A mixed working fluid dual-temperature refrigerator system using a double-nozzle ejector and a control method thereof

Abstract

A mixed refrigerant dual-temperature refrigerator system using a dual-nozzle ejector and a control method thereof. The dual-temperature refrigerator system includes a compressor, a condenser, an ejector, a throttle valve, a solenoid valve, a gas-liquid separator, a regenerator, an evaporative condenser, a refrigeration evaporator, a freezing evaporator, and a control module. The dual-temperature refrigeration system uses a multi-component non-azeotropic mixed refrigerant. By providing a bypass at the outlet of the regenerator, the system adjusts the flow rate of the refrigerant entering the two evaporators and the composition of the mixed refrigerant when the heat load of the freezing evaporator or the refrigeration evaporator changes, and simultaneously coordinately adjusts the throttle valve openings in front of the freezing evaporator and the refrigeration evaporator. The dual-temperature refrigeration system uses a dual-nozzle ejector to couple the high-pressure side refrigerant liquid with the medium-pressure side liquid to jointly eject the low-pressure side gas, which can effectively increase the compressor suction pressure and reduce its pressure ratio, thereby achieving the purpose of improving system performance.

Description

Technical Field

[0001] The present invention relates to the technical field of dual-temperature refrigerators, and in particular to a mixed working medium dual-temperature refrigerator system using a double-nozzle ejector and a control method thereof. Background Art

[0002] When a dual-temperature refrigerator refrigeration system uses a mixed working fluid, its temperature glide characteristics can be used to effectively reduce irreversible losses in the heat exchanger and improve the energy-saving efficiency of the system. It has been widely used.

[0003] Traditional dual-temperature refrigerator refrigeration systems use a series connection between a freezer evaporator and a refrigerator evaporator. The system prioritizes the freezer evaporator's lower evaporation temperature to match the freezer's temperature requirements. Consequently, the freezer evaporator operates first, followed by the refrigerator evaporator. However, this leads to significant losses due to the temperature mismatch in the refrigerator evaporator. Furthermore, the compressor's pressure is high, resulting in increased energy consumption and lower performance. Summary of the Invention

[0004] To address the challenges of existing dual-temperature refrigeration systems, the present invention provides a dual-temperature refrigerator system utilizing a dual-nozzle ejector and its control method. By combining the dual-nozzle ejector with the dual-temperature refrigeration system, the system improves the suction pressure of the compression ratio and reduces the compressor pressure ratio, thereby enhancing system performance. When the heat load on the refrigeration evaporator 5 and the freezing evaporator 10 changes, the control module C1 acquires the parameters of the first monitoring device M1 at the outlet of the refrigeration evaporator 5 and the second monitoring device M2 at the outlet of the freezing evaporator 10 in real time. The control module then adjusts the solenoid valve 7 and the first and second electronic expansion valves 4 and 9 to meet the evaporator's cooling requirements.

[0005] In order to achieve the above technical objectives, the present invention adopts the following technical solutions:

[0006] A mixed working medium dual-temperature refrigerator system using a double-nozzle ejector includes a compressor 1, wherein the outlet of the compressor 1 is connected to the inlet of the condenser 2, and the outlet of the condenser 2 is connected to the inlet of the heat flow side of the regenerator 3; the outlet of the heat flow side of the regenerator 3 is divided into two branches, the first branch is connected to the inlet of the solenoid valve 7, and the outlet of the solenoid valve 7 is connected to the first nozzle 101 of the ejector 11; the second branch is connected to the inlet of the first electronic expansion valve 4, and the outlet of the first electronic expansion valve 4 is connected to the inlet of the refrigeration evaporator 5, and the outlet of the refrigeration evaporator 5 is connected to the inlet of the gas-liquid separator 6; the gas-liquid separator 6 The gas phase outlet is connected to the hot flow inlet of evaporative condenser 8, and the liquid phase outlet of gas-liquid separator 6 is connected to second nozzle 102 of ejector 11. The hot flow outlet of evaporative condenser 8 is connected to the inlet of second electronic expansion valve 9. The outlet of second electronic expansion valve 9 is connected to the inlet of refrigerated evaporator 10, which is connected to suction port 103 of ejector 11. The outlet of ejector 11 is connected to the cold flow inlet of evaporative condenser 8. The cold flow outlet of evaporative condenser 8 is connected to the cold flow inlet of regenerator 3, which is connected to the inlet of compressor 1. Control module C1 is connected to first electronic expansion valve 4, second electronic expansion valve 9, and solenoid valve 7, as well as to first monitoring device M1 at the outlet of refrigerated evaporator 5 and second monitoring device M2 at the outlet of refrigerated evaporator 10.

[0007] The control method for a dual-temperature refrigerator system using a mixed refrigerant using a dual-nozzle ejector determines the evaporator heat load based on the pressure P1, mass flow V1, and temperature T1 monitored by a first monitoring device M1 at the outlet of the refrigeration evaporator 5, and the pressure P2, mass flow V2, and temperature T2 monitored by a second monitoring device M2 at the outlet of the freezing evaporator 10. The heat load of the refrigeration evaporator 5 is determined by comparing temperature T1 with a set value T1*, where T1* is the saturation temperature at the pressure and composition corresponding to the monitored pressure P1. When T1 is greater than T1*, the heat load of the refrigeration evaporator 5 is increased. The heat load of the freezing evaporator 10 is determined by comparing temperature T2 with a set value T2*, where T* is the saturation temperature at the pressure and composition corresponding to the monitored pressure P2. When T2 is greater than T2*, the heat load of the freezing evaporator 10 is increased. This method adjusts the refrigerant flow rate entering the evaporator to meet the cooling temperature requirements of the dual-temperature refrigerator system.

[0008] When the heat load of the refrigeration evaporator 5 or the condenser evaporator 10 increases, or when the heat load of either evaporator increases, the control module C1 reduces the opening of the solenoid valve 7, increasing the refrigerant flow rate entering the branch circuit of the refrigeration evaporator 5 and / or the condenser evaporator 10. Simultaneously, the control module C1 coordinates the opening of the first electronic expansion valve 4 or the second electronic expansion valve 9 to ensure that T1, as detected by the first monitoring device (M1), is less than T1*, and T2, as detected by the second monitoring device M2, is less than T2*. When the heat load of the refrigeration evaporator 5 and the condenser evaporator 10 increases simultaneously, the control module C1 coordinates the reduction of the opening of the first electronic expansion valve 4 and the second electronic expansion valve 9. When the heat load of the refrigeration evaporator 5 increases and the heat load of the condenser evaporator 10 remains unchanged, the control module C1 coordinates the reduction of the opening of the first electronic expansion valve 4 and the increase of the opening of the second electronic expansion valve 9. When the heat load of the refrigeration evaporator 5 remains unchanged and the heat load of the condenser evaporator 10 increases, the control module C1 coordinates the increase of the opening of the first electronic expansion valve 4 and the reduction of the opening of the second electronic expansion valve 9.

[0009] When the heat load of the refrigeration evaporator 5 and the freezing evaporator 10 decreases or the heat load of any evaporator decreases, the control module C1 increases the opening of the solenoid valve 7 and reduces the refrigerant flow entering the refrigeration evaporator 5 and / or the freezing evaporator 10. At the same time, the control module C1 coordinates the adjustment of the first electronic expansion valve 4 or the second electronic expansion valve 9 to ensure that T1 monitored by the first monitoring device M1 is less than T1* and T2 monitored by the second monitoring device M2 is less than T2*. When the heat load of the refrigeration evaporator 5 and the condensing evaporator 10 decreases at the same time, the control module C1 coordinates the increase of the opening of the first electronic expansion valve 4 and the second electronic expansion valve (9). When the heat load of the refrigeration evaporator 5 decreases and the heat load of the condensing evaporator 10 remains unchanged, the control module C1 coordinates the increase of the opening of the first electronic expansion valve 4 and the decrease of the opening of the second electronic expansion valve 9. When the heat load of the refrigeration evaporator 5 remains unchanged and the heat load of the condensing evaporator 10 decreases, the control module C1 coordinates the decrease of the opening of the first electronic expansion valve 4 and the increase of the opening of the second electronic expansion valve 9.

[0010] Compared with the prior art, the present invention has the following advantages:

[0011] 1. The present invention proposes a mixed refrigerant dual-temperature refrigerator system using a dual-nozzle ejector and a control method thereof. Combining the dual-nozzle ejector with the dual-temperature refrigerator system, the system uses a high-pressure side refrigerant liquid coupled with a medium-pressure side refrigerant liquid to jointly eject the low-pressure side refrigerant gas. This effectively increases the suction pressure of the compressor, reduces the compressor's pressure ratio, reduces compressor energy consumption, and improves system performance.

[0012] 2. The present invention proposes a mixed refrigerant dual-temperature refrigerator system using a dual-nozzle ejector and a control method thereof. This changes the series connection of traditional dual-temperature refrigerator systems and can flexibly adjust physical parameters such as the refrigerant flow rate and mixed refrigerant composition in the evaporator according to the heat load of the refrigeration evaporator and the freezing evaporator to meet the cooling needs of the evaporator. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 This is a schematic diagram of a mixed working fluid dual-temperature refrigerator system using a double-nozzle ejector according to the present invention. DETAILED DESCRIPTION

[0014] The specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0015] like Figure 1 As shown, a mixed refrigerant dual-temperature refrigerator system using a double-nozzle ejector includes a compressor 1, wherein the outlet of the compressor 1 is connected to the inlet of the condenser 2, and the outlet of the condenser 2 is connected to the inlet of the heat flow side of the regenerator 3; the outlet of the heat flow side of the regenerator 3 is divided into two branches, the first branch is connected to the inlet of the solenoid valve 7, and the outlet of the solenoid valve 7 is connected to the first nozzle 101 of the ejector 11; the second branch is connected to the inlet of the first electronic expansion valve 4, and the outlet of the first electronic expansion valve 4 is connected to the inlet of the refrigeration evaporator 5, and the outlet of the refrigeration evaporator 5 is connected to the inlet of the gas-liquid separator 6; the gas-liquid separator The gas phase outlet of the condenser 6 is connected to the hot flow side inlet of the evaporative condenser 8, and the liquid phase outlet of the gas-liquid separator 6 is connected to the second nozzle 102 of the ejector 11; the hot flow side outlet of the evaporative condenser 8 is connected to the inlet of the second electronic expansion valve 9; the outlet of the second electronic expansion valve 9 is connected to the inlet of the refrigerated evaporator 10, the outlet of the refrigerated evaporator 10 is connected to the suction port 103 of the ejector 11, and the outlet of the ejector 11 is connected to the cold flow side inlet of the evaporative condenser 8; the cold flow side outlet of the evaporative condenser 8 is connected to the cold flow side inlet of the regenerator 3, and the cold flow side outlet of the regenerator 3 is connected to the inlet of the compressor 1. The control module C1 is connected to the first electronic expansion valve 4, the second electronic expansion valve 9, and the solenoid valve 7, as well as to the first monitoring device M1 at the outlet of the refrigerated evaporator 5 and the second monitoring device M2 at the outlet of the refrigerated evaporator 10.

[0016] The working process of the mixed refrigerant dual-temperature refrigerator system using a double-nozzle ejector described in the present invention is as follows: the system adopts a multi-element non-azeotropic mixed refrigerant, and the high-temperature and high-pressure gas-phase refrigerant compressed by the compressor 1 is condensed by the condenser 2 and enters the hot flow side inlet of the regenerator 3, and is supercooled in the regenerator 3 and is divided into two branches; the first branch after supercooling in the regenerator 3 passes through the solenoid valve 7 and enters the first nozzle 101 of the ejector 11; the second branch enters the refrigeration evaporator 5 after throttling by the first electronic expansion valve 4 and evaporates, and then enters the gas-liquid separator 6; the liquid-phase refrigerant in the gas-liquid separator 6, that is, the refrigerant rich in high-boiling-point components, enters the second nozzle 102 of the ejector 11; the gas-phase refrigerant in the gas-liquid separator 6, that is, the refrigerant rich in low-boiling-point components, enters The hot flow enters the evaporative condenser 8, condenses in the evaporative condenser 8, and then enters the second electronic expansion valve 9 for throttling. After throttling, it enters the freezing evaporator 10 for evaporation, and then enters the suction port 103 of the ejector 11. The working fluid (high-pressure side refrigerant liquid) entering the first nozzle 101 of the ejector 11 and the working fluid (intermediate-pressure side refrigerant liquid rich in high boiling point) entering the second nozzle 102 are mixed and then ejected into the working fluid (low-pressure side refrigerant gas rich in low boiling point) at the suction port 103, thereby achieving the effect of high-pressure and intermediate-pressure mixing and then ejecting low-pressure side refrigerant. These three refrigerant fluids are then mixed and pressurized in the ejector 11. After being pressurized, they enter the evaporative condenser 8 for heating, then enter the cold flow side of the regenerator 3 for heating, and then enter the inlet of the compressor 1. The solution of coupling the high-pressure side refrigerant liquid with the intermediate-pressure side refrigerant liquid to jointly eject the low-pressure side refrigerant gas can effectively increase the suction pressure of the compressor, reduce the compressor's pressure ratio, reduce the compressor's energy consumption, and improve system performance.

[0017] The present invention discloses a control method for a dual-temperature refrigerator system using a mixed refrigerant using a dual-nozzle ejector. The dual-temperature refrigerator system determines the heat load of the refrigerating evaporator 5 and the freezing evaporator 10 based on the pressure P1, mass flow V1, and temperature T1 monitored by a first monitoring device M1 at the outlet of the refrigerating evaporator 5, and the pressure P2, mass flow V2, and temperature T2 monitored by a second monitoring device M2 at the outlet of the freezing evaporator 10. The heat load of the refrigerating evaporator 5 is determined by comparing temperature T1 with a set value T1*, where T1* is the saturation temperature at the pressure and composition corresponding to the monitored pressure P1. When T1 is greater than T1*, the heat load of the refrigerating evaporator 5 is increased. The heat load of the freezing evaporator 10 is determined by comparing temperature T2 with a set value T2*, where T* is the saturation temperature at the pressure and composition corresponding to the monitored pressure P2. When T2 is greater than T2*, the heat load of the freezing evaporator 10 is increased. This method adjusts the refrigerant flow rate entering the refrigerating evaporator 5 and the freezing evaporator 10 to meet the refrigeration temperature requirements of the dual-temperature refrigerator system. It should be noted that the Coriolis force method is used in this application to measure the mass flow rate or density, and the components of each branch are obtained based on the mixed refrigerant physical parameter equation Z = f(T, P, ρ). The control method of the refrigeration system is as follows:

[0018] 1. When the heat load of the refrigeration evaporator 5 and the condenser evaporator 10 increases, or when the heat load of either evaporator increases, the opening of the solenoid valve 7 is reduced to 10% to 30% of full opening, thereby increasing the refrigerant flow rate entering the branch circuit of the refrigeration evaporator 5 and / or the condenser evaporator 10. Simultaneously, the first electronic expansion valve 4 and the second electronic expansion valve 9 are coordinated to ensure that T1 detected by the first monitoring device M1 is less than T1*, and T2 detected by the second monitoring device M2 is less than T2*. When the heat load of the refrigeration evaporator 5 and the condenser evaporator 10 increases simultaneously, the openings of the first electronic expansion valve 4 and the second electronic expansion valve 9 are coordinated to be reduced to 10% to 20% of full opening. When the heat load of the refrigeration evaporator 5 increases while the heat load of the condenser evaporator 10 remains unchanged, the opening of the first electronic expansion valve 4 is coordinated to be reduced to 5% to 10% of full opening, and the opening of the second electronic expansion valve 9 is increased to 5% to 15% of full opening. When the heat load of the refrigeration evaporator 5 remains unchanged and the heat load of the condensing evaporator 10 increases, the opening of the first electronic expansion valve 4 is collaboratively increased to 5% to 10% of the full opening, and the opening of the second electronic expansion valve 9 is reduced to 5% to 15% of the full opening.

[0019] 2. When the heat load of the refrigeration evaporator 5 and the freezing evaporator 10 decreases, or when the heat load of either evaporator decreases, the opening of the solenoid valve 7 is increased to 10% to 30% of full opening, thereby reducing the refrigerant flow rate entering the branch circuit of the refrigeration evaporator 5 and / or the condensing evaporator 10. Simultaneously, the first electronic expansion valve 4 and the second electronic expansion valve 9 are coordinated to ensure that T1 detected by the first monitoring device M1 is less than T1*, and T2 detected by the second monitoring device M2 is less than T2*. When the heat load of the refrigeration evaporator 5 and the condensing evaporator 10 decreases simultaneously, the openings of the first electronic expansion valve 4 and the second electronic expansion valve 9 are coordinated to increase to 10% to 20% of full opening. When the heat load of the refrigeration evaporator 5 decreases and the heat load of the condensing evaporator 10 remains unchanged, the opening of the first electronic expansion valve 4 is coordinated to increase to 5% to 10% of full opening, and the opening of the second electronic expansion valve 9 is decreased to 5% to 15% of full opening. When the heat load of the refrigeration evaporator 5 remains unchanged and the heat load of the condensing evaporator 10 decreases, the opening of the first electronic expansion valve 4 is collaboratively reduced to 5% to 10% of the full opening, and the opening of the second electronic expansion valve 9 is increased to 5% to 15% of the full opening.

[0020] The system of the present invention sets a bypass at the outlet of the regenerator to adjust the flow rate and mixed working fluid components of the refrigerant entering the two evaporators when the heat load of the freezing evaporator or the refrigeration evaporator changes, and at the same time coordinately adjusts the throttle valve opening in front of the freezing evaporator and the refrigeration evaporator; the dual-temperature refrigeration system adopts a double-nozzle ejector to utilize the high-pressure side refrigerant liquid to couple the medium-pressure side liquid to jointly eject the low-pressure side gas, which can effectively increase the compressor suction pressure and reduce its pressure ratio, thereby achieving the purpose of improving system performance.

Claims

1. A mixed working fluid dual-temperature refrigerator system using a dual-nozzle ejector, characterized in that: The invention comprises a compressor (1), wherein the outlet of the compressor (1) is connected to the inlet of the condenser (2), and the outlet of the condenser (2) is connected to the inlet of the heat flow side of the regenerator (3); the outlet of the heat flow side of the regenerator (3) is divided into two branches, the first branch is connected to the inlet of the electromagnetic valve (7), and the outlet of the electromagnetic valve (7) is connected to the first nozzle (101) of the ejector (11); the second branch is connected to the inlet of the first electronic expansion valve (4), and the outlet of the first electronic expansion valve (4) is connected to the inlet of the refrigeration evaporator (5), and the outlet of the refrigeration evaporator (5) is connected to the inlet of the gas-liquid separator (6); the gas phase outlet of the gas-liquid separator (6) is connected to the inlet of the heat flow side of the evaporation condenser (8), and the liquid phase outlet of the gas-liquid separator (6) is connected to the second nozzle (102) of the ejector (11); the evaporation The hot flow side outlet of the condenser (8) is connected to the inlet of the second electronic expansion valve (9); the outlet of the second electronic expansion valve (9) is connected to the inlet of the freezing evaporator (10), the outlet of the freezing evaporator (10) is connected to the suction port (103) of the ejector (11), and the outlet of the ejector (11) is connected to the cold flow side inlet of the evaporative condenser (8); the cold flow side outlet of the evaporative condenser (8) is connected to the cold flow side inlet of the regenerator (3), and the cold flow side outlet of the regenerator (3) is connected to the inlet of the compressor (1); the control module (C1) is connected to the first electronic expansion valve (4), the second electronic expansion valve (9) and the solenoid valve (7), and is also connected to the first monitoring device (M1) at the outlet of the refrigeration evaporator (5) and the second monitoring device (M2) at the outlet of the freezing evaporator (10).

2. The mixed-refrigerant dual-temperature refrigerator system using a dual-nozzle ejector according to claim 1, characterized in that: The system adopts a multi-element non-azeotropic mixed refrigerant. The high-temperature and high-pressure gaseous refrigerant compressed by the compressor (1) enters the heat flow side inlet of the regenerator (3) after condensation by the condenser (2), and is divided into two branches after being supercooled in the regenerator (3); the first branch after being supercooled in the regenerator (3) passes through the electromagnetic valve (7) and enters the first nozzle (101) of the ejector (11); the second branch enters the refrigeration evaporator (5) after being throttled by the first electronic expansion valve (4) and evaporates, and then enters the gas-liquid separator (6); the liquid phase refrigerant in the gas-liquid separator (6), i.e., the refrigerant rich in high boiling point components, enters the second nozzle (102) of the ejector (11); the gas phase refrigerant in the gas-liquid separator (6), i.e., the refrigerant rich in low boiling point components, enters On the hot flow side of the evaporative condenser (8), the liquid enters the second electronic expansion valve (9) for throttling after condensing in the evaporative condenser (8); after throttling, it enters the freezing evaporator (10) for evaporation and then enters the suction port (103) of the ejector (11); the working fluid of the first nozzle (101) and the working fluid of the second nozzle (102) entering the ejector (11) are mixed and then ejected into the working fluid of the suction port (103), thereby achieving the goal that the high-pressure side liquid and the refrigerant liquid rich in high-boiling-point components on the medium-pressure side jointly eject the refrigerant gas rich in low-boiling-point components on the low-pressure side; then, the liquid is mixed in the ejector (11) and pressurized; after pressurization, it enters the evaporative condenser (8) for heating, then enters the regenerator (3) for heating again and then enters the inlet of the compressor (1).

3. The control method of the dual-nozzle ejector mixed working medium dual-temperature refrigerator system according to any one of claims 1 to 2, characterized in that: The dual-temperature refrigerator system determines the heat load of the refrigerating evaporator (5) and the freezing evaporator (10) based on the pressure P1, mass flow V1 and temperature T1 monitored by the first monitoring device (M1) at the outlet of the refrigerating evaporator (5), and the pressure P2, mass flow V2 and temperature T2 monitored by the second monitoring device (M2) at the outlet of the freezing evaporator (10); the heat load determination method of the refrigerating evaporator (5) is to compare the temperature T1 with the set value T1*, where T1* is the saturation temperature under the pressure and component corresponding to the monitoring pressure P1. When T1 is greater than T1*, it is proved that the heat load of the refrigerating evaporator (5) has increased; the heat load determination method of the freezing evaporator (10) is to compare the temperature T2 with the set value T2*, where T* is the saturation temperature under the pressure and component corresponding to the monitoring pressure P2. When T2 is greater than T2*, it is proved that the heat load of the freezing evaporator (10) has increased; thereby adjusting the refrigerant flow entering the refrigerating evaporator (5) and the freezing evaporator (10) to ensure the refrigeration temperature requirement of the dual-temperature refrigerator system; the control method is as follows: 1) When the heat load of the refrigeration evaporator (5) and the freezing evaporator (10) increases or the heat load of any evaporator increases, the opening of the solenoid valve (7) is reduced to increase the refrigerant flow rate entering the refrigeration evaporator (5) and / or the freezing evaporator (10); at the same time, the first electronic expansion valve (4) or the second electronic expansion valve (9) is coordinated to ensure that T1 monitored by the first monitoring device (M1) is less than T1*, and T2 monitored by the second monitoring device (M2) is less than T2*; when the refrigeration evaporator (5) and the freezing evaporator (10) are in a state of When the heat load of the refrigeration evaporator (5) increases and the heat load of the freezing evaporator (10) remains unchanged, the opening of the first electronic expansion valve (4) or the second electronic expansion valve (9) is collaboratively reduced; when the heat load of the refrigeration evaporator (5) increases and the heat load of the freezing evaporator (10) remains unchanged, the opening of the first electronic expansion valve (4) is collaboratively reduced and the opening of the second electronic expansion valve (9) is increased; when the heat load of the refrigeration evaporator (5) remains unchanged and the heat load of the freezing evaporator (10) increases, the opening of the first electronic expansion valve (4) is collaboratively increased and the opening of the second electronic expansion valve (9) is reduced; 2) When the heat load of the refrigeration evaporator (5) and the freezing evaporator (10) is reduced or the heat load of any evaporator is reduced, the opening of the solenoid valve (7) is increased to reduce the refrigerant flow rate entering the refrigeration evaporator (5) and / or the freezing evaporator (10); at the same time, the first electronic expansion valve (4) or the second electronic expansion valve (9) is coordinated to ensure that T1 detected by the first monitoring device (M1) is less than T1*, and T2 detected by the second monitoring device (M2) is less than T2*; when the refrigeration evaporator (5) and the freezing evaporator (10) are in the same temperature range, the first electronic expansion valve (4) or the second electronic expansion valve (9) is adjusted to ensure that T1 detected by the first monitoring device (M1) is less than T1*, and T2 detected by the second monitoring device (M2) is less than T2*. When the heat load of the refrigeration evaporator (5) decreases and the heat load of the freezing evaporator (10) remains unchanged, the opening of the first electronic expansion valve (4) is coordinated to increase and the opening of the second electronic expansion valve (9) is reduced; when the heat load of the refrigeration evaporator (5) remains unchanged and the heat load of the freezing evaporator (10) decreases, the opening of the first electronic expansion valve (4) is coordinated to decrease and the opening of the second electronic expansion valve (9) is increased. When the heat load of the refrigeration evaporator (5) remains unchanged and the heat load of the freezing evaporator (10) decreases, the opening of the first electronic expansion valve (4) is coordinated to decrease and the opening of the second electronic expansion valve (9) is increased.

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