-base condenser, a low-base expansion valve, a low-base evaporator, a low-base liquid receiver, and a low-base liquid receiver arranged between the low-base liquid receiver and the low-base expansion valve. It has a solenoid valve located between the low-base compressor and the low-base condenser, and a check valve disposed between the low-base compressor and the low-base condenser. In this refrigeration system, when the low-source compressor is stopped, the low-source refrigerant is collected between the solenoid valve and the check valve by closing the solenoid valve, and the low-pressure pressure of the low-source refrigeration cycle is kept below a predetermined value. If this occurs, the low-end compressor will be stopped. As a result, even when the low source compressor is stopped, the low source refrigerant is recovered to the low source liquid receiver and the low source liquid receiver is cooled, thereby efficiently cooling the low source refrigerant and reducing the associated Efforts are being made to suppress the rise in pressure of the original refrigerant.

Patent No. 5323023

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

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

The present invention provides a low-base compressor, a low-base condenser, a low-base expansion valve, a low-base evaporator, a solenoid valve disposed between the low-base condenser and the low-base expansion valve, and a low-base compressor. a low-source refrigeration cycle that has a check valve disposed between the machine and the low-source condenser, circulates carbon dioxide as a low-source refrigerant, and cools objects in the low-source evaporator; , a high-base refrigeration cycle that has a high-base compressor, a high-base condenser, a high-base expansion valve, and a high-base evaporator and circulates a high-base refrigerant, and the low-base condenser and the high-base evaporator. a cascade condenser capable of exchanging heat between the low-base refrigerant and the high-base refrigerant and storing the liquefied low-base refrigerant; and measuring the suction pressure of the low-base compressor in the low-base refrigeration cycle. A pressure sensor is used to collect and store the liquefied low-source refrigerant in the cascade condenser by closing the solenoid valve when cooling of the object in the low-source refrigeration cycle is no longer necessary; A refrigeration system is provided, comprising: a control device that stops the low-end compressor when the measured suction pressure becomes equal to or less than a lower limit value.

According to this configuration, the low-base refrigerant can be recovered and stored in the cascade condenser before stopping the low-base compressor. The low source refrigerant in the cascade condenser is cooled by heat exchange with the high source refrigerant. Thereby, even when the low-base compressor is stopped, the low-base refrigerant can be efficiently cooled in one place (cascade condenser). In particular, since there is no need to additionally provide a low-source liquid receiver for separately storing the low-source refrigerant and a configuration for cooling the low-source liquid receiver, it can be realized with a very simple configuration.

A design pressure may be specified for the cascade condenser, the high-base compressor may be controllable in rotational speed, and the control device controls the rotation speed of the high-base compressor after stopping the low-base compressor. The rotational speed of the high source compressor may be controlled so that the pressure of the low source refrigerant is lower than the design pressure within a certain range. For example, the design pressure may be a value of 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-source refrigerant in the cascade condenser lower than the design pressure. In addition, by operating the high source compressor so that the value obtained by subtracting the pressure of the low source refrigerant in the cascade condenser from the design pressure is less than a certain range, it is possible to prevent overcooling or insufficient cooling of the low source refrigerant. 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 lower refrigerant in the cascade condenser may be 0.20 to 0.25 MPaA.

The refrigeration device may further include a mid-stage refrigeration cycle having a mid-stage compressor, a mid-stage condenser, a mid-stage expansion valve, and a mid-stage evaporator, and circulating a mid-stage refrigerant; the cascade condenser may further include the mid-stage evaporator, and perform heat exchange between the low-stage refrigerant and the mid-stage refrigerant; and the mid-stage compressor may have a smaller capacity than the high-stage compressor.

According to this configuration, the high-end refrigeration cycle or the middle-end refrigeration cycle can be selected depending on the cooling demand of the object to be cooled, so that the operating efficiency of the refrigeration system can be improved. That is, when the demand for cooling the object to be cooled is high, the high-end refrigeration cycle can be used, and when the demand for cooling the object to be cooled is low, the middle-order refrigeration cycle can be used. Here, "capacity" is a performance value of the compressor that is defined in design based on 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 taken as the "capacity" of the compressor.

The control device is configured to stop the high compressor and start the middle compressor after the low compressor is stopped and the rotational speed of the high compressor reaches a minimum allowable value. Good too.

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

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

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

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

1 is a refrigerant circuit diagram of a refrigeration apparatus according to a first embodiment of the present invention. FIG. 2 is a perspective view showing an example of a cascade capacitor in the first embodiment. 5 is a flowchart showing control in the first embodiment. 4 is a flowchart showing details of the low-source refrigeration cycle stop operation of FIG. 3. FIG. 7 is a perspective view showing another example of the cascade capacitor in the first embodiment. FIG. 3 is a refrigerant circuit diagram of a refrigeration system according to a second embodiment. FIG. 7 is a perspective view showing an example of a cascade capacitor in a second embodiment. 7 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-base refrigeration cycle 10, a high-base refrigeration cycle 20, and a control device 30. The lower refrigeration cycle 10 and the higher refrigeration cycle 20 are thermally connected by a cascade condenser 5. That is, the refrigeration device 1 is a dual refrigeration device.

In the low-source refrigeration cycle 10, CO2 (carbon dioxide) is used as a low-source refrigerant. The low-base refrigeration cycle 10 includes a low-base compressor 11, an oil recovery device 12, a check valve 16, a low-base condenser 5a, a solenoid valve 15, a low-base expansion valve 13, and a low-base evaporator 14. and in this order.

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

The cascade condenser 5 includes a low-base condenser 5a and a high-base evaporator 5b, and is configured to exchange heat between the low-base refrigerant and the high-base refrigerant and to store the liquefied low-base refrigerant. . The structure of the cascade capacitor 5 will be described in detail later.

First, the low-end refrigeration cycle 10 will be explained.

The low source compressor 11 is of a screw type and compresses the low source refrigerant. The low-base compressor 11 has a low-base motor 11a serving as a driving source, and an inverter 11b is electrically connected to the low-base motor 11a. Therefore, the current flowing through the low-power compressor 11 can be adjusted by the inverter 11b, and thereby the rotational speed of the low-power compressor 21 can be adjusted. A rated current value, which is the maximum current value for which performance is guaranteed, is set for the low-power motor 11a. The current flowing to the low 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-base compressor 11 sucks the low-base refrigerant through the suction port 11c, compresses it internally, and discharges it from the discharge port 11d. In this embodiment, the low-base compressor 11 is of an oil supply type, and the discharged low-base refrigerant contains oil. The discharged low-source refrigerant and oil are sent to the oil recovery device 12. In the oil recovery device 12, oil is recovered. The recovered oil is supplied to the low-end compressor 11 and recycled. The low-base refrigerant from which oil has been separated in the oil recovery device 12 passes through the check valve 16 and is sent to the low-base condenser 5a of the cascade condenser 5. The check valve 16 is a valve for preventing backflow of low-grade refrigerant. Note that the low-end compressor 11 is not limited to a lubricated type, and may be a non-lubricated type.

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

The solenoid valve 15 is an on-off valve whose opening and closing are controlled by the control device 30 . The electromagnetic valve 15 is arranged between the low source condenser 5a and the low source expansion valve 13.

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

In the low source evaporator 14, the low source refrigerant is evaporated, and the evaporated low source refrigerant is sent to the low source compressor 11. The low-base evaporator 14 has a function of cooling the object to be cooled C (schematically shown in FIG. 1) by heat exchange with the low-base refrigerant.

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

Next, the high-temperature refrigeration cycle 20 will be explained.

In this embodiment, the high source compressor 21 is of a screw type and compresses high source refrigerant. The high-base compressor 21 has a high-base motor 21a serving as a driving source, and an inverter 21b is electrically connected to the high-base motor 21a. Therefore, the rotation speed of the high-end compressor 21 can be adjusted by the inverter 21b. A rated current value, which is the maximum current value for which performance is guaranteed, is set for the high-end motor 21a. The current flowing to the high 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-pressure compressor 21 may be, for example, a scroll type or a reciprocating type.

In the high source compressor 21, high source refrigerant is sucked in through the suction port 21c, compressed inside, and discharged from the discharge port 21d. In this embodiment, the high source compressor 21 is of an oil supply type, and the discharged high source refrigerant contains oil. The discharged low-source refrigerant and oil are sent to the oil recovery device 22. In the oil recovery device 22, oil is recovered. The recovered oil is supplied to the high-pressure compressor 21 and recycled. The high-grade refrigerant from which oil has been separated in the oil recovery device 22 is sent to the high-grade condenser 23 . Note that the high-base compressor 21 is not limited to a lubricated type, and may be of a non-lubricated type.

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

In the high-phase evaporator 5b of the cascade condenser 5, the high-phase refrigerant is heated and evaporated. The high-phase refrigerant evaporated in the high-phase evaporator 5b is sent to the high-phase 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-base refrigerant inlet 5e for introducing the low-base refrigerant, a low-base refrigerant outlet 5f for leading out the low-base refrigerant, a high-base refrigerant inlet 5g for introducing the high-base refrigerant, and a high-base refrigerant inlet 5g for introducing the high-base refrigerant. It has a former refrigerant outlet 5h. In the illustrated example, the low-source refrigerant inlet 5e is arranged at the upper part of the casing 5d, and the low-source refrigerant outlet 5f is arranged at the lower part of the casing 5d. The high source refrigerant inlet 5g is arranged at the lower part of the side surface of the casing 5d, and the high source refrigerant outlet 5h is arranged at the upper part of the same side surface of the casing 5d.

The cascade capacitor 5 has a plurality of disc-shaped plates 5i inside a casing 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 the groove forms a flow path through which the refrigerant passes. Further, each of the plurality of plates 5i is provided with a through hole 5j. The through holes 5j of the plurality of plates 5i are arranged in line and constitute a coolant flow path.

The high source refrigerant is introduced from the high source refrigerant inlet 5g, flows through the through hole 5j and between the plurality of plates 5i, and is led out from the high source refrigerant outlet 5h (see thin arrow A). The low-base refrigerant is introduced from the low-base refrigerant inlet 5e, flows between and outside the plurality of plates 5i, and is led out from the low-base refrigerant outlet 5f (see thick arrow B). The high-source refrigerant and the low-source refrigerant flow in adjacent channels via the plurality of plates 5i so as not to mix. Therefore, in the cascade condenser 5, heat exchange is performed between the high source refrigerant and the low source refrigerant, so that the high source refrigerant is heated and the low source refrigerant is cooled.

Next, the control device 30 will be explained.

The control device 30 performs arithmetic processing and overall control in the refrigeration device 1. The control device 30 includes, for example, a CPU (Central Processing Unit) or an MPU (Micro Processing Unit) that cooperates with software to realize predetermined functions. The control device 30 may be configured with a hardware circuit such as a dedicated electronic circuit or a reconfigurable electronic circuit designed to realize a predetermined function, or may be configured with various semiconductor integrated circuits. good. Examples of various semiconductor integrated circuits include, in addition to CPUs and MPUs, microcomputers, DSPs (Digital Signal Processors), FPGAs (Field Programmable Gate Arrays), and ASICs (Application Specific Integrated Circuits). Further, the control device 30 may include a storage device such as a RAM (Random Access Memory) and a ROM (Read Only Memory). Specifically, the control device 30 may be configured with, 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 realizes predetermined functions by reading stored data and programs and performing various calculation processes. The program executed by the control device 30 may be provided from the outside using a communication unit that communicates according to a predetermined communication standard, or may be stored in a portable recording medium.

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

The control device 30 closes the solenoid valve 15 when cooling of the object C to be cooled in the low-source refrigeration cycle 10 becomes unnecessary (when the cooling demand becomes zero). When the solenoid valve 15 is closed, the piping on the upstream side of the solenoid valve 15 is gradually filled with low-grade refrigerant. When the pipe from the electromagnetic valve 15 to the cascade condenser 5 is filled with the low-grade refrigerant, the inside of the casing 5d of the cascade condenser 5 is gradually filled with the low-grade refrigerant from below. In this way, by closing the solenoid valve 15, the liquefied low-grade refrigerant can be recovered and stored in the cascade condenser 5. In addition, since the flow paths of the high-source refrigerant and the low-source refrigerant are separated from each other in the cascade condenser 5, even when the low-source refrigerant is stored in the cascade condenser 5, the high-source refrigerant cannot flow inside the cascade condenser 5. can.

The solenoid valve 15 may be arranged at the low-source refrigerant outlet 5f or near the low-source refrigerant outlet 5f, and by shortening the piping distance from the solenoid valve 15 to the cascade condenser 5, the The amount of the original refrigerant may be reduced. As a result, much of the low-grade refrigerant can be recovered into the cascade condenser 5. The cascade condenser 5 may have a volume capable of storing almost all of the low-grade refrigerant.

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

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

When the control device 30 starts operating the refrigeration device 1, it starts the high-end compressor 21 (step S3-1), starts the low-end 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 in which the object C to be cooled is cooled. After that, the control device 30 receives the cooling demand for the object to be cooled C as described above, and determines whether 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-source refrigeration cycle stop operation is executed (step S3-5).

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

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

Next, it is determined whether the pressure P2 of the low-grade 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 the current I flowing through the high motor 21a is less than the rated current Ir of the high 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-power compressor 21 is increased (step S4-5). When the rotation speed of the high source compressor 21 is increased, the cooling capacity of the high source refrigeration cycle 20 increases, the temperature of the low source refrigerant in the cascade condenser 5 decreases, and the pressure P2 decreases. Therefore, the pressure P2 of the lower source refrigerant can be adjusted so that the pressure P2 is less than the design pressure Ps. Further, if the current I is not less than the rated current Ir (N: step S4-4), the rotation speed of the high-pressure 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 may 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 S4-7), the rotational speed of the high-pressure compressor 21 is maintained (step S4-8 ). That is, the cooling capacity of the high source condenser 5b of the high source refrigeration cycle 20 is maintained, that is, the cooling of the low source refrigerant in the cascade condenser 5 is maintained. Further, if 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 rotation speed of the high-pressure compressor 21 is reduced (step S4- 6). When the rotation speed of the high source compressor 21 is reduced, the cooling capacity of the high source refrigeration cycle 20 decreases, the temperature of the low source refrigerant in the cascade condenser 5 increases, and the pressure P2 of the low source refrigerant increases. Therefore, the pressure P2 of the lower source 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.

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

According to the refrigeration device 1 according to this embodiment, the following effects are achieved.

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

Moreover, the cascade condenser 5 can be used safely by making the pressure P2 of the low-source refrigerant smaller than the design pressure Ps. By operating the high-base 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, it is possible to prevent overcooling or insufficient cooling of the low-base refrigerant, and to avoid the necessary The above power consumption can be prevented and the desired cooling capacity can be achieved.

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

Referring to FIG. 5, as a modification, cascade condenser 5 may be a shell-and-tube heat exchanger. The shell and tube heat exchanger is a shell and plate heat exchanger in which the plurality of plates 5i are replaced with a plurality of tubes 5k.

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

The high source refrigerant is introduced from the high source refrigerant inlet 5g, flows through the inside of the plurality of tubes 5k, and is led out from the high source refrigerant outlet 5h (see thin arrow A). The low-base refrigerant is introduced from the low-base refrigerant inlet 5e, flows through the outside of the plurality of tubes 5k, and is led out from the low-base refrigerant outlet 5f (see thick arrow B). Also in this modification, the low-source refrigerant can be stored in the casing 5d without mixing of the high-source refrigerant and the low-source refrigerant, and the flow paths of the high-source refrigerant and the low-source refrigerant are partitioned off. Therefore, in the cascade condenser 5, heat exchange is performed between the high source refrigerant and the low source refrigerant, so that the high source refrigerant is heated and the low source refrigerant is cooled.

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

(Second embodiment)
The refrigeration system 1 according to the second embodiment shown in FIG. 6 differs from the first embodiment in that it additionally includes a middle refrigeration cycle 40. The parts other than this are substantially the same as the first embodiment. Therefore, the description of the parts shown in the first embodiment may be omitted.

The refrigeration apparatus 1 according to the present embodiment includes a low-base refrigeration cycle 10, a high-base refrigeration cycle 20, and a middle-base refrigeration cycle 40. The lower refrigeration cycle 10, the higher refrigeration cycle 20, and the middle refrigeration cycle 40 are thermally connected by a cascade condenser 5.

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

The cascade condenser 5 has a low-base condenser 5a, a high-base evaporator 5b, and a middle-base evaporator 5c, and performs heat exchange between the low-base refrigerant and high-base refrigerant and between the low-base refrigerant and the middle base refrigerant. The structure is configured to exchange heat between the refrigerants and to store liquefied low-grade refrigerant. The structure of the cascade capacitor 5 will be described in detail later.

In this embodiment, the intermediate compressor 41 is of a screw type and compresses the intermediate refrigerant. The core compressor 41 has a core motor 41a serving as a driving source, and an inverter 41b is electrically connected to the core motor 41a. Therefore, the rotation speed of the middle compressor 41 can be adjusted by the inverter 41b. A rated current value, which is the maximum current value for which performance is guaranteed, is set for the middle motor 41a. The current flowing to 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 middle compressor 41 may be, for example, of a scroll type or a reciprocating type.

In the core compressor 41, the core refrigerant is sucked in through the suction port 41c, compressed inside, and discharged from the discharge port 41d. In this embodiment, the intermediate compressor 41 is of an oil supply type, and the discharged high-grade refrigerant contains oil. The discharged low-source refrigerant and oil are sent to the oil recovery device 42. In the oil recovery device 42, oil is recovered. The recovered oil is supplied to the middle compressor 41 and recycled. The high-grade refrigerant from which oil has been separated in the oil recovery device 42 is sent to the medium-grade condenser 43 . Note that the middle compressor 41 is not limited to a lubricated type, and may be an oil-free type.

The medium compressor 41 has a smaller capacity than the high compressor 21. Here, "capacity" is a performance value of the compressor that is defined in design based on 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 taken as the "capacity" of the compressor.

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

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

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

In this embodiment, the cascade capacitor 5 has a plurality of tubes 5k and 5l inside the casing 5d. The plurality of tubes 5k extend approximately horizontally from the high-base refrigerant inlet 5g to the high-base refrigerant outlet 5h, and the plurality of tubes 5l extend horizontally from the mid-base refrigerant inlet 5m to the mid-base refrigerant outlet 5n.

The high source refrigerant is introduced from the high source refrigerant inlet 5g, flows through the inside of the plurality of tubes 5k, and is led out from the high source refrigerant outlet 5h (see thin arrow A). The low-base refrigerant is introduced from the low-base refrigerant inlet 5e, flows through the outside of the plurality of tubes 5k and 5l, and is led out from the low-base refrigerant outlet 5f (see thick arrow B). The core refrigerant is introduced from the core refrigerant inlet 5m, flows through the inside of the plurality of tubes 5l, and is led out from the core refrigerant outlet 5n (see thin arrow C). Therefore, in the cascade condenser 5, heat exchange is performed between the high source refrigerant and the low source refrigerant, and heat exchange is performed between the middle source refrigerant and the low source refrigerant. Specifically, the high source refrigerant is heated and the low source refrigerant is cooled. Moreover, the middle base refrigerant is heated and the low base refrigerant is cooled.

Also in this embodiment, when the solenoid valve 15 is closed, low-source refrigerant gradually accumulates in the piping on the upstream side of the solenoid valve 15. When the piping from the solenoid valve 15 to the cascade condenser 5 is filled with the low-grade refrigerant, the inside of the cascade condenser 5 is gradually filled with the low-grade refrigerant from below. In this way, by closing the solenoid valve 15, the liquefied low-grade refrigerant can be recovered and stored in the cascade condenser 5. In addition, since the flow paths of the high-source refrigerant and the low-source refrigerant are separated from each other in the cascade condenser 5, even when the low-source refrigerant is stored in the cascade condenser 5, the high-source refrigerant cannot flow inside the cascade condenser 5. can. Similarly, in the cascade condenser 5, the flow paths of the middle-grade refrigerant and the low-grade refrigerant are separated from each other, so even when the low-grade refrigerant is stored in the cascade condenser 5, the middle-grade refrigerant does not flow inside the cascade condenser 5. I can do it.

The solenoid valve 15 may be arranged at the low-source refrigerant outlet 5f or near the low-source refrigerant outlet 5f, and by shortening the piping distance from the solenoid valve 15 to the cascade condenser 5, the The amount of the original refrigerant may be reduced. As a result, much of the low-grade refrigerant can be recovered into the cascade condenser 5. At this time, the cascade condenser 5 may have a volume capable of storing almost all of the low-grade refrigerant.

In the refrigeration system 1 of this embodiment, the middle refrigeration cycle 40 is used when the use of the high refrigeration cycle 20 causes the cooling capacity of the refrigeration system 1 to be excessive with respect to the cooling demand. Therefore, in this embodiment, the details of the low-source refrigeration cycle stop operation (step S3-5) in FIG. 3 are different from the first embodiment.

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

In the low-source refrigeration cycle stop operation in this embodiment, the solenoid valve 15 is closed (step S8-1). Then, the operation of the low source compressor 11 is continued until the suction pressure P1 measured by the pressure sensor 15a reaches the lower limit value Pm, and after the pressure is reduced until the suction pressure P1 becomes equal to or lower than the lower limit value Pm, the low source compressor 11 is stopped. (Step S8-2). That is, similarly to the first embodiment, a pump-down operation for recovering and storing the low-grade refrigerant in the cascade condenser 5 is executed.

Next, it is determined whether the pressure P2 of the low-grade 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 the current I flowing through the low source motor 11a is less than the rated current Ir of the low source motor 11a (step S8-3). 4). If the current I is less than the rated current Ir (Y: step S8-4), the rotational speed of the high-power compressor 21 is increased (step S8-5). If the current I is not less than the rated current Ir (N: step S8-4), the rotational speed of the high-power compressor 21 is reduced (step S8-6).

Further, when the pressure P2 is less than the design pressure Ps (Y: step S8-3), the control device 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 may 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-pressure 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 the certain range ΔP (N: step S8-7), the rotation speed of the high-base compressor 21 is reduced (step S8-6), It is determined whether the rotational speed R of the high-end compressor 21 matches the allowable minimum value Rm (step S8-9). The minimum allowable value Rm is the lower limit of the allowable rotational speed adjustment range of the high-end compressor 21. If the rotational speed R of the high-end compressor 21 matches the allowable minimum value Rm (Y: step S8-9), the high-end compressor 21 is stopped and the middle-end compressor 41 is started (step S8-9). 10). If the rotational speed R of the high-end compressor 21 does not match the allowable minimum value Rm (N: step S8-9), no special processing is performed.

As described above, in the present embodiment, the control device 30 stops the high-compressor 21 after the low-compressor 11 is stopped and when the rotational speed R of the high-compressor 21 reaches the allowable minimum value Rm. At the same time, the middle compressor 41 is started. That is, the thermal connection destination of the low-base refrigeration cycle 10 is switched from the high-base refrigeration cycle 20 to the middle-base refrigeration cycle 40.

According to the refrigeration system 1 of the present embodiment, the high-end refrigeration cycle 20 or the middle refrigeration cycle 40 can be selected depending on 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 to be cooled C is high, the high-temperature refrigeration cycle 20 can be used, and when the cooling demand of the object to be cooled C is low, the middle-center refrigeration cycle 40 can be used.

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

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

Although specific embodiments of the present invention and modifications thereof have been described above, the present invention is not limited to the above embodiments, and can be implemented with various modifications within the scope of the present invention.

1 Refrigeration equipment 5 Cascade condenser 5a Low source condenser 5b High source evaporator 5c Middle source evaporator 5d Casing 5e Low source refrigerant inlet 5f Low source refrigerant outlet 5g High source refrigerant inlet 5h High source refrigerant outlet 5i Plate 5j Through hole 5k, 5l tube 5m mid-base refrigerant inlet 5n mid-base refrigerant outlet 10 low-base refrigeration cycle 11 low-base compressor 11a low-base motor 11b inverter 11c suction port 11d discharge port 12 oil recovery device 13 low-base expansion valve 14 low-base evaporator 15a, 15b Pressure sensor 20 High source refrigeration cycle 21 High source compressor 21a High source motor 21b Inverter 21c Suction port 21d Discharge port 22 Oil recovery device 23 High source condenser 24 High source expansion valve 30 Control device 40 Nakamoto refrigeration cycle 41 Nakamoto Compressor 41a Nakamoto motor 41b Inverter 41c Suction port 41d Discharge port 42 Oil recovery device 43 Nakamoto condenser 44 Nakamoto expansion valve

The present invention provides a low-base compressor, a low-base condenser, a low-base expansion valve, a low-base evaporator, a solenoid valve disposed between the low-base condenser and the low-base expansion valve, and a low-base compressor. a low-source refrigeration cycle that has a check valve disposed between the machine and the low-source condenser, circulates carbon dioxide as a low-source refrigerant, and cools objects in the low-source evaporator; , a high-base refrigeration cycle that has a high-base compressor, a high-base condenser, a high-base expansion valve, and a high-base evaporator and circulates a high-base refrigerant, and the low-base condenser and the high-base evaporator. a cascade condenser capable of exchanging heat between the low-base refrigerant and the high-base refrigerant and storing the liquefied low-base refrigerant; and measuring the suction pressure of the low-base compressor in the low-base refrigeration cycle. A pressure sensor is used to collect and store the liquefied low-source refrigerant in the cascade condenser by closing the solenoid valve when cooling of the object in the low-source refrigeration cycle is no longer necessary; a control device that stops the low-end compressor when the measured suction pressure becomes equal to or lower than a lower limit value; The cascade condenser further includes an intermediate refrigerating cycle that circulates the original refrigerant, the cascade condenser further includes the intermediate refrigerant, and the intermediate refrigerant exchanges heat between the lower refrigerant and the intermediate refrigerant. , provides a refrigeration system having a smaller capacity than the high-end compressor .

According to this configuration, the low-base refrigerant can be recovered and stored in the cascade condenser before stopping the low-base compressor. The low source refrigerant in the cascade condenser is cooled by heat exchange with the high source refrigerant. Thereby, even when the low-base compressor is stopped, the low-base refrigerant can be efficiently cooled in one place (cascade condenser). In particular, since there is no need to additionally provide a low-source liquid receiver for separately storing the low-source refrigerant and a configuration for cooling the low-source liquid receiver, it can be realized with a very simple configuration. Further, since the high-end refrigeration cycle or the middle-end refrigeration cycle can be selected depending on the cooling demand of the object to be cooled, the operating efficiency of the refrigeration system can be improved. That is, when the demand for cooling the object to be cooled is high, the high-end refrigeration cycle can be used, and when the demand for cooling the object to be cooled is low, the middle-order refrigeration cycle can be used. Here, "capacity" is a performance value of the compressor that is defined in design based on 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 taken as the "capacity" of the compressor.

The low source compressor 11 is of a screw type and compresses the low source refrigerant. The low-base compressor 11 has a low-base motor 11a serving as a driving source, and an inverter 11b is electrically connected to the low-base motor 11a. Therefore, the current flowing through the low-power compressor 11 can be adjusted by the inverter 11b, and thereby the rotational speed of the low-power compressor 11 can be adjusted. A rated current value, which is the maximum current value for which performance is guaranteed, is set for the low-power motor 11a. The current flowing to the low 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.

In the high source compressor 21, high source refrigerant is sucked in through the suction port 21c, compressed inside, and discharged from the discharge port 21d. In this embodiment, the high source compressor 21 is of an oil supply type, and the discharged high source refrigerant contains oil. The discharged high -grade refrigerant and oil are sent to the oil recovery device 22. In the oil recovery device 22, oil is recovered. The recovered oil is supplied to the high-pressure compressor 21 and recycled. The high-grade refrigerant from which oil has been separated in the oil recovery device 22 is sent to the high-grade condenser 23 . Note that the high-base compressor 21 is not limited to a lubricated type, and may be of a non-lubricated type.

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 may 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 S4-7), the rotational speed of the high-pressure compressor 21 is maintained (step S4-8 ). That is, the cooling capacity of the high source evaporator 5b of the high source refrigeration cycle 20 is maintained, that is, the cooling of the low source refrigerant in the cascade condenser 5 is maintained. Further, if 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 rotation speed of the high-pressure compressor 21 is reduced (step S4- 6). When the rotation speed of the high source compressor 21 is reduced, the cooling capacity of the high source refrigeration cycle 20 decreases, the temperature of the low source refrigerant in the cascade condenser 5 increases, and the pressure P2 of the low source refrigerant increases. Therefore, the pressure P2 of the lower source 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.

In the core compressor 41, the core refrigerant is sucked in through the suction port 41c, compressed inside, and discharged from the discharge port 41d. In this embodiment, the core compressor 41 is of an oil supply type, and the discharged core refrigerant contains oil. The discharged intermediate refrigerant and oil are sent to the oil recovery device 42. In the oil recovery device 42, oil is recovered. The recovered oil is supplied to the middle compressor 41 and recycled. The core refrigerant from which oil has been separated in the oil recovery device 42 is sent to the core condenser 43. Note that the middle compressor 41 is not limited to a lubricated type, and may be an oil-free type.

Next, it is determined whether the pressure P2 of the low-grade 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 the current I1 flowing through the low source motor 11a is less than the rated current Ir of the low source 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-power compressor 21 is increased (step S8-5). If the current I1 is not less than the rated current Ir (N: step S8-4), the rotational speed of the high-end compressor 21 is reduced (step S8-6).

1 Refrigeration equipment 5 Cascade condenser 5a Low source condenser 5b High source evaporator 5c Middle source evaporator 5d Casing 5e Low source refrigerant inlet 5f Low source refrigerant outlet 5g High source refrigerant inlet 5h High source refrigerant outlet 5i Plate 5j Through hole 5k, 5l tube 5m mid-base refrigerant inlet 5n mid-base refrigerant outlet 10 low-base refrigeration cycle 11 low-base compressor 11a low-base motor 11b inverter 11c suction port 11d discharge port 12 oil recovery device 13 low-base expansion valve 14 low-base evaporator
15 Solenoid valve
15a, 15b Pressure sensor 20 High source refrigeration cycle 21 High source compressor 21a High source motor 21b Inverter 21c Suction port 21d Discharge port 22 Oil recovery device 23 High source condenser 24 High source expansion valve 30 Control device 40 Nakamoto refrigeration cycle 41 Nakamoto compressor 41a Nakamoto motor 41b Inverter 41c Suction port 41d Discharge port 42 Oil recovery device 43 Nakamoto condenser 44 Nakamoto expansion valve

Claims (6)

a low source compressor, a low source condenser, a low source expansion valve, a low source evaporator, a solenoid valve disposed between the low source condenser and the low source expansion valve, and a low source compressor and the low source expansion valve. a low-source refrigeration cycle that has a check valve disposed between the source condenser, circulates carbon dioxide as a low-source refrigerant, and cools an object to be cooled in the low-source evaporator;
A high-base refrigeration cycle that has a high-base compressor, a high-base condenser, a high-base expansion valve, and a high-base evaporator, and circulates a high-base refrigerant;
a cascade condenser having the low-base condenser and the high-base evaporator, capable of exchanging heat between the low-base refrigerant and the high-base refrigerant and storing the liquefied low-base refrigerant;
a pressure sensor that measures the suction pressure of the low source compressor in the low source refrigeration cycle;
When it is no longer necessary to cool the object to be cooled in the low-source refrigeration cycle, the solenoid valve is closed to recover and store the low-source refrigerant liquefied in the cascade condenser. A refrigeration system comprising: a control device that stops the low-end compressor when the suction pressure becomes equal to or less than a lower limit value. A design pressure is specified for the cascade capacitor,
The high-pressure compressor can control its rotational speed,
The control device controls the rotational speed of the high-base compressor so that the pressure of the low-base refrigerant in the cascade condenser is lower than the design pressure within a certain range after the low-base compressor is stopped. The refrigeration device according to claim 1. The design pressure is a value of 0.3 MPaA or more and 0.4 MPaA or less,
The refrigeration apparatus according to claim 2, wherein the certain range is 0.05 MPaA or more and 0.1 MPaA or less. It further includes a midstream refrigeration cycle that has a midstream compressor, a midstream condenser, a midstream expansion valve, and a midstream evaporator, and circulates a midstream refrigerant,
The cascade condenser further includes the middle base evaporator, and performs heat exchange between the low base refrigerant and the middle base refrigerant,
The refrigeration system according to any one of claims 1 to 3, wherein the middle compressor has a smaller capacity than the high compressor. The control device stops the high base compressor and starts the middle compressor after the low base compressor is stopped and the rotational speed of the high base compressor reaches a minimum allowable value. The refrigeration device according to claim 4. The refrigeration system according to any one of claims 1 to 3, wherein the cascade condenser is a shell-and-plate heat exchanger.

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