Two-stage compression phase change refrigeration system and refrigeration equipment

Abstract

The utility model discloses a two-stage compression phase change refrigerating system which comprises a two-stage compressor, an air-cooled condenser, an evaporative condenser and a gas-liquid separator, the air-cooled condenser and the evaporative condenser are connected in series, an outlet pipeline of the air-cooled condenser is communicated with the evaporative condenser and the gas-liquid separator through a first three-way valve, and an outlet pipeline of the air-cooled condenser is communicated with the evaporative condenser and the gas-liquid separator through a second three-way valve. A gaseous refrigerant in the gas-liquid separator is introduced into the evaporative condenser to be condensed, and a liquid refrigerant is converged with a refrigerant at an outlet of the evaporative condenser through a first branch, and then enters a first throttle valve to be throttled to provide cooling capacity for a data center. According to the utility model, two refrigeration modes of natural cooling and mechanical refrigeration are adopted, so that the PUE value of the data center is greatly reduced.

Description

Technical Field

[0001] The utility model relates to the technical field of refrigeration, in particular to a two-stage compression phase change refrigeration system and a refrigeration device. Background Art

[0002] With the rapid development of the Internet, the scale and integration degree of data centers are developing faster and faster. A data center includes many computer devices, and these devices will generate a large amount of heat during operation. If the generated heat is not processed in time, these devices may malfunction due to overheating, affecting the normal operation of the data center. Most existing data centers use a refrigeration cycle system with a cooling tower to cool the devices. This solution has many heat exchange links, high energy consumption, a high PUE value (the ratio of all energy consumed by the data center to the energy consumed by the load), poor overall energy saving performance, and lack of good flexibility and economy.

[0003] How to well solve the heat dissipation problem of the data center and reduce the energy consumption of the devices at the same time is a technical problem urgently to be solved in the industry. Summary of the Utility Model

[0004] The utility model provides a two-stage compression phase change refrigeration system and a refrigeration device to solve the problem of high energy consumption of existing data center refrigeration devices.

[0005] The two-stage compression phase change refrigeration system provided by the utility model includes a two-stage compressor and a first throttle valve. An air-cooled condenser and an evaporative condenser are connected in series between them. It is characterized in that it further includes a gas-liquid separator. The refrigerant outlet pipeline of the air-cooled condenser is respectively communicated with the evaporative condenser and the gas-liquid separator through a first three-way valve. The gaseous refrigerant in the gas-liquid separator is introduced into the evaporative condenser for condensation. The liquid refrigerant converges with the refrigerant at the outlet of the evaporative condenser through a first branch, and then enters the first throttle valve.

[0006] Further, the two-stage compression phase change refrigeration system further includes a flash evaporator. The upper opening of the flash evaporator is communicated with the gas replenishing pipeline between the two-stage compressor. The middle opening of the flash evaporator is communicated with the outlet pipeline of the first throttle valve. The lower opening of the flash evaporator is communicated with a second throttle valve through a pipeline, and the second throttle valve is communicated with the heat exchange end.

[0007] Further, the two-stage compression phase change refrigeration system further includes an intermediate heat exchanger. The refrigerant from the flash evaporator is introduced into the main path refrigerant inlet pipeline of the intermediate heat exchanger. The discharged main path refrigerant is divided into two paths after passing through a first one-way valve. One path is introduced into the intermediate heat exchanger to supercool the main path refrigerant after passing through a third throttle valve, and then is communicated with the suction port of the low-pressure stage compressor in the two-stage compressor through a third branch. A first electric valve is provided on the third branch. The other path is communicated with the second throttle valve.

[0008] Furthermore, a bypass is connected in parallel at both ends of the first one-way valve. A fluorine pump is provided on the bypass. The outlet of the evaporative condenser is connected to the inlet of the main refrigerant pipe of the intermediate heat exchanger through a second branch. A second electric valve is provided on the second branch. A fourth branch is led out from the front end of the first electric valve on the third branch. A third electric valve is provided on the fourth branch, and the other end thereof converges with the outlet pipe of the main refrigerant of the intermediate heat exchanger. A fifth branch is connected between the inlet pipe of the air-cooled condenser and the outlet pipe of the heat exchange terminal, and a second one-way valve is provided thereon.

[0009] Preferably, a first liquid storage tank is provided on the outlet pipe of the main refrigerant of the intermediate heat exchanger, and a second liquid storage tank is provided on the fourth branch.

[0010] Preferably, the volume of the first liquid storage tank is larger than that of the second liquid storage tank. The second liquid storage tank is kept full of liquid so that the refrigerant at the inlet of the fluorine pump has sufficient subcooling degree.

[0011] When the double-stage compression phase change refrigeration system operates in the mechanical refrigeration mode in summer, the first electric valve is opened, the second electric valve and the third electric valve are closed, the fluorine pump is closed, the second one-way valve is closed, and the gas-liquid separator works.

[0012] When the double-stage compression phase change refrigeration system operates in the natural cooling mode in winter, the double-stage compressor is closed, the first one-way valve is closed, the second one-way valve is opened, the first electric valve is closed, the second electric valve and the third electric valve are opened, the first throttle valve is closed, the fluorine pump is opened, the second throttle valve and the third throttle valve are opened, the gas-liquid separator does not work, and the fan of the air-cooled condenser is set to open or close according to the ambient dry bulb temperature and the outlet temperature of the heat exchange terminal.

[0013] If the outlet temperature of the heat exchange terminal is lower than the ambient dry bulb temperature, the fan of the air-cooled condenser is closed; if the outlet temperature of the heat exchange terminal is higher than or equal to the ambient dry bulb temperature, the fan of the air-cooled condenser is opened.

[0014] The present invention also provides a refrigeration device, which adopts the above-mentioned double-stage compression phase change refrigeration system.

[0015] Compared with the prior art, the present invention has the following beneficial effects:

[0016] The present invention adopts the double-condenser technology of combining an air-cooled condenser and an evaporative condenser, and combines with a gas-liquid separator, which can effectively increase the condensation area and reduce the condensation pressure;

[0017] The present invention reduces the compression ratio of a single compressor by introducing double-stage compression, so that the working state of the compressor remains good.

[0018] The utility model adopts a flash evaporator as an inter-stage structure, which can save part of the compression work and increase the cycle efficiency of the system.

[0019] In addition, an intermediate heat exchanger and a liquid storage tank are used to subcool the refrigerant, improving the cooling capacity and energy efficiency of the system. Description of the Drawings

[0020] The following describes the utility model in detail with reference to the drawings and embodiments, where:

[0021] Figure 1 is the system diagram of the two-stage compression phase change refrigeration system proposed by the utility model;

[0022] Figure 2 is the schematic diagram showing the refrigerant flow direction in the mechanical refrigeration mode of the two-stage compression phase change refrigeration system;

[0023] Figure 3 is the schematic diagram showing the operation of the two-stage compression phase change refrigeration system in the natural cooling mode.

[0024] Wherein:

[0025] 1 two-stage compressor, 1a low-pressure stage compressor, 1b high-pressure stage compressor, 2 air-cooled condenser, 3 evaporative condenser, 41 first throttle valve, 42 second throttle valve, 43 third throttle valve, 51 first control valve, 52 second control valve, 53 third control valve, 61 first check valve, 62 second check valve, 71 first liquid storage tank, 72 second liquid storage tank, 8 flash evaporator, 9 intermediate heat exchanger, 10 fluorine pump, 11 heat exchange terminal, 12 gas-liquid separator, 13 make-up air pipeline, 14 first branch, 15 second branch, 16 third branch, 17 fourth branch, 18 fifth branch, 131 first three-way valve, 132 second three-way valve. Specific Embodiments

[0026] In order to make the purpose, technical solutions and advantages of the utility model clearer, the following describes the utility model in detail with reference to the drawings and embodiments.

[0027] The following embodiments are only used to illustrate the specific implementation manners of the utility model. For the technologies, methods and devices known to those of ordinary skill in the relevant fields, no detailed discussion is made in this specification, but in appropriate cases, the said technologies, methods and devices should be regarded as a part of this specification. Any specific value in this specification should be interpreted as merely exemplary and not as a limitation to the present invention.

[0028] For ease of description, the terms used in the specification to describe positions, such as "above...", "to the left of...", "in front of...", etc., are only used to describe the spatial position relationship between a certain component of the embodiment shown in the figure and other components. When the position where the component is placed is different, the relative position will change. Therefore, the positional relationship of the embodiments in the drawings should not constitute a limitation to the present invention.

[0029] In addition, it should be noted that the terms "first", "second", etc. used in the specification are only for differentiating similar components and there is no sequential order, so it should not be understood as constituting a limitation to the protection scope of the present invention.

[0030] As mentioned in the background art, most of the existing data centers use a refrigeration cycle system with a cooling tower to cool the equipment. This solution has many heat exchange links and high energy consumption. The improvement idea of the present utility model is as follows: an air-cooled condenser and an evaporative condenser are connected in series in the refrigeration system, and a gas-liquid separator is added between the two to improve the condensation speed and heat exchange efficiency in the condensation section, so as to achieve the purpose of reducing the pressure ratio and energy consumption.

[0031] The refrigerant used in the two-stage compression refrigeration system proposed by the present utility model is a phase change heat transfer working medium, which converts the liquid refrigerant into a gaseous refrigerant by absorbing heat and converts the gaseous refrigerant into a liquid refrigerant by releasing heat. The system can operate in two refrigeration modes according to the ambient temperature: mechanical refrigeration mode and natural cooling mode.

[0032] Figure 1 This is a diagram of the two-stage compression phase change refrigeration system proposed by the present utility model. The two-stage compression phase change refrigeration system proposed by the present utility model includes a two-stage compressor 1, an air-cooled condenser 2 and an evaporative condenser 3 connected in series, a first throttle valve 41, a flash tank 8, an intermediate heat exchanger 9, a second throttle valve 42 and a heat exchange terminal 11 connected by pipelines.

[0033] The heat exchange efficiency of the air-cooled condenser is not high in summer. Its main function is to reduce the exhaust temperature and at the same time condense part of the refrigerant, and this part of the refrigerant will vary according to the ambient temperature. The present utility model adds a gas-liquid separator between the air-cooled condenser and the evaporative condenser, and introduces the refrigerant liquefied in the air-cooled condenser into the gas-liquid separator. Its function is to separate the gas-liquid refrigerant coming out of the air-cooled condenser. The separated gaseous refrigerant enters the subsequent evaporative condenser to continue condensation. The gaseous refrigerant enters the evaporative condenser to continue condensation, which can improve the condensation speed and heat exchange efficiency and make the refrigerant fully condensed.

[0034] The two-stage compressor 1 is composed of a low-pressure stage compressor 1a and a high-pressure stage compressor 1b.

[0035] The utility model is based on a two-stage compression system, which uses an air-cooled condenser and an evaporative condenser in combination, operates mechanical refrigeration and natural cooling modes according to the ambient temperature, reduces the exhaust temperature of the compressor, reduces the superheat loss, and reduces the proportion of mechanical refrigeration, so as to achieve the purpose of improving the energy efficiency of the system.

[0036] The two-stage compression phase change refrigeration system further includes a gas-liquid separator 12. The refrigerant outlet pipe of the air-cooled condenser 2 is respectively communicated with the evaporative condenser 3 and the gas-liquid separator 12 through a first three-way valve 131. The gaseous refrigerant in the gas-liquid separator is introduced into the evaporative condenser for condensation through a second three-way valve 132. The liquid refrigerant converges with the refrigerant at the outlet of the evaporative condenser through a first branch 14, and then enters the first throttle valve 41. The refrigerant liquefied in the air-cooled condenser 2 is introduced into the gas-liquid separator for separation, so that all the refrigerant entering the evaporative condenser is gaseous refrigerant, which can improve the heat exchange efficiency of the evaporative condenser, further reduce the condensation temperature, and increase the condensation speed.

[0037] The two-stage compression phase change refrigeration system further includes a flash evaporator 8 and an intermediate heat exchanger 9. The upper gaseous refrigerant of the flash evaporator is communicated with the make-up air pipe 13 between the two-stage compressor for enthalpy-increasing make-up air to the high-pressure stage compressor 1b. The middle opening of the flash evaporator 8 is communicated with the outlet pipe of the first throttle valve 41, and the lower opening is communicated with the intermediate heat exchanger 9 through a pipe. The main path refrigerant discharged from the intermediate heat exchanger is divided into two paths after passing through the first one-way valve 61. One path is introduced into the intermediate heat exchanger through the third throttle valve 43 to subcool the main path refrigerant, and then is communicated with the suction port of the low-pressure stage compressor 1a in the two-stage compressor through a third branch 16. A first electric valve 51 is provided on the third branch. The other path is communicated with the second throttle valve 42, and the throttled refrigerant cools the heat exchange terminal 11.

[0038] Further, a bypass is connected in parallel at both ends of the first one-way valve 61, and a fluorine pump 10 is provided on the bypass. The outlet of the evaporative condenser 3 is communicated with the main path refrigerant inlet pipe of the intermediate heat exchanger 9 through a second branch 15, and a second electric valve 52 is provided on the second branch. A fourth branch 17 is led out from the front end of the first electric valve 51 on the third branch 16, and a third electric valve 53 is provided on it, and the other end of it converges with the main path refrigerant outlet pipe of the intermediate heat exchanger. A fifth branch 18 is connected between the intake pipe of the air-cooled condenser 2 and the outlet pipe of the heat exchange terminal, and a second one-way valve 62 is provided on it.

[0039] Preferably, a first liquid storage tank 71 is provided on the main path refrigerant outlet pipe of the intermediate heat exchanger, and a second liquid storage tank 72 is provided on the fourth branch 17. The volume of the first liquid storage tank is larger than that of the second liquid storage tank, and the second liquid storage tank is kept full of liquid, so that the refrigerant at the inlet of the fluorine pump has sufficient subcooling degree.

[0040] The utility model supercools the refrigerant in the main circuit by using an intermediate heat exchanger and a liquid storage tank, ensuring that the refrigerant at the inlet of the fluorine pump is in a liquid state in the natural cooling mode, so that the fluorine pump refrigeration system can operate normally.

[0041] The two-stage compression phase change refrigeration system proposed by the utility model includes a mechanical refrigeration mode and a natural cooling mode in winter for the summer system operation.

[0042] Figure 2 Show the schematic diagram of the refrigerant flow in the two-stage compression phase change refrigeration system in the mechanical refrigeration mode.

[0043] In the mechanical refrigeration mode in summer, the first control valve 51 is opened, the second control valve 52 is closed, and the third control valve 53 is closed. The main circuit refrigerant circulation of the system is: low-pressure stage compressor 1a - high-pressure stage compressor 1b - air-cooled condenser 2 - first three-way valve 131 - gas-liquid separator 12 - second three-way valve 132 - evaporation condenser 3 - first throttle valve 41 - flash evaporator 8 - intermediate heat exchanger 9 - first liquid storage tank 71 - first one-way valve 61, and then it is divided into two paths. One path flows through the second throttle valve 42 and then exchanges heat in the heat exchange terminal 11 to provide cooling for the equipment in the data center, and then returns to the low-pressure stage compressor 1a for recycling; the other path is the auxiliary path, which flows through the third throttle valve 43 and then enters the intermediate heat exchanger 9 to supercool the refrigerant in the main circuit, improving the supercooling degree of the refrigerant before the second throttle valve 42, increasing the amount of liquid refrigerant flowing into the heat exchange terminal 11, and improving the refrigeration capacity and energy efficiency of the system.

[0044] Figure 3 Show the schematic diagram of the refrigerant flow in the two-stage compression phase change refrigeration system in the natural cooling mode.

[0045] When the winter system operates in the natural cooling mode, the two-stage compressor 1 is turned off, the first check valve 61 is closed, the second check valve 62 is opened, the first electric valve 51 is closed, the second electric valve 52 and the third electric valve 53 are opened, the first throttle valve 41 is closed, the refrigerant pump 10 is opened, the second throttle valve 42 and the third throttle valve 43 are opened, and the gas-liquid separator 12 does not work. The refrigerant circulation of the system is as follows: After the refrigerant pump 10, it is divided into two paths. One path goes to the second throttle valve 42 - the heat exchange terminal 11 (providing cooling capacity for the data center) - the second check valve 62 - the air-cooled condenser 2 - the evaporative condenser 3 - the second branch 15 - the intermediate heat exchanger 9 - the first liquid storage tank 71 - returns to the refrigerant pump 10 for recirculation; the other path flows through the third throttle valve 43 and then enters the intermediate heat exchanger 9 to subcool the refrigerant in the main path, and then converges with the refrigerant in the main path through the third branch 16, the third electric valve 53, and the fourth branch 17, and returns to the refrigerant pump for recirculation. By introducing the refrigerant throttled by the third throttle valve into the intermediate heat exchanger 9 to subcool the refrigerant in the main path, the subcooling degree of the refrigerant before the refrigerant pump 10 and the second throttle valve 42 is increased, so that there is sufficient subcooling degree at the inlet of the refrigerant pump and the temperature of the liquid refrigerant flowing into the heat exchange terminal 11 after throttling is lower. This not only improves the refrigeration capacity and energy efficiency of the system, but also increases the duration of using natural cold sources. The operation of the natural cooling mode does not require starting the compressor, and fully utilizes the cold in the environment to provide cooling capacity for the data center, with remarkable energy-saving effect.

[0046] In the natural cooling mode, the fan of the air-cooled condenser is set to start and stop according to the ambient dry bulb temperature and the outlet temperature of the heat exchange terminal.

[0047] If the outlet temperature of the heat exchange terminal is lower than the ambient dry bulb temperature, the fan of the air-cooled condenser is turned off, and natural cooling can be used to achieve the heat exchange purpose without starting the fan, further saving energy; if the outlet temperature of the heat exchange terminal is higher than or equal to the ambient dry bulb temperature, the fan of the air-cooled condenser is turned on.

[0048] When the ambient temperature is close to or below the freezing point, the evaporative condenser automatically drains water to prevent icing.

[0049] In the present invention, the volume of the first liquid storage tank 71 is larger than that of the second liquid storage tank 72. The first liquid storage tank 71 is used to store the excess refrigerant in the system. The second liquid storage tank 72 is a small-volume liquid storage tank, which keeps full of liquid to ensure that the liquid refrigerant will not vaporize in the second liquid storage tank 72, so that the refrigerant at the inlet of the refrigerant pump 10 has sufficient subcooling degree.

[0050] The present invention uses an air-cooled condenser and an evaporative condenser in combination. The air-cooled condenser 2 is used as the primary condenser to reduce the exhaust temperature and condense part of the refrigerant. Since the condensation effect of the air-cooled condenser is determined by the ambient dry-bulb temperature, when the ambient temperature is lower, the temperature difference between the condenser and the surrounding environment is larger, and the condensation effect is better, and more liquid refrigerant can be condensed. The liquefied refrigerant is discharged from the system in advance through the gas-liquid separator 12, and the gaseous refrigerant enters the evaporative condenser 3 to continue condensation. Since the condensation effect of the evaporative condenser is determined by the ambient wet-bulb temperature. The refrigerant after passing through the air-cooled condenser 2 can reduce the exhaust temperature, improve the heat exchange capacity of the evaporative condenser 3 in the superheat degree, further reduce the condensation temperature, and facilitate the adjustment of the heat rejection load of the condenser.

[0051] Compared with the single-stage compression cycle, both compressors in the two-stage compression cycle operate under relatively small pressure ratio conditions, and the volumetric efficiency and electrical efficiency are improved. The two-stage compression can not only reduce the exhaust temperature of the compressor, but also reduce the superheat loss and the total power consumption of the compressor, ensuring the safe operation of the compressor and having obvious energy-saving effects.

[0052] In order to further improve the performance of the two-stage compression cycle, a flash tank 8 is used as the inter-stage structure. The flash tank 8 is essentially a gas-liquid separator. Its principle is that the refrigerant at the outlet of the condenser enters the flash tank 8 in a gas-liquid two-phase state after throttling through the first throttle valve. Due to the reduction in speed, gas-liquid separation occurs, and the saturated gas is "extracted" and then mixed with the exhaust of the low-pressure stage compressor 1a and enters the high-pressure stage compressor 1b together. This can save a part of the compression work. At the same time, since the saturated gas is separated, the specific enthalpy value of the refrigerant entering the evaporator decreases, increasing the refrigerating capacity per unit mass.

[0053] In order to make full use of natural resources, the present invention controls the use of the air-cooled condenser and the evaporative condenser according to the ambient temperature.

[0054] (1) In summer, the system adopts a mechanical refrigeration mode, and the refrigerant first passes through the air-cooled condenser 2 and then flows into the evaporative condenser 3. At this time, the heat exchange efficiency of the air-cooled condenser 2 in summer is not high and it cannot reduce the condensation temperature, but it can reduce the exhaust temperature. Part of the refrigerant is condensed in the air-cooled condenser 2, and the condensed liquid refrigerant is discharged from the system after passing through the gas-liquid separator 12. The gaseous refrigerant enters the evaporative condenser 3 to continue condensation, improving the heat exchange capacity of the evaporative condenser 3 in the superheat section, further reducing the condensation temperature, enhancing the condensation effect of the evaporative condenser 3, and reducing the energy consumption of the evaporative condenser 3 in a high-temperature environment.

[0055] (2) In winter, the system adopts a natural cooling mode, and the second one-way valve 62 is opened and the compressor does not work. At this time, the evaporative condenser 3 works, and the air-cooled condenser 2 needs to set the opening and closing of the fan of the air-cooled condenser 2 according to the ambient dry-bulb temperature and the outlet temperature of the heat exchange terminal 11:

[0056] When the ambient dry bulb temperature is higher than the outlet temperature of the heat exchange terminal 11, the air-cooled condenser 2 shuts down the fan, and the refrigerant flows to the evaporative condenser 3 after passing through the air-cooled condenser 2. At this time, the first three-way valve 131 and the second three-way valve 132 need to change the flow direction, bypassing the gas-liquid separator 12, and being cooled by the evaporative condenser 3 to reduce the power consumption of the air-cooled condenser 2.

[0057] When the ambient dry bulb temperature is lower than the outlet temperature of the heat exchange terminal, the air-cooled condenser 2 turns on the fan to jointly participate in the condensation process, increasing the condensation area, reducing the condensation temperature, increasing the subcooling degree, and thus improving the refrigeration capacity of the refrigeration system.

[0058] (3)When the ambient temperature is close to or below freezing point, the air-cooled condenser 2 can independently achieve the natural cooling mode. At this time, the evaporative condenser 3 automatically drains water to prevent the evaporation condenser pipes from bursting due to ice formation.

[0059] The combined use of the air-cooled condenser and the evaporative condenser proposed by the present utility model can achieve multiple mode switches, effectively utilize the advantages of the air-cooled condenser and the evaporative condenser in different seasons, reduce water resources and have high energy efficiency compared with a single condenser, realize the optimal utilization of energy, reduce the overall energy consumption of the system, and have greater energy-saving advantages.

[0060] It should be noted that for those of ordinary skill in the art, without departing from the concept of the present utility model, several modifications and variations can still be made, and all these modifications and variations should fall within the protection scope of the present utility model.

Claims

1. A two-stage compression phase change refrigeration system, comprising a two-stage compressor and a first throttle valve, between which an air-cooled condenser and an evaporative condenser are connected in series, characterized in that: It also includes a gas-liquid separator. The refrigerant outlet pipe of the air-cooled condenser is connected to the evaporative condenser and the gas-liquid separator respectively through a first three-way valve. The gaseous refrigerant in the gas-liquid separator is introduced into the evaporative condenser for condensation, and the liquid refrigerant merges with the refrigerant at the outlet of the evaporative condenser through a first branch, and then enters the first throttle valve.

2. The two-stage compression phase change refrigeration system according to claim 1, characterized in that: It also includes an intermediate heat exchanger. The liquid main refrigerant coming from the first throttle valve enters the intermediate heat exchanger for heat exchange. The discharged main refrigerant is divided into two paths after passing through the first one-way valve. One path is introduced into the intermediate heat exchanger after passing through the third throttle valve to supercool the main refrigerant, and then connected to the suction port of the low-pressure stage compressor in the two-stage compressor through the third branch. The third branch is provided with a first electric valve; the other path is connected to the second throttle valve.

3. The two-stage compression phase change refrigeration system according to claim 2, characterized in that: It also includes a flash evaporator, whose upper opening is connected to the air supply pipeline of the high-pressure stage compressor of the two-stage compressor, the middle opening is connected to the outlet pipe of the first throttle valve, and the lower opening is connected to the intermediate heat exchanger through a pipeline.

4. The two-stage compression phase change refrigeration system according to claim 3, characterized in that: A bypass is connected in parallel at both ends of the first one-way valve, and a fluorine pump is provided on the bypass. The outlet of the evaporative condenser is connected to the main refrigerant inlet pipeline of the intermediate heat exchanger through the second branch. A second electric valve is provided on the second branch. The third branch leads to a fourth branch at the front end of the first electric valve. A third electric valve is provided on the fourth branch, and the other end of the fourth branch merges with the main refrigerant outlet pipeline of the intermediate heat exchanger. A fifth branch is connected between the air inlet pipe of the air-cooled condenser and the outlet pipeline at the heat exchange end, and a second one-way valve is provided on the fifth branch.

5. The two-stage compression phase change refrigeration system according to claim 4, characterized in that: A first liquid storage tank is provided on the refrigerant outlet pipeline of the main circuit of the intermediate heat exchanger, and a second liquid storage tank is provided on the fourth branch circuit.

6. The two-stage compression phase change refrigeration system according to claim 5, characterized in that: The volume of the first liquid storage tank is greater than that of the second liquid storage tank, and the second liquid storage tank is kept full of liquid so that the refrigerant at the inlet of the fluorine pump has sufficient supercooling.

7. The two-stage compression phase change refrigeration system according to claim 6, characterized in that: When the system operates in the mechanical refrigeration mode in summer, the first electric valve is opened, the second electric valve and the third electric valve are closed, the fluorine pump is closed, the second one-way valve is closed, and the gas-liquid separator works.

8. The two-stage compression phase change refrigeration system according to claim 7, characterized in that: When the system operates in natural cooling mode in winter, the two-stage compressor is turned off, the first one-way valve is closed, the second one-way valve is opened, the first electric valve is closed, the second electric valve and the third electric valve are opened, the first throttle valve is closed, the fluorine pump is opened, the second throttle valve and the third throttle valve are opened, the gas-liquid separator does not work, and the fan of the air-cooled condenser is set to start and stop according to the ambient dry-bulb temperature and the heat exchange end outlet temperature.

9. The two-stage compression phase change refrigeration system according to claim 8, characterized in that: If the outlet temperature of the heat exchange end is lower than the ambient dry bulb temperature, the fan of the air-cooled condenser is turned off; if the outlet temperature of the heat exchange end is higher than or equal to the ambient dry bulb temperature, the fan of the air-cooled condenser is turned on.

10. A refrigeration device, characterized in that: The refrigeration equipment comprises the two-stage compression phase change refrigeration system according to any one of claims 1-9.

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