Cascade high-temperature heat pump system and control method thereof

Abstract

The present invention relates to a cascade high-temperature heat pump system and a control method thereof in the field of thermal equipment, comprising a high-temperature compressor and a jet heat-increasing compressor. The high-temperature compressor, a plate heat exchanger, a third electronic expansion valve, and an evaporative condensing heat exchanger form a cycle. The jet heat-increasing compressor, a four-way valve, a first plate heat exchanger, a fin heat exchanger, an evaporative condensing heat exchanger, and a second electronic expansion valve form another cycle. Heat is exchanged between the two in the evaporative condensing heat exchanger. A spiral sleeve and a spiral single tube are provided inside the evaporative condensing heat exchanger. The spiral sleeve and the spiral single tube are integrally arranged in low-temperature water. The device can perform cascade heating, so that the high-temperature hot water output can reach a maximum of 80-85°C, while also providing low-temperature hot water of 7-50°C. In addition, the device can also perform single cooling operation. It has high heat exchange efficiency and can perform high-temperature heating or hot water output.

Description

Technical Field

[0001] The present invention relates to a thermal device, and in particular to a high-temperature heat pump system and a control method thereof. Background Art

[0002] Prior art describes a cascade CO2 heat pump and a cascade CO2 heat pump defrosting method using a four-way valve reversing system. Publication number: CN106016802A, Publication Date: October 12, 2016. This device utilizes the proven four-way valve reversing defrosting technology of conventional refrigerant systems. When the system detects that the air-source evaporator has met defrost requirements, it shuts down the second compressor, halting the CO2 heating cycle. Simultaneously, the four-way valve of the conventional refrigerant system is controlled, allowing the system to draw heat from the user's hot water demand side to remove frost from the air-source heat exchanger. This method significantly reduces the defrost time of a cascade CO2 system and improves its defrost efficiency, providing a technical solution for the reliable operation of heat pump systems in extremely low ambient temperatures.

[0003] The usual cascade high-temperature heat pump system adopts a two-stage heat pump system, namely a low-temperature heat pump system and a high-temperature heat pump system. The low-temperature heat pump system absorbs heat energy from the air, heats the medium to a certain temperature, and then supplies it to the high-temperature heat pump system. The high-temperature heat pump further heats the hot water, so that it can be used in lower ambient temperatures and can supply hot water with a maximum temperature of 80-85°C.

[0004] The disadvantages of existing cascade high-temperature heat pump systems are that their heat exchange efficiency is not high enough, and the utilization of thermal energy is insufficient. In addition, existing cascade heat pump systems do not have a cooling function and cannot simultaneously supply domestic hot water. Summary of the Invention

[0005] The purpose of the present invention is to provide a control method for a cascade high-temperature heat pump system, which can efficiently utilize air thermal energy, improve heat utilization efficiency, and simultaneously provide refrigeration and high and low temperature hot water.

[0006] The object of the present invention is achieved as follows: a cascade high-temperature heat pump system includes a high-temperature compressor, a gas-liquid separator 2 is provided at the inlet end of the high-temperature compressor, the outlet of the high-temperature compressor is connected to the refrigerant inlet of the plate heat exchanger 2, the refrigerant outlet of the plate heat exchanger 2 is connected to the inlet of the liquid reservoir 2, the outlet of the liquid reservoir 2 is connected to the interface 1 of the evaporative condensing heat exchanger through the electronic expansion valve 3, the interface 2 of the evaporative condensing heat exchanger is connected to the gas-liquid separator 2, and the plate heat exchanger 2 is also provided with a high-temperature water inlet and a high-temperature water outlet; the device also The jet enthalpy increasing compressor includes two inlets, one of which is connected to the interface a of the four-way valve through the gas-liquid separator, and the other is the enthalpy increasing port, which is connected to the inlet and outlet of the plate heat exchanger. The four-way valve includes interfaces a, b, c and d. The four-way valve has two working states. When heating is in operation, its interface a is connected to interface b, and interface c is connected to interface d; when cooling and defrosting are in operation, its interface a is connected to interface d, and interface b is connected to interface c; interface b of the four-way valve is connected to the fin exchanger. The inlet and outlet 1 of the heat exchanger, the inlet and outlet 2 of the fin heat exchanger are connected to the inlet and outlet 4 of the plate heat exchanger 1 through the electronic expansion valve 2, the interface d of the four-way valve is connected to the interface 3 of the evaporative condensing heat exchanger, the interface 4 of the evaporative condensing heat exchanger is connected to the inlet and outlet 3 of the plate heat exchanger 1 after passing through the liquid reservoir 1, the inlet and outlet 2 of the plate heat exchanger 1 is connected to the inlet and outlet 4 of the plate heat exchanger 1 through the electronic expansion valve 1, the inlet and outlet 1 of the plate heat exchanger 1 is internally connected to the inlet and outlet 2 of the heat exchanger 1, the inlet and outlet 3 of the plate heat exchanger 1 is connected to the inlet and outlet 4 of the heat exchanger 1 They are connected internally; the evaporative condensing heat exchanger is also provided with a low-temperature water inlet and a low-temperature water outlet; a spiral sleeve and a spiral single tube are provided inside the evaporative condensing heat exchanger, and the spiral sleeve and the spiral single tube are arranged in low-temperature water as a whole. The spiral sleeve includes an inner tube and an outer tube, and the two ends of the outer tube are respectively connected to the interface three of the evaporative condensing heat exchanger and the interface four of the evaporative condensing heat exchanger, one end of the inner tube is connected to the interface two of the evaporative condensing heat exchanger, the interface one of the evaporative condensing heat exchanger is connected to the inlet of the spiral single tube, and the outlet of the spiral single tube is connected to the other end of the inner tube.

[0007] When the present invention is working, it can perform cascade heating, so that the high-temperature hot water output can reach a maximum of 80-85°C, while also providing low-temperature hot water of 7-50°C. In addition, the device can also perform single cooling operation. Compared with the existing technology, the beneficial effect of the present invention is that: due to the use of the spiral sleeve and the spiral single tube, the low-temperature and high-temperature heat exchanges can be partially carried out directly in the spiral sleeve, reducing the impact of the low-temperature hot water on the high-temperature hot water during use, making the temperature fluctuation of the high-temperature hot water smaller. In addition, through the arrangement of the enthalpy increase port, the electronic expansion valve and the plate heat exchanger, the low-temperature stage can also work under extremely low external temperatures, and the lowest operating temperature can reach minus 35°C. The device can efficiently utilize air thermal energy and improve heat utilization efficiency.

[0008] Furthermore, the evaporative condensing heat exchanger includes a water tank, the spiral sleeve and the spiral single tube are arranged in the water tank, the low-temperature water inlet and the low-temperature water outlet are arranged on the water tank, and an insulation layer is provided outside the water tank.

[0009] As a further improvement of the present invention, an exhaust valve is provided on the top of the water tank to discharge part of the non-condensable gas in the water tank.

[0010] The cross section of the inner tube is a polygon with waves, and the crests of the waves touch the inner wall of the outer tube. This structure can greatly increase the heat area of ​​the inner tube, making the heat exchange between the refrigerant in the inner tube and the refrigerant in the outer tube more complete.

[0011] The present invention also provides a method for controlling steam generation in a cascade high-temperature heat pump system, including the following operating modes:

[0012] Mode 1. Cascade heating mode 1: The four-way valve is in the heating operation state, the high-temperature compressor and the jet reheat compressor are running at the same time, the reheat port is closed, and the refrigerant exchanges heat through the evaporative condensing heat exchanger, condenses itself, and then evaporates in the fin heat exchanger after passing through the electronic expansion valve 2, absorbing external atmospheric heat energy, and then returns to the jet reheat compressor for compression to complete the low-temperature stage heat cycle; the high-temperature and high-pressure refrigerant at the outlet of the high-temperature compressor transfers heat to water in the plate heat exchanger 2 to form high-temperature hot water output. After condensing itself, it evaporates and absorbs heat in the evaporative condensing heat exchanger through the electronic expansion valve 3. In the evaporative condenser, the heat from the jet reheat compressor is absorbed by heat conduction and convection, completing the high-temperature stage heat cycle.

[0013] Mode 2. Cascade Heating Mode 2: The four-way valve is in heating operation, the high-temperature compressor and the jet reheating compressor are operating simultaneously, and the reheating port is open. After exchanging heat in the evaporative-condensing heat exchanger and condensing itself, the refrigerant passes through electronic expansion valve 2 and evaporates in the fin heat exchanger, absorbing heat energy from the outside atmosphere. It then returns to the jet reheating compressor for compression. The other path passes through electronic expansion valve 1 and evaporates in plate heat exchanger 1, directly absorbing heat energy from the refrigerant condensed in the evaporative-condensing heat exchanger. It then enters the jet reheating compressor through the reheating port, completing the low-temperature heat cycle. The high-temperature, high-pressure refrigerant at the outlet of the high-temperature compressor transfers heat to water in plate heat exchanger 2, producing high-temperature hot water output. After condensing itself, it passes through electronic expansion valve 3 and evaporates in the evaporative-condensing heat exchanger, absorbing heat. In the evaporative condenser, it absorbs heat from the jet reheating compressor through heat conduction and convection, completing the high-temperature heat cycle.

[0014] Mode 3. Single cooling mode: The four-way valve is in the cooling operation state, the high-temperature compressor stops, the jet enthalpy increase compressor runs, the enthalpy increase port is closed, the refrigerant condenses in the fin heat exchanger, passes through the second electronic expansion valve, and evaporates in the evaporative condensing heat exchanger, absorbing the heat in the water to form low-temperature water for external cooling.

[0015] Mode 4. Low-temperature defrosting: The four-way valve is in the refrigeration operation state. When frost forms on the surface of the fin heat exchanger, the jet enthalpy increase compressor starts operating, the enthalpy increase port is closed, and the refrigerant condenses in the fin heat exchanger to release heat for defrosting. After passing through the second electronic expansion valve, the refrigerant evaporates in the evaporative condensing heat exchanger, absorbing the heat in the water for defrosting. The defrosting operation stops when the water temperature is lower than the set temperature.

[0016] Mode 5. Low-temperature hot water usage mode: The four-way valve is in the heating operation state, the jet reheat compressor is running, and the refrigerant exchanges heat through the evaporative condensing heat exchanger, condenses itself, and then evaporates in the fin heat exchanger after passing through the second electronic expansion valve, absorbing external atmospheric heat energy, and then returns to the jet reheat compressor for compression to complete the low-temperature heat cycle; in the evaporative condensing heat exchanger, the refrigerant condenses and releases heat to form low-temperature hot water for external use.

[0017] Furthermore, in Mode 5, when the ambient temperature is below zero, the enthalpy increase port and electronic expansion valve 1 are opened to increase enthalpy and perform a low-temperature heat cycle to provide low-temperature hot water. This mode is particularly effective when used at -10°C.

[0018] Furthermore, when operating in Mode 5, the high-temperature compressor can work simultaneously to provide high-temperature hot water.

[0019] Figure 1 This is a working principle diagram of the present invention.

[0020] Figure 2 for Figure 1 Schematic diagram of the evaporative condensing heat exchanger structure.

[0021] Figure 3 Schematic diagram of the cross-sectional structure of the spiral casing and the spiral single tube.

[0022] Figure 4 for Figure 3 A partial enlarged view of middle A.

[0023] Figure 5 This is the working principle diagram of cascade heating mode 1.

[0024] Figure 6 This is the working principle diagram of cascade heating mode 2.

[0025] Figure 7 This is the working principle diagram of the single cooling mode.

[0026] Figure 8 This is the working principle diagram of the low temperature stage defrost mode.

[0027] Figure 9 This is a working principle diagram of the low-temperature hot water usage mode.

[0028] In the figure, 1 is a gas-liquid separator, 2 is a fin heat exchanger, 2a is an inlet and outlet 1 of the fin heat exchanger, 2b is an inlet and outlet 2 of the fin heat exchanger, 3 is a four-way valve, 4 is an air jet enthalpy increase compressor, 4a is an enthalpy increase port, 5 is an electronic expansion valve, 6 is a plate heat exchanger, 6a is an inlet and outlet 1 of the plate heat exchanger, 6b is an inlet and outlet 2 of the plate heat exchanger, 6c is an inlet and outlet 3 of the plate heat exchanger, 6d is an inlet and outlet 4 of the plate heat exchanger, 7 is an electronic expansion valve, 8 is a liquid reservoir, 9 is an evaporative condensing heat exchanger, 9a is an interface 1 of the evaporative condensing heat exchanger, 9b is an interface 2 of the evaporative condensing heat exchanger, 9c is an interface 3 of the evaporative condensing heat exchanger, 9d is an interface 4 of the evaporative condensing heat exchanger, 9e is a low-temperature water inlet, 9f is a low-temperature water outlet, 901 is a water tank, 902 is a spiral single tube, 903 is a spiral casing, 903a is an outer tube, 903b is an inner tube, 903c is an outer flow channel, 903d is an inner flow channel, 10 Gas-liquid separator 2, 11 High-temperature compressor, 12 Liquid receiver 2, 13 Electronic expansion valve 3, 14 Plate heat exchanger 2, 14a Refrigerant inlet of plate heat exchanger 2, 14b Refrigerant outlet of plate heat exchanger 2, 14c High-temperature water inlet, 14d High-temperature water outlet, 15 Exhaust valve. DETAILED DESCRIPTION

[0029] like Figure 1-4As shown, a cascade high-temperature heat pump system includes a high-temperature compressor 11. The inlet end of the high-temperature compressor 11 is provided with a gas-liquid separator 10. The outlet of the high-temperature compressor 11 is connected to the refrigerant inlet 14a of the plate heat exchanger 2. The refrigerant outlet 14b of the plate heat exchanger 2 is connected to the inlet of the liquid reservoir 2 12. The outlet of the liquid reservoir 2 12 is connected to the interface 1 9a of the evaporative condensing heat exchanger through the electronic expansion valve 3 13. The interface 2 9b of the evaporative condensing heat exchanger is connected to the gas-liquid separator 2 10. The plate heat exchanger 2 14 is also provided with a high-temperature water inlet 14c and a high-temperature water outlet 14d. The device also includes a jet The enthalpy increasing compressor 4 has two inlets, one of which is connected to the interface a of the four-way valve 3 through the gas-liquid separator 1, and the other is the enthalpy increasing port 4a. The enthalpy increasing port 4a is connected to the inlet and outlet 6a of the plate heat exchanger 1. The four-way valve 3 includes interfaces a, b, c and d. The four-way valve 3 has two working states. When the heating operation is in progress, its interface a is connected to the interface b, and the interface c is connected to the interface d; when the cooling and defrosting operation is in progress, its interface a is connected to the interface d, and the interface b is connected to the interface c; the interface b of the four-way valve 3 is connected to the inlet and outlet 2a of the fin heat exchanger, and the inlet and outlet 2 of the fin heat exchanger are connected. 2b is connected to the inlet and outlet 4 6d of the plate heat exchanger 1 through the electronic expansion valve 2 7, the interface d of the four-way valve 3 is connected to the interface 3 9c of the evaporative condensing heat exchanger, the interface 4 9d of the evaporative condensing heat exchanger is connected to the inlet and outlet 3 6c of the plate heat exchanger 1 through the liquid reservoir 1 8, the inlet and outlet 2 6b of the plate heat exchanger 1 is connected to the inlet and outlet 4 6d of the plate heat exchanger 1 through the electronic expansion valve 1 5, the inlet and outlet 1 6a of the plate heat exchanger 1 is internally connected to the inlet and outlet 2 of the heat exchanger 1, and the inlet and outlet 3 6c of the plate heat exchanger 1 is internally connected to the inlet and outlet 4 of the heat exchanger 1; the evaporative condensing heat exchanger 9 is also provided with a low-temperature water inlet 9e. and a low-temperature water outlet 9f; a spiral sleeve 903 and a spiral single tube 902 are provided inside the evaporative condensing heat exchanger 9, and the spiral sleeve 903 and the spiral single tube 902 are arranged as a whole in low-temperature water, the spiral sleeve 903 includes an inner tube 903b and an outer tube 903a, and the two ends of the outer tube 903a are respectively connected to the interface three 9c of the evaporative condensing heat exchanger and the interface four 9d of the evaporative condensing heat exchanger, one end of the inner tube 903b is connected to the interface two 9b of the evaporative condensing heat exchanger, the interface one 9a of the evaporative condensing heat exchanger is connected to the inlet of the spiral single tube 902, and the outlet of the spiral single tube 902 is connected to the other end of the inner tube 903b.

[0030] The evaporative-condensing heat exchanger 9 includes a water tank 901, a spiral casing 903 and a spiral single tube 902 disposed within the water tank 901, a low-temperature water inlet 9e and a low-temperature water outlet 9f disposed on the water tank 901, and an insulating layer disposed on the outside of the water tank 901. An exhaust valve 15 is provided at the top of the water tank 901 to discharge some of the non-condensable gases within the water tank 901.

[0031] The cross-section of inner tube 903b is a polygon with waves, the crests of which contact the inner wall of outer tube 903a. This structure greatly increases the heat transfer area of ​​inner tube 903b, enabling more efficient heat exchange between the refrigerant in inner tube 903b and the refrigerant in outer tube 903a. The space between inner tube 903b and outer tube 903a forms an outer flow channel 903c for the flow of low-temperature refrigerant, which uses R410A. An inner flow channel 903d is formed within inner tube 903b for the flow of high-temperature refrigerant, which uses R314A.

[0032] The control method of the cascade high-temperature heat pump system includes the following operating modes:

[0033] Mode 1. Cascade heating mode 1: Figure 5 As shown, the four-way valve 3 is in the heating operation state, the high-temperature stage compressor 11 and the jet reheating compressor 4 are running at the same time, the reheating port 4a is closed, and the refrigerant condenses itself after passing through the evaporative condensing heat exchanger 9, and then evaporates in the fin heat exchanger 2 after passing through the electronic expansion valve 2 7, absorbs external atmospheric heat energy, and then returns to the jet reheating compressor 4 for compression, completing the low-temperature stage heat cycle; the high-temperature and high-pressure refrigerant at the outlet of the high-temperature stage compressor 11 transfers heat to water in the plate heat exchanger 2 14 to form high-temperature hot water output, and after condensing itself, evaporates and absorbs heat in the evaporative condensing heat exchanger 9 through the electronic expansion valve 3 13. In the evaporative condenser, the heat from the jet reheating compressor 4 is absorbed by heat conduction and convection, completing the high-temperature stage heat cycle.

[0034] Mode 2. Cascade heating mode 2: Figure 6 As shown, the four-way valve 3 is in the heating operation state, the high-temperature stage compressor 11 and the jet reheating compressor 4 are running simultaneously, and the reheating port 4a is open. After the refrigerant exchanges heat through the evaporative condensing heat exchanger 9 and condenses itself, one path passes through the electronic expansion valve 2 7 and evaporates in the fin heat exchanger 2, absorbing heat energy from the external atmosphere, and then returns to the jet reheating compressor 4 for compression. The other path passes through the electronic expansion valve 1 5 and evaporates in the plate heat exchanger 1 6, directly absorbing heat energy from the refrigerant condensed in the evaporative condensing heat exchanger 9, and then enters the jet reheating compressor 4 through the reheating port 4a, completing the low-temperature stage heat cycle; the high-temperature and high-pressure refrigerant at the outlet of the high-temperature stage compressor 11 transfers heat to water in the plate heat exchanger 2 14 to form high-temperature hot water output. After condensing itself, it evaporates and absorbs heat in the evaporative condensing heat exchanger 9 through the electronic expansion valve 3 13. In the evaporative condenser, the heat from the jet reheating compressor 4 is absorbed by heat conduction and convection, completing the high-temperature stage heat cycle.

[0035] Mode 3. Cooling mode only: Figure 7As shown, the four-way valve 3 is in the cooling operation state, the high-temperature stage compressor 11 is stopped, the jet reheat compressor 4 is running, the reheat port 4a is closed, and the refrigerant condenses in the fin heat exchanger 2, passes through the electronic expansion valve 2 7, and evaporates in the evaporative condensing heat exchanger 9, absorbing the heat in the water to form low-temperature water for external cooling.

[0036] Mode 4. Low temperature defrost: Figure 8 As shown, the four-way valve 3 is in the cooling operation state. When frost forms on the surface of the fin heat exchanger 2, the jet enthalpy increase compressor 4 is in operation, the enthalpy increase port 4a is closed, and the refrigerant condenses in the fin heat exchanger 2 to release heat for defrosting. After passing through the electronic expansion valve 2 7, the refrigerant evaporates in the evaporative condensing heat exchanger 9, absorbing heat from the water for defrosting. The defrosting operation stops when the water temperature is lower than the set temperature.

[0037] Mode 5. Low temperature hot water usage mode: Figure 9 As shown, the four-way valve 3 is in the heating operation state, the jet enthalpy increase compressor 4 is running, and the refrigerant condenses after passing through the evaporative condensing heat exchanger 9. Then, after passing through the electronic expansion valve 2 7, it evaporates in the fin heat exchanger 2, absorbs the heat energy of the external atmosphere, and then returns to the jet enthalpy increase compressor 4 for compression, completing the low-temperature heat cycle. In the evaporative condensing heat exchanger 9, the refrigerant condenses and releases heat, forming low-temperature hot water for external use. When operating in mode 5 and the external temperature is below zero, the enthalpy increase port 4a and the electronic expansion valve 1 5 are opened, and a low-temperature heat cycle is carried out through enthalpy increase to provide low-temperature hot water. It can operate at extremely low temperatures, and the effect is particularly obvious when used in low-temperature environments below -10°C. At -30°C, it can still achieve a relatively ideal high-temperature hot water supply effect. When operating in mode 5, the high-temperature compressor 11 can work simultaneously to provide high-temperature hot water.

[0038] During operation, the present invention can perform cascade heating, enabling high-temperature hot water output to reach a maximum of 80-85°C, while also providing low-temperature hot water at 7-50°C. Furthermore, the device can also operate solely for cooling. Compared to the prior art, the present invention offers the following advantages: Due to the use of spiral casing 903 and spiral single tube 902, heat exchange between the low- and high-temperature stages can be partially performed directly within spiral casing 903, reducing the impact of low-temperature hot water on the high-temperature stage during use and minimizing temperature fluctuations in the high-temperature stage. Furthermore, the provision of enthalpy increase port 4a, electronic expansion valve 5, and plate heat exchanger 6 allows the low-temperature stage to operate even in extremely low ambient temperatures, with a minimum operating temperature of -35°C. This device efficiently utilizes air thermal energy, improving heat utilization efficiency.

[0039] The present invention is not limited to the above-mentioned embodiments. On the basis of the technical solutions disclosed in the present invention, those skilled in the art can make some substitutions and modifications to some of the technical features therein according to the disclosed technical content without creative labor, and these substitutions and modifications are all within the protection scope of the present invention.

Claims

1. A cascade high-temperature heat pump system, comprising a high-temperature compressor, the inlet of which is provided with a second gas-liquid separator, the outlet of which is connected to the refrigerant inlet of a second plate heat exchanger, the refrigerant outlet of which is connected to the inlet of a second liquid reservoir, the outlet of which is connected via a third electronic expansion valve to a first interface of an evaporative-condensing heat exchanger, the second interface of which is connected to the second gas-liquid separator, and the second plate heat exchanger is further provided with a high-temperature water inlet and a high-temperature water outlet; characterized in that: It also includes a jet reheat increasing compressor, which has two inlets, one of which is connected to the interface a of the four-way valve through the gas-liquid separator, and the other is the reheat increasing port, which is connected to the inlet and outlet 1 of the plate heat exchanger. The four-way valve includes interfaces a, b, c and d, and has two working states. When the heating operation is in progress, its interface a is connected to the interface b, and the interface c is connected to the interface d; when the cooling and defrosting operation is in progress, its interface a is connected to the interface d, and the interface b is connected to the interface c; the interface b of the four-way valve is connected to the inlet and outlet 1 of the fin heat exchanger, the inlet and outlet 2 of the fin heat exchanger is connected to the inlet and outlet 4 of the plate heat exchanger through the electronic expansion valve 2, the interface d of the four-way valve is connected to the interface 3 of the evaporative condensing heat exchanger, and the interface 4 of the evaporative condensing heat exchanger is connected to the plate heat exchanger after passing through the liquid reservoir 1. The inlet and outlet three of the plate heat exchanger are connected to the inlet and outlet four of the plate heat exchanger one through the electronic expansion valve one. The inlet and outlet one of the plate heat exchanger one is internally connected to the inlet and outlet two of the heat exchanger one, and the inlet and outlet three of the plate heat exchanger one is internally connected to the inlet and outlet four of the heat exchanger one; the evaporative condensing heat exchanger is also provided with a low-temperature water inlet and a low-temperature water outlet; a spiral casing and a spiral single tube are provided inside the evaporative condensing heat exchanger, and the spiral casing and the spiral single tube are arranged in low-temperature water as a whole. The spiral casing includes an inner tube and an outer tube, and the two ends of the outer tube are respectively connected to the interface three of the evaporative condensing heat exchanger and the interface four of the evaporative condensing heat exchanger, one end of the inner tube is connected to the interface two of the evaporative condensing heat exchanger, the interface one of the evaporative condensing heat exchanger is connected to the inlet of the spiral single tube, and the outlet of the spiral single tube is connected to the other end of the inner tube.

2. The cascade high-temperature heat pump system according to claim 1, characterized in that: The evaporative condensing heat exchanger comprises a water tank, a spiral sleeve and a spiral single tube are arranged in the water tank, a low-temperature water inlet and a low-temperature water outlet are arranged on the water tank, and an insulation layer is arranged outside the water tank.

3. The cascade high-temperature heat pump system according to claim 2, characterized in that: An exhaust valve is provided on the top of the water tank.

4. The cascade high-temperature heat pump system according to any one of claims 1 to 3, characterized in that: The cross section of the inner tube is a polygon with waves, and the crests of the waves abut against the inner wall of the outer tube.

5. The control method of the cascade high-temperature heat pump system according to claim 1, characterized in that: The following operating modes are included: Mode 1. Cascade Heating Mode 1: The four-way valve is in the heating operation state, the high-temperature compressor and the jet reheat compressor are running simultaneously, the reheat port is closed, and the refrigerant exchanges heat through the evaporative condensing heat exchanger, condenses itself, and then evaporates in the fin heat exchanger after passing through the electronic expansion valve 2, absorbing external atmospheric heat energy, and then returns to the jet reheat compressor for compression, completing the low-temperature stage heat cycle; the high-temperature and high-pressure refrigerant at the outlet of the high-temperature compressor transfers heat to water in the plate heat exchanger 2, forming high-temperature hot water output, and after condensing itself, evaporates and absorbs heat in the evaporative condensing heat exchanger through the electronic expansion valve 3. In the evaporative condenser, the heat from the jet reheat compressor is absorbed by heat conduction and convection, completing the high-temperature stage heat cycle; Mode 2. Cascade Heating Mode 2: The four-way valve is in heating operation, the high-temperature compressor and the jet reheating compressor are operating simultaneously, and the reheating port is open. After exchanging heat in the evaporative-condensing heat exchanger and condensing itself, the refrigerant passes through electronic expansion valve 2 and evaporates in the fin heat exchanger, absorbing heat energy from the outside atmosphere. It then returns to the jet reheating compressor for compression. The other path passes through electronic expansion valve 1 and evaporates in plate heat exchanger 1, directly absorbing heat energy from the refrigerant condensed in the evaporative-condensing heat exchanger. It then enters the jet reheating compressor through the reheating port, completing the low-temperature heat cycle. The high-temperature, high-pressure refrigerant at the outlet of the high-temperature compressor transfers heat to water in plate heat exchanger 2, producing high-temperature hot water output. After condensing itself, it evaporates and absorbs heat in the evaporative-condensing heat exchanger through electronic expansion valve 3. In the evaporative condenser, it absorbs heat from the jet reheating compressor through heat conduction and convection, completing the high-temperature heat cycle. Mode 3. Single cooling mode: The four-way valve is in cooling operation, the high-temperature compressor is stopped, the jet enthalpy increase compressor is running, the enthalpy increase port is closed, and the refrigerant condenses in the fin heat exchanger. After passing through the second electronic expansion valve, it evaporates in the evaporative condensing heat exchanger, absorbing the heat in the water to form low-temperature water for external cooling; Mode 4. Low-temperature defrost mode: The four-way valve is in refrigeration operation. When frost forms on the surface of the fin heat exchanger, the jet enthalpy increase compressor operates, the enthalpy increase port is closed, and the refrigerant condenses in the fin heat exchanger, releasing heat to defrost. After passing through the second electronic expansion valve, the refrigerant evaporates in the evaporative condensing heat exchanger, absorbing heat from the water for defrosting. The defrost operation stops when the water temperature falls below the set temperature. Mode 5. Low-temperature hot water usage mode: The four-way valve is in the heating operation state, the jet reheat compressor is running, and the refrigerant exchanges heat through the evaporative condensing heat exchanger, condenses itself, and then evaporates in the fin heat exchanger after passing through the second electronic expansion valve, absorbing external atmospheric heat energy, and then returns to the jet reheat compressor for compression to complete the low-temperature heat cycle; in the evaporative condensing heat exchanger, the refrigerant condenses and releases heat to form low-temperature hot water for external use.

6. The control method of the cascade high-temperature heat pump system according to claim 5, characterized in that: When operating in mode 5 and the outside temperature is below zero, the enthalpy increase port and electronic expansion valve 1 are opened to perform a low-temperature heat cycle through enthalpy increase to provide low-temperature hot water.

7. The control method of the cascade high-temperature heat pump system according to claim 5 or 6, characterized in that: When operating in Mode 5, the high-temperature stage compressor works simultaneously to provide high-temperature hot water.

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