Carbon dioxide refrigeration system and method of controlling the same

Abstract

The present application relates to the field of refrigeration technology, in particular to a carbon dioxide refrigeration system and a control method thereof. The carbon dioxide refrigeration system comprises an ejector circuit, one end of the ejector circuit is connected to an inlet end of an ejector, and the other end is respectively connected to an outlet end of a first evaporator and an inlet end of a compressor. The present application also provides a control method of the carbon dioxide refrigeration system, which is applied to the carbon dioxide refrigeration system. Compared with the prior art, the present application has the advantages that the throttling effect of the system is ensured, the evaporation temperature of the first evaporator can be flexibly adjusted, the first evaporator can quickly cool the target temperature zone, the ejector and the ejector circuit can make two temperature zones share one compressor with small load, so that the system as a whole reduces the cost and improves the flexibility of the system.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of refrigeration technology, in particular to a carbon dioxide refrigeration system and a control method thereof. BACKGROUND

[0002] Due to the ozone depletion caused by chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs), and the global warming effect of hydrofluorocarbons (HFCs), 197 countries around the world reached an agreement to reduce the emission of chemical refrigerants. With the acceleration of the implementation process of the Montreal Protocol and the Kigali Amendment, it is expected to reduce the emission of greenhouse gas hydrofluorocarbon (HFC) by 88% in the 21st century. In order to reduce the environmental impact of chemical refrigerants, CO2, as a natural refrigerant (ODP is 0, GWP can be ignored), has become an important refrigerant replacement material. In fact, CO2 is the most environmentally friendly refrigerant in the field of commercial refrigeration, which is a non-toxic, non-flammable, inexpensive and easily available natural working medium with superior thermophysical properties.

[0003] In the application of carbon dioxide refrigeration system, for different temperature zones, the existing design usually has three ways of double-stage compression, configuration of different temperature zone compressors and direct use of low temperature compressor. The conventional double-stage compression is limited by the intermediate pressure, and the flexibility of temperature regulation of the medium temperature system is poor; the configuration of multi-temperature zone compressor is relatively complex, and the investment cost is high; the direct use of low temperature compressor is simple, but the overheat vapor evaporated by the first evaporator is throttled to low pressure and mixed with low temperature vapor to enter the low temperature compressor, which will cause the displacement of the low temperature compressor to increase, and the economy of the equipment is poor. SUMMARY

[0004] Therefore, in view of the above technical problems, the present application provides a carbon dioxide refrigeration system in an embodiment.

[0005] In order to solve the above technical problems, the present application provides the following technical solutions in an embodiment.

[0006] A carbon dioxide refrigeration system, comprising a compressor, an air cooler, an ejector, a first evaporator and a second evaporator, the air cooler being connected between the outlet end of the compressor and the inlet end of the ejector, the outlet end of the ejector being connected to the inlet end of the first evaporator and the inlet end of the second evaporator, and the outlet end of the first evaporator being connected to the inlet end of the compressor; the carbon dioxide refrigeration system further comprises an ejector circuit, one end of the ejector circuit being connected to the inlet end of the ejector, and the other end being connected to the outlet end of the first evaporator and the inlet end of the compressor, respectively.

[0007] It can be understood that the application sets the ejector circuit in the carbon dioxide refrigeration system, so that the ejector can eject the superheated vapor after the evaporation of the first evaporator, thereby ensuring the throttling effect of the ejector and flexibly adjusting the evaporation temperature of the first evaporator to accelerate the cooling speed of the corresponding temperature zone of the first evaporator; the setting of the ejector and the ejector circuit can make two temperature zones share one compressor, which can be replaced by a compressor with smaller load, so that the overall system design can greatly reduce the cost and greatly improve the flexibility of the system.

[0008] In one embodiment, the carbon dioxide refrigeration system further comprises a liquid accumulator and a secondary recooling heat exchanger, the liquid accumulator is connected between the outlet end of the ejector and the inlet end of the first evaporator, the secondary recooling heat exchanger has a first end, a second end, a third end and a fourth end, the first end and the second end are connected to the ejector and the air cooler respectively, the compressor has a gas supplementing and enthalpy increasing port, the third end is connected to the liquid accumulator, the fourth end is connected to the gas supplementing and enthalpy increasing port, the first end and the second end are in communication, and the third end and the fourth end are in communication.

[0009] In this way, the temperature of the medium at the inlet end of the ejector is reduced and the energy efficiency of the system is improved through heat exchange between the medium in the passage between the first end and the second end and the medium in the passage between the third end and the fourth end; the refrigerant gas in the liquid accumulator is reduced and the pressure of the liquid accumulator is ensured by connecting one end of the secondary recooling heat exchanger to the liquid accumulator and the other end to the gas supplementing and enthalpy increasing port.

[0010] In one embodiment, the carbon dioxide refrigeration system further comprises a primary recooling heat exchanger, the primary recooling heat exchanger has a fifth end, a sixth end, a seventh end and an eighth end, the fifth end and the sixth end are connected to the secondary recooling heat exchanger and the air cooler respectively, the seventh end is connected to the ejector circuit, and the eighth end is connected to the liquid accumulator, the fifth end and the sixth end are in communication, and the seventh end and the eighth end are in communication.

[0011] It can be understood that by connecting the seventh end to the inlet end of the ejector and the first evaporator respectively, the first evaporator can replace the function of the first evaporator to the ejector circuit when the first evaporator is not working; and the temperature of the carbon dioxide before throttling is effectively reduced, the energy efficiency of the system is greatly improved, the equipment cost is reduced, and the economy of the system is improved through heat exchange between the medium in the passage between the fifth end and the sixth end and the medium in the passage between the seventh end and the eighth end.

[0012] In one of the embodiments, the carbon dioxide refrigeration system further comprises a second evaporator, one end of the second evaporator is connected to the liquid accumulator, and the other end of the second evaporator is connected to the outlet end of the compressor and the air cooler respectively.

[0013] It can be understood that, by connecting the second evaporator between the liquid accumulator and the outlet end of the compressor, the hot gas is bypassed to the second evaporator to defrost the second evaporator.

[0014] In one of the embodiments, one end of the second evaporator is connected to the liquid accumulator, the eighth end and the inlet end of the first evaporator respectively, and the other end of the second evaporator is connected to the inlet end of the compressor.

[0015] In one of the embodiments, the carbon dioxide refrigeration system further comprises a first electromagnetic valve, a second electromagnetic valve, a third electromagnetic valve and a fourth electromagnetic valve, the first electromagnetic valve is connected between the liquid accumulator and the third end, one end of the second electromagnetic valve is connected to the ejector circuit and the outlet end of the first evaporator respectively, and the other end of the second electromagnetic valve is connected to the inlet end of the compressor, the third electromagnetic valve is connected between the liquid accumulator and the inlet end of the first evaporator, and the fourth electromagnetic valve is connected between the liquid accumulator and the eighth end; the carbon dioxide refrigeration system comprises a first throttling element, a second throttling element, a third throttling element and a fourth throttling element, the first throttling element is connected between the first electromagnetic valve and the third end, the second throttling element is connected between the second electromagnetic valve and the compressor, the third throttling element is connected between the third electromagnetic valve and the first evaporator, and the fourth throttling element is connected between the fourth electromagnetic valve and the eighth end.

[0016] It can be understood that, by setting the electromagnetic valves, the on-off of the circuits of different temperature zones is controlled.

[0017] In one of the embodiments, the carbon dioxide refrigeration system comprises a fifth electromagnetic valve and a sixth electromagnetic valve, the fifth electromagnetic valve is connected between the liquid accumulator and the second evaporator, and the sixth electromagnetic valve is connected between the second evaporator and the inlet end of the compressor; the carbon dioxide refrigeration system comprises a fifth throttling element, and the fifth throttling element is connected between the fifth electromagnetic valve and the second evaporator.

[0018] It can be understood that, by setting the electromagnetic valves, the on-off of the circuits of different temperature zones is controlled.

[0019] In one of the embodiments, the carbon dioxide refrigeration system comprises a seventh electromagnetic valve and a sixth throttling element, one end of the seventh electromagnetic valve is connected to the outlet end of the compressor and the air cooler respectively, and the other end is connected to the sixth throttling element, and one end of the sixth throttling element away from the seventh electromagnetic valve is connected to the second evaporator and the sixth electromagnetic valve respectively; the carbon dioxide refrigeration system comprises a constant pressure valve, one end of the constant pressure valve is connected to the second evaporator and the fifth throttling element respectively, and the other end is connected to the liquid accumulator.

[0020] In one of the embodiments, the carbon dioxide refrigeration system comprises an eighth electromagnetic valve, and the eighth electromagnetic valve is arranged on the ejector circuit.

[0021] In one of the embodiments, the carbon dioxide refrigeration system comprises an eighth electromagnetic valve, and the eighth electromagnetic valve is arranged on the ejector circuit.

[0022] A carbon dioxide refrigeration system control method is applied to a carbon dioxide refrigeration system, and the carbon dioxide refrigeration system further comprises a primary recooling heat exchanger, a fourth electromagnetic valve, an eighth electromagnetic valve and a second electromagnetic valve, the primary recooling heat exchanger is connected between the air cooler and the ejector, the fourth electromagnetic valve is connected between the ejector and the first recooling heat exchanger, the eighth electromagnetic valve is arranged on the ejector circuit, and one end of the second electromagnetic valve is connected to the first evaporator and the ejector circuit, and the other end is connected to the inlet end of the compressor; the carbon dioxide refrigeration system control method comprises: detecting the return gas superheat A at the first evaporator and comparing the return gas superheat A with a first preset superheat A1; if A>A1 and the condition A>A1 lasts for a first preset time T1, the fourth electromagnetic valve is closed, and the eighth electromagnetic valve is opened; if A>A1 and the condition A>A1 lasts for a second preset time T2, the second electromagnetic valve is opened, wherein T2>T1; and if A≤A1 and the condition A≤A1 lasts for a third preset time T3, the second electromagnetic valve is closed.

[0023] In this way, the amount of medium ejected from the outlet end of the first evaporator can be increased, so as to accelerate the cooling speed of the corresponding temperature zone of the first evaporator.

[0024] In one of the embodiments, the carbon dioxide refrigeration system comprises an eighth electromagnetic valve, and the eighth electromagnetic valve is arranged on the ejector circuit.

[0025] The application discloses a carbon dioxide refrigeration system control method applied to a carbon dioxide refrigeration system, wherein the carbon dioxide refrigeration system comprises a second evaporator, a liquid accumulator and a second electromagnetic valve; the liquid accumulator is connected between the ejector and the first evaporator; one end of the second evaporator is connected to the liquid accumulator; the other end of the second evaporator is connected to the air cooler and the outlet end of the compressor respectively; the second electromagnetic valve is connected between the inlet end of the compressor and the outlet end of the first evaporator; the carbon dioxide refrigeration system control method comprises the following steps: detecting the return gas superheat B at the second evaporator and comparing the return gas superheat B with a second preset superheat B1; if B < B1 and the condition lasts for a fourth preset time T4, the second electromagnetic valve is opened; if B >= B1 and the condition lasts for a fifth preset time T5, the second electromagnetic valve is closed.

[0026] Therefore, when the temperature of the temperature zone corresponding to the first evaporator has not been reduced to the target value, the compressor can be ensured to operate normally without being stopped.

[0027] Compared with the prior art, the carbon dioxide refrigeration system provided in the embodiment of the application can ensure the throttling effect of the system and flexibly adjust the evaporation temperature of the first evaporator by arranging the ejector circuit in the carbon dioxide refrigeration system, so that the ejector can eject the superheated vapor after the first evaporator evaporates; the arrangement of the ejector and the ejector circuit can make two temperatures share one compressor with a smaller load, so that the cost is greatly reduced and the flexibility of the system is greatly improved in the overall design of the system. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 A principle schematic diagram of the carbon dioxide refrigeration system provided by the application is shown in the figure;

[0029] Figure 2 A principle schematic diagram of the first refrigeration mode in the carbon dioxide refrigeration system provided by the application is shown in the figure;

[0030] Figure 3 A principle schematic diagram of the second refrigeration mode in the carbon dioxide refrigeration system provided by the application is shown in the figure;

[0031] Figure 4 A principle schematic diagram of the third refrigeration mode in the carbon dioxide refrigeration system provided by the application is shown in the figure;

[0032] Figure 5 A principle schematic diagram of the defrosting mode in the carbon dioxide refrigeration system provided by the application is shown in the figure.

[0033] The meanings of the symbols in the figure are as follows:

[0034] 100, carbon dioxide refrigeration system; 10, compressor; 11, gassing and enthalpy increasing port; 20, air cooler; 30, ejector; 31, ejector circuit; 32, ejector bypass circuit; 40, first evaporator; 41, second evaporator; 411, hot gas bypass circuit; 50, liquid accumulator; 60, primary subcooling heat exchanger; 601, fifth end; 602, sixth end; 603, seventh end; 604, eighth end; 61, secondary subcooling heat exchanger; 611, first end; 612, second end; 613, third end; 614, fourth end; 70, first solenoid valve; 71, second solenoid valve; 72, third solenoid valve; 73, fourth solenoid valve; 74, fifth solenoid valve; 75, sixth solenoid valve; 76, seventh solenoid valve; 77, eighth solenoid valve; 78, constant pressure valve; 80, first throttling element; 81, second throttling element; 82, third throttling element; 83, fourth throttling element; 84, fifth throttling element; 85, sixth throttling element; 90, gas-liquid separator; 91, suction filter; 92, oil separator. DETAILED DESCRIPTION

[0035] In order to make the objectives, technical solutions, and advantages of the present application clearer, the present application will be further described in detail below with reference to the drawings and specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and do not limit the protection scope of the present application.

[0036] It should be noted that when a component is referred to as being "mounted on" another component, it can be directly on the other component or there can be a middle component. When a component is referred to as being "disposed on" another component, it can be directly disposed on the other component or there can be a middle component. When a component is referred to as being "fixed on" another component, it can be directly fixed on the other component or there can be a middle component. The terms "vertical", "horizontal", "left", "right", and similar expressions used herein are for illustrative purposes only and are not intended to be the only implementation.

[0037] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used in the description herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise.

[0038] See Figures 1 to 5The carbon dioxide refrigeration system 100 provided in an embodiment of the present application can be applied to supermarkets and cold storage, and is used for refrigerating the supermarkets and cold storage. The carbon dioxide refrigeration system 100 provided by the present application is a carbon dioxide multi-temperature zone refrigeration system.

[0039] In the application of the carbon dioxide refrigeration system, for different temperature zones, the existing design usually has three ways of double-stage compression, configuration of different temperature zone compressors and direct use of low-temperature compressors. The conventional double-stage compression is limited by the intermediate pressure, and the flexibility of temperature adjustment of the medium-temperature system is poor; the configuration of the multi-temperature zone compressor is relatively complex, and the investment cost is high; the direct use of the low-temperature compressor is simple, but the overheat steam evaporated by the first evaporator is throttled to low pressure and mixed with the low-temperature steam to enter the low-temperature compressor, which causes the displacement of the low-temperature compressor to increase, and the economy of the equipment is poor.

[0040] To solve the problems existing in the existing carbon dioxide refrigeration system, a carbon dioxide refrigeration system 100 is provided in an embodiment of the present application, which comprises a compressor 10, an air cooler 20, an ejector 30, a first evaporator 40 and a second evaporator 41. The air cooler 20 is connected between the outlet end of the compressor 10 and the inlet end of the ejector 30. The outlet end of the ejector 30 is connected to the inlet end of the first evaporator 40 and the inlet end of the second evaporator 41. The outlet end of the first evaporator 40 is connected to the inlet end of the compressor 10. The carbon dioxide refrigeration system 100 further comprises an ejector circuit 31, one end of which is connected to the inlet end of the ejector 30, and the other end is connected to the outlet end of the first evaporator 40 and the inlet end of the compressor 10, respectively. It should be explained that the connection in the present application can be direct connection or indirect connection, that is, other elements can be connected between the two connected elements. In the present embodiment, two evaporators are provided to refrigerate two target temperature zones. Of course, in other embodiments, three or more evaporators can be provided to realize refrigeration of multiple temperature zones.

[0041] The present application provides the ejector circuit 31 in the carbon dioxide refrigeration system 100, so that the ejector 30 can eject the overheat steam after the evaporation of the first evaporator 40. In this way, the throttling effect of the system is ensured, and the evaporation temperature of the first evaporator 40 can be flexibly adjusted to realize rapid cooling of the target temperature zone by the first evaporator. The provision of the ejector 30 and the ejector circuit 31 can make two temperature zones share one compressor with small load, that is, the compressor only needs to be configured with small medium-temperature load. In this way, the overall design of the system greatly reduces the cost and greatly improves the flexibility of the system.

[0042] It should be noted that in an embodiment of the present application, the ejector 30 is used to replace the throttling element in the existing system, and the ejector circuit 31 is arranged between the ejector 30 and the first evaporator 40. On the one hand, the ejector circuit 31 can eject the superheated vapor after the evaporation of the first evaporator 40, so as to accelerate the refrigeration effect of the first evaporator 40, so as to ensure the throttling effect and flexibly adjust the evaporation temperature in the system. On the other hand, the arrangement of the ejector circuit 31 can replace the configuration of the medium-temperature compressor in the existing system. When the medium-temperature zone (the target temperature zone corresponding to the first evaporator) has a large load, the outlet of the first evaporator is connected with the inlet end of the low-temperature compressor. In this way, the low-temperature compressor only needs to be configured with a small medium-temperature load to realize operation. In the overall design of the carbon dioxide refrigeration system, the investment cost of the compressor is greatly reduced, and the flexibility of the system is greatly improved.

[0043] As shown in Figure 1 The carbon dioxide refrigeration system 100 further comprises a liquid accumulator 50. The liquid accumulator 50 is connected between the ejector 30 and the second evaporator 41. The liquid accumulator 50 has a gas port and a liquid port. The second evaporator 41 is connected between the liquid port of the liquid accumulator 50 and the inlet end of the compressor 10. Specifically, the liquid accumulator 50 is connected to the outlet end of the ejector 30, and the second evaporator 41 is connected to the inlet end of the compressor 10. It should be noted that the refrigerant from the ejector 30 is in a gas-liquid two-phase state, enters the liquid accumulator 50 for gas-liquid separation, and the liquid accumulator 50 has a plurality of gas ports and a plurality of liquid ports. The gas ports are located at the upper end of the liquid accumulator 50, and the liquid ports are located at the lower end of the liquid accumulator 50.

[0044] In this embodiment, the first evaporator 40 is a medium-temperature evaporator, and the second evaporator 41 is a low-temperature evaporator. By arranging the medium-temperature evaporator and the low-temperature evaporator in the carbon dioxide refrigeration system 100, dual-temperature-zone refrigeration in the carbon dioxide refrigeration system 100 is realized.

[0045] It should be noted that the dual-temperature zone refers to two temperature values of the refrigeration object. The first evaporator 40 and the second evaporator 41 are set to different temperatures, and then placed or acted on different areas. Generally, the evaporation temperature of the first evaporator 40 is set to-8℃~10℃, such as 4℃ or 5℃. In a normal case, frost will not form, so the first evaporator 40 does not need to be defrosted, or the first evaporator 40 will be automatically defrosted when it is stopped running. For the second evaporator 41, the evaporation temperature is set to below zero degrees, such as-20℃, so it is easy to frost. Therefore, a hot gas bypass circuit 411 is generally arranged in the carbon dioxide refrigeration system 100 to defrost the second evaporator 41.

[0046] In existing multi-temperature zone CO2 refrigeration systems, defrosting methods for low-temperature systems typically include water defrosting, electric defrosting, and hot gas defrosting. Water defrosting systems require an additional defrosting water system, resulting in higher initial investment costs; electric defrosting systems consume a lot of energy and are less economical; relatively speaking, hot gas defrosting systems are the most economical. Conventional CO2 transcritical systems often use four-way reversing valves to interchange the functions of the gas cooler and evaporator for hot gas defrosting. During defrosting, the low-temperature system cannot cool. When there are multiple low-temperature evaporators in the system, they need to be defrosted simultaneously, leading to large temperature fluctuations in the cold storage and high pressure requirements on the evaporators.

[0047] To address the above issues, the carbon dioxide refrigeration system 100 provided by this invention bypasses hot gas to the return pipe of the second evaporator 41, i.e., a hot gas bypass circuit 411 is provided. After throttling and pressure reduction, the hot gas enters the second evaporator 41 for defrosting. The cooled refrigerant enters the liquid receiver 50 from the gas port, which improves the system's application flexibility and effectively reduces the pressure on the second evaporator 41. Here, the pressure refers to the design pressure of the evaporator. The higher the design pressure of the evaporator, the thicker the wall, and the higher the equipment cost.

[0048] Specifically, the hot gas bypass circuit 411, i.e., the second evaporator 41, is connected at one end to the gas port of the liquid receiver 50, and at the other end to the outlet of the compressor 10 and the circuit of the air cooler 20. The compressor 10 compresses the low-temperature, low-pressure refrigerant into a high-temperature, high-pressure refrigerant, which then flows out from the outlet of the compressor 10. Part of the refrigerant enters the air cooler 20, while the other part enters the second evaporator 41 through the hot gas bypass circuit 411 for defrosting. By connecting the second evaporator 41 between the liquid receiver 50 and the air cooler 20, hot gas is bypassed to the return pipe of the second evaporator 41, and after throttling and pressure reduction, enters the second evaporator 41 for defrosting. It is important to note that at this time, the circuit between the second evaporator 41 and the outlet of the liquid receiver 50 needs to be closed to stop the operation of the second evaporator 41, i.e., to stop the second evaporator 41 from cooling the target temperature range. This increases the defrosting efficiency of the second evaporator 41 and saves energy.

[0049] Further, the carbon dioxide refrigeration system 100 further comprises a primary recooling heat exchanger 60 and a secondary recooling heat exchanger 61. The primary recooling heat exchanger 60 has a fifth end 601, a sixth end 602, a seventh end 603 and an eighth end 604, and the secondary recooling heat exchanger 61 has a first end 611, a second end 612, a third end 613 and a fourth end 614. The first end 611 and the second end 612 are in communication, the third end 613 and the fourth end 614 are in communication, the fifth end 601 and the sixth end 602 are in communication, and the seventh end 603 and the eighth end 604 are in communication. The outlet end of the air cooler 20 is connected to the sixth end 602, the fifth end 601 is connected to the second end 612, the first end 611 is connected to the inlet end of the ejector 30, the seventh end 603 is connected to the ejecting bypass circuit 32, the eighth end 604 is connected to the liquid port of the liquid reservoir 50, and the third end 613 is connected to the gas port of the liquid reservoir 50.

[0050] It should be noted that according to the load size of the first evaporator 40, the system opens the ejecting bypass circuit 32, that is, the circuit from the liquid reservoir 50 to the eighth end 604, then from the seventh end 603 to the inlet end of the ejector 30, and finally from the outlet end of the ejector 30 to the liquid reservoir 50. When the ejecting circuit 31 is cut off and does not participate in the work, the ejector 30 performs the ejection of the low-pressure refrigerant through the ejecting bypass circuit 32, which not only reduces the temperature of the carbon dioxide gas before the first throttling, greatly improves the system energy efficiency, but also ensures the normal work of the ejector 30.

[0051] Specifically, the compressor 10 has a gas supplementing and enthalpy increasing port 11, and the fourth end 614 is connected to the gas supplementing and enthalpy increasing port 11. It should be noted that in the carbon dioxide refrigeration system 100, since the refrigerant is carbon dioxide, due to the characteristics of the refrigerant itself, the carbon dioxide cannot be condensed in the air cooler 20, that is, the lower the outlet temperature of the air cooler 20, the higher the system energy efficiency. In order to reduce the gas temperature, the prior art usually uses supercooling technology to recool the carbon dioxide gas from the air cooler 20. The conventional supercooling technology usually uses an independent small freon refrigeration system to cool it, which reduces the environmental protection and economy of the system. In the carbon dioxide system using multi-stage throttling, the gas separated from the liquid in the liquid reservoir 50 after the first throttling is usually compressed in parallel to the air cooler 20 for cooling, which also leads to a large investment in the system. In view of the above problems, the carbon dioxide refrigeration system 100 provided by the present application throttles the gas separated from the liquid in the liquid reservoir 50 after the first throttling into a gas-liquid two-phase mixture, absorbs heat in the secondary recooling heat exchanger 61 and returns to the gas supplementing and enthalpy increasing port 11 of the compressor 10, which can save energy consumption and reduce the use amount of the compressor 10 in the carbon dioxide refrigeration system 100.

[0052] Further, the carbon dioxide refrigeration system 100 comprises a first electromagnetic valve 70, a second electromagnetic valve 71, a third electromagnetic valve 72 and a fourth electromagnetic valve 73, the first electromagnetic valve 70 is connected between the reservoir 50 and the third end 613, one end of the second electromagnetic valve 71 is connected to the outlet end of the first evaporator 40 and the ejector circuit 31 respectively, and the other end is connected to the inlet end of the compressor 10, the third electromagnetic valve 72 is connected between the liquid port of the reservoir 50 and the inlet end of the first evaporator 40, and the fourth electromagnetic valve 73 is connected between the liquid port of the reservoir 50 and the eighth end 604; the carbon dioxide refrigeration system 100 comprises a first throttling element 80, a second throttling element 81, a third throttling element 82 and a fourth throttling element 83, the first throttling element 80 is connected between the first electromagnetic valve 70 and the third end 613, the second throttling element 81 is connected between the second electromagnetic valve 71 and the compressor 10, the third throttling element 82 is connected between the third electromagnetic valve 72 and the first evaporator 40, and the fourth throttling element 83 is connected between the fourth electromagnetic valve 73 and the eighth end 604.

[0053] Further, the carbon dioxide refrigeration system 100 comprises a fifth electromagnetic valve 74 and a sixth electromagnetic valve 75, the fifth electromagnetic valve 74 is connected between the reservoir 50 and the second evaporator 41, and the sixth electromagnetic valve 75 is connected between the second evaporator 41 and the inlet end of the compressor 10; the carbon dioxide refrigeration system 100 comprises a fifth throttling element 84, and the fifth throttling element 84 is connected between the fifth electromagnetic valve 74 and the second evaporator 41.

[0054] Further, the carbon dioxide refrigeration system 100 comprises a seventh electromagnetic valve 76, an eighth electromagnetic valve 77 and a sixth throttling element 85, one end of the seventh electromagnetic valve 76 is connected to the outlet end of the compressor 10 and the air cooler 20 respectively, and the other end is connected to the sixth throttling element 85, one end of the sixth throttling element 85 away from the seventh electromagnetic valve is connected to the second evaporator 41 and the sixth electromagnetic valve 75 respectively, the eighth electromagnetic valve 77 is arranged on the ejector circuit 31, one end of the eighth electromagnetic valve 77 is connected to the outlet end of the first evaporator 40 and the inlet end of the compressor 10 respectively, and the other end is connected to the ejector 30 and the seventh end 603 respectively; the carbon dioxide refrigeration system 100 further comprises a constant pressure valve 78, one end of the constant pressure valve 78 is connected to the second evaporator 41 and the fifth throttling element 84 respectively, and the other end is connected to the gas port of the reservoir 50.

[0055] Further, the carbon dioxide double-temperature-zone refrigeration system further comprises a gas-liquid separator 90, a suction filter 91 and an oil separator 92. The inlet end of the gas-liquid separator 90 is connected to the second throttling element 81 and the sixth electromagnetic valve 75 respectively, the outlet end of the gas-liquid separator 90 is connected to the suction filter 91, the suction filter 91 is connected between the inlet end of the compressor 10 and the outlet end of the gas-liquid separator 90; the oil separator 92 is connected between the outlet end of the compressor 10 and the air cooler 20, the oil separator 92 has an oil return port, and the oil return port is connected to the compressor 10 for returning oil to the compressor 10.

[0056] As shown in FIG. 1, Figure 2 The present application provides a first refrigeration mode, when the carbon dioxide refrigeration system 100 is in the first refrigeration system mode, the first evaporator 40 and the second evaporator 41 are both in operation, that is, the medium-low temperature system is running at this time. In the present embodiment, the medium temperature generally refers to an evaporation temperature of -8℃~10℃, and the library temperature generally ranges from 0℃ to 2℃.

[0057] When the carbon dioxide refrigeration system 100 is in the first refrigeration system mode, only the constant pressure valve 78 and the seventh solenoid valve 76 are closed, which means the hot gas bypass circuit 411 is closed. The compressor 10 compresses the low-temperature, low-pressure carbon dioxide gas into high-temperature, high-pressure superheated vapor. After the high-pressure gas is separated into oil and gas in the oil separator 92, it enters the air cooler 20 for cooling. After being cooled, the carbon dioxide gas passes through the primary recooling heat exchanger 60 and the secondary recooling heat exchanger 61. Then, it is mixed with the low-pressure refrigerant from the first evaporator 40 and / or the primary recooling heat exchanger 60 via the ejector 30. The mixture is then throttled and depressurized to medium-temperature, medium-pressure refrigerant and enters the liquid receiver 50. The gas in the liquid receiver 50 is throttled by the first throttling element 80 and enters the secondary recooling heat exchanger 61 to absorb heat. It then flows out from the fourth end 614 and enters the compressor 10's gas injection enthalpy-increasing port 11 via a pipeline. The liquid outlet of the liquid reservoir 50 is divided into three paths. One path passes through the third solenoid valve 72 and is throttled by the third throttling element 82 before entering the first evaporator 40 for evaporation. The return gas path after evaporation is divided into two paths. One path passes through the ejector circuit 31 and enters the ejector 30 to complete most of the gas ejection. The other path connects to the return gas path of the compressor 10, passes through the second solenoid valve 71 and is throttled by the second throttling element 81 before entering the gas-liquid separator 90, and then enters the inlet of the compressor 10 through the suction filter 91. When the medium temperature load is large, the eighth solenoid valve 77 is opened, i.e. The ejector circuit 31 is opened to achieve rapid cooling in the medium temperature zone; one path passes through the fourth solenoid valve 73 and is throttled by the fourth throttling element 83 before entering the eighth end 604 of the primary recooler for evaporation, and is then ejected into the ejector 30 along with the return gas from the first evaporator 40; another path passes through the fifth solenoid valve 74 and is throttled by the fifth throttling element 84 before entering the second evaporator 41. After evaporation, the low-temperature and low-pressure refrigerant passes through the sixth solenoid valve 75, the gas-liquid separator 90, and the suction filter 91 from the inlet end of the compressor 10 and enters the compressor 10 for compression, and so on.

[0058] like Figure 3 As shown, the present invention provides a second refrigeration mode. When the carbon dioxide refrigeration system 100 is in the second refrigeration system mode, the first evaporator 40 is in operation and the second evaporator 41 is in non-operation state. That is to say, only the medium temperature system is in operation at this time.

[0059] When the carbon dioxide refrigeration system 100 is in the second refrigeration system mode, in addition to closing the constant pressure valve 78 and the seventh solenoid valve 76, the fifth solenoid valve 74 and the eighth solenoid valve 77 must also be closed. The liquid pipeline from the receiver 50 is divided into three paths, with the fifth solenoid valve 74 closed, and the third solenoid valve 72 and the second and fourth solenoid valves 73 open. One path passes through the fourth solenoid valve 73 and is throttled by the fourth throttling element 83 before entering the eighth terminal 604 of the primary recooler for evaporation. After evaporation, the gas is ejected into the ejector 30 via the ejector bypass circuit 32. The other path passes through the third solenoid valve 72 and is throttled by the third throttling element 82 before entering the first evaporator 40 for evaporation. The evaporated gas passes through the second solenoid valve 71 and is throttled by the second throttling element 81 before returning to the compressor 10 via the return gas pipeline connected to the compressor 10. The gas from the gas port of the receiver 50 is throttled by the first throttling element 80 before entering the third terminal 613 of the secondary recooler for evaporation, and then enters the make-up enthalpy port 11 of the compressor 10 via a pipeline. The low-temperature, low-pressure refrigerant evaporated in the first evaporator 40 is compressed into high-temperature, high-pressure superheated vapor by the compressor 10 through the gas-liquid separator 90 and the suction filter 91. After oil-gas separation by the oil separator 92, it enters the air cooler 20 for cooling. The carbon dioxide gas coming out of the air cooler 20 passes through the primary recooling heat exchanger 60 and the secondary recooling heat exchanger 61, and then mixes with the gas from the seventh end 603 of the primary recooling heat exchanger 60 through the ejector 30. The mixture is throttled and depressurized to medium-temperature, medium-pressure refrigerant, which then enters the liquid receiver 50. This cycle repeats continuously.

[0060] It should be noted that when only the medium-temperature system is running, the eighth solenoid valve 77 is closed to shut down the ejector circuit 31. When one evaporator in the carbon dioxide refrigeration system 100 is shut down, one compressor 10 is sufficient to drive the system. Therefore, it is not necessary to open the ejector circuit 31 to accelerate the cooling effect of the first evaporator 40. The purpose of opening the ejector bypass circuit 32 instead of the ejector circuit 31 is based on the inherent characteristics of the ejector 30. The ejector 30 is a device that uses high-pressure fluid to eject low-pressure fluid. After the high and low-pressure fluids mix inside the ejector 30, they flow to the outlet of the ejector 30, where the outlet pressure is generally between the high and low pressure fluids being ejected. Therefore, in addition to the flow channel for high-pressure fluid, the ejector 30 also needs a flow channel for low-pressure fluid. The ejector bypass circuit 32 is used to allow low-pressure fluid to flow into the ejector 30, thus ensuring the normal operation of the ejector 30.

[0061] like Figure 4 As shown, the present invention provides a third refrigeration mode. When the carbon dioxide refrigeration system 100 is in the third refrigeration system mode, the first evaporator 40 is in a non-operating state, and the second evaporator 41 is in an operating state. That is to say, only the low temperature system is operating at this time.

[0062] When the carbon dioxide refrigeration system 100 is in the third refrigeration system mode, in addition to closing the constant pressure valve 78 and the seventh solenoid valve 76, the second solenoid valve 71, the third solenoid valve 72, and the eighth solenoid valve 77 must also be closed. When only the cryogenic system is running, the liquid pipeline from the receiver 50 is divided into three paths. The third solenoid valve 72, which supplies liquid to the first evaporator 40, is closed. The other two paths are open, namely, the fourth solenoid valve 73 and the fifth solenoid valve 74 are open. One path passes through the fourth solenoid valve 73, is throttled by the fourth throttling element 83, and then enters the eighth end 604 of the primary recooling heat exchanger 60 for evaporation. After evaporation, it is ejected into the ejector 30 via the ejector bypass circuit 32. The other path passes through the fifth solenoid valve 74 and the fifth throttling element 84 to enter the second evaporator. The evaporated gas passes through the sixth solenoid valve 75, gas-liquid separator 90, and suction filter 91, and is compressed into high-temperature, high-pressure superheated vapor by compressor 10. After oil-gas separation by oil separator 92, it enters air cooler 20 for cooling. Carbon dioxide gas exiting air cooler 20 passes through primary recooling heat exchanger 60 and secondary recooling heat exchanger 61, and then mixes with gas exiting from the seventh end 603 of primary recooling heat exchanger 60 via ejector 30. This mixture is throttled and depressurized to a medium-temperature, medium-pressure refrigerant, which then enters receiver 50. Gas exiting receiver 50 is throttled by first throttling element 80 and enters the third end 613 of secondary recooling heat exchanger 61 to absorb heat. It then enters the enthalpy-boosting port 11 of compressor 10 via pipeline, and this cycle repeats continuously.

[0063] It should be noted that when only the cryogenic system is running, the eighth solenoid valve 77 is closed to shut down the ejector circuit 31. When the first evaporator 40 in the carbon dioxide refrigeration system 100 is shut down, all circuits related to the first evaporator 40 will be closed, including the ejector circuit 31, which is used to accelerate the cooling effect of the first evaporator 40. Since the first evaporator 40 is already shut down, there is no need to accelerate its cooling effect through the ejector circuit 31. Therefore, when only the cryogenic system is running, the eighth solenoid valve 77 is closed to shut down the ejector circuit 31. The ejector bypass circuit 32 is opened to ensure the normal operation of the ejector 30.

[0064] like Figure 5 As shown, the present invention provides a defrosting mode in which the first evaporator 40 and the second evaporator 41 are both in operation when the carbon dioxide refrigeration system 100 is in defrosting mode.

[0065] When the carbon dioxide refrigeration system 100 is in the defrosting mode, the eighth solenoid valve 77, the fifth solenoid valve 74 and the sixth solenoid valve 75 are closed, and the constant pressure valve 78 and the seventh solenoid valve 76 are opened. The high-temperature and high-pressure refrigerant vapor discharged from the compressor 10 is separated into two paths after oil-gas separation in the oil separator 92. One path enters the second evaporator 41 to defrost the second evaporator 41 after throttling and pressure reduction by the seventh solenoid valve 76 in the hot gas bypass circuit 411 and the sixth throttling element 85, and the cooled gas enters the receiver 50 from the gas port of the receiver 50 through the constant pressure valve 78 from the outlet end of the second evaporator 41, and the gas in the receiver 50 enters the third end 613 of the secondary re-cooler after throttling by the first throttling element 80 to absorb heat, and then enters the gas supplementing and enthalpy increasing port 11 of the compressor 10 through the pipeline. The other path enters the air cooler 20, and after the primary re-cooling heat exchanger 60 and the secondary re-cooling heat exchanger 61, the mixed gas from the primary re-cooling heat exchanger 60 is throttled and pressure-reduced by the ejector 30 to become medium-temperature and medium-pressure refrigerant, and enters the receiver 50. The liquid pipeline from the receiver 50 is divided into three paths, of which the fifth solenoid valve 74 supplying liquid to the second evaporator 41 is closed, and the other two paths are opened to supply liquid. One path enters the primary re-cooling heat exchanger 60 after throttling by the fourth throttling element 83 through the fourth solenoid valve 73, evaporates, and is injected into the ejector 30 through the ejector bypass circuit 32. The other path enters the first evaporator 40 after throttling by the third throttling element 82 through the third solenoid valve 72, evaporates, and the gas returns to the compressor 10 through the return gas pipe connected to the compressor 10.

[0066] It is worth noting that when the hot gas bypass circuit 411 is opened to defrost the second evaporator 41, the eighth solenoid valve 77 also needs to be closed. Since the defrosting mode of the second evaporator 41 is hot gas defrosting, and the refrigeration and defrosting of the first evaporator 40 and the second evaporator 41 cannot be operated simultaneously. If the injection circuit 31 and the suction circuit of the second evaporator 41 are opened at the same time, the first evaporator 40 will soon reach the designed temperature, the superheat degree of the outlet of the first evaporator 40 will be too low, and the compressor 10 will stop running, which will cause the defrosting to fail to operate normally. Moreover, when the second evaporator 41 is defrosted, the second evaporator 41 also needs to be inoperative, i.e., the fifth solenoid valve 74 is closed, to avoid the second evaporator 41 from refrigerating during the defrosting process. In this way, energy loss can be saved, and defrosting efficiency can be improved.

[0067] The embodiment of the present application further provides a carbon dioxide refrigeration system 100 control method, which is applied to the carbon dioxide refrigeration system 100 and mainly aims at the first refrigeration mode. The carbon dioxide refrigeration system 100 control method comprises the following steps: detecting the back gas superheat A at the first evaporator 40 and comparing the back gas superheat A with the first preset superheat A1; if A>A1 and the condition A>A1 lasts for a first preset time T1, then the fourth electromagnetic valve 73 is closed and the eighth electromagnetic valve 77 is opened; if A>A1 and the condition A>A1 lasts for a second preset time T2, then the second electromagnetic valve 71 is opened, wherein T2>T1; if A≤A1 and the condition A≤A1 lasts for a third preset time T3, then the second electromagnetic valve 71 is closed.

[0068] It should be noted that when the back gas superheat A at the outlet end of the first evaporator 40 is too large, it indicates that the first evaporator 40 has not reached the required refrigeration capacity, and therefore it is necessary to accelerate the refrigeration of the first evaporator 40, at this time the eighth electromagnetic valve 77 is opened to open the ejector circuit 31, so as to accelerate the refrigeration efficiency of the first evaporator 40; and the fourth electromagnetic valve 73 is closed mainly because the opening of the fourth electromagnetic valve 73 will open the ejector bypass circuit 32, since the ejecting amount entering the ejector 30 is constant, therefore the opening of the ejector bypass circuit 32 will divert part of the flow of the ejector circuit 31, thereby reducing the refrigeration efficiency of the first evaporator 40 to some extent, and therefore the fourth electromagnetic valve 73 needs to be closed at this time to improve the refrigeration efficiency of the first evaporator 40. When the back gas superheat A at the outlet end of the first evaporator 40 is still too large after a period of time, the second electromagnetic valve 71 needs to be opened at this time, so that the first evaporator 40 is connected with the inlet end of the compressor 10, so that the refrigeration capacity of the first evaporator 40 can be further increased on the basis of the ejector circuit 31. When the back gas superheat A at the outlet end of the first evaporator 40 is too small, the second electromagnetic valve 71 is closed for the same reason.

[0069] The embodiment of the present application further provides a carbon dioxide refrigeration system 100 control method, which is applied to the carbon dioxide refrigeration system 100 and mainly aims at the first refrigeration mode. The carbon dioxide refrigeration system 100 control method comprises the following steps: detecting the back gas superheat A at the first evaporator 40 and comparing the back gas superheat A with the first preset superheat A1; if A>A1 and the condition A>A1 lasts for a first preset time T1, then the fourth electromagnetic valve 73 is closed and the eighth electromagnetic valve 77 is opened; if A>A1 and the condition A>A1 lasts for a second preset time T2, then the second electromagnetic valve 71 is opened, wherein T2>T1; if A≤A1 and the condition A≤A1 lasts for a third preset time T3, then the second electromagnetic valve 71 is closed.

[0070] It should be noted that when the superheat A of the return gas at the outlet end of the second evaporator 41 is too small, it indicates that the second evaporator 41 has reached the required refrigerating capacity, at this time the opening of the fifth throttling element 84 will also be small, when the opening of the fifth throttling element 84 is small, the compressor 10 will be in a low pressure protection state, at this time the second electromagnetic valve 71 is opened to increase the suction pressure of the compressor 10, to ensure the normal operation of the compressor 10, to avoid the compressor 10 from being unable to work due to low pressure protection. When the superheat B of the return gas at the outlet end of the second evaporator 41 is too large, the second electromagnetic valve 71 is closed.

[0071] The technical features of the above-described embodiments can be combined in any manner. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described, but it should be considered that any combination of the technical features is within the scope of the present disclosure as long as the combination does not result in a contradiction.

[0072] The above-described embodiments only express several implementation manners of the present application, and the description is relatively specific and detailed, but it should not be understood as a limitation on the scope of the patent. It should be noted that for those skilled in the art, some modifications and improvements can be made without departing from the concept of the present application, and these are within the protection scope of the present application. Therefore, the protection scope of the patent of the present application should be subject to the appended claims.

Claims

1. A carbon dioxide refrigeration system, characterized by, The carbon dioxide refrigeration system comprises a compressor (10), an air cooler (20), an ejector (30), a first evaporator (40), a second evaporator (41), a liquid accumulator (50), a primary recooling heat exchanger (60) and a secondary recooling heat exchanger (61), the air cooler (20) is connected between the outlet end of the compressor (10) and the inlet end of the ejector (30), the outlet end of the ejector (30) is connected to the inlet end of the first evaporator (40) and the inlet end of the second evaporator (41), and the outlet end of the first evaporator (40) is connected to the inlet end of the compressor (10); The carbon dioxide refrigeration system further comprises an ejector circuit (31), one end of the ejector circuit (31) is connected to the inlet end of the ejector (30), and the other end is respectively connected to the outlet end of the first evaporator (40) and the inlet end of the compressor (10); The liquid accumulator (50) is connected between the outlet end of the ejector (30) and the inlet end of the first evaporator (40), and the second evaporator (41) is connected between the liquid accumulator (50) and the inlet end of the compressor (10); The secondary recooling heat exchanger (61) has a first end (611) and a second end (612), the first end (611) and the second end (612) are respectively connected to the ejector (30) and the air cooler (20), and the first end (611) and the second end (612) are in communication; The primary recooling heat exchanger (60) has a fifth end (601), a sixth end (602), a seventh end (603) and an eighth end (604), the fifth end (601) and the sixth end (602) are respectively connected to the secondary recooling heat exchanger (61) and the air cooler (20), the seventh end (603) is connected to the ejector circuit (31), the eighth end (604) is connected to the liquid accumulator (50), the fifth end (601) and the sixth end (602) are in communication, and the seventh end (603) and the eighth end (604) are in communication.

2. The carbon dioxide refrigeration system of claim 1, wherein, The secondary recooling heat exchanger (61) further has a third end (613) and a fourth end (614), the compressor (10) has a gas supplementing and enthalpy increasing port (11), the third end (613) is connected to the liquid accumulator (50), the fourth end (614) is connected to the gas supplementing and enthalpy increasing port (11), and the third end (613) and the fourth end (614) are in communication.

3. The carbon dioxide refrigeration system of claim 2, wherein, One end of the second evaporator (41) is connected to the liquid accumulator (50), and the other end of the second evaporator (41) is respectively connected to the outlet end of the compressor (10) and the air cooler (20).

4. The carbon dioxide refrigeration system of claim 3, wherein, One end of the second evaporator (41) is respectively connected to the liquid accumulator (50), the eighth end (604) and the inlet end of the first evaporator (40), and the other end of the second evaporator (41) is connected to the inlet end of the compressor (10).

5. The carbon dioxide refrigeration system of claim 3, wherein, The carbon dioxide refrigeration system further comprises a first electromagnetic valve (70), a second electromagnetic valve (71), a third electromagnetic valve (72) and a fourth electromagnetic valve (73), the first electromagnetic valve (70) is connected between the reservoir (50) and the third end (613), one end of the second electromagnetic valve (71) is connected to the ejector circuit (31) and the outlet end of the first evaporator (40) respectively, the other end is connected to the inlet end of the compressor (10), the third electromagnetic valve (72) is connected between the reservoir (50) and the inlet end of the first evaporator (40), and the fourth electromagnetic valve (73) is connected between the reservoir (50) and the eighth end (604). The carbon dioxide refrigeration system comprises a first throttling element (80), a second throttling element (81), a third throttling element (82) and a fourth throttling element (83), the first throttling element (80) is connected between the first electromagnetic valve (70) and the third end (613), the second throttling element (81) is connected between the second electromagnetic valve (71) and the compressor (10), the third throttling element (82) is connected between the third electromagnetic valve (72) and the first evaporator (40), and the fourth throttling element (83) is connected between the fourth electromagnetic valve (73) and the eighth end (604).

6. The carbon dioxide refrigeration system of claim 3 or 4, wherein, The carbon dioxide refrigeration system comprises a fifth electromagnetic valve (74) and a sixth electromagnetic valve (75), the fifth electromagnetic valve (74) is connected between the reservoir (50) and the second evaporator (41), and the sixth electromagnetic valve (75) is connected between the second evaporator (41) and the inlet end of the compressor (10). The carbon dioxide refrigeration system comprises a fifth throttling element (84), the fifth throttling element (84) is connected between the fifth electromagnetic valve (74) and the second evaporator (41).

7. The carbon dioxide refrigeration system of claim 6, wherein, The carbon dioxide refrigeration system comprises a seventh electromagnetic valve (76) and a sixth throttling element (85), one end of the seventh electromagnetic valve (76) is connected to the outlet end of the compressor (10) and the air cooler (20) respectively, the other end is connected to the sixth throttling element (85), and one end of the sixth throttling element (85) away from the seventh electromagnetic valve is connected to the second evaporator (41) and the sixth electromagnetic valve (75) respectively. The carbon dioxide refrigeration system comprises a constant pressure valve (78), one end of the constant pressure valve (78) is connected to the second evaporator (41) and the fifth throttling element (84) respectively, and the other end is connected to the reservoir (50).

8. The carbon dioxide refrigeration system of claim 1, wherein, The carbon dioxide refrigeration system comprises an eighth electromagnetic valve (77), and the eighth electromagnetic valve (77) is arranged on the ejector circuit (31).

9. A carbon dioxide refrigeration system control method characterized by, The carbon dioxide refrigeration system control method is applied to the carbon dioxide refrigeration system as claimed in any one of claims 1-8, and the carbon dioxide refrigeration system further comprises a primary recooling heat exchanger (60), a fourth electromagnetic valve (73), an eighth electromagnetic valve (77) and a second electromagnetic valve (71), the primary recooling heat exchanger (60) is connected between the air cooler (20) and the ejector (30), the fourth electromagnetic valve (73) is connected between the ejector (30) and the primary recooling heat exchanger (60), the eighth electromagnetic valve (77) is arranged on the ejector circuit (31), and one end of the second electromagnetic valve (71) is connected to the first evaporator (40) and the ejector circuit (31), and the other end is connected to the inlet end of the compressor (10); The carbon dioxide refrigeration system control method comprises: detecting the return gas superheat A at the first evaporator (40) and comparing the return gas superheat A with a first preset superheat A1; If A>A1 and the condition lasts for a first preset time T1, the fourth electromagnetic valve (73) is closed, and the eighth electromagnetic valve (77) is opened; If A>A1 and the condition lasts for a second preset time T2, the second electromagnetic valve (71) is opened, wherein T2>T1; If A≤A1 and the condition lasts for a third preset time T3, the second electromagnetic valve (71) is closed.

10. A carbon dioxide refrigeration system control method characterized by, The carbon dioxide refrigeration system control method is applied to the carbon dioxide refrigeration system as claimed in any one of claims 1-8, and the carbon dioxide refrigeration system comprises a second evaporator (41), a liquid accumulator (50) and a second electromagnetic valve (71), the liquid accumulator (50) is connected between the ejector (30) and the first evaporator (40), one end of the second evaporator (41) is connected to the liquid accumulator (50), the other end of the second evaporator (41) is connected to the air cooler (20) and the outlet end of the compressor (10) respectively, and the second electromagnetic valve (71) is connected between the inlet end of the compressor (10) and the outlet end of the first evaporator (40); The carbon dioxide refrigeration system control method comprises: detecting the return gas superheat B at the second evaporator (41) and comparing the return gas superheat B with a second preset superheat B1; If B If B≥B1 and the condition lasts for a fifth preset time T5, the second electromagnetic valve (71) is closed.

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