Cascade heat pump system

Abstract

The invention relates to the technical field of heating equipment, in particular to a cascade heat pump system which comprises a compressor, a condenser, a primary gas-liquid separator, a gas phase pipeline connected with the gas phase output end of the primary gas-liquid separator and a liquid phase pipeline connected with the liquid phase output end of the primary gas-liquid separator, the gas-phase separator is used for separating a liquid-phase working medium mixed in the gas-phase working medium; and the liquid-phase separator is used for separating a gas-phase working medium mixed in the liquid-phase working medium. After a primary gas-liquid separator is used for primarily separating a cooled gas-phase working medium and a cooled liquid-phase working medium, a gas-phase separator and a liquid-phase separator are respectively used for separating a small amount of gas-phase working medium mixed into the gas-phase working medium in a gas-phase pipeline and a small amount of gas-phase working medium mixed into the liquid-phase working medium in a liquid-phase pipeline again; the refrigerant separation efficiency is higher, the low-boiling-point refrigerant can obtain the very low evaporation temperature, more heat can be absorbed in the extremely cold environment, and the heating operation energy efficiency of the system is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of heating equipment, and particularly relates to a cascade heat pump system. Background Art

[0002] When a single refrigerant single-cycle heat pump operates for heating in cold regions, due to the too low outdoor air temperature, the evaporation temperature of the system decreases, and the corresponding evaporation pressure decreases. With the condensation temperature unchanged, the compression ratio increases, and the exhaust temperature of the compressor will also increase accordingly. If it exceeds the normal working range of the compressor, it will cause the compressor to start and stop frequently, unable to work efficiently or even unable to work. The auto-cascade heat pump technology can meet the demand of heating at low ambient temperatures. This technology uses two non-azeotropic refrigerants, through the separation function of the gas-liquid separator and the heat exchange between the two working fluids in the intermediate cooler, condenses the low-temperature refrigerant, so that the low-temperature working fluid after throttling has a lower evaporation temperature, which can solve problems such as too large compression ratio and low refrigeration efficiency of the system. It operates more stably in cold regions than conventional single-refrigerant heat pumps, has a simpler and more reliable structure than conventional cascade heat pumps, and has higher energy efficiency in cold regions.

[0003] However, when the existing cascade heat pump operates, it cannot ensure complete separation of the high-boiling liquid refrigerant mixed in the low-boiling gaseous refrigerant, nor can it ensure complete separation of the low-boiling gaseous refrigerant mixed in the high-boiling liquid refrigerant, resulting in liquid carrying during exhaust and gas carrying during liquid drainage after separation, which limits the operating power of the auto-cascade heat pump, and the heating capacity during its operation differs greatly from the theoretical calculation effect. Summary of the Invention

[0004] Therefore, the technical problem to be solved by the present invention is to overcome the defect that the auto-cascade heat pump in the prior art has liquid carrying during exhaust and gas carrying during liquid drainage after refrigerant separation during operation, resulting in limited heating capacity, so as to provide a cascade heat pump system.

[0005] To solve the above technical problem, the present invention provides a cascade heat pump system, including a compressor and a condenser connected to each other, a primary gas-liquid separator, a gas-phase pipeline connected to the gas-phase output end of the primary gas-liquid separator, and a liquid-phase pipeline connected to the liquid-phase output end of the primary gas-liquid separator; further including

[0006] a liquid-phase separator for separating the gas-phase working fluid mixed in the liquid-phase working fluid. The liquid-phase separator includes a first fluid input end, a first liquid-phase output end, and a first gas-phase output end. The first fluid input end and the first liquid-phase output end are both communicated with the liquid-phase pipeline, and the first gas-phase output end is communicated with the gas-phase pipeline;

[0007] A gas-liquid separator is used to separate the liquid-phase working medium mixed in the gas-phase working medium. The gas-liquid separator includes a second fluid input end, a second gas-phase output end, and a second liquid-phase output end. The second fluid input end and the second gas-phase output end are both connected to the gas pipeline, and the second liquid-phase output end is connected to the liquid pipeline;

[0008] The cascade heat pump system provided by the present invention has the following beneficial effects: During the heating operation, the high-temperature and high-pressure mixed gaseous refrigerant discharged from the exhaust port of the compressor enters the condenser for condensation and heat release. The condensation temperature of the high-boiling refrigerant is higher than that of the low-boiling refrigerant. After flowing through the condenser, the high-boiling refrigerant can be condensed into a liquid state, while the low-boiling refrigerant remains in a gaseous state. Then, it is preliminarily separated in the primary gas-liquid separator. The liquid high-boiling refrigerant and the gaseous low-boiling refrigerant are respectively output from the liquid pipeline and the gas pipeline of the primary gas-liquid separator. The gas-phase working medium mixed with a small amount of liquid-phase working medium output from the gas pipeline enters the gas-liquid separator, and the liquid-phase working medium mixed with a small amount of gas-phase working medium output from the liquid pipeline enters the liquid-liquid separator for secondary gas-liquid separation of the refrigerant. After the cooled gas-phase working medium and liquid-phase working medium are preliminarily separated by using the primary gas-liquid separator, the gas-liquid separator and the liquid-liquid separator are respectively used to separate the small amount of liquid-phase working medium mixed in the gas-phase working medium in the gas pipeline and the small amount of gas-phase working medium mixed in the liquid-phase working medium in the liquid pipeline again, so that the separation efficiency of the high-boiling refrigerant and the low-boiling refrigerant is higher, the low-boiling refrigerant can obtain a very low evaporation temperature, and more heat can be absorbed from the environment in an extremely cold environment, thereby improving the energy efficiency of the system during the heating operation. Moreover, the high-boiling refrigerant and the low-boiling refrigerant are completely separated before heat exchange, so that all the low-boiling points can participate in the subsequent heat exchange, which is beneficial to improving the heat exchange efficiency and thus beneficial to improving the energy efficiency of the system.

[0009] Optionally, the outlet of the first fluid input end is arranged to incline downward, and the outlet of the second fluid input end is arranged horizontally or to incline upward.

[0010] In the cascade heat pump system provided by the present invention, by arranging the outlet of the first fluid input end to incline downward and the outlet of the second fluid input end to be horizontal or to incline upward. The high-boiling liquid refrigerant mixed with a small amount of low-boiling gaseous refrigerant is introduced into the liquid-liquid separator. By fully stirring the liquid high-boiling refrigerant at the bottom of the gas-liquid separator, the small amount of low-boiling gaseous refrigerant mixed therein is discharged; the low-boiling gaseous refrigerant mixed with a small amount of high-boiling liquid refrigerant is introduced into the gas-liquid separator. By making the gaseous low-boiling refrigerant fully impact the wall surface, the liquid refrigerant with a larger viscosity is separated. The separation ability of the gas-liquid separator for the high-boiling refrigerant and the low-boiling refrigerant is improved.

[0011] Optionally, the included angle between the outlet of the first fluid input end and the inner side wall of the liquid-liquid separator is 30° - 60°;

[0012] The included angle between the outlet of the first fluid input end and the inner side wall of the gas-phase separator is 90°.

[0013] Optionally, the outlet height of the first fluid input end is not higher than the inlet height of the first gas-phase output end;

[0014] and / or the outlet height of the second fluid input end is not higher than the inlet height of the second gas-phase output end.

[0015] Optionally, a first deceleration throttle valve is installed at the first gas-phase output end; and / or a second deceleration throttle valve is installed at the second liquid-phase output end.

[0016] For the cascade heat pump system provided by the present invention, setting the first deceleration throttle valve can control the gas flow velocity of the gaseous refrigerant output from the first gas-phase output end of the liquid-phase separator, preventing liquid from being carried when the liquid-phase separator exhausts; setting the second deceleration throttle valve can control the liquid flow velocity of the liquid refrigerant output from the second liquid-phase output end of the gas-phase separator, preventing the liquid discharge velocity from being too large and entraining and mixing some gaseous refrigerant.

[0017] Optionally, an evaporator is further included, and the output end of the gas-phase pipeline is communicated with the input end of the evaporator, and the output end of the liquid-phase pipeline is communicated with the output pipeline of the evaporator.

[0018] Optionally, a four-way valve body is further included, and its four valve ports are respectively communicated with the output end of the evaporator, the input end of the compressor, the input end of the condenser, and the output end of the compressor.

[0019] Optionally, an intermediate heat exchanger is further included, with one side communicated with the gas-phase pipeline downstream of the liquid-phase separator and the other side communicated with the liquid-phase pipeline downstream of the liquid-phase separator.

[0020] For the cascade heat pump system provided by the present invention, by setting the intermediate heat exchanger, heat exchange occurs between the high-boiling refrigerant and the low-boiling refrigerant after splitting, further increasing the temperature of the low-boiling refrigerant, reducing the operating power of the subsequent evaporator, and improving the overall heating efficiency of the system.

[0021] Optionally, a first throttle valve is installed on the liquid-phase pipeline between the liquid-phase separator and the intermediate heat exchanger;

[0022] and / or a second throttle valve is installed on the gas-phase pipeline downstream of the intermediate heat exchanger.

[0023] Optionally, an auxiliary gas-liquid separator is installed between the output end of the evaporator and the input end of the compressor. Description of the Drawings

[0024] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for the description of the specific embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0025] Figure 1 It is a system schematic diagram of the cascade heat pump system provided in the embodiments of the present invention.

[0026] Figure 2 It is a structural schematic diagram of the liquid separator provided in the embodiments of the present invention.

[0027] Figure 3 It is a structural schematic diagram of the gas separator provided in the embodiments of the present invention.

[0028] Explanation of reference numerals: 1. Condenser; 2. First throttle valve; 3. Liquid separator; 4. Second throttle valve; 5. Gas separator; 6. First throttle valve; 7. Intermediate heat exchanger; 8. Second throttle valve; 9. Evaporator; 10. Auxiliary gas-liquid separator; 11. Compressor; 12. Four-way valve; 13. First fluid input end; 14. First liquid output end; 15. First gas output end; 16. Second fluid input end; 17. Second liquid output end; 18. Second gas output end; 19. Primary gas-liquid separator; 20. Gas pipeline; 21. Liquid pipeline. Specific embodiments

[0029] The following will clearly and completely describe the technical solutions of the present invention with reference to the drawings. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts fall within the protection scope of the present invention.

[0030] In the description of the present invention, it should be noted that the orientation or positional relationship indicated by the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc. is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the present invention. In addition, the terms "first", "second", "third" are only used for descriptive purposes and cannot be construed as indicating or implying relative importance.

[0031] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "coupled" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium, and it can be the communication inside two components. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific situations.

[0032] In addition, the technical features involved in different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0033] Figure 1 Shown is a cascade heat pump system provided by this embodiment, including a compressor 11 connected to a condenser 1, a primary gas-liquid separator 19, a gas pipeline 20 connected to the gas-phase output end of the primary gas-liquid separator 19, a liquid pipeline 21 connected to the liquid-phase output end of the primary gas-liquid separator 19, and an evaporator 9. The output end of the evaporator 9 is in communication with the input end of the compressor 11. A heat supply pipeline is connected in parallel to the condenser 1 for extracting heat from the condenser 1 to supply heat to the user end.

[0034] The cascade heat pump system provided by this embodiment further includes a liquid-phase separator 3 and a gas-phase separator 5. The liquid-phase separator 3 is used for separating the gas-phase working medium mixed in the liquid-phase working medium. The liquid-phase separator 3 includes a first fluid input end 13, a first liquid-phase output end 14, and a first gas-phase output end 15. The first fluid input end 13 and the first liquid-phase output end 14 are both in communication with the liquid pipeline 21, and the first gas-phase output end 15 is in communication with the gas pipeline 20. The gas-phase separator 5 is used for separating the liquid-phase working medium mixed in the gas-phase working medium. The gas-phase separator 5 includes a second fluid input end 16, a second gas-phase output end 18, and a second liquid-phase output end 17. The second fluid input end 16 and the second gas-phase output end 18 are both in communication with the gas pipeline 20, and the second liquid-phase output end 17 is in communication with the liquid pipeline 21.

[0035] The outlet of the input end of the liquid separator 3 is arranged to slope downward, and the outlet of the input end of the gas separator 5 is arranged horizontally or to slope upward. Specifically, the included angle between the outlet of the first fluid input end 13 of the liquid separator 3 and the inner side wall of the liquid separator 3 is 30° - 60°, and is set to 45° in this embodiment; the included angle between the outlet of the second fluid input end 16 of the gas separator 5 and the inner side wall of the gas separator 5 is 90°. The liquid phase outlet of the condenser 1 is communicated with the input end of the liquid separator 3, and the gas phase outlet of the condenser 1 is communicated with the input end of the gas separator 5. In the liquid separator 3, the outlet height of the first fluid input end 13 is not higher than the inlet height of the first gas output end 15, and in the gas separator 5, the outlet height of the second fluid input end 16 is not higher than the inlet height of the second gas output end 18.

[0036] In order to prevent liquid-phase refrigerant from mixing into the gas-phase refrigerant output by the liquid separator 3, and at the same time prevent gas-phase refrigerant from being entrained and mixed into the liquid-phase refrigerant output by the gas separator 5, a first throttle valve 2 is installed at the first gas output end 15 of the liquid separator 3, and a second throttle valve 4 is installed at the second liquid output end 17 of the gas separator 5.

[0037] The output end of the gas pipeline 20 is communicated with the input end of the evaporator 9, and the output end of the gas-liquid pipeline 21 is communicated with the pipeline at the output end of the evaporator 9. That is, the low-boiling-point gas-phase refrigerant output from the gas-liquid separator group is liquefied by the evaporator 9 and then mixed with the high-boiling-point liquid-phase refrigerant output from the gas-liquid separator group.

[0038] The cascade heat pump system provided in this embodiment further includes a four-way valve 12 body, and its four valve ports are respectively communicated with the output end of the evaporator 9, the input end of the compressor 11, the input end of the condenser 1, and the output end of the compressor 11.

[0039] In order to improve the overall heating efficiency of the system, the cascade heat pump system further includes an intermediate heat exchanger 7. One side of the intermediate heat exchanger 7 is communicated with the gas pipeline 20 downstream of the liquid separator 3, and the other side is communicated with the liquid pipeline 21 downstream of the liquid separator 3.

[0040] A first throttle valve 6 is installed on the liquid pipeline 21 between the liquid separator 3 and the intermediate heat exchanger 7, which is used to throttle and expand the high-boiling-point liquid-phase refrigerant input into the intermediate heat exchanger 7, reduce the temperature of the high-boiling-point liquid-phase refrigerant, so that the high-boiling-point liquid-phase refrigerant cools the low-boiling-point gas-phase refrigerant in the intermediate heat exchanger 7. Part of the cooled low-boiling-point gas-phase refrigerant may become liquid phase. A second throttle valve 8 is installed on the gas pipeline 20 downstream of the intermediate heat exchanger 7, which is used to throttle and expand the low-boiling-point refrigerant output from the intermediate heat exchanger 7 and then enter the evaporator 9 for evaporation and heat absorption to improve the heat exchange capacity of the low-boiling-point refrigerant in the evaporator 9.

[0041] An auxiliary gas-liquid separator 10 is installed between the output end of the evaporator 9 and the input end of the compressor 11, which is used to separate the gas and liquid of the mixed refrigerant input into the compressor 11, ensure that the mixed refrigerant entering the compressor 11 is in a gaseous state, avoid liquid hammer on the compressor 11 caused by the mixed refrigerant, and ensure the continuous temperature operation of the compressor 11.

[0042] When the cascade heat pump system operates in the heating mode, the compressor 11 discharges high-temperature and high-pressure mixed gaseous refrigerant from the exhaust port. After passing through the four-way valve 12, it enters the condenser 1 together for condensation and heat release. The condensation temperature of the high-boiling refrigerant is higher than that of the low-boiling refrigerant. When there is a degree of subcooling in the high-boiling refrigerant, the high-boiling refrigerant can be condensed into a liquid state, but the low-boiling refrigerant cannot be condensed into a liquid state. Under the action of gravity, the high-boiling liquid refrigerant sinks, and the gaseous refrigerant is in the upper part. Under the action of the pressure in the tank body, the high-boiling liquid refrigerant is discharged from the drain pipe of the condenser 1 and enters the liquid-phase separator 3 to perform secondary gas-liquid separation on the high-boiling liquid refrigerant.

[0043] The main difference between the liquid-phase separator 3 and the conventional gas-liquid separator is that it does not require liquid return and oil return, that is, there is no oil return hole in the exhaust pipe. It mainly consists of a first fluid input end 13, a first liquid-phase output end 14 and a first gas-phase output end 15, as Figure 2 shown. In the liquid-phase separator 3, what is mainly separated is the low-boiling gaseous refrigerant mixed in the high-boiling liquid refrigerant. The liquid inlet is made at an angle of 45°, so that the high-boiling liquid refrigerant can be fully stirred at the bottom to separate the mixed low-boiling gaseous refrigerant. The high-boiling liquid refrigerant in the liquid-phase separator 3 accounts for the majority, and the low-boiling gaseous refrigerant is less. When the gas discharge speed is too fast, it may eject some liquid refrigerant, causing the separated refrigerant to be mixed again. Therefore, a gaseous refrigerant deceleration throttle valve is added at the exhaust port to increase the gas flow path resistance and reduce the gas flow speed, which can prevent liquid from being carried during exhaust.

[0044] The gas-phase separator 5 mainly consists of a second fluid input end 16, a second liquid-phase output end 17 and a second gas-phase output end 18, as Figure 3As shown. In the gas-liquid separator 5, a small amount of high-boiling liquid refrigerant mixed in the gaseous low-boiling refrigerant is mainly separated. Therefore, the air inlet is made into a right angle so that the gaseous low-boiling refrigerant fully impacts the wall surface to separate the liquid refrigerant with a larger viscosity. At this time, there is more gas and less liquid in the gas-liquid separator. If the liquid discharge speed is too large, it may entrain and mix some gaseous refrigerant. Therefore, a throttle valve is set at the liquid discharge port. Here, the throttle valve only serves to reduce the liquid flow rate and a throttle valve with a larger number of steps is selected, which will not cause the high-boiling liquid refrigerant to expand into a gas. The liquid high-boiling refrigerant separated in the liquid-phase separator 3 is discharged from the liquid-phase output end of the liquid-phase separator 3 and, together with the liquid high-boiling refrigerant separated in the gas-liquid separator 5, undergoes throttling expansion through the first throttle valve 6 and then enters the intermediate heat exchanger 7 to condense the low-boiling refrigerant.

[0045] The gaseous low-boiling refrigerant is preliminarily separated in the condenser 1 and enters the gas-liquid separator 5 to separate the liquid high-boiling refrigerant mixed in the gaseous low-boiling refrigerant. The liquid high-boiling refrigerant separated here, together with the liquid high-boiling refrigerant separated from the liquid-phase separator 3, passes through the first throttle valve 6, undergoes throttling expansion, and then enters the intermediate heat exchanger 7 to conduct intermediate heat exchange with the low-boiling refrigerant. The separated gaseous low-boiling refrigerant enters the intermediate heat exchanger 7 to conduct intermediate heat exchange with the high-boiling refrigerant after throttling and pressure reduction. The low-boiling gaseous refrigerant is condensed into a liquid with a certain degree of subcooling. After throttling expansion through the second throttle valve 8, it enters the evaporator 9 for evaporation and heat absorption. After heat absorption, the high-boiling refrigerant becomes gaseous, mixes with the high-boiling gaseous refrigerant after heat absorption in the intermediate heat exchanger 7, and then passes through the four-way valve 12 together, and then enters the auxiliary gas-liquid separator 10 for gas-liquid separation. The auxiliary gas-liquid separator 10 ensures that the fluid entering the compressor 11 does not cause liquid hammer to the compressor 11. The mixed gaseous refrigerant passes through the four-way valve 12, enters the compressor 11, is compressed into a high-temperature and high-pressure gas, and enters the condenser 1 for efficient heat exchange.

[0046] By setting the outlets of the first fluid input ends 13 and the second fluid input ends 16 of the liquid-phase separator 3 and the gas-liquid separator 5 to face their respective inner side walls, when the refrigerant enters the gas-liquid separator, the liquid high-boiling refrigerant can be fully stirred at the bottom to separate the mixed low-boiling gaseous refrigerant, or the gaseous low-boiling refrigerant can fully impact the wall surface to separate the mixed liquid refrigerant with a larger viscosity. This makes the separation efficiency of the high-boiling refrigerant and the low-boiling refrigerant higher, enables the low-boiling refrigerant to obtain a very low evaporation temperature, can absorb more heat from the environment in an extremely cold environment, and the system has higher operating energy efficiency.

[0047] Obviously, the above embodiments are merely examples for clear illustration and not limitations on the implementation manners. For those of ordinary skill in the art, other different forms of changes or variations can be made based on the above description. It is not necessary and impossible to list all implementation manners here. And the obvious changes or variations derived therefrom still fall within the protection scope of the present invention.

Claims

1. A cascade heat pump system, characterized in that, It includes a connected compressor (11) and condenser (1), a primary gas-liquid separator (19), a gas-phase pipeline (20) connected to the gas-phase output end of the primary gas-liquid separator (19), and a liquid-phase pipeline (21) connected to the liquid-phase output end of the primary gas-liquid separator (19); it also includes a liquid-phase separator (3) for separating the gas-phase working medium mixed in the liquid-phase working medium. The liquid-phase separator (3) includes a first fluid input end (13), a first gas-phase output end (15), and a first liquid-phase output end (14). Both the first fluid input end (13) and the first liquid-phase output end (14) are communicated with the liquid-phase pipeline (21), and the first gas-phase output end (15) is communicated with the gas-phase pipeline (20); a gas-phase separator (5) for separating the liquid-phase working medium mixed in the gas-phase working medium. The liquid-phase separator (3) includes a second fluid input end (16), a second liquid-phase output end (17), and a second gas-phase output end (18). Both the second fluid input end (16) and the second gas-phase output end (18) are communicated with the gas-phase pipeline (20), and the second liquid-phase output end (17) is communicated with the liquid-phase pipeline (21).

2. The cascade heat pump system according to claim 1, characterized in that The outlet of the first fluid input end (13) is arranged to incline downward, and the outlet of the second fluid input end (16) is arranged horizontally or to incline upward.

3. The cascade heat pump system according to claim 2, characterized in that, The included angle between the outlet of the first fluid input end (13) and the inner side wall of the liquid-phase separator (3) is 30° - 60°; and / or, the included angle between the outlet of the second fluid input end (16) and the inner side wall of the gas-phase separator (5) is 90°.

4. The cascade heat pump system according to any one of claims 1 to 3, characterized in that, The outlet height of the first fluid input end (13) is not higher than the inlet height of the first gas-phase output end (15); and / or the outlet height of the second fluid input end (16) is not higher than the inlet height of the second gas-phase output end (18).

5. The cascade heat pump system according to any one of claims 1 to 3, characterized in that, A first throttle valve (2) is installed at the first gas-phase output end (15); and / or a second throttle valve (4) is installed at the second liquid-phase output end (17).

6. The cascade heat pump system according to any one of claims 1 to 3, characterized in that It also includes an evaporator (9). The output end of the gas-phase pipeline (20) is communicated with the input end of the evaporator (9), and the output end of the liquid-phase pipeline (21) is communicated with the output end of the evaporator (9) through a pipeline.

7. The cascade heat pump system according to claim 6, characterized in that, It also includes a four-way valve (12) body, and its four valve ports are respectively communicated with the output end of the evaporator (9), the input end of the compressor (11), the input end of the condenser (1), and the output end of the compressor (11).

8. The cascade heat pump system according to any one of claims 1 to 3, characterized in that It also includes an intermediate heat exchanger (7), one side of which is communicated with the gas-phase pipeline (20) downstream of the liquid-phase separator (3), and the other side is communicated with the liquid-phase pipeline (21) downstream of the liquid-phase separator (3).

9. The cascade heat pump system according to claim 8, characterized in that, A first throttle valve (6) is installed on the liquid-phase pipeline (21) between the liquid-phase separator (3) and the intermediate heat exchanger (7); and / or a second throttle valve (8) is installed on the gas-phase pipeline (20) downstream of the intermediate heat exchanger (7).

10. The cascade heat pump system according to claim 6, wherein An auxiliary gas-liquid separator (10) is installed between the output end of the evaporator (9) and the input end of the compressor (11).

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