A cascade heat pump system adapted to low temperature environments

Abstract

The application provides a cascade heat pump system suitable for low-temperature environment, which comprises a low-temperature system, a high-temperature system and a hot water circulating system; wherein the low-temperature system comprises a low-temperature gas-liquid separator, a low-temperature compressor, a low-temperature oil separator, a low-temperature heat exchanger, a heat exchange condenser, a low-temperature liquid accumulator, a low-temperature throttling expansion valve and an evaporation condenser; the high-temperature system comprises a high-temperature gas-liquid separator, a high-temperature compressor, a high-temperature oil separator, a high-temperature heat exchange condenser, a high-temperature liquid accumulator, a high-temperature throttling expansion valve and a heat exchange condenser; and the hot water circulating system comprises a cold and hot water tank, a circulating water pump, a low-temperature heat exchanger and a high-temperature heat exchange condenser; the application adopts a double-refrigerant cascade circulation framework, can stably provide hot water through the cooperation of the low-temperature system and the high-temperature system when the outdoor temperature is extremely low, and can grade heat the hot water without greatly increasing the compression ratio of the compressor for maintaining the temperature of the hot water, thereby effectively avoiding the defects of energy consumption rising and heating capacity greatly decreasing.

Description

Technical Field

[0001] This invention relates to the field of heating equipment technology, and more specifically to a cascade heat pump system adapted to low-temperature environments. Background Technology

[0002] Heat pump units, which can absorb low-grade heat energy from the air through a circulation system to achieve efficient heating or cooling, are expected to become core clean energy equipment to replace traditional electric heating and gas boilers. They can be widely used in residential communities, commercial complexes (such as shopping malls and hotels), bath centers, industrial plants and other scenarios, undertaking key functions such as winter heating, year-round domestic hot water preparation and summer indoor cooling.

[0003] Currently, the mainstream technology for heat pump units in the market is a single-unit system or a single-unit two-stage system. Their core design feature is the use of a single type of refrigerant to construct the circulation system, achieving heat transfer and exchange through single-stage or two-stage compression processes to meet heating and cooling demands. However, these single-refrigerant heat pump units have the following problems in practical applications:

[0004] 1) In northern my country, low-temperature refrigerants are often used to adapt to lower ambient temperatures. In summer, when the ambient temperature is high, these refrigerants can achieve stable evaporation in the evaporator and meet the operating requirements of the refrigeration condition. However, in winter, when the outdoor temperature is below 0℃ and the return water temperature is above 40℃, the maximum water temperature of the hot water provided is only 50℃ (the standard requirement is 65℃-85℃), which cannot meet the actual needs.

[0005] 2) When the outdoor temperature is too low in winter, the system energy efficiency (COP) of existing heat pump units drops significantly, that is, energy consumption increases and heating capacity decreases sharply. Specifically, as the outdoor ambient temperature drops below 0°C, the heat exchange temperature difference between the evaporator and the outdoor air decreases, and the refrigerant needs to lower its evaporation temperature to absorb heat. At this time, the system uses the expansion valve to reduce the pressure of the refrigerant and throttle it to maintain the basic heat absorption cycle. However, this will also cause the compressor's suction pressure to drop. In order to ensure that the compressor's discharge pressure is maintained at a stable value that matches the target condensing temperature, the compressor's compression ratio needs to be increased, resulting in a sharp increase in compressor power consumption and a significant decrease in system energy efficiency.

[0006] 3) Increasing the compression ratio of the compressor not only leads to a significant decrease in system energy efficiency, but may also cause the refrigerant to overheat during the compression process, resulting in compressor overheating and affecting the stable operation of the unit.

[0007] Therefore, how to design a cascade heat pump system that can stably generate heat and provide high-temperature hot water in low-temperature environments is a technical problem that has not yet been solved in the existing technology. Summary of the Invention

[0008] Therefore, the technical problem to be solved by the present invention is to overcome the technical defects of the heat pump unit in the prior art, such as reduced system energy efficiency, significant reduction in heating capacity and failure to meet hot water temperature standards in low-temperature environments, so as to provide a cascade heat pump system that can stably heat and provide high-temperature hot water in low-temperature environments.

[0009] Therefore, this invention provides a cascade heat pump system adapted to low-temperature environments, comprising: a low-temperature system, including a low-temperature refrigerant, and a low-temperature gas-liquid separator, a low-temperature compressor, a low-temperature oil separator, a low-temperature heat exchanger, a heat exchange condenser, a low-temperature liquid receiver, a low-temperature expansion valve, and an evaporative condenser, all connected in a ring topology and internally circulating with the low-temperature refrigerant; the low-temperature refrigerant in the low-temperature liquid receiver expands and cools down through the low-temperature expansion valve, then enters the evaporative condenser to absorb outdoor heat and heat up, and is further heated by the low-temperature compressor, then sequentially enters the low-temperature heat exchanger and the heat exchange condenser for heat exchange, and finally returns to the low-temperature liquid receiver for the next cycle; a high-temperature system, including a high-temperature refrigerant, and a high-temperature gas-liquid separator, a high-temperature compressor, a high-temperature oil separator, a high-temperature heat exchange condenser, a high-temperature liquid receiver, a high-temperature expansion valve, and the heat exchange condenser, all connected in a ring topology and internally circulating with the high-temperature refrigerant; the high-temperature refrigerant in the high-temperature liquid receiver... The refrigerant expands and cools down after passing through the high-temperature throttling expansion valve, then enters the heat exchange condenser where it exchanges heat with the low-temperature refrigerant and heats up. After being further heated by the high-temperature compressor, it enters the high-temperature heat exchange condenser for heat exchange again, and finally returns to the high-temperature liquid receiver for the next cycle. The hot water circulation system includes a cold and hot water tank, a circulating water pump, the low-temperature heat exchanger, and the high-temperature heat exchange condenser connected in a ring topology. The circulating water pump drives the water in the cold and hot water tank to first flow through the low-temperature heat exchanger to exchange heat with the low-temperature refrigerant, then through the high-temperature heat exchange condenser to exchange heat with the high-temperature refrigerant, and then return to the cold and hot water tank. This cycle is repeated at least once to produce hot water. The temperature of the low-temperature refrigerant after exiting the low-temperature compressor is lower than the temperature of the high-temperature refrigerant after exiting the high-temperature compressor. The temperature of the low-temperature refrigerant after exiting the low-temperature throttling expansion valve is also lower than the temperature of the high-temperature refrigerant after exiting the high-temperature throttling expansion valve.

[0010] As a preferred embodiment, the system also includes a low-temperature regenerator disposed in the low-temperature system; the low-temperature regenerator includes a first low-temperature refrigerant channel and a second low-temperature refrigerant channel; the first low-temperature refrigerant channel is connected in series between the evaporator-condenser and the low-temperature gas-liquid separator; the second low-temperature refrigerant channel is connected in series between the low-temperature heat exchanger and the heat exchange condenser.

[0011] As a preferred embodiment, the system also includes a high-temperature regenerator disposed in the high-temperature system; the high-temperature regenerator includes a first high-temperature refrigerant channel and a second high-temperature refrigerant channel; the first high-temperature refrigerant channel is connected in series between the heat exchange condenser and the high-temperature gas-liquid separator; the second high-temperature refrigerant channel is connected in series between the high-temperature heat exchange condenser and the high-temperature liquid receiver.

[0012] As a preferred embodiment, the system further includes: a first four-way valve connected to the cryogenic oil separator, the cryogenic heat exchanger, the cryogenic throttling expansion valve, and the evaporator-condenser; and a second four-way valve connected to the cryogenic gas-liquid separator, the cryogenic heat exchanger, the heat exchange condenser, and the evaporator-condenser. During the heating cycle, the cryogenic oil separator is connected to the cryogenic heat exchanger via the first four-way valve, and the cryogenic throttling expansion valve is connected to the evaporator-condenser via the first four-way valve; the cryogenic heat exchanger is connected to the heat exchange condenser via the second four-way valve, and the evaporator-condenser is connected to the cryogenic gas-liquid separator via the second four-way valve. During the cooling cycle, the cryogenic oil separator is connected to the evaporator-condenser via the first four-way valve, and the cryogenic throttling expansion valve is connected to the cryogenic heat exchanger via the first four-way valve; the cryogenic heat exchanger is connected to the cryogenic gas-liquid separator via the second four-way valve, and the evaporator-condenser is connected to the heat exchange condenser via the second four-way valve.

[0013] As a preferred embodiment, the system also includes a chilled water circulation system, which is activated during refrigeration cycles. The chilled water circulation system includes a circulating water pump, a low-temperature heat exchanger, and a water-cooled fan connected in sequence. The circulating water pump drives ambient temperature water in the pipeline to enter the low-temperature heat exchanger, where it exchanges heat with the low-temperature refrigerant. As the water temperature decreases, it flows into the water-cooled fan to absorb heat from the indoor environment. The water is then driven to flow again by the circulating water pump. This cycle is repeated at least once to lower the indoor temperature and achieve refrigeration.

[0014] As a preferred embodiment, an electric heater is also included, connected in series between the first four-way valve and the evaporator-condenser; when defrosting the evaporator-condenser, the electric heater is activated to further heat the low-temperature refrigerant compressed by the low-temperature compressor in order to defrost the evaporator-condenser.

[0015] As a preferred embodiment, the system also includes a defrosting preheating hot water circulation system, comprising the circulating water pump, the low-temperature heat exchanger, and a hot and cold water buffer tank connected in sequence; the hot and cold water buffer tank stores hot water; the circulating water pump drives the high-temperature hot water in the hot and cold water buffer tank into the low-temperature heat exchanger to heat the low-temperature refrigerant, and then the hot and cold water flows back to the hot and cold water buffer tank, and then flows again driven by the circulating water pump, thus circulating at least once, thereby achieving refrigerant heating.

[0016] The technical solution provided by this invention has the following advantages:

[0017] This invention relates to a cascade heat pump system adapted to low-temperature environments, comprising a low-temperature system, a high-temperature system, and a hot water circulation system. The low-temperature system includes a low-temperature refrigerant and a ring-shaped topologically connected system containing a low-temperature gas-liquid separator, a low-temperature compressor, a low-temperature oil separator, a low-temperature heat exchanger, a heat exchange condenser, a low-temperature liquid receiver, a low-temperature expansion valve, and an evaporative condenser. The low-temperature refrigerant in the liquid receiver expands and cools through the low-temperature expansion valve, then enters the evaporative condenser to absorb outdoor heat and warm up. After further warming by the low-temperature compressor, it sequentially enters the low-temperature heat exchanger and the heat exchange condenser for heat exchange, finally returning to the liquid receiver for the next cycle. The high-temperature system includes a high-temperature refrigerant and a ring-shaped topologically connected system containing a high-temperature gas-liquid separator, a high-temperature compressor, a high-temperature oil separator, a high-temperature heat exchange condenser, a high-temperature liquid receiver, and a high-temperature expansion valve. The system includes a heat exchange condenser; the high-temperature refrigerant in the high-temperature receiver expands and cools down through the high-temperature expansion valve, then enters the heat exchange condenser to exchange heat with the low-temperature refrigerant and heats up. After being further heated by the high-temperature compressor, it enters the high-temperature heat exchange condenser for heat exchange again, and finally returns to the high-temperature receiver for the next cycle; the hot water circulation system includes a cold and hot water tank, a circulating water pump, a low-temperature heat exchanger, and a high-temperature heat exchange condenser connected in a ring topology; the circulating water pump drives the water in the cold and hot water tanks to first flow through the low-temperature heat exchanger to exchange heat with the low-temperature refrigerant, then through the high-temperature heat exchange condenser to exchange heat with the high-temperature refrigerant, and then return to the cold and hot water tanks, thus circulating at least once to produce hot water; the temperature of the low-temperature refrigerant after exiting the low-temperature compressor is lower than the temperature of the high-temperature refrigerant after exiting the high-temperature compressor; the temperature of the low-temperature refrigerant after exiting the low-temperature expansion valve is lower than the temperature of the high-temperature refrigerant after exiting the high-temperature expansion valve.

[0018] The cascade heat pump system adapted to low-temperature environments of this invention adopts a dual-refrigerant cascade circulation architecture. The low-temperature system uses low-temperature refrigerants, such as R32, R508B, and R23, while the high-temperature system uses high-temperature refrigerants, such as R515B, R450a, R600a, and R1234ze. Because the evaporation temperature of the low-temperature refrigerants is extremely low, even when the outdoor temperature is as low as -60°C, this heat pump system can still absorb heat from the outdoor air through the low-temperature refrigerant in the evaporator condenser of the low-temperature system. Then, after the low-temperature compressor increases the temperature and pressure, the hot water is initially heated. The remaining heat is then transferred to the high-temperature system through the heat exchange condenser. After absorbing the residual heat from the low-temperature system, the high-temperature system further heats the hot water to 70°C-75°C through the high-temperature compressor, thereby stably providing high-temperature hot water in low-temperature environments. Compared to existing single-refrigerant units, the cascade heat pump system adapted to low-temperature environments of this invention can heat hot water in stages without significantly increasing the compressor's compression ratio to maintain the hot water temperature, effectively avoiding the drawbacks of increased energy consumption and significant reduction in heating capacity. The compressor of the cascade heat pump system adapted to low-temperature environments of this invention does not need to withstand excessively high compression ratios, thereby avoiding compressor overheating problems caused by excessive refrigerant temperature rise and ensuring stable operation of the unit in low-temperature environments. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the prior art or specific embodiments of the present invention, the accompanying drawings used in the description of the prior art or specific embodiments are briefly introduced below.

[0020] Figure 1 This is a system architecture diagram of the present invention under heating conditions.

[0021] Figure 2 This is a system architecture diagram of the present invention under refrigeration conditions.

[0022] Reference numerals: 1. Low-temperature gas-liquid separator; 10. Hot and cold water buffer tank; 11. High-temperature gas-liquid separator; 12. High-temperature compressor; 13. High-temperature oil separator; 14. High-temperature heat exchange condenser; 15. High-temperature regenerator; 151. First high-temperature refrigerant flow channel; 152. Second high-temperature refrigerant flow channel; 16. High-temperature liquid receiver; 17. High-temperature throttling expansion valve; 18. Hot and cold water tank; 19. Circulating water pump; 2. Low-temperature compressor; 20. First four-way valve; 21. Second four-way valve; 22. Electric heater; 3. Low-temperature oil separator; 4. Low-temperature heat exchanger; 5. Low-temperature regenerator; 51. First low-temperature refrigerant flow channel; 52. Second low-temperature refrigerant flow channel; 6. Heat exchange condenser; 7. Low-temperature liquid receiver; 8. Low-temperature throttling expansion valve; 9. Evaporative condenser; 23. Water-cooled fan. Detailed Implementation

[0023] To enable those skilled in the art to better understand this solution, the technical solutions in the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of this application.

[0024] It should be noted that the terms "first," "second," etc., in the claims and specification of this application are used to distinguish similar objects and are not used to describe a specific order or sequence. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover a non-exclusive inclusion, such as a process, method, system, product, or device that includes a series of steps or units, not limited to those steps or units explicitly listed, but may also include other steps or units not explicitly listed or inherent to these processes, methods, products, or devices.

[0025] In this application, the terms "upper," "lower," "left," "right," "front," "rear," "top," "bottom," "inner," "outer," "middle," "vertical," "horizontal," "lateral," and "longitudinal" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. These terms are primarily for better description of this application and its embodiments, and are not intended to limit the indicated device, element, or component to having a specific orientation, or to be constructed and operated in a specific orientation. Furthermore, some of the above terms may be used to indicate other meanings besides orientation or positional relationship; for example, the term "upper" may also be used in some cases to indicate a certain dependency or connection relationship. Those skilled in the art can understand the specific meaning of these terms in this application according to the specific circumstances. In addition, the term "multiple" should mean two or more. It should be noted that, unless otherwise specified, the embodiments and features in the embodiments of this application can be combined with each other.

[0026] The present application will now be described in detail with reference to the accompanying drawings and embodiments. Example

[0027] This embodiment provides a cascade heat pump system adapted to low-temperature environments, such as... Figure 1-2As shown, it includes: a low-temperature system, a high-temperature system, and a hot water circulation system; wherein the low-temperature system includes a low-temperature refrigerant, and a low-temperature gas-liquid separator 1, a low-temperature compressor 2, a low-temperature oil separator 3, a low-temperature heat exchanger 4, a heat exchange condenser 6, a low-temperature liquid receiver 7, a low-temperature throttling expansion valve 8, and an evaporative condenser 9, which are connected in a ring topology and internally circulate the low-temperature refrigerant; the low-temperature refrigerant in the low-temperature liquid receiver 7 expands and cools down through the low-temperature throttling expansion valve 8, and then enters the evaporative condenser 9 to absorb outdoor heat and heat up, and then... After the cryogenic compressor 2 is further heated, it sequentially enters the cryogenic heat exchanger 4 and the heat exchange condenser 6 for heat exchange, and finally returns to the cryogenic liquid receiver 7 for the next cycle; the high-temperature system includes a high-temperature refrigerant, and a high-temperature gas-liquid separator 11, a high-temperature compressor 12, a high-temperature oil separator 13, a high-temperature heat exchange condenser 14, a high-temperature liquid receiver 16, a high-temperature throttling expansion valve 17, and the heat exchange condenser 6, which are connected in a ring topology and internally circulate the high-temperature refrigerant; the high-temperature refrigerant in the high-temperature liquid receiver 16 After expanding and cooling through the high-temperature throttling expansion valve 17, the water enters the heat exchange condenser 6 and exchanges heat with the low-temperature refrigerant to raise its temperature. After being further heated by the high-temperature compressor 12, it enters the high-temperature heat exchange condenser 14 for heat exchange, and finally returns to the high-temperature liquid receiver 16 for the next cycle. The hot water circulation system includes a cold and hot water tank 18, a circulating water pump 19, the low-temperature heat exchanger 4, and the high-temperature heat exchange condenser 14 connected in a ring topology. The circulating water pump 19 drives the water in the cold and hot water tank 18 to flow through the... The low-temperature heat exchanger 4 exchanges heat with the low-temperature refrigerant, then exchanges heat with the high-temperature refrigerant through the high-temperature heat exchange condenser 14, and then returns to the hot and cold water tank 18. This cycle is repeated at least once to produce hot water. The temperature of the low-temperature refrigerant after exiting the low-temperature compressor 2 is lower than the temperature of the high-temperature refrigerant after exiting the high-temperature compressor 12. The temperature of the low-temperature refrigerant after exiting the low-temperature throttling expansion valve 8 is lower than the temperature of the high-temperature refrigerant after exiting the high-temperature throttling expansion valve 17.

[0028] It also includes a low-temperature regenerator 5, which is installed in the low-temperature system; the low-temperature regenerator 5 includes a first low-temperature refrigerant channel 51 and a second low-temperature refrigerant channel 52; the first low-temperature refrigerant channel 51 is connected in series between the evaporator condenser 9 and the low-temperature gas-liquid separator 1; the second low-temperature refrigerant channel 52 is connected in series between the low-temperature heat exchanger 4 and the heat exchange condenser 6.

[0029] It also includes a high-temperature regenerator 15, which is disposed in the high-temperature system; the high-temperature regenerator 15 includes a first high-temperature refrigerant channel 151 and a second high-temperature refrigerant channel 152; the first high-temperature refrigerant channel 151 is connected in series between the heat exchange condenser 6 and the high-temperature gas-liquid separator 11; the second high-temperature refrigerant channel 152 is connected in series between the high-temperature heat exchange condenser 14 and the high-temperature liquid receiver 16.

[0030] It also includes a first four-way valve 20 and a second four-way valve 21; wherein the first four-way valve 20 is connected to the low-temperature oil separator 3, the low-temperature heat exchanger 4, the low-temperature throttling expansion valve 8 and the evaporator condenser 9 respectively; the second four-way valve 21 is connected to the low-temperature gas-liquid separator 1, the low-temperature heat exchanger 4, the heat exchange condenser 6 and the evaporator condenser 9 respectively.

[0031] During the heating cycle, the low-temperature oil separator 3 is connected to the low-temperature heat exchanger 4 through the first four-way valve 20, and the low-temperature throttling expansion valve 8 is connected to the evaporator condenser 9 through the first four-way valve 20; the low-temperature heat exchanger 4 is connected to the heat exchange condenser 6 through the second four-way valve 21, and the evaporator condenser 9 is connected to the low-temperature gas-liquid separator 1 through the second four-way valve 21.

[0032] During the refrigeration cycle, the low-temperature oil separator 3 is connected to the evaporator-condenser 9 through the first four-way valve 20, and the low-temperature throttling expansion valve 8 is connected to the low-temperature heat exchanger 4 through the first four-way valve 20; the low-temperature heat exchanger 4 is connected to the low-temperature gas-liquid separator 1 through the second four-way valve 21, and the evaporator-condenser 9 is connected to the heat exchange condenser 6 through the second four-way valve 21.

[0033] It also includes a cold water circulation system, which is activated during refrigeration. The cold water circulation system includes a circulating water pump 19, a low-temperature heat exchanger 4, and a water-cooled fan 23 connected in sequence. The circulating water pump 19 drives ambient temperature water in the pipeline to enter the low-temperature heat exchanger 4, where it exchanges heat with the low-temperature refrigerant, lowering the water temperature. The water then flows into the water-cooled fan 23 to absorb heat from the indoor environment. Afterward, it is driven to flow again by the circulating water pump 19. This cycle is repeated at least once to lower the indoor temperature and achieve refrigeration.

[0034] It also includes an electric heater 22, which is connected in series between the first four-way valve 20 and the evaporator condenser 9; when defrosting the evaporator condenser 9, the electric heater 22 is activated to further heat the low-temperature refrigerant compressed by the low-temperature compressor 2 in order to defrost the evaporator condenser 9.

[0035] It also includes a defrosting preheating hot water circulation system, which includes the circulating water pump 19, the low-temperature heat exchanger 4, and the hot and cold water buffer tank 10 connected in sequence; the hot and cold water buffer tank 10 stores hot water; the circulating water pump 19 drives the high-temperature hot water in the hot and cold water buffer tank 10 into the low-temperature heat exchanger 4 to heat the low-temperature refrigerant, and then flows back to the hot and cold water buffer tank 10, and then flows again driven by the circulating water pump 19, and so on, at least once, thereby realizing refrigerant heating.

[0036] This embodiment of the cascade heat pump system, adapted to low-temperature environments, employs a dual-refrigerant cascade circulation architecture. The low-temperature system uses low-temperature refrigerants, such as R32, R508B, and R23, while the high-temperature system uses high-temperature refrigerants, such as R515B, R450a, R600a, and R1234ze. Because the evaporation temperature of the low-temperature refrigerants is extremely low, even when the outdoor temperature is as low as -60°C, this heat pump system can still absorb heat from the outdoor air through the low-temperature refrigerant in the evaporator-condenser of the low-temperature system. This heat is then initially heated by the low-temperature compressor, and the remaining heat is transferred to the high-temperature system through the heat exchange condenser. After absorbing waste heat from the low-temperature system, the hot water is further heated to 70℃-75℃ by the high-temperature compressor, thus stably providing high-temperature hot water in a low-temperature environment. Secondly, compared with existing single-refrigerant units, the cascade heat pump system adapted to low-temperature environments in this embodiment can heat the hot water in stages without significantly increasing the compressor's compression ratio to maintain the hot water temperature, effectively avoiding the defects of increased energy consumption and significant reduction in heating capacity. In addition, the compressor of the cascade heat pump system adapted to low-temperature environments in this embodiment does not need to withstand an excessively high compression ratio, thereby avoiding compressor overheating caused by excessive refrigerant temperature rise and ensuring stable operation of the unit in a low-temperature environment.

[0037] The following section will elaborate on the heating operation of this system, including the startup sequence of each system, the specific path of refrigerant and water circulation, and the heat exchange logic. The specific process is as follows:

[0038] like Figure 1 As shown, the hot water circulation system is started first, allowing water to circulate in the pipes. Then, the high-temperature system is started, and finally, the low-temperature system is started. Here, the hot water circulation system is started in advance to ensure that the refrigerant has a stable heat exchange medium when the high-temperature system is running, providing a basis for heat transfer. After the hot water circulation system is stable, the high-temperature system is started, and the refrigerant inside the high-temperature system will begin to circulate. At this time, the refrigerant can enter the heat exchange condenser 6, carrying away the heat of the refrigerant on the low-temperature system side. This helps the refrigerant on the low-temperature system side to release heat in advance before starting, reducing pressure and creating conditions for the safe start-up of the low-temperature system.

[0039] It should be noted that the temperature and other values ​​in the following steps are for demonstration purposes only and are not the highest, lowest, or fixed values ​​of this system; in actual use, adjustments need to be made based on the outdoor temperature and the required hot water temperature.

[0040] The refrigerant cycle in a cryogenic system consists of the following steps A1-A10:

[0041] It should be noted that the first four-way valve 20 has four ports, of which port 1 is connected to the low-temperature heat exchanger 4, port 2 is connected to the low-temperature throttling expansion valve 8, port 3 is connected to the electric heater 22, and port 4 is connected to the low-temperature oil separator 3; the second four-way valve 21 has four ports, of which port 1 is connected to the first low-temperature refrigerant channel 51, port 2 is connected to the second low-temperature refrigerant channel 52, port 3 is connected to the heat exchange condenser 6, and port 4 is connected to the evaporator condenser 9.

[0042] A1. Cryogenic Receiver 7 → Cryogenic Throttling Expansion Valve 8: The high-pressure liquid refrigerant at approximately 10°C stored in the cryogenic receiver 7 enters the cryogenic throttling expansion valve 8. After being processed by the cryogenic throttling expansion valve 8, the refrigerant is transformed into a low-pressure gas-liquid mixture at approximately -30°C, and then flows to the first four-way valve 20. Here, the cryogenic receiver 7 can store liquid refrigerant in the cryogenic system; the cryogenic throttling expansion valve 8 can perform pressure reduction and throttling treatment on the refrigerant, using the throttling and pressure reduction effect to cause the refrigerant temperature to drop sharply, changing from a high-pressure liquid to a low-pressure, low-temperature gas-liquid mixture.

[0043] A2. Low-temperature throttling expansion valve 8 → First four-way valve 20 → Electric heater 22 → Evaporator-condenser 9: The refrigerant enters the first four-way valve 20 and flows to the electric heater 22 via a "2 in, 3 out" path, then enters the evaporator-condenser 9. Inside the evaporator-condenser 9, the low-pressure gas-liquid mixture refrigerant at approximately -30°C absorbs heat from the outdoor air and heats up, becoming a low-pressure gaseous refrigerant at approximately -25°C, which then flows to the second four-way valve 21. Here, the first four-way valve 20 can only adjust the refrigerant flow direction and does not change the refrigerant's temperature, pressure, or form. In addition, the electric heater 22 is not used under normal circumstances; it only assists in raising the refrigerant temperature in extreme low-temperature environments when defrosting the evaporator-condenser 9 is required, facilitating defrosting of the evaporator-condenser 9.

[0044] A3. Evaporator-Condenser 9 → Second Four-Way Valve 21 → Low-Temperature Regenerator 5: Low-pressure gaseous refrigerant at approximately -25°C flows through the second four-way valve 21, following a "4-in-1-out" path, to the first low-temperature refrigerant channel 51 of the low-temperature regenerator 5. After exchanging heat with the refrigerant in the second low-temperature refrigerant channel 52, it absorbs heat and becomes low-pressure gaseous refrigerant at approximately 0°C, subsequently flowing to the low-temperature gas-liquid separator 1. Here, the first low-temperature refrigerant channel 51 of the low-temperature regenerator 5 enables bidirectional heat exchange of the refrigerant within the low-temperature system, allowing the low-pressure gaseous refrigerant to absorb heat and rise in temperature.

[0045] A4. Low-temperature regenerator 5 → Low-temperature gas-liquid separator 1: Low-pressure gaseous refrigerant at approximately 0°C enters the low-temperature gas-liquid separator 1; after separation, the refrigerant becomes low-pressure pure gaseous refrigerant at 0°C, and then flows to the low-temperature compressor 2; here, the low-temperature gas-liquid separator 1 can separate any trace amounts of liquid components that may remain in the refrigerant, ensuring that the refrigerant entering the low-temperature compressor 2 is pure gaseous, and avoiding damage caused by liquid refrigerant impacting the compressor.

[0046] A5. Low-temperature gas-liquid separator 1 → Low-temperature compressor 2: Low-pressure pure gaseous refrigerant at about 0°C enters the low-temperature compressor 2; after compression, it becomes high-pressure gaseous refrigerant at about 60°C, and then flows to the low-temperature oil separator 3; here, the low-temperature compressor 2 can compress and pressurize the low-pressure pure gaseous refrigerant in the low-temperature system, so that the refrigerant is transformed into a high-pressure high-temperature gaseous state, providing a heat basis for subsequent heat exchange.

[0047] A6. Cryogenic compressor 2 → Cryogenic oil separator 3: High-pressure, high-temperature gaseous refrigerant at approximately 60°C enters the cryogenic oil separator 3. After separation, the refrigerant temperature drops slightly to approximately 59°C, maintaining a high-pressure gaseous state, and then flows to the first four-way valve 20. Here, the cryogenic oil separator 3 can separate the lubricating oil mixed in the gas discharged from the cryogenic compressor 2, preventing the lubricating oil from entering subsequent heat exchange components and affecting the heat exchange efficiency.

[0048] A7. Low-temperature oil separator 3 → First four-way valve 20 → Low-temperature heat exchanger 4: High-pressure gaseous refrigerant at approximately 59°C flows through the first four-way valve 20 and is guided to the low-temperature heat exchanger 4 via a "4 in - 1 out" path. After heat exchange in the low-temperature heat exchanger 4, the refrigerant becomes high-pressure gaseous refrigerant at approximately 50°C and then flows to the low-temperature regenerator 5. Here, the low-temperature heat exchanger 4 can realize the heat exchange between the low-temperature system and the hot water circulation system: the refrigerant releases heat to heat the circulating water and initially cools itself.

[0049] A8, Low-temperature heat exchanger 4 → Low-temperature regenerator 5: High-pressure gaseous refrigerant at approximately 50°C enters the second low-temperature refrigerant flow channel 52 of the low-temperature regenerator 5; after heat exchange, it becomes high-pressure gaseous refrigerant at approximately 45°C, and then flows to the second four-way valve 21; here, the second low-temperature refrigerant flow channel 52 of the low-temperature regenerator 5 can exchange heat with the low-temperature, low-pressure refrigerant from the evaporator condenser 9, allowing the high-pressure gaseous refrigerant to further release heat, while providing heat for the low-temperature, low-pressure refrigerant.

[0050] A9, Low-temperature regenerator 5 → Second four-way valve 21 → Heat exchange condenser 6: High-pressure gaseous refrigerant at approximately 45°C flows through the second four-way valve 21, following a "2 in - 3 out" path to the heat exchange condenser 6; after heat exchange in the heat exchange condenser 6, it becomes high-pressure liquid refrigerant at approximately 10°C, and then flows to the low-temperature liquid receiver 7; here, the heat exchange condenser 6 allows the high-pressure gaseous refrigerant to release heat, causing it to condense and liquefy into high-pressure liquid refrigerant.

[0051] A10, Heat exchange condenser 6 → Low temperature liquid receiver 7: High-pressure liquid refrigerant at about 10°C flows back into the low temperature liquid receiver 7, consistent with the initial liquid state. At this point, the low temperature system completes a complete heating cycle.

[0052] The refrigerant cycle in the high-temperature system consists of the following steps B1-B9:

[0053] B1. Start-up self-test and high-temperature compressor 12 start-up: First, the equipment performs a self-test. After the test is normal, low-pressure gaseous refrigerant at about 25°C enters the high-temperature compressor 12. After being compressed by the high-temperature compressor 12, the refrigerant becomes high-pressure gaseous refrigerant at about 80°C, and then is delivered to the high-temperature oil separator 13. Here, the high-temperature compressor 12 can compress and pressurize the refrigerant in the high-temperature system, so that the refrigerant changes from the initial low-temperature and low-pressure state to a high-temperature and high-pressure state.

[0054] B2, High-temperature compressor 12 → High-temperature oil separator 13: High-pressure gaseous refrigerant at 80°C enters the high-temperature oil separator 13. After separating the liquid in the refrigerant, the refrigerant becomes a high-pressure pure gas with a slightly lower temperature of 79°C, and then flows to the high-temperature heat exchange condenser 14. Here, the high-temperature oil separator 13 can separate the lubricating oil mixed in the gas discharged from the high-temperature compressor 12, preventing the lubricating oil from entering the subsequent heat exchange components and affecting the heat exchange efficiency.

[0055] B3, High-temperature oil separator 13 → High-temperature heat exchange condenser 14: High-pressure gaseous refrigerant at about 79°C enters the high-temperature heat exchange condenser 14 and exchanges heat with the circulating water in the hot water circulation system; during the heat exchange process, the gaseous refrigerant releases heat and gradually condenses into high-pressure liquid refrigerant at about 50°C, and then flows to the high-temperature regenerator 15.

[0056] B4, High-temperature heat exchange condenser 14 → High-temperature regenerator 15: High-pressure liquid refrigerant at about 50°C enters the second high-temperature refrigerant flow channel 152 of the high-temperature regenerator 15. After heat exchange, the refrigerant is cooled to a high-pressure liquid refrigerant at 35°C and then flows to the high-temperature liquid reservoir 16. Here, the high-temperature regenerator 15 can realize heat exchange inside the high-temperature system and preheat the low-temperature, low-pressure refrigerant while further cooling itself.

[0057] B5, High-temperature regenerator 15 → High-temperature liquid receiver 16: High-pressure liquid refrigerant at about 35°C enters the high-temperature liquid receiver 16. The high-temperature liquid receiver 16 only has the function of storing liquid for heat preservation and pressure preservation, and then flows to the high-temperature throttling expansion valve 17.

[0058] B6, High-temperature liquid receiver 16 → High-temperature throttling expansion valve 17: High-pressure liquid refrigerant at about 35°C enters the high-temperature throttling expansion valve 17. After throttling and depressurization, the refrigerant changes from liquid to a low-pressure gas-liquid mixture at about 5°C, and then flows to the heat exchange condenser 6. Here, the high-temperature throttling expansion valve 17 can depressurize and throttle the liquid refrigerant, causing it to vaporize and form a gas-liquid mixture.

[0059] B7, High-temperature throttling expansion valve 17 → Heat exchange condenser 6: Low-pressure gas-liquid mixture refrigerant at about 5°C enters the heat exchange condenser 6. After absorbing heat, the gas-liquid mixture changes to a gas, the temperature rises to about 15°C, the pressure remains low, and then flows to the high-temperature regenerator 15. Here, the heat exchange condenser 6 is located at the top of the low-temperature liquid storage tank 7. It can absorb the heat of the low-temperature refrigerant in the low-temperature liquid storage tank 7 by utilizing the principle of hot gas rising, which helps the low-temperature refrigerant to liquefy, while it further vaporizes itself.

[0060] B8, Heat exchange condenser 6 → High-temperature regenerator 15: Low-pressure gaseous refrigerant at about 15°C enters the first high-temperature refrigerant flow channel 151 of the high-temperature regenerator 15. After heat exchange, the refrigerant is heated to a low-pressure gaseous refrigerant at about 25°C, and then flows to the high-temperature gas-liquid separator 11. Here, the first high-temperature refrigerant flow channel 151 of the high-temperature regenerator 15 can absorb the heat of the liquid refrigerant on the high-temperature side and increase the refrigerant temperature.

[0061] B9. High-temperature regenerator 15 → High-temperature gas-liquid separator 11: Low-pressure gaseous refrigerant at approximately 25°C enters the high-temperature gas-liquid separator 11. After gas-liquid separation, the refrigerant becomes low-pressure pure gaseous refrigerant at approximately 25°C. At this point, the high-temperature system has completed one heating cycle. The refrigerant then re-enters the high-temperature compressor 12 to start the next cycle. Here, the high-temperature gas-liquid separator 11 can separate any trace amounts of liquid components that may remain in the low-pressure refrigerant of the high-temperature system, ensuring that the refrigerant entering the high-temperature compressor 12 is pure gaseous and preventing liquid refrigerant from impacting the high-temperature compressor 12 and causing damage.

[0062] The water circulation in the hot water circulation system consists of the following steps C1-C4:

[0063] C1. Driven by circulating water pump 19: Ambient water at approximately 20°C enters the circulating water pump 19; after being driven by the circulating water pump 19, it is transported to the low-temperature heat exchanger 4.

[0064] C2, Circulating water pump 19 → Low-temperature heat exchanger 4 (primary heating): Ambient water at approximately 20°C enters the low-temperature heat exchanger 4 and exchanges heat with the high-pressure gaseous refrigerant at approximately 59°C in the low-temperature system, becoming initially heated water at approximately 25°C, and then flows to the high-temperature heat exchange condenser 14; Here, the low-temperature heat exchanger 4 can realize the heat exchange between the low-temperature system and the hot water circulation system: the heat released by the refrigerant is used to initially heat the ambient water.

[0065] C3, Low-temperature heat exchanger 4 → High-temperature heat exchanger condenser 14 (secondary heating): Initially heated water at approximately 25°C enters the high-temperature heat exchanger condenser 14 and exchanges heat with the high-pressure gaseous refrigerant at approximately 79°C in the high-temperature system, raising the final temperature to approximately 70°C, thus completing the hot water preparation. Here, the high-temperature heat exchanger condenser 14 can realize the heat exchange between the high-temperature system and the hot water circulation system: through the deep heat exchange between the refrigerant and the initially heated water, the water temperature is further increased to the target value, completing the hot water preparation.

[0066] C4. High-temperature heat exchange condenser 14 → hot and cold water buffer tank 10 → hot and cold water tank 18: Hot water at about 70°C is mixed and stabilized in the hot and cold water buffer tank 10, then flows into the hot and cold water tank 18 for storage and is output to the water user as needed; at the same time, the water supply pipe of the hot and cold water tank 18 replenishes the water at an ambient temperature of about 20°C in real time to ensure the continuous circulation of the hot water circulation system.

[0067] It should be noted that in actual hot water production, the ambient water temperature is not raised to the set temperature in one water circulation. Instead, it goes through multiple water circulations until the water temperature reaches the standard, and then is output to the water user or heating system as needed to provide hot water or heating.

[0068] In addition, if the water temperature is lower than the starting condition of the high-temperature compressor (e.g., 3℃), the low-temperature system will be started first to preheat the water at the ambient temperature of the hot water circulation system. After the water temperature rises to the starting threshold of the high-temperature compressor (e.g., 20℃), the high-temperature compressor will start, and the unit will switch to normal heating mode. The reason for this operation is that the high-temperature refrigerant used in the high-temperature system needs to release its latent heat of condensation in the high-temperature heat exchange condenser 14. If the water temperature is only 3℃, the high-temperature refrigerant may release heat too quickly and condense excessively in the high-temperature heat exchange condenser 14. Without fully participating in the circulation, the excessive cooling will cause abnormal system pressure, disrupt the phase change balance of the high-temperature system, and even cause the refrigerant circulation to be interrupted. The temperatures of 3℃ and 20℃ are not the only standard temperatures and need to be adjusted according to the type of refrigerant used.

[0069] In addition to the heating mode described above, this cascade heat pump system also has a cooling mode, which can cool indoor areas. The cooling mode of this system will be described in detail below:

[0070] like Figure 2 As shown, under refrigeration conditions, the high-temperature system is shut down, the cold water circulation system is started to circulate water in the pipes, and then the low-temperature system is started.

[0071] In the cryogenic system, the liquid refrigerant in the cryogenic storage tank 7 is cooled and depressurized by the cryogenic throttling expansion valve 8 and then guided to the cryogenic heat exchanger 4 through the first four-way valve 20 in a "2 in - 1 out" path, where it exchanges heat with the circulating water in the cold water circulation system: the circulating water cools down and the refrigerant heats up. Afterward, the refrigerant enters the second cryogenic refrigerant channel 52 of the cryogenic regenerator 5, and is guided to the first cryogenic refrigerant channel 51 through the second four-way valve 21 in a "2 in - 1 out" path, subsequently entering the cryogenic gas-liquid separator 1 for gas-liquid separation. After separation, the refrigerant enters the low-temperature compressor 2, where it is heated and pressurized to become a high-pressure, high-temperature gaseous refrigerant. It then enters the low-temperature oil separator 3 to complete oil-gas separation. Next, it passes through the first four-way valve 20 and flows through the electric heater 22 (without heating, only flowing through) in a "4 in - 3 out" path to the evaporator condenser 9, where it releases heat to the outside air and condenses into liquid. Then, it passes through the second four-way valve 21 and flows through the heat exchange condenser 6 (only flowing through, without heat exchange) in a "4 in - 3 out" path, returning to the low-temperature liquid receiver 7 to complete one refrigeration cycle.

[0072] In the cold water circulation system, ambient temperature water enters the circulating water pump 19 through a pipe. The circulating water pump 19 drives the ambient temperature water to flow into the low-temperature heat exchanger 4, where it exchanges heat with the refrigerant, and the water temperature decreases to become cold water. Then, it flows sequentially into the high-temperature heat exchange condenser 14 (only flows through, without heat exchange) and the hot and cold water buffer tank 10, and then flows into the water-cooled fan 23. The water-cooled fan 23 has a cold water flow channel inside. When the fan starts, it draws in hot air from the target space. The hot air exchanges heat directly or indirectly with the low-temperature cold water in the flow channel. The heat of the hot air is absorbed by the cold water and becomes cold air. Then, it is blown back to the target space by the fan, thereby achieving the cooling effect of the indoor area. The water after heat exchange returns to the inlet of the circulating water pump 19 through the return water pipe, and is driven by the circulating water pump 19 again to enter the next cold water cycle.

[0073] This cascade heat pump system also features a defrosting mode;

[0074] During winter heating operation, the outdoor evaporator condenser 9 is constantly exchanging heat with the low-temperature air, and frost is easily condensed on its surface. If the frost layer is too thick, it will greatly hinder heat transfer, resulting in a decrease in the system's heating capacity, an increase in energy consumption, and even affecting the stability of the refrigerant circulation. Therefore, the defrosting mode of this system can quickly remove the frost buildup on the surface of the evaporator condenser 9, improving the system's operational reliability and adaptability in low-temperature winter environments.

[0075] The following section will elaborate on the defrosting conditions of this system:

[0076] During defrosting, stop producing hot water, shut down the high-temperature system, start the defrosting preheating hot water circulation system to circulate water in the pipeline, and then start the low-temperature system.

[0077] In the defrosting preheating hot water circulation system, the hot and cold water buffer tank 10 stores hot water. The circulating water pump 19 drives the hot water to flow into the low-temperature heat exchanger 4 to exchange heat with the refrigerant. At this time, the water temperature decreases and the refrigerant temperature rises, thereby preheating the refrigerant and effectively reducing the initial compression temperature difference of the low-temperature compressor 2. This avoids problems such as abnormal power consumption and overheating of the machine body caused by the need to significantly increase the compression ratio when compressing the low-temperature refrigerant. Afterward, the circulating water flows through the high-temperature heat exchange condenser 14 (only flows through, without heat exchange) and returns to the hot and cold water buffer tank 10. Then, it is driven to flow again by the circulating water pump 19. This cycle is repeated at least once to achieve the preheating of the refrigerant.

[0078] In the cryogenic system, the operating state is the same as that of the cryogenic system in refrigeration mode, except that the electric heater 22 is activated to further heat the refrigerant and accelerate defrosting. Specifically, the liquid refrigerant in the cryogenic receiver 7 is cooled and depressurized by the cryogenic throttling expansion valve 8 and then guided to the cryogenic heat exchanger 4 through the first four-way valve 20 in a "2 in - 1 out" path to exchange heat with the circulating water in the defrosting preheating hot water circulation system: the circulating water cools down and the refrigerant heats up. After that, the refrigerant enters the second cryogenic refrigerant channel 52 of the cryogenic regenerator 5 and is guided to the first cryogenic refrigerant channel 51 through the second four-way valve 21 in a "2 in - 1 out" path, and then enters the cryogenic gas-liquid separator 1 for gas-liquid separation. After separation The refrigerant enters the cryogenic compressor 2, where it is heated and pressurized, becoming a high-pressure, high-temperature gaseous refrigerant. It then enters the cryogenic oil separator 3 to complete oil-gas separation. Next, it passes through the first four-way valve 20, following a "4 in - 3 out" path, and enters the electric heater 22. The electric heater 22 further heats the refrigerant, which then enters the evaporator-condenser 9. At this point, the frost layer absorbs a large amount of heat released by the refrigerant and melts, gradually removing the frost layer adhering to its surface and restoring the effective heat exchange area between the evaporator-condenser 9 and the outdoor air. Simultaneously, the refrigerant also condenses and liquefies, then passes through the second four-way valve 21, following a "4 in - 3 out" path, and is guided to the heat exchange condenser 6 (flowing only, without heat exchange), returning to the cryogenic liquid receiver 7, completing one defrosting cycle.

[0079] Among them, the heating rod of the electric heater 22 adopts an external design. Specifically, the electric heater 22 is a shell and tube type heater with independent through channels inside. The heating rod is inserted into the corresponding channel and does not come into direct contact with the low-temperature refrigerant. This avoids chemical corrosion or physical contamination between the heating rod and the refrigerant, and can efficiently transfer heat through the shell and tube wall to ensure a stable increase in refrigerant temperature.

[0080] This system also has a pressure relief system, which will be described in detail below:

[0081] The pressure relief system includes a pressure relief pipeline installed between the cryogenic liquid receiver 7 and the cryogenic gas-liquid separator 1, and a self-regulating pressure regulating valve installed on the pressure relief pipeline. The self-regulating pressure regulating valve automatically opens when the pressure in the cryogenic liquid receiver 7 reaches its set value, connecting the cryogenic liquid receiver 7 and the cryogenic gas-liquid separator 1. The high-pressure gaseous refrigerant accumulated in the cryogenic liquid receiver 7 is directed into the cryogenic gas-liquid separator 1 through a separate pressure relief pipeline. The introduced high-pressure refrigerant mixes with the existing low-pressure gaseous refrigerant in the cryogenic gas-liquid separator 1, preventing the cryogenic liquid receiver 7 from exceeding its pressure limit, damaging the sealing interface, or leaking refrigerant due to continuous increase in internal pressure. This provides a basic guarantee for the stable storage and circulation of cryogenic refrigerant.

[0082] Secondly, the pressure relief system also includes a safety valve, which is installed on the cryogenic liquid receiver 7. Its pressure setting value is higher than that of the self-regulating pressure regulating valve. When the self-regulating pressure regulating valve fails to open normally, causing the pressure inside the cryogenic liquid receiver 7 to continuously rise to the pressure setting value of the safety valve, the valve will automatically open and discharge the overpressured high-pressure gaseous refrigerant directly to the outside, providing secondary safety protection for the system.

[0083] In addition, the pressure relief system also includes a bypass valve, which is installed on the cryogenic receiver 7. When both the self-regulating pressure regulating valve and the safety valve fail, and the pressure inside the cryogenic receiver 7 continues to rise, approaching or reaching its limit pressure value, the maintenance personnel will manually open the bypass valve to directly discharge the overpressured high-pressure gaseous refrigerant to the outside. Through manual intervention to force pressure relief, damage to the cryogenic receiver 7 and the entire cryogenic system is avoided, while time is bought for the repair of the faulty valve, providing a final safety guarantee for the system.

[0084] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art can make other variations or modifications based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the protection scope of this innovative technical solution.

Claims

1. A cascade heat pump system adapted to low-temperature environments, characterized in that, include: The low-temperature system includes a low-temperature refrigerant and a low-temperature gas-liquid separator (1), a low-temperature compressor (2), a low-temperature oil separator (3), a low-temperature heat exchanger (4), a heat exchange condenser (6), a low-temperature liquid storage tank (7), a low-temperature throttling expansion valve (8), and an evaporative condenser (9) connected in a ring topology and internally circulating with the low-temperature refrigerant. The low-temperature refrigerant in the low-temperature liquid storage tank (7) expands and cools down through the low-temperature throttling expansion valve (8), then enters the evaporative condenser (9) to absorb outdoor heat and heat up. After being further heated by the low-temperature compressor (2), it enters the low-temperature heat exchanger (4) and the heat exchange condenser (6) in sequence for heat exchange, and finally returns to the low-temperature liquid storage tank (7) for the next cycle. The high-temperature system includes a high-temperature refrigerant and a high-temperature gas-liquid separator (11), a high-temperature compressor (12), a high-temperature oil separator (13), a high-temperature heat exchange condenser (14), a high-temperature liquid receiver (16), a high-temperature throttling expansion valve (17), and the heat exchange condenser (6) connected in a ring topology and circulating the high-temperature refrigerant. The high-temperature refrigerant in the high-temperature liquid receiver (16) expands and cools down through the high-temperature throttling expansion valve (17), then enters the heat exchange condenser (6) and exchanges heat with the low-temperature refrigerant to raise its temperature. After being further heated by the high-temperature compressor (12), it enters the high-temperature heat exchange condenser (14) for heat exchange, and finally returns to the high-temperature liquid receiver (16) for the next cycle. The hot water circulation system includes a hot and cold water tank (18) connected in a ring topology, a circulating water pump (19), the low-temperature heat exchanger (4), and the high-temperature heat exchange condenser (14); the circulating water pump (19) drives the water in the hot and cold water tank (18) to first flow through the low-temperature heat exchanger (4) to exchange heat with the low-temperature refrigerant, then through the high-temperature heat exchange condenser (14) to exchange heat with the high-temperature refrigerant, and then return to the hot and cold water tank (18), and so on, at least once, to produce hot water; The temperature of the low-temperature refrigerant after it exits the low-temperature compressor (2) is lower than the temperature of the high-temperature refrigerant after it exits the high-temperature compressor (12); The temperature of the low-temperature refrigerant after it exits the low-temperature throttling expansion valve (8) is lower than the temperature of the high-temperature refrigerant after it exits the high-temperature throttling expansion valve (17). The startup sequence is as follows: first start the hot water circulation system, then start the high-temperature system, and finally start the low-temperature system. Also includes: The first four-way valve (20) is connected to the low-temperature oil separator (3), the low-temperature heat exchanger (4), the low-temperature throttling expansion valve (8) and the evaporator-condenser (9), respectively. The second four-way valve (21) is connected to the low-temperature gas-liquid separator (1), the low-temperature heat exchanger (4), the heat exchange condenser (6) and the evaporator condenser (9) respectively. A cold water circulation system is activated during refrigeration; the cold water circulation system includes the circulating water pump (19), the low-temperature heat exchanger (4), and the water-cooled fan (23) connected in sequence. The defrosting preheating hot water circulation system includes the circulating water pump (19), the low-temperature heat exchanger (4), and the hot and cold water buffer tank (10) connected in sequence. The hot and cold water buffer tank (10) stores hot water. The circulating water pump (19) drives the high-temperature hot water inside the hot and cold water buffer tank (10) into the low-temperature heat exchanger (4) to heat the low-temperature refrigerant. Then the hot and cold water flows back to the hot and cold water buffer tank (10) and is then driven to flow again by the circulating water pump (19). This cycle is repeated at least once to achieve refrigerant heating.

2. The cascade heat pump system adapted to low-temperature environments according to claim 1, characterized in that: It also includes a low-temperature regenerator (5), which is installed in the low-temperature system; The low-temperature regenerator (5) includes a first low-temperature refrigerant channel (51) and a second low-temperature refrigerant channel (52); the first low-temperature refrigerant channel (51) is connected in series between the evaporator condenser (9) and the low-temperature gas-liquid separator (1); the second low-temperature refrigerant channel (52) is connected in series between the low-temperature heat exchanger (4) and the heat exchange condenser (6).

3. The cascade heat pump system adapted to low-temperature environments according to claim 2, characterized in that: It also includes a high-temperature regenerator (15), which is installed in the high-temperature system; The high-temperature regenerator (15) includes a first high-temperature refrigerant channel (151) and a second high-temperature refrigerant channel (152); the first high-temperature refrigerant channel (151) is connected in series between the heat exchange condenser (6) and the high-temperature gas-liquid separator (11); the second high-temperature refrigerant channel (152) is connected in series between the high-temperature heat exchange condenser (14) and the high-temperature liquid storage tank (16).

4. The cascade heat pump system adapted to low-temperature environments according to claim 1, characterized in that: During the heating cycle, the low-temperature oil separator (3) is connected to the low-temperature heat exchanger (4) through the first four-way valve (20), and the low-temperature throttling expansion valve (8) is connected to the evaporator condenser (9) through the first four-way valve (20); the low-temperature heat exchanger (4) is connected to the heat exchange condenser (6) through the second four-way valve (21), and the evaporator condenser (9) is connected to the low-temperature gas-liquid separator (1) through the second four-way valve (21); During the refrigeration cycle, the low-temperature oil separator (3) is connected to the evaporator condenser (9) through the first four-way valve (20), and the low-temperature throttling expansion valve (8) is connected to the low-temperature heat exchanger (4) through the first four-way valve (20); the low-temperature heat exchanger (4) is connected to the low-temperature gas-liquid separator (1) through the second four-way valve (21), and the evaporator condenser (9) is connected to the heat exchange condenser (6) through the second four-way valve (21).

5. The cascade heat pump system adapted to low-temperature environments according to claim 4, characterized in that: The circulating water pump (19) drives the ambient temperature water in the pipeline to enter the low temperature heat exchanger (4) to exchange heat with the low temperature refrigerant. The water temperature decreases and flows into the water-cooled fan (23) to absorb the heat of the indoor environment. Then it is driven to flow again by the circulating water pump (19). This cycle is repeated at least once to reduce the indoor temperature and achieve cooling.

6. The cascade heat pump system adapted to low-temperature environments according to claim 4, characterized in that: It also includes an electric heater (22), connected in series between the first four-way valve (20) and the evaporator-condenser (9); When defrosting the evaporator condenser (9), the electric heater (22) is activated to further heat the low-temperature refrigerant compressed by the low-temperature compressor (2) to defrost the evaporator condenser (9).

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