Cascade heat pump machine based on quadruple heat exchange and cold and heat balance control method thereof

Abstract

The invention discloses a cascade heat pump machine based on quadruple heat exchange and a cold and heat balance control method thereof, and belongs to the technical field of cascade heat pump machines. A composite heat exchanger in the cascade heat pump machine comprises a low-temperature working medium channel, a supplementary heat source working medium channel, a high-temperature working medium channel and a heat dissipation working medium channel, and a low-temperature working medium of a low-temperature heat pump unit circulates in the low-temperature working medium channel; a high-temperature working medium of the high-temperature heat pump unit circulates in the high-temperature working medium A supplementary working medium carrying a supplementary heat source circulates in the supplementary heat source working medium channel; a heat dissipation working medium for transferring heat inside the composite heat exchanger to the outside of the composite heat exchanger circulates in the heat dissipation working medium channel. According to the cascade heat pump machine, the heat source supplementing working medium channel and the heat dissipation working medium channel are additionally arranged on the composite heat exchanger, the corresponding control method is designed, the problem of fluctuation of heat absorption of the low-temperature heat pump unit in the low-temperature and high-temperature environments can be solved, heat balance control is achieved, and then the cascade heat pump machine can stably operate.

Description

Technical Field

[0001] The present invention relates to the technical field of cascade heat pumps, and more specifically, to a cascade heat pump based on quadruple heat exchange and its control method for cold and heat balance. Background Technique

[0002] The two-stage cascade heat pump technology solves the problems of low performance of a single-stage air source heat pump system at low ambient temperatures in winter and the inability to reach the required outlet water temperature or outlet air temperature, and has been increasingly applied to heating, hot water, drying, etc. in cold regions in the north. Moreover, a two-stage cascade heat pump formed by cascading a primary heat pump cycle system and a secondary heat pump cycle system has the following working principle: the first refrigerant in the evaporator of the primary heat pump cycle system absorbs heat from the low-temperature environment, and transfers the absorbed heat to the secondary heat pump cycle system through a condensation heat exchanger. The secondary heat pump cycle system does work on the heat absorbed by the second refrigerant to further improve the quality of the heat carried by the second refrigerant, and finally releases the heat source it carries through the condenser in the secondary heat pump cycle system. According to the needs of end customers, the condenser in the secondary heat pump cycle system transfers the heat it carries to the heat medium on the user side, where the heat medium on the user side is generally water or air.

[0003] The heat balance technology is a key technology in the use of cascade heat pumps. Because in a cascade heat pump system, the low-temperature stage system and the high-temperature stage system need to exchange heat through an intermediate-coupled evaporative condenser, the heating capacity of the low-temperature stage system must be equal to the heat absorption of the high-temperature stage system, that is, heat balance is achieved, so that the system can operate stably. However, since the low-temperature stage system absorbs heat from the ambient air, its heating capacity will inevitably be affected by the ambient temperature. The heating capacity of the low-temperature stage system is low when the ambient temperature is low, and the heating capacity of the low-temperature stage system is high when the ambient temperature is high. Although the system can achieve heat balance through the temperature change of the intermediate-coupled evaporative condenser. For example, when the ambient temperature rises, the heating capacity of the low-temperature stage system will be greater than the set heat absorption of the high-temperature stage system. At this time, the temperature of the evaporative condenser will rise, thereby increasing the heat absorption of the high-temperature stage system to achieve heat balance and the machine can operate stably. However, due to the limitations of the compressor operating conditions, the compressor cannot work at too high evaporation and condensation temperatures, and the condensation temperature of the low-temperature stage system and the evaporation temperature of the high-temperature stage system just correspond to their temperatures on the evaporative condenser, that is, the temperature of the evaporative condenser cannot always rise. Therefore, it may cause the compressor of the high-temperature stage system to fail to work properly when the temperature is too high. Moreover, in some application environments where the output temperature of the high-temperature stage system needs to be strictly restricted, the cascade heat pump may not be applicable due to excessive coupling fluctuations.

[0004] In actual matching, to ensure the heating capacity at low ambient temperatures, existing designs often match the heating capacities of the two systems at low ambient temperatures. As a result, the heating capacity at high ambient temperatures cannot be well balanced. That is, when the ambient temperature is high, the heating capacity of the low-temperature stage system will definitely exceed the heat absorption set by the high-temperature stage system, which will affect the normal operation of the system. The heat balance problem greatly restricts the applicable temperature range of the cascade heat pump.

[0005] To solve the above technical problems, Chinese Patent Application No. 2008100248938 discloses a single / double-stage hybrid cascade heat pump air conditioner unit that uses a three-channel heat exchanger to form a refrigerant connection with the high-temperature stage system and the low-temperature stage system respectively. It switches between single-stage heating and double-stage cascade heating operations according to the outdoor ambient temperature, using single-stage heating at high ambient temperatures and double-stage cascade heating at low ambient temperatures, improving the adaptability of the system application and the utilization rate of the equipment. However, in this application, when the ambient temperature is high, it actually uses single-stage heating and cannot solve the coupling problem of the cascade heat pump at high ambient temperatures.

[0006] Chinese Patent Application No. 2018113460459 discloses a two-stage self-cascade heat pump system and its usage method, which adds an evaporator in parallel with the evaporative condenser in the high-temperature stage system. By switching the heat exchanger, it uses single-stage heating at high ambient temperatures and double-stage cascade heating at low ambient temperatures. However, in this application, when the ambient temperature is high, it actually uses single-stage heating, and additional devices such as an evaporator and refrigerant switching valves are required, resulting in a complex system, increased volume, and high cost.

[0007] Chinese Patent Application No. 2019105640346 discloses a cascade high-temperature heat pump steam generator. Its low-temperature stage system uses a variable-frequency compressor, and by adjusting the compressor power, the temperature of the intermediate evaporative condenser can be kept constant and the system can be stabilized at different ambient temperatures. However, this technology requires the use of a variable-frequency compressor, resulting in a relatively high cost.

[0008] In summary, in the prior art, to solve the technical problem of heat imbalance in low-temperature and high-temperature heat pump units, the devices and control implementation paths are relatively complex and the cost is relatively high. Summary of the Invention

[0009] In view of the technical problem of thermal imbalance in the low-temperature heat pump unit and the high-temperature heat pump unit of the existing cascade heat pump machine under low ambient temperature and high ambient temperature, the present invention provides a cascade heat pump machine based on quadruple heat exchange and its thermal balance control method. By optimizing the design of the composite heat exchanger, adding a supplementary heat source working medium channel and a heat dissipation working medium channel, and designing the corresponding control method, this solution can solve the problem of heat absorption fluctuation of the cascade heat pump unit under low and high temperature environments, achieve heat balance control, and further enable the cascade heat pump machine to operate stably.

[0010] In the first aspect of the present invention, a cascade heat pump machine based on quadruple heat exchange is provided, including: a low-temperature heat pump unit in which a low-temperature working medium circulates; a high-temperature heat pump unit in which a high-temperature working medium circulates, and the high-temperature condenser in the high-temperature heat pump unit exchanges heat with the heat medium in the user-side heat medium channel; the low-temperature heat pump unit and the high-temperature heat pump unit are coupled for heat exchange through a composite heat exchanger, and the composite heat exchanger includes a low-temperature working medium channel, a supplementary heat source working medium channel, a high-temperature working medium channel, and a heat dissipation working medium channel. Among them, the low-temperature working medium channel is connected to the low-temperature heat pump unit and circulates the low-temperature working medium; the high-temperature working medium channel is connected to the high-temperature heat pump unit and circulates the high-temperature working medium; the supplementary heat source working medium channel is connected to the supplementary heat source and internally circulates a supplementary working medium carrying the supplementary heat source, which is used to supplement the heat absorption of the high-temperature working medium to increase it to its set value range; the heat dissipation working medium channel circulates a heat dissipation working medium for transferring the internal heat of the composite heat exchanger to the outside, which is used to reduce the heat absorption of the high-temperature working medium to reduce it to its set value range.

[0011] Further, the composite heat exchanger is a double-pipe heat exchanger, which includes an inner sleeve, an intermediate sleeve, an outer sleeve nested in sequence from the inside to the outside, and a heat insulation cover wrapped outside the outer sleeve. The inside of the inner sleeve forms the supplementary heat source working medium channel; the high-temperature working medium channel is formed between the inner sleeve and the intermediate sleeve, and the low-temperature working medium channel is formed between the intermediate sleeve and the outer sleeve; the heat dissipation working medium channel is formed between the heat insulation cover and the outer sleeve.

[0012] Further, the supplementary working medium is hot water, and its temperature range is 50~60°C.

[0013] Further, the heat dissipation working medium is air, and a fan is fixedly arranged on the inner wall of the heat insulation cover. The fan is used to control the air flow speed in the heat dissipation working medium channel; the switch of the fan is connected to the control system for realizing the automatic start-stop and power adjustment control of the fan.

[0014] Further, a first solenoid valve is arranged at the inlet of the supplementary heat source working medium channel, and the first solenoid valve is used to control the opening and closing of the supplementary heat source working medium channel; a second solenoid valve is arranged at the inlet of the heat dissipation working medium channel, and the second solenoid valve is used to control the opening and closing of the heat dissipation working medium channel.

[0015] Further, a first temperature sensor is provided at the inlet of the heat medium channel on the user side, and the first temperature sensor is used to detect the inlet temperature of the heat medium channel on the user side; a flow sensor and a second temperature sensor are provided at the outlet of the heat medium channel on the user side, and the flow sensor and the second temperature sensor are respectively used to detect the flow rate and the outlet temperature of the heat medium channel on the user side.

[0016] Further, the cascade heat pump includes a pressure sensor, and the pressure sensor is arranged at the inlet of the low-temperature working medium channel in the composite heat exchanger and is used to detect the condensation pressure at the inlet of the low-temperature working medium channel.

[0017] In a second aspect of the present invention, a method for controlling the heat and cold balance of a cascade heat pump based on quadruple heat exchange as described above is provided, including: if the calorific value increase value of the heat medium in the heat medium channel on the user side is less than the low limit set value Q1, then control the supplementary heat source working medium channel to open and the heat dissipation working medium channel to close; if the calorific value increase value of the heat medium in the heat medium channel on the user side is greater than the high limit set value Q2, then control the supplementary heat source working medium channel to close and the heat dissipation working medium channel to open; if the calorific value increase value of the heat medium in the heat medium channel on the user side is between Q1 and Q2, then control both the supplementary heat source working medium channel and the heat dissipation working medium channel to close; wherein a flow sensor for detecting the flow rate therein, a first temperature sensor for detecting the fluid inlet temperature therein, and a second temperature sensor for detecting the fluid outlet temperature therein are provided in the heat medium channel on the user side; the calorific value increase value of the heat medium is calculated from the feedback value of the heat medium channel on the user side; Q2 is greater than Q1, and Q2 is 1.05 to 1.1 times of Q1.

[0018] In a third aspect of the present invention, another method for controlling the heat and cold balance of a cascade heat pump based on quadruple heat exchange as described above is provided, including: if the condensation pressure at the inlet of the low-temperature working medium channel in the composite heat exchanger is less than the low limit set value P1, then control the supplementary heat source working medium channel to open and the heat dissipation working medium channel to close; if the condensation pressure at the inlet of the low-temperature working medium channel in the composite heat exchanger is greater than the high limit set value P2, then control the supplementary heat source working medium channel to close and the heat dissipation working medium channel to open; if the condensation pressure at the inlet of the low-temperature working medium channel in the composite heat exchanger is between P1 and P2, then control both the supplementary heat source working medium channel and the heat dissipation working medium channel to close; wherein the condensation pressure is obtained from the feedback value of the pressure sensor at the inlet of the low-temperature working medium channel in the composite heat exchanger; P2 is greater than P1, and P2 is 1.05 to 1.1 times of P1.

[0019] By optimizing the structure of the composite heat exchanger in the cascade heat pump, a supplementary heat source working medium channel and a heat dissipation working medium channel are added on the basis of double heat exchange, realizing a four-channel heat exchange for the composite heat exchanger. When the ambient temperature is high, the heat dissipation working medium flowing in the heat dissipation working medium channel transfers the internal heat of the composite heat exchanger to the outside, reducing the heat absorption of the high-temperature working medium to the set value range to maintain the relative stability of the heat absorption of the high-temperature working medium. When the ambient temperature is low, the supplementary working medium flowing in the supplementary heat source working medium channel carries heat from the outside of the composite heat exchanger to the inside to supplement the heat absorption of the high-temperature working medium to the set value range to maintain the relative stability of the heat absorption of the high-temperature working medium. In summary, by improving the structure of the composite heat exchanger, the technical problem of cold and heat imbalance existing at low and high ambient temperatures can be solved. In the prior art, although some technologies for adjusting the cascade heat exchanger are also disclosed, including adjusting the evaporation of the low-temperature heat pump unit, the compression of the low-temperature heat pump unit, and the intermediate coupled heat exchange between the low-temperature heat pump unit and the high-temperature heat pump unit in the cascade heat pump, such as controlling the air volume inhaled by the evaporator in the low-temperature heat pump unit to cope with ambient temperature changes; controlling the power of the compressor by adopting variable frequency compression technology; and placing the composite heat exchanger in a water tank or in a phase change material to maintain the relative stability of the heat in the composite heat exchanger. However, compared with the technical means adopted in this application, the above technical means are relatively complex and have limited adjustment adaptability at low and high ambient temperatures.

[0020] Adopting the technical solution provided by the present invention, compared with the prior art, it has the following beneficial effects: (1) By optimizing the design of the composite heat exchanger in the cascade heat pump, specifically, by adding a supplementary heat source working medium channel and a heat dissipation working medium channel in the composite heat exchanger where the low-temperature heat pump unit and the high-temperature heat pump unit are coupled. When the ambient temperature is high, the excess heat released by the condensation of the low-temperature heat pump unit is transferred to the outside of the composite heat exchanger through the heat dissipation working medium channel, thereby reducing the heat absorption of the evaporator in the high-temperature heat pump unit. At the same time, when the ambient temperature is low, the cascade heat pump makes up for the insufficient heat release of the condenser in the low-temperature heat pump unit through the supplementary heat source working medium channel, thereby maintaining the stability of the heat absorption of the evaporator in the high-temperature heat pump unit. In summary, the cascade heat pump can operate stably under both low and high ambient temperatures.

[0021] (2) The present invention further optimizes the structure design of the composite heat exchanger. Specifically, the composite heat exchanger is a double-pipe heat exchanger. The structure of the double-pipe heat exchanger is simple and convenient for nesting to increase the number of its internal channels, which is beneficial to reducing the cost of the composite heat exchanger. Further, the supplementary working medium and the heat dissipation working medium used are optimized. Specifically, the supplementary working medium is selected as hot water, and the heat dissipation working medium is selected as air. The sources of these two working media are extensive and the operating costs are relatively low. The flow rate of the heat dissipation working medium in the heat dissipation working medium channel is controlled by a fan, so as to control the heat transferred to the outside of the composite heat exchanger through the heat dissipation working medium.

[0022] (3) The present invention further optimizes the control method for the heat and cold balance of the cascade heat pump based on quadruple heat exchange. Specifically, a control logic based on the calorific value increase value of the heat medium in the user-side heat medium channel is provided to control the opening and closing of the supplementary heat source working medium channel and the heat dissipation working medium channel. In addition, a control logic based on the condensation pressure at the inlet of the low-temperature working medium channel in the composite heat exchanger is provided. Through the detection of the condensation pressure, the opening and closing of the supplementary heat source working medium channel and the heat dissipation working medium channel are controlled. The above control methods can accurately control the stability of the heat absorption of the evaporator in the high-temperature heat pump unit. Brief Description of the Drawings

[0023] Figure 1 It is a schematic diagram of the principle of the cascade heat pump based on quadruple heat exchange according to an embodiment of the present invention.

[0024] Figure 2 It is a schematic diagram of the internal structure of the composite heat exchange tube in the cascade heat pump based on quadruple heat exchange according to an embodiment of the present invention.

[0025] Figure 3 It is a schematic diagram of the external structure of the composite heat exchange tube in the cascade heat pump based on quadruple heat exchange according to an embodiment of the present invention.

[0026] Figure 4 It is a logic block diagram of the control method based on the calorific value increase value of the heat medium according to an embodiment of the present invention.

[0027] Figure 5 It is a logic block diagram of the control method based on the condensation pressure at the inlet of the low-temperature working medium channel according to an embodiment of the present invention.

[0028] Description of the Reference Numerals 1. Composite heat exchanger; 101. Outer sleeve; 102. Intermediate sleeve; 103. Inner sleeve; 104. Thermal insulation cover; 105. Fan; 2. Low-temperature stage evaporator; 3. Low-temperature stage compressor; 4. Low-temperature stage expansion valve; 5. High-temperature stage compressor; 6. High-temperature stage expansion valve; 7. High-temperature stage condenser; 8. User-side heat medium channel; 100. Low-temperature heat pump unit; 200. High-temperature heat pump unit. Detailed Embodiments

[0029] To further understand the content of the present invention, the present invention will be described in detail in combination with the accompanying drawings and embodiments.

[0030] The structures, proportions, sizes, etc. shown in the attached drawings of this specification are only used to cooperate with the content disclosed in the specification for those familiar with this technology to understand and read, and are not used to limit the conditions under which the present invention can be implemented. Therefore, they do not have any technical substance. Any modification of the structure, change of the proportional relationship or adjustment of the size, without affecting the effects that the present invention can produce and the purposes that can be achieved, should still fall within the scope that can be covered by the technical content disclosed in the present invention. At the same time, the terms such as "upper", "lower", "left", "right", "middle", etc. cited in this specification are only for the convenience of clear narration and are not used to limit the scope that can be implemented. The change or adjustment of their relative relationship, without substantial change in the technical content, should also be regarded as the scope in which the present invention can be implemented.

[0031] Embodiment 1 This embodiment provides a cascade heat pump machine based on quadruple heat exchange, including a low-temperature heat pump unit 100 and a high-temperature heat pump unit 200. Refer to Figure 1 As shown, the low-temperature heat pump unit 100 includes a low-temperature stage evaporator 2, a low-temperature stage compressor 3, a low-temperature stage expansion valve 4, and a low-temperature working medium channel in the composite heat exchanger 1, which are connected in sequence through pipelines; a low-temperature working medium circulates in the low-temperature heat pump unit 100. The high-temperature heat pump unit 200 includes a high-temperature working medium channel in the composite heat exchanger 1, a high-temperature stage compressor 5, a high-temperature stage condenser 7, and a high-temperature stage expansion valve 6, which are connected in sequence through pipelines; a high-temperature working medium circulates in the high-temperature heat pump unit 200. The low-temperature heat pump unit 100 and the high-temperature heat pump unit 200 are coupled for heat exchange through the composite heat exchanger 1. The high-temperature stage condenser 7 in the high-temperature heat pump unit 200 exchanges heat with the heat medium in the user-side heat medium channel 8; it is used to supply heat to the heat medium used on the user side.

[0032] Among them, the used composite heat exchanger 1 includes a low-temperature working medium channel, a supplementary heat source working medium channel, a high-temperature working medium channel, and a heat dissipation working medium channel. Among them, the low-temperature working medium channel circulates the low-temperature working medium of the low-temperature heat pump unit 100; the high-temperature working medium channel circulates the high-temperature working medium of the high-temperature heat pump unit 200; the supplementary heat source working medium channel is connected to the supplementary heat source, and the supplementary working medium carrying the supplementary heat source circulates inside, which is used to supplement the heat absorption of the high-temperature working medium to increase it to its set value range; the heat dissipation working medium channel circulates the heat dissipation working medium used to transfer the internal heat of the composite heat exchanger 1 to the outside, which is used to reduce the heat absorption of the high-temperature working medium to reduce it to its set value range.

[0033] Refer to Figure 2 、 Figure 3As shown in the figure, as a preferred embodiment of the composite heat exchanger 1, the composite heat exchanger 1 is selected as a shell-and-tube heat exchanger, which includes an inner casing 103, an intermediate casing 102, an outer casing 101 nested in sequence from the inside to the outside, and a thermal insulation cover 104 wrapped around the outside of the outer casing 101. The inside of the inner casing 103 constitutes a supplementary heat source working medium channel, the space between the inner casing 103 and the intermediate casing 102 constitutes a high-temperature working medium channel, and the space between the intermediate casing 102 and the outer casing 101 constitutes a low-temperature working medium channel; the space between the thermal insulation cover 104 and the outer casing 101 constitutes a heat dissipation working medium channel.

[0034] Among them, compared with other forms of heat exchangers, the shell-and-tube heat exchanger has a simple structure and relatively low cost. Preferably, multiple fins are provided on the outside of the inner casing 103, the intermediate casing 102, and the outer casing 101, which are circumferentially arranged around them and evenly spaced. The fins extend radially, thereby increasing the heat transfer area of the corresponding casing.

[0035] To further improve the efficiency of the supplementary heat source, the supplementary working medium is selected as hot water, and its temperature range is 50 - 60 °C.

[0036] Specifically, the heat dissipation working medium is selected as air, and a fan 105 is fixedly arranged on the inner wall of the thermal insulation cover 104. The fan 105 is used to control the air flow velocity in the heat dissipation working medium channel. When the fan 105 is turned on, the air flow velocity in the heat dissipation working medium channel increases, which is beneficial to improving the speed of dissipating part of the heat in the composite heat exchanger 1 to the outside. The switch of the fan 105 is connected to the control system to realize the automatic start-stop and power adjustment control of the fan 105. The switches of the first solenoid valve, the second solenoid valve, and the fan 105 are all connected to the control system, and the control module of the control system can be selected as a PLC, a single-chip microcomputer, etc.

[0037] It should be noted that the two ends of the thermal insulation cover 104 or the two ends of the outer cover of the composite heat exchanger 1 are respectively provided with inlets and outlets for the low-temperature working medium channel, the supplementary heat source working medium channel, the high-temperature working medium channel, and the heat dissipation working medium channel.

[0038] Preferably, a first solenoid valve is provided at the inlet of the supplementary heat source working medium channel, and the first solenoid valve is used to control the opening and closing of the supplementary heat source working medium channel; a second solenoid valve is provided at the inlet of the heat dissipation working medium channel, and the second solenoid valve is used to control the opening and closing of the heat dissipation working medium channel.

[0039] More preferably, a first temperature sensor is provided at the inlet of the user-side heat medium channel 8, and the first temperature sensor is used to detect the inlet temperature of the user-side heat medium channel 8. A flow sensor and a second temperature sensor are provided at the outlet of the user-side heat medium channel 8, and the flow sensor and the second temperature sensor are respectively used to detect the flow rate and the outlet temperature of the user-side heat medium channel 8.

[0040] For the cooling and heating balance control method of the cascade heat pump unit based on quadruple heat exchange involved in any of the above embodiments, refer to Figure 4 As shown, it specifically includes: If the calorific value increase value of the heat medium in the user-side heat medium channel 8 is less than the low limit setting value Q1, control the supplementary heat source working medium channel to open and the heat dissipation working medium channel to close; if the calorific value increase value of the heat medium in the user-side heat medium channel 8 is greater than the high limit setting value Q2, control the supplementary heat source working medium channel to close and the heat dissipation working medium channel to open; if the calorific value increase value of the heat medium in the user-side heat medium channel 8 is between Q1 and Q2, control both the supplementary heat source working medium channel and the heat dissipation working medium channel to close; where Q2 is greater than Q1, and Q2 is 1.05 to 1.1 times of Q1.

[0041] Specifically, the detection values of the flow sensor, the first temperature sensor, and the second temperature sensor are fed back to the control system, and based on this, the calorific value increase value of the heat medium in the user-side heat medium channel 8 is calculated.

[0042] During the heating operation of the cascade heat pump unit, both the low-temperature heat pump unit 100 and the high-temperature heat pump unit 200 are operating, and the low-temperature working medium channels and the high-temperature working medium channels in both are correspondingly opened.

[0043] In winter, for example, when the temperature is below -10°C, the heat absorbed by the low-temperature stage evaporator 2 decreases, resulting in a reduction in the heat absorbed by the high-temperature heat pump unit 200 from the low-temperature heat pump unit 100. When the control system detects that the calorific value increase value of the heat medium on the user side is less than the low limit preset value Q1, control the supplementary heat source working medium channel to open and introduce hot water into the supplementary heat source working medium channel, so as to supplement the gap in the heat released by the condenser in the low-temperature heat pump unit 100 and maintain the relative stability of the heat absorbed by the high-temperature working medium in the high-temperature heat pump unit 200, thereby maintaining the relative stability of the calorific value increase value of the heat medium in the user-side heat medium channel 8.

[0044] In summer, for example, when the ambient temperature is above 30°C, the heat absorbed by the low-temperature stage evaporator 2 increases, resulting in an increase in the heat absorbed by the high-temperature heat pump unit 200 from the low-temperature heat pump unit 100. When the control system detects that the calorific value increase value of the heat medium on the user side is greater than the high limit preset value Q2, control the heat dissipation working medium channel to open, so as to transfer the excessive heat released by the condenser in the low-temperature heat pump unit 100 to the outside of the composite heat exchanger 1 and maintain the relative stability of the heat absorbed by the high-temperature working medium in the high-temperature heat pump unit 200, thereby maintaining the relative stability of the calorific value increase value of the heat medium in the user-side heat medium channel 8.

[0045] Embodiment 2 The device used in this embodiment is substantially the same as that in Embodiment 1. The difference lies in that the heat value increase value of the heat medium in the heat medium channel 8 on the user side is replaced by the condensation pressure as the cold and heat balance detection index of this cascade heat pump unit. Correspondingly, this cascade heat pump unit includes a pressure sensor, which is arranged at the inlet of the low-temperature working medium channel in the composite heat exchanger 1 and is used to detect the condensation pressure at the inlet of the low-temperature working medium channel.

[0046] Refer to Figure 5 As shown, the cold and heat balance control method through condensation pressure detection is as follows: If the condensation pressure at the inlet of the low-temperature working medium channel in the composite heat exchanger 1 is less than the low limit set value P1, control the supplementary heat source working medium channel to open and the heat dissipation working medium channel to close; If the condensation pressure at the inlet of the low-temperature working medium channel in the composite heat exchanger 1 is greater than the high limit set value P2, control the supplementary heat source working medium channel to close and the heat dissipation working medium channel to open; If the condensation pressure at the inlet of the low-temperature working medium channel in the composite heat exchanger 1 is between P1 and P2, control both the supplementary heat source working medium channel and the heat dissipation working medium channel to close; where P2 is greater than P1, and P2 is 1.05 - 1.1 times of P1.

[0047] The condensation pressure is obtained according to the feedback value of the pressure sensor arranged at the inlet of the low-temperature working medium channel in the composite heat exchanger 1.

[0048] During the heating operation of the cascade heat pump unit, both the low-temperature heat pump unit 100 and the high-temperature heat pump unit 200 are operating, and the low-temperature working medium channels and high-temperature working medium channels in both are correspondingly opened.

[0049] In winter, the low-temperature evaporator 2 absorbs less heat, and the condensation pressure at the inlet of the low-temperature working medium channel in the composite heat exchanger 1 is less than the low limit preset value P1. Control the supplementary heat source working medium channel to open, and pass hot water into the supplementary heat source working medium channel, so as to supplement the heat gap released in the condensation link of the low-temperature heat pump unit 100 and maintain the relative stability of the heat absorbed by the high-temperature working medium in the high-temperature heat pump unit 200.

[0050] In summer, the low-temperature evaporator 2 absorbs more heat, and the condensation pressure at the inlet of the low-temperature working medium channel in the composite heat exchanger 1 is greater than the high limit preset value P2. Control the heat dissipation working medium channel to open, so as to transfer the excessive heat released in the condensation link of the low-temperature heat pump unit 100 to the outside of the composite heat exchanger 1 and maintain the relative stability of the heat absorbed by the high-temperature working medium in the high-temperature heat pump unit 200.

[0051] The above has schematically described the present invention and its embodiments. Such description is not restrictive. What is shown in the drawings is only one of the embodiments of the present invention, and the actual structure is not limited thereto. Therefore, if those of ordinary skill in the art are inspired by it and, without departing from the gist of the present invention, design similar structural modes and embodiments to this technical solution without creative efforts, they shall fall within the protection scope of the present invention.

Claims

1. A cascade heat pump based on quadruple heat exchange, characterized in that, Comprising: A low-temperature heat pump unit (100), in which a low-temperature working medium circulates internally; A high-temperature heat pump unit (200), in which a high-temperature working medium circulates internally, and the high-temperature condenser (7) in the high-temperature heat pump unit (200) exchanges heat with the heat medium in the user-side heat medium channel (8); The low-temperature heat pump unit (100) and the high-temperature heat pump unit (200) are coupled for heat exchange through a composite heat exchanger (1). The composite heat exchanger (1) includes a low-temperature working medium channel, a supplementary heat source working medium channel, a high-temperature working medium channel, and a heat dissipation working medium channel. Among them, the low-temperature working medium channel is connected to the low-temperature heat pump unit (100) and circulates a low-temperature working medium; the high-temperature working medium channel is connected to the high-temperature heat pump unit (200) and circulates a high-temperature working medium; the supplementary heat source working medium channel is connected to a supplementary heat source and internally circulates a supplementary working medium carrying the supplementary heat source, which is used to supplement the heat absorption of the high-temperature working medium to increase it to its set value range; the heat dissipation working medium channel circulates a heat dissipation working medium for transferring the internal heat of the composite heat exchanger (1) to the outside, which is used to reduce the heat absorption of the high-temperature working medium to reduce it to its set value range.

2. The cascade heat pump based on quadruple heat exchange according to claim 1, wherein The composite heat exchanger (1) is a double-pipe heat exchanger, which includes an inner sleeve (103), an intermediate sleeve (102), an outer sleeve (101) nested in sequence from the inside to the outside, and a heat insulation cover (104) wrapped outside the outer sleeve (101). The inside of the inner sleeve (103) forms a supplementary heat source working medium channel; a high-temperature working medium channel is formed between the inner sleeve (103) and the intermediate sleeve (102), and a low-temperature working medium channel is formed between the intermediate sleeve (102) and the outer sleeve (101); a heat dissipation working medium channel is formed between the heat insulation cover (104) and the outer sleeve (101).

3. The cascade heat pump machine based on quadruple heat exchange according to claim 2, wherein The supplementary working medium is hot water, and its temperature range is 50 - 60 °C.

4. The cascade heat pump machine based on quadruple heat exchange according to claim 2, characterized in that, The heat dissipation working medium is air. A fan (105) is fixedly arranged on the inner wall of the heat insulation cover (104), and the fan (105) is used to control the air flow speed in the heat dissipation working medium channel; the switch of the fan (105) is connected to a control system for realizing the automatic start-stop and power adjustment control of the fan (105).

5. The cascade heat pump machine based on quadruple heat exchange according to claim 2, characterized in that, A first solenoid valve is arranged at the inlet of the supplementary heat source working medium channel, and the first solenoid valve is used to control the opening and closing of the supplementary heat source working medium channel; A second solenoid valve is arranged at the inlet of the heat dissipation working medium channel, and the second solenoid valve is used to control the opening and closing of the heat dissipation working medium channel.

6. The cascade heat pump machine based on quadruple heat exchange according to any one of claims 1-5, characterized in that, A first temperature sensor is arranged at the inlet of the user-side heat medium channel (8), and the first temperature sensor is used to detect the inlet temperature of the user-side heat medium channel (8); a flow sensor and a second temperature sensor are arranged at the outlet of the user-side heat medium channel (8), and the flow sensor and the second temperature sensor are respectively used to detect the flow rate and the outlet temperature of the user-side heat medium channel (8).

7. The cascade heat pump machine based on quadruple heat exchange according to any one of claims 1-5, characterized in that, This cascade heat pump includes a pressure sensor, which is arranged at the inlet of the low-temperature working medium channel in the composite heat exchanger (1) and is used to detect the condensation pressure at the inlet of the low-temperature working medium channel.

8. A method for controlling the thermal balance of a cascade heat pump based on quadruple heat exchange as described in any one of claims 1-5, characterized in that, Comprising: If the calorific value increase value of the heat medium in the user-side heat medium channel (8) is less than the low limit set value Q1, control the supplementary heat source working medium channel to open and the heat dissipation working medium channel to close; If the calorific value increase value of the heat medium in the user-side heat medium channel (8) is greater than the high limit set value Q2, control the supplementary heat source working medium channel to close and the heat dissipation working medium channel to open; If the calorific value increase value of the heat medium in the user-side heat medium channel (8) is between Q1 and Q2, control both the supplementary heat source working medium channel and the heat dissipation working medium channel to close; Wherein the user-side heat medium channel (8) is provided with a flow sensor for detecting the flow rate therein, a first temperature sensor for the fluid inlet temperature therein, and a second temperature sensor for the fluid outlet temperature therein; the calorific value increase value of the heat medium is calculated from the feedback value of the user-side heat medium channel (8); Q2 is greater than Q1, and Q2 is 1.05 to 1.1 times that of Q1.

9. A method for controlling the thermal balance of a cascade heat pump based on quadruple heat exchange as described in any one of claims 1-5, characterized in that, Including: If the condensation pressure at the inlet of the low-temperature working medium channel in the composite heat exchanger (1) is less than the low limit set value P1, control the supplementary heat source working medium channel to open and the heat dissipation working medium channel to close; If the condensation pressure at the inlet of the low-temperature working medium channel in the composite heat exchanger (1) is greater than the high limit set value P2, control the supplementary heat source working medium channel to close and the heat dissipation working medium channel to open; If the condensation pressure at the inlet of the low-temperature working medium channel in the composite heat exchanger (1) is between P1 and P2, control both the supplementary heat source working medium channel and the heat dissipation working medium channel to close; Wherein the condensation pressure is obtained from the feedback value of the pressure sensor provided at the inlet of the low-temperature working medium channel in the composite heat exchanger (1); P2 is greater than P1, and P2 is 1.05 to 1.1 times that of P1.

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