A cascade heat pump based on quadruple heat exchange and its cooling and heating balance control method

Abstract

The present invention discloses a cascade heat pump based on quadruple heat exchange and a method for controlling heat and cold balance thereof, belonging to the technical field of cascade heat pumps. The composite heat exchanger in the cascade heat pump includes a low-temperature working fluid channel, a supplementary heat source working fluid channel, a high-temperature working fluid channel, and a heat dissipation working fluid channel, wherein the low-temperature working fluid of the low-temperature heat pump unit flows through the low-temperature working fluid channel; the high-temperature working fluid of the high-temperature heat pump unit flows through the high-temperature working fluid channel; the supplementary heat source working fluid channel flows through the supplementary working fluid carrying the supplementary heat source; and the heat dissipation working fluid channel flows through the heat dissipation working fluid for transferring heat from the internal part of the composite heat exchanger to the outside. The composite heat exchanger in the cascade heat pump has additional supplementary heat source working fluid channels and heat dissipation working fluid channels, and a corresponding control method is designed, which can solve the problem of heat absorption fluctuation of the low-temperature heat pump unit in low-temperature and high-temperature environments, realize heat balance control, and thus enable the cascade heat pump to operate stably.

Description

Technical Field

[0001] The present invention relates to the technical field of cascade heat pumps, and more particularly to a cascade heat pump based on quadruple heat exchange and a cooling and heating balance control method thereof. Background Art

[0002] Two-stage cascade heat pump technology solves the problem of single-stage air-source heat pump systems experiencing poor performance and substandard water or air outlet temperatures during low winter temperatures. It has been increasingly used in cold northern regions for heating, hot water, and drying applications. Furthermore, the two-stage cascade heat pump, formed by the cascade of a primary and a secondary heat pump circulation system, operates as follows: The primary refrigerant in the evaporator of the primary heat pump circulation system absorbs heat from the low-temperature environment and transfers this absorbed heat to the secondary heat pump circulation system through a condensing heat exchanger. The heat absorbed by the secondary refrigerant in the secondary heat pump circulation system is then processed by the compressor, further enhancing the heat carried by the second refrigerant. Finally, the heat carried by the second refrigerant is released through the condenser in the secondary heat pump circulation system. Based on the needs of the end user, the condenser in the secondary heat pump circulation system transfers the heat it carries to the user-side heat medium, which is typically water or air.

[0003] Heat balance technology is a key technology in the use of cascade heat pumps. In a cascade heat pump system, the low-temperature and high-temperature systems need to exchange heat through an intermediate coupled evaporative condenser. Therefore, the heating capacity of the low-temperature system must be equal to the heat absorption of the high-temperature system, that is, heat balance is achieved, so that the system can operate stably. However, since the low-temperature system absorbs heat from the ambient air, its heating capacity is inevitably affected by the ambient temperature. When the ambient temperature is low, the heating capacity of the low-temperature system is low, and when the ambient temperature is high, the heating capacity of the low-temperature system 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 system will be greater than the heat absorption set by the high-temperature system. At this time, the temperature of the evaporative condenser will rise, thereby increasing the heat absorption of the high-temperature system, achieving heat balance and the machine can operate stably. However, due to the limitations of the compressor's operating conditions, the compressor cannot operate at excessively high evaporation and condensing temperatures. The condensing temperature of the low-temperature system and the evaporation temperature of the high-temperature system just correspond to the temperature on the evaporative condenser, which means that the temperature of the evaporative condenser cannot continue to rise. Therefore, when the temperature is too high, the compressor of the high-temperature system may not work properly. Moreover, in some application environments where the output temperature of the high-temperature system needs to be strictly limited, the cascade heat pump cannot be used due to the excessive coupling fluctuations.

[0004] In practice, to ensure heating capacity at low ambient temperatures, existing designs often match the heating capacity of the two systems at low ambient temperatures. This fails to adequately account for heating capacity at high ambient temperatures. In other words, when the ambient temperature is high, the heating capacity of the low-temperature system will undoubtedly exceed the heat absorption capacity of the high-temperature system, affecting the normal operation of the system. This heat balance issue significantly limits the applicable temperature range of cascade heat pumps.

[0005] To address the aforementioned technical issues, Chinese patent application No. 2008100248938 discloses a single- / two-stage hybrid cascade heat pump air conditioning unit. This unit utilizes a three-channel heat exchanger, connected to the high- and low-temperature systems for refrigerant. The unit switches between single-stage heating and two-stage cascade heating depending on the outdoor ambient temperature, employing single-stage heating at high ambient temperatures and two-stage cascade heating at low ambient temperatures. This improves the system's adaptability and equipment utilization. However, this application utilizes single-stage heating at high ambient temperatures, failing to address the coupling issues associated with cascade heat pumps at high ambient temperatures.

[0006] The Chinese patent application with patent number 2018113460459 discloses a two-stage self-cascade heat pump system and its use method. It adds an evaporator in parallel with the evaporative condenser to the high-temperature stage system. By switching the heat exchanger, single-stage heating is adopted when the ambient temperature is high, and two-stage cascade heating is adopted when the ambient temperature is low. However, this application actually adopts single-stage heating when the ambient temperature is high, and requires the addition of additional evaporators and refrigerant switching valves and other devices. The system is complex, the volume is increased, and the cost is high.

[0007] Chinese patent application number 2019105640346 discloses a cascade high-temperature heat pump steam generator. Its low-temperature stage uses a variable-frequency compressor. By adjusting the compressor power, it can maintain a constant temperature in the intermediate evaporator condenser and maintain system stability under varying ambient temperatures. However, this technology requires a variable-frequency compressor, which is relatively expensive.

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

[0009] To address the technical issue of heat and cold imbalance in existing cascade heat pumps, both low-temperature and high-temperature units, in low and high ambient temperatures, the present invention provides a cascade heat pump based on quadruple heat exchange and a heat and cold balance control method. This solution optimizes the design of the composite heat exchanger, adds channels for supplementary heat source and heat dissipation, and designs corresponding control methods. This solution addresses the issue of fluctuating heat absorption in cascade heat pump units in both low and high temperature environments, achieving heat balance control and ultimately ensuring stable operation of the cascade heat pump.

[0010] The first aspect of the present invention provides a cascade heat pump based on quadruple heat exchange, comprising: a low-temperature heat pump unit, wherein a low-temperature working medium circulates in the low-temperature heat pump unit; a high-temperature heat pump unit, wherein a high-temperature working medium circulates in the high-temperature heat pump unit, and a high-temperature stage condenser in the high-temperature heat pump unit exchanges heat with a heat medium in a 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, wherein the composite heat exchanger 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, wherein In the embodiment, the low-temperature working fluid channel is connected to the low-temperature heat pump unit and has a low-temperature working fluid flowing therethrough; the high-temperature working fluid channel is connected to the high-temperature heat pump unit and has a high-temperature working fluid flowing therethrough; the supplementary heat source working fluid channel is connected to the supplementary heat source and has a supplementary working fluid carrying the supplementary heat source flowing therethrough, which is used to supplement the heat absorption of the high-temperature working fluid to increase it to its set value range; the heat dissipation working fluid channel has a heat dissipation working fluid used to transfer the internal heat of the composite heat exchanger to the outside thereof, which is used to reduce the heat absorption of the high-temperature working fluid to reduce it to its set value range.

[0011] Furthermore, the composite heat exchanger is a shell-and-tube heat exchanger, which includes an inner shell, an intermediate shell, an outer shell, and an insulation cover wrapped around the outside of the outer shell, which are nested in sequence from the inside to the outside. The interior of the inner shell constitutes a supplementary heat source working fluid channel; the high-temperature working fluid channel is formed between the inner shell and the intermediate shell, and the low-temperature working fluid channel is formed between the intermediate shell and the outer shell; and the heat dissipation working fluid channel is formed between the insulation cover and the outer shell.

[0012] Furthermore, the supplementary working fluid is hot water, and its temperature ranges from 50 to 60°C.

[0013] Furthermore, the heat dissipation medium is air, and a fan is fixedly installed on the inner wall of the thermal insulation cover, and the fan is used to control the air flow speed in the heat dissipation medium channel; the fan switch is connected to the control system to realize automatic start and stop of the fan and power regulation control.

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

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

[0016] Furthermore, the 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 and is used to detect the condensation pressure at the inlet of the low-temperature working medium channel.

[0017] The second aspect of the present invention provides a method for controlling the cold and heat balance of a cascade heat pump machine based on quadruple heat exchange as described above, comprising: if the calorific value increase value of the heat medium in the user-side heat medium channel is less than the lower limit setting value Q1, the supplementary heat source working fluid channel is controlled to be opened and the heat dissipation working fluid channel is closed; if the calorific value increase value of the heat medium in the user-side heat medium channel is greater than the upper limit setting value Q2, the supplementary heat source working fluid channel is controlled to be closed and the heat dissipation working fluid channel is opened; if the calorific value increase value of the heat medium in the user-side heat medium channel is between Q1 and Q2, both the supplementary heat source working fluid channel and the heat dissipation working fluid channel are controlled to be closed; wherein the user-side heat medium channel 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 by the feedback value of the user-side heat medium channel; Q2 is greater than Q1, and Q2 is 1.05 to 1.1 times that of Q1.

[0018] The third aspect of the present invention also provides another method for controlling the heat and cold balance of a cascade heat pump machine based on quadruple heat exchange as described above, including: if the condensing pressure at the inlet of the low-temperature working fluid channel in the compound heat exchanger is less than the lower limit setting value P1, the supplementary heat source working fluid channel is controlled to be opened and the heat dissipation working fluid channel is closed; if the condensing pressure at the inlet of the low-temperature working fluid channel in the compound heat exchanger is greater than the upper limit setting value P2, the supplementary heat source working fluid channel is controlled to be closed and the heat dissipation working fluid channel is opened; if the condensing pressure at the inlet of the low-temperature working fluid channel in the compound heat exchanger is between P1 and P2, both the supplementary heat source working fluid channel and the heat dissipation working fluid channel are controlled to be closed; wherein the condensing pressure is obtained based on the feedback value of the pressure sensor at the inlet of the low-temperature working fluid channel in the compound heat exchanger; P2 is greater than P1, and P2 is 1.05 to 1.1 times of P1.

[0019] The present invention optimizes the structure of the composite heat exchanger in the cascade heat pump machine, and adds a supplementary heat source working fluid channel and a heat dissipation working fluid channel on the basis of the double heat exchange, thereby realizing a quadruple heat exchange channel of the composite heat exchanger. When the ambient temperature is high, the heat dissipation working fluid circulating in the heat dissipation working fluid channel is used to transfer the heat inside the composite heat exchanger to its outside, so as to reduce the heat absorption of the high-temperature working fluid to its set value range, so as to maintain the relative stability of the heat absorption of the high-temperature working fluid. When the ambient temperature is low, the supplementary working fluid circulating in the supplementary heat source working fluid channel is used to carry heat from the outside of the composite heat exchanger to its inside, so as to supplement the heat absorption of the high-temperature working fluid to its set value range, so as to maintain the relative stability of the heat absorption of the high-temperature working fluid. In summary, by improving the structure of the composite heat exchanger, the technical problem of heat and cold imbalance existing in low and high ambient temperatures can be solved. In the prior art, although some technologies for regulating cascade heat exchangers are disclosed, including regulating the evaporation of the low-temperature heat pump unit in the cascade heat pump, the compression of the low-temperature heat pump unit, and the intermediate coupling heat exchange between the low-temperature heat pump unit and the high-temperature heat pump unit, for example, by controlling the air volume sucked into the evaporator of the low-temperature heat pump unit to cope with changes in ambient temperature; by adopting variable frequency compression technology to control the power of the compressor; and by placing the composite heat exchanger in a water tank or in a phase change material to maintain relative stability of the heat in the composite heat exchanger. However, compared with the technical means adopted in this application, the above-mentioned technical means are relatively complex and have limited adaptability to low and high ambient temperatures.

[0020] Compared with the prior art, the technical solution provided by the present invention has the following beneficial effects:

[0021] (1) The present invention optimizes the design of the composite heat exchanger in the cascade heat pump. Specifically, a supplementary heat source working fluid channel and a heat dissipation working fluid channel are added to the composite heat exchanger that couples the low-temperature heat pump unit with the high-temperature heat pump unit. 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 fluid 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 compensates for the insufficient heat release of the condenser in the low-temperature heat pump unit through the supplementary heat source working fluid 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.

[0022] (2) The present invention further optimizes the structure of the composite heat exchanger. Specifically, the composite heat exchanger is a shell-and-tube heat exchanger. The shell-and-tube heat exchanger has a simple structure and is easy to nest to increase the number of its internal channels, which is conducive to reducing the cost of the composite heat exchanger. Furthermore, the supplementary working fluid and the heat dissipation working fluid used are optimized. Specifically, the supplementary working fluid is selected as hot water, and the heat dissipation working fluid is selected as air. These two working fluids are widely available and have low operating costs. The flow rate of the heat dissipation working fluid in the heat dissipation working fluid channel is controlled by a fan, thereby controlling the amount of heat transferred to the outside of the composite heat exchanger by the heat dissipation working fluid.

[0023] (3) The present invention further optimizes the heat balance control method of the cascade heat pump based on quadruple heat exchange. Specifically, it provides a control logic based on the calorific value increase of the heat medium in the user-side heat medium channel to control the opening and closing of the supplementary heat source working fluid channel and the heat dissipation working fluid channel. In addition, it provides a control logic based on the condensing pressure at the inlet of the low-temperature working fluid channel in the composite heat exchanger to control the opening and closing of the supplementary heat source working fluid channel and the heat dissipation working fluid channel by detecting the condensing pressure. 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

[0024] Figure 1 Schematic diagram of the principle of a cascade heat pump based on quadruple heat exchange according to an embodiment of the present invention.

[0025] Figure 2 Schematic diagram of the internal structure of the composite heat exchange tube in a cascade heat pump machine based on quadruple heat exchange in an embodiment of the present invention.

[0026] Figure 3 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.

[0027] Figure 4 This is a logic block diagram of a heat value enhancement control method based on heat medium according to an embodiment of the present invention.

[0028] Figure 5 This is a logic block diagram of a condensation pressure control method at the inlet of a low-temperature working medium channel according to an embodiment of the present invention.

[0029] Description of Reference Numerals

[0030] 1. Composite heat exchanger; 101. Outer casing; 102. Intermediate casing; 103. Inner casing; 104. Insulation cover; 105. Fan; 2. Low-temperature evaporator; 3. Low-temperature compressor; 4. Low-temperature expansion valve; 5. High-temperature compressor; 6. High-temperature expansion valve; 7. High-temperature condenser; 8. User-side heat medium channel; 100. Low-temperature heat pump unit; 200. High-temperature heat pump unit. DETAILED DESCRIPTION

[0031] In order to further understand the content of the present invention, the present invention is described in detail with reference to the accompanying drawings and embodiments.

[0032] The structures, proportions, sizes, etc. illustrated in the drawings of this specification are only used to match the contents disclosed in the specification for understanding and reading by those familiar with this technology. They are not used to limit the conditions for implementation of the present invention and therefore have no substantial technical significance. Any modification of the structure, change in the proportional relationship, or adjustment of the size should still fall within the scope of the technical content disclosed by the present invention without affecting the efficacy and purpose of the present invention. At the same time, terms such as "upper", "lower", "left", "right", and "middle" quoted in this specification are only for the convenience of description and are not used to limit the scope of implementation. Changes or adjustments in their relative relationships should also be considered as the scope of implementation of the present invention without substantially changing the technical content.

[0033] Example 1

[0034] This embodiment provides a cascade heat pump based on quadruple heat exchange, including a low-temperature heat pump unit 100 and a high-temperature heat pump unit 200. Figure 1 As shown, the low-temperature heat pump unit 100 includes a low-temperature evaporator 2, a low-temperature compressor 3, a low-temperature expansion valve 4, and a low-temperature working medium passage in a composite heat exchanger 1, all connected sequentially via pipes. A low-temperature working medium circulates within the low-temperature heat pump unit 100. The high-temperature heat pump unit 200 includes a high-temperature working medium passage in a composite heat exchanger 1, a high-temperature compressor 5, a high-temperature condenser 7, and a high-temperature expansion valve 6, all connected sequentially via pipes. A high-temperature working medium circulates within 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 via the composite heat exchanger 1. 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 passage 8, thereby providing heat to the heat medium used by the user.

[0035] Among them, the composite heat exchanger 1 used includes a low-temperature working fluid channel, a supplementary heat source working fluid channel, a high-temperature working fluid channel and a heat dissipation working fluid channel, wherein the low-temperature working fluid of the low-temperature heat pump unit 100 flows through the low-temperature working fluid channel; the high-temperature working fluid of the high-temperature heat pump unit 200 flows through the high-temperature working fluid channel; the supplementary heat source working fluid channel is connected to the supplementary heat source, and the supplementary working fluid carrying the supplementary heat source flows inside, which is used to supplement the heat absorption of the high-temperature working fluid to increase it to its set value range; the heat dissipation working fluid channel flows with a heat dissipation working fluid used to transfer the internal heat of the composite heat exchanger 1 to its outside, which is used to reduce the heat absorption of the high-temperature working fluid to reduce it to its set value range.

[0036] refer to Figure 2 、 Figure 3As shown, 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 sleeve 103, an intermediate sleeve 102, an outer sleeve 101 and a heat preservation cover 104 wrapped around the outer sleeve 101, which are nested in sequence from the inside to the outside. The interior of the inner sleeve 103 constitutes a supplementary heat source working fluid channel, a high-temperature working fluid channel is formed between the inner sleeve 103 and the intermediate sleeve 102, and a low-temperature working fluid channel is formed between the intermediate sleeve 102 and the outer sleeve 101; a heat dissipation working fluid channel is formed between the heat preservation cover 104 and the outer sleeve 101.

[0037] Compared to other types of heat exchangers, a double-tube heat exchanger has a simple structure and relatively low cost. Preferably, the inner tube 103, the middle tube 102, and the outer tube 101 are each provided with a plurality of fins circumferentially and evenly spaced, extending radially to increase the heat exchange area of ​​the corresponding tubes.

[0038] In order to further improve the efficiency of the supplementary heat source, the supplementary working fluid is selected as hot water, and its temperature range is 50~60℃.

[0039] Specifically, the heat dissipation medium is air, and a fan 105 is fixedly installed on the inner wall of the heat insulation cover 104. The fan 105 is used to control the air flow rate in the heat dissipation medium channel. When the fan 105 is turned on, the flow rate of the air in the heat dissipation medium channel increases, which helps to increase the speed at which some heat in the composite heat exchanger 1 is dissipated to the outside. The switch of the fan 105 is connected to the control system to realize the automatic start and stop of the fan 105 and the power regulation control. The first solenoid valve, the second solenoid valve, and the switch of the fan 105 are all connected to the control system. The control module of the control system can be selected as a PLC, a single-chip microcomputer, etc.

[0040] It should be noted that the two ends of the insulation cover 104 or the two ends of the outer cover in the composite heat exchanger 1 are respectively provided with inlets and outlets of 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.

[0041] Preferably, a first solenoid valve is provided at the inlet of the supplementary heat source working fluid channel, and the first solenoid valve is used to control the opening and closing of the supplementary heat source working fluid channel; a second solenoid valve is provided at the inlet of the heat dissipation working fluid channel, and the second solenoid valve is used to control the opening and closing of the heat dissipation working fluid channel.

[0042] Further 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 used to detect the flow rate and outlet temperature of the user-side heat medium channel 8, respectively.

[0043] For any of the above embodiments involving the heat and cold balance control method of the cascade heat pump based on quadruple heat exchange, refer to Figure 4 As shown, specifically, it includes: if the calorific value increase value of the heat medium in the user-side heat medium channel 8 is less than the lower limit setting value Q1, the supplementary heat source working fluid channel is controlled to be opened and the heat dissipation working fluid channel is closed; if the calorific value increase value of the heat medium in the user-side heat medium channel 8 is greater than the upper limit setting value Q2, the supplementary heat source working fluid channel is controlled to be closed and the heat dissipation working fluid channel is opened; if the calorific value increase value of the heat medium in the user-side heat medium channel 8 is between Q1 and Q2, both the supplementary heat source working fluid channel and the heat dissipation working fluid channel are controlled to be closed; wherein Q2 is greater than Q1, and Q2 is 1.05 to 1.1 times of Q1.

[0044] 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 the values, the calorific value increase value of the heat medium in the user-side heat medium channel 8 is calculated.

[0045] During the heating operation of the cascade heat pump mechanism, both the low-temperature heat pump unit 100 and the high-temperature heat pump unit 200 are in operation, and the low-temperature working medium channels and the high-temperature working medium channels in the two units are correspondingly opened.

[0046] In winter, for example, when the temperature is below -10°C, the heat absorbed by the low-temperature evaporator 2 decreases, resulting in a decrease 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 of the user-side heat medium is less than the lower limit preset value Q1, it controls the supplementary heat source working fluid channel to open and introduces hot water into the supplementary heat source working fluid channel, thereby supplementing the gap in heat release by the condenser in the low-temperature heat pump unit 100, maintaining the relative stability of the heat absorption of the high-temperature working fluid in the high-temperature heat pump unit 200, and thus maintaining the relative stability of the calorific value increase of the heat medium in the user-side heat medium channel 8.

[0047] In summer, for example, when the ambient temperature is above 30°C, the heat absorbed by the low-temperature 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 of the user-side heat medium is greater than the upper limit preset value Q2, the heat dissipation medium channel is controlled to open, thereby transferring the excess heat released by the condenser in the low-temperature heat pump unit 100 to the outside of the composite heat exchanger 1, maintaining the relative stability of the heat absorption of the high-temperature working medium in the high-temperature heat pump unit 200, thereby maintaining the relative stability of the calorific value increase of the heat medium in the user-side heat medium channel 8.

[0048] Example 2

[0049] The device used in this embodiment is substantially the same as that in Example 1, except that the calorific value increase of the heat medium in the user-side heat medium channel 8 is replaced by the condensing pressure as the cold and heat balance detection index of the cascade heat pump. Accordingly, the cascade heat pump includes a pressure sensor, which is arranged at the inlet of the low-temperature working medium channel in the compound heat exchanger 1 and is used to detect the condensing pressure at the inlet of the low-temperature working medium channel.

[0050] refer to Figure 5 As shown, the hot and cold balance control method through condensing pressure detection is as follows: if the condensing pressure at the inlet of the low-temperature working fluid channel in the composite heat exchanger 1 is less than the lower limit set value P1, the supplementary heat source working fluid channel is controlled to be opened and the heat dissipation working fluid channel is closed; if the condensing pressure at the inlet of the low-temperature working fluid channel in the composite heat exchanger 1 is greater than the upper limit set value P2, the supplementary heat source working fluid channel is controlled to be closed and the heat dissipation working fluid channel is opened; if the condensing pressure at the inlet of the low-temperature working fluid channel in the composite heat exchanger 1 is between P1 and P2, both the supplementary heat source working fluid channel and the heat dissipation working fluid channel are controlled to be closed; wherein P2 is greater than P1, and P2 is 1.05 to 1.1 times of P1.

[0051] The condensing pressure is obtained according to the feedback value of the pressure sensor provided at the inlet of the low-temperature working medium channel in the composite heat exchanger 1 .

[0052] During the heating operation of the cascade heat pump mechanism, both the low-temperature heat pump unit 100 and the high-temperature heat pump unit 200 are in operation, and the low-temperature working medium channels and the high-temperature working medium channels in the two units are correspondingly opened.

[0053] In winter, the low-temperature evaporator 2 absorbs less heat, and the condensing pressure at the inlet of the low-temperature working fluid channel in the composite heat exchanger 1 is less than the lower preset value P1. The supplementary heat source working fluid channel is controlled to open, and hot water is introduced into the supplementary heat source working fluid channel, thereby supplementing the heat gap released by the condensation link in the low-temperature heat pump unit 100 and maintaining the relative stability of the heat absorption of the high-temperature working fluid in the high-temperature heat pump unit 200.

[0054] 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 compound heat exchanger 1 is greater than the upper limit preset value P2. The heat dissipation working medium channel is controlled to open, thereby transferring the excess heat released by the condensation link in the low-temperature heat pump unit 100 to the outside of the compound heat exchanger 1, maintaining the relative stability of the heat absorption of the high-temperature working medium in the high-temperature heat pump unit 200.

[0055] The above is a schematic description of the present invention and its embodiments, which is not restrictive. The drawings show only one embodiment of the present invention, and the actual structure is not limited thereto. Therefore, if a person skilled in the art is inspired by this and, without departing from the purpose of the present invention, designs structures and embodiments similar to this technical solution without inventive means, they shall fall within the scope of protection of the present invention.

Claims

1. A cascade heat pump based on quadruple heat exchange, characterized in that: include: A low-temperature heat pump unit (100), wherein a low-temperature working medium circulates within the low-temperature heat pump unit (100); A high-temperature heat pump unit (200), wherein a high-temperature working medium circulates within the high-temperature heat pump unit (200), and a high-temperature stage condenser (7) in the high-temperature heat pump unit (200) exchanges heat with a heat medium in a 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 via a composite heat exchanger (1). The composite heat exchanger (1) 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, wherein the low-temperature working medium channel is connected to the low-temperature heat pump unit (100) and has a low-temperature working medium flowing therethrough; the high-temperature working medium channel is connected to the high-temperature heat pump unit (200) and has a high-temperature working medium flowing therethrough; the supplementary heat source working medium channel is connected to the supplementary heat source and has a supplementary working medium carrying the supplementary heat source flowing therethrough for replenishing the heat absorption of the high-temperature working medium to increase it to a set value range; the heat dissipation working medium channel has a heat dissipation working medium for transferring heat from the internal portion of the composite heat exchanger (1) to the outside thereof for reducing the heat absorption of the high-temperature working medium to reduce it to a set value range; The composite heat exchanger (1) is a shell-and-tube heat exchanger, comprising an inner shell (103), an intermediate shell (102), an outer shell (101) and a heat-insulating cover (104) arranged to be nested in sequence from the inside to the outside. The interior of the inner shell (103) constitutes a supplementary heat source working medium channel; a high-temperature working medium channel is formed between the inner shell (103) and the intermediate shell (102); a low-temperature working medium channel is formed between the intermediate shell (102) and the outer shell (101); and a heat dissipation working medium channel is formed between the heat-insulating cover (104) and the outer shell (101).

2. The cascade heat pump based on quadruple heat exchange according to claim 1, characterized in that: The supplementary working fluid is hot water, and its temperature range is 50-60°C.

3. The cascade heat pump based on quadruple heat exchange according to claim 1, characterized in that: The heat dissipation medium is air, and a fan (105) is fixedly provided on the inner wall of the heat-insulating cover (104). The fan (105) is used to control the air flow speed in the heat dissipation medium channel; the switch of the fan (105) is connected to the control system to realize automatic start and stop of the fan (105) and power regulation control.

4. The cascade heat pump based on quadruple heat exchange according to claim 1, characterized in that: 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 medium channel, and the second solenoid valve is used to control the opening and closing of the heat dissipation medium channel.

5. The cascade heat pump based on quadruple heat exchange according to any one of claims 1 to 4, characterized in that: 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 used to detect the flow rate and the outlet temperature of the user-side heat medium channel (8), respectively.

6. The cascade heat pump based on quadruple heat exchange according to any one of claims 1 to 4, characterized in that: The cascade heat pump comprises 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.

7. A method for controlling the cooling and heating balance of a cascade heat pump based on quadruple heat exchange according to any one of claims 1 to 4, characterized in that: include: If the calorific value increase of the heat medium in the user side heat medium channel (8) is less than the lower limit set value Q1, the control of the supplementary heat source working medium channel is opened and the heat dissipation working medium channel is closed; If the calorific value increase of the heat medium in the user side heat medium channel (8) is greater than the upper limit set value Q2, the supplementary heat source working medium channel is controlled to be closed and the heat dissipation working medium channel is opened; If the calorific value of the heat medium in the user side heat medium channel (8) is increased to Q1~Q2, the supplementary heat source working medium channel and the heat dissipation working medium channel are controlled to be closed; The user-side heat medium channel (8) is provided with 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; the calorific value increase of the heat medium is calculated based on 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 of Q1.

8. A method for controlling the cooling and heating balance of a cascade heat pump based on quadruple heat exchange according to any one of claims 1 to 4, characterized in that: include: If the condensing pressure at the inlet of the low-temperature working medium channel in the composite heat exchanger (1) is less than the lower limit set value P1, the supplementary heat source working medium channel is controlled to be opened and the heat dissipation working medium channel is closed; If the condensing pressure at the inlet of the low-temperature working medium channel in the composite heat exchanger (1) is greater than the upper limit set value P2, the supplementary heat source working medium channel is controlled to be closed and the heat dissipation working medium channel is opened; If the condensing pressure at the inlet of the low-temperature working medium channel in the composite heat exchanger (1) is between P1 and P2, the supplementary heat source working medium channel and the heat dissipation working medium channel are controlled to be closed; The condensing pressure is obtained based on 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 of P1.

Images