Cascade heat pump and adjusting method

Abstract

The invention provides a cascade heat pump and an adjusting method, and relates to the technical field of heat pumps. The cascade heat pump comprises a first-stage heat pump circulation system, a second-stage heat pump circulation system and a tail end pipeline, the first-stage heat pump circulation system comprises a first compressor, a hot side channel of a gas cooler, a hot side channel of a cascade heat exchanger, a first expansion valve and an evaporator which are sequentially connected to form a first refrigerant circulation; the second-stage heat pump circulation system comprises a second compressor, a condenser, a second expansion valve and a cold side channel of the cascade heat exchanger which are sequentially connected to form a second refrigerant circulation; the tail end pipeline is sequentially communicated with a cold side channel of the gas cooler and a cold side channel of the condenser in the conveying direction. According to the cascade type heat pump, due to the flow direction arrangement of the gas cooler and the tail end pipeline, the effective energy of the hot side channel and the cold side channel in the condenser in the heat exchange process can be effectively improved, the heating load of the condenser is effectively reduced, and therefore the overall performance coefficient of the cascade type heat pump is improved.

Description

Technical Field

[0001] This invention relates to the field of heat pump technology, and more specifically, to a cascade heat pump and its regulation method. Background Technology

[0002] In recent years, heat pumps have been expanding their market as a substitute for boilers, effectively achieving the decarbonization of industrial heating engineering. Heat pumps mainly include heat recovery methods that use wastewater as a heat source and air heat source methods that use the external environment as a heat source. Among them, air heat source methods are widely used due to their advantages of high heating efficiency and wide applicability.

[0003] In related technologies, air-source heat pumps employ a cascade circulation system to improve their heating efficiency under conditions of low evaporation temperature, such as winter. However, how to further improve the coefficient of performance (COP) of cascade heat pumps remains an urgent problem to be solved. Summary of the Invention

[0004] The purpose of this invention is to provide a cascade heat pump and its regulation method to solve the technical problem that the coefficient of performance of cascade heat pumps still needs to be improved in related technologies.

[0005] To address the above problems, the present invention provides a cascade heat pump, comprising: A primary heat pump cycle system includes a first compressor, a hot-side passage of a gas cooler, a hot-side passage of a cascade heat exchanger, a first expansion valve, and an evaporator connected in sequence to form a first refrigerant cycle; A two-stage heat pump cycle system includes a second compressor, a condenser, a second expansion valve, and a cold-side passage of the cascade heat exchanger connected in sequence to form a second refrigerant cycle; and, The terminal pipeline is connected sequentially to the cold side channel of the gas cooler and the cold side channel of the condenser along the conveying direction.

[0006] In the cascade heat pump provided by this invention, on the one hand, the gas cooler enables the primary heat pump cycle system to preheat the working fluid in the terminal pipe, thereby reducing the effective energy loss of the primary heat pump cycle system during the heating process and improving the overall performance coefficient of the cascade heat pump. On the other hand, the working fluid in the terminal pipe is preheated by first passing through the gas cooler before flowing into the condenser for heat exchange. During the process of the working fluid in the terminal pipe flowing through the gas cooler, it exchanges heat with the working fluid in the first refrigerant cycle, and the working fluid in the first refrigerant cycle transfers heat to the working fluid in the terminal pipe to preheat it before flowing into the condenser. While the working fluid temperature increases, the working fluid temperature flowing into the cascade heat exchanger in the first refrigerant circulation decreases. Correspondingly, the heat transferred from the first-stage heat pump circulation system to the second-stage heat pump circulation system through the cascade heat exchanger decreases, resulting in a decrease in the working fluid temperature flowing into the condenser in the second refrigerant circulation. As the working fluid temperature in the hot-side channel of the condenser decreases, the working fluid temperature in the cold-side channel increases, thereby doubly reducing the working fluid temperature difference between the hot-side and cold-side channels in the condenser. This improves the effective energy of the heat exchange process in the hot-side and cold-side channels of the condenser and effectively reduces the heating load of the condenser, thereby further improving the overall performance coefficient of the cascade heat pump.

[0007] Optionally, the terminal pipeline includes a first pipeline and a second pipeline. The output end of the first pipeline is connected to the inlet end of the cold side channel in the gas cooler. The input end of the second pipeline is connected to the outlet end of the cold side channel in the gas cooler, and the output end is connected to the inlet end of the cold side channel in the condenser. The second pipeline is equipped with a three-way valve, and a branch pipeline is connected between the branch interface of the three-way valve and the first pipeline.

[0008] Optionally, the first pipeline is provided with a first detection element in the section upstream of the branch pipeline, and the first detection element is used to detect the working fluid temperature at the corresponding position of the first pipeline; the pipeline connected to the exhaust side of the first compressor in the first refrigerant circulation is provided with a second detection element, and the second detection element is used to detect the working fluid temperature in the corresponding pipeline.

[0009] Optionally, the cascade heat pump further includes a controller, and the three-way valve, the first detection element, and the second detection element are all connected to the controller.

[0010] Optionally, the primary heat pump cycle system further includes an internal heat exchanger, wherein the hot-side passage of the internal heat exchanger is connected between the hot-side passage of the cascade heat exchanger and the first expansion valve, and the cold-side passage of the internal heat exchanger is connected between the cold-side passage of the evaporator and the first compressor.

[0011] Optionally, the pipeline for the first refrigerant circulation located between the hot-side passage of the internal heat exchanger and the hot-side passage of the cascade heat exchanger is equipped with a third expansion valve.

[0012] Optionally, a third detection element is provided on the output side of the cold side channel of the condenser, and the third detection element is used to detect the working fluid temperature output by the cold side channel of the condenser.

[0013] Optionally, the frequency of the first compressor is equal to the frequency of the second compressor.

[0014] The present invention also provides an adjustment method, which is applied to the above-mentioned cascade heat pump, the adjustment method comprising: Obtain the working fluid temperatures entering the hot-side and cold-side channels of the gas cooler; Determine whether the working fluid temperature in the hot-side channel of the gas cooler is greater than the working fluid temperature in the cold-side channel; If so, adjust the three-way valve so that the working fluid in the first pipeline flows to the second pipeline through the cold side channel of the gas cooler; If not, adjust the three-way valve to allow the working fluid in the first pipeline to flow through the branch pipeline to the second pipeline.

[0015] The present invention also provides an adjustment method, which is applied to the above-mentioned cascade heat pump, and the adjustment method further includes: Obtain the temperature of the working fluid discharged from the first compressor; The temperature of the working fluid discharged from the first compressor is compared with the target upper limit. If the temperature of the working fluid discharged from the first compressor is greater than the target upper limit, the opening of the third expansion valve is reduced. If the temperature of the working fluid discharged from the first compressor is equal to the target upper limit, the third expansion valve is kept at its current opening. If the temperature of the working fluid discharged from the first compressor is less than the target upper limit, the opening of the third expansion valve is increased. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0017] Figure 1 This is a schematic diagram of the process of a cascade heat pump in related technologies; Figure 2 for Figure 1 Schematic diagram of the enthalpy-temperature cycle of the working fluid in a cascade heat pump under the first operating condition; Figure 3 A schematic diagram of the first form of the cascade heat pump provided by the present invention; Figure 4A schematic diagram of the process when the cascade heat pump provided by the present invention is of the second form; Figure 5 for Figure 4 Schematic diagram of the enthalpy-temperature cycle of the working fluid in a cascade heat pump under the first operating condition; Figure 6 for Figure 4 Schematic diagram of the enthalpy-temperature cycle of the working fluid in a cascade heat pump under the second operating condition; Figure 7 A schematic diagram of the process when the cascade heat pump provided by the present invention is of the third type; Figure 8 for Figure 7 Schematic diagram of the enthalpy-temperature cycle of the working fluid in a cascade heat pump under the second operating condition; Figure 9 This is a first flowchart of an adjustment method provided according to an embodiment of the present invention; Figure 10 This is a second flowchart of an adjustment method provided according to an embodiment of the present invention.

[0018] Explanation of reference numerals in the attached figures: 100 - Primary heat pump cycle system; 110 - First compressor; 120 - Gas cooler; 130 - Cascade heat exchanger; 140 - Third expansion valve; 150 - Internal heat exchanger; 160 - First expansion valve; 170 - Evaporator; 200 - Secondary heat pump cycle system; 210 - Second compressor; 220 - Condenser; 230 - Second expansion valve; 300 - Terminal piping; 310 - First piping; 320 - Second piping; 330 - Third piping; 340 - Branch piping; 410 - Three-way valve; 420 - First detection element; 430 - Second detection element; 440 - Third detection element; 500 - Controller; 510 - First control unit; 520 - Second control unit; 530 - Third control unit. Detailed Implementation

[0019] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0020] Figure 1 This is a schematic diagram of the process of a cascade heat pump in related technologies. For example... Figure 1As shown, the cascade heat pump includes a primary heat pump cycle system 100, a secondary heat pump cycle system 200, and a terminal pipe 300. The primary heat pump cycle system 100 includes a first compressor 110, a hot-side passage of a cascade heat exchanger 130, a first expansion valve 160, and an evaporator 170 connected in sequence to form a first refrigerant cycle. The secondary heat pump cycle system 200 includes a second compressor 210, a condenser 220, a second expansion valve 230, and a cold-side passage of the cascade heat exchanger 130 connected in sequence to form a second refrigerant cycle. The terminal pipe 300 is connected to the cold-side passage of the condenser 220. During operation, the secondary heat pump cycle system 200 absorbs heat from the primary heat pump cycle system 100 through the cascade heat exchanger 130. The working fluid i entering the hot side channel of the condenser 220 has a higher temperature, while the working fluid w1 initially delivered by the terminal pipe 300 has a lower temperature and directly enters the cold side channel of the condenser 220. As a result, the temperature difference between the working fluid i in the hot side channel and the working fluid w1 in the cold side channel of the condenser 220 is large, leading to a large effective energy loss in the heat exchange process of the condenser 220. In addition, the heating load of the condenser 220 is high, resulting in a low overall coefficient of performance of the cascade heat pump, which still needs to be improved.

[0021] This embodiment provides a cascade heat pump, such as Figure 3 As shown, the system includes a primary heat pump cycle system 100, a secondary heat pump cycle system 200, and a terminal pipeline 300. The primary heat pump cycle system 100 includes a first compressor 110, a hot-side passage of a gas cooler 120, a hot-side passage of a cascade heat exchanger 130, a first expansion valve 160, and an evaporator 170 connected in sequence to form a first refrigerant cycle. The secondary heat pump cycle system 200 includes a second compressor 210, a condenser 220, a second expansion valve 230, and a cold-side passage of a cascade heat exchanger 130 connected in sequence to form a second refrigerant cycle. The terminal pipeline 300 is connected in sequence along the delivery direction to the cold-side passage of the gas cooler 120 and the cold-side passage of the condenser 220.

[0022] In the cascade heat pump provided in this embodiment, the primary heat pump cycle system 100 serves as the low-level heat pump cycle system, and the secondary heat pump cycle system 200 serves as the high-level heat pump cycle system. The primary heat pump cycle system 100 and the secondary heat pump cycle system 200 are coupled and connected through a cascade heat exchanger 130, and the secondary heat pump cycle system 200 absorbs heat from the primary heat pump cycle system 100 through the cascade heat exchanger 130. In the primary heat pump cycle system 100, the first compressor 110, the hot-side passage of the gas cooler 120, the hot-side passage of the cascade heat exchanger 130, the first expansion valve 160, and the cold and hot passages of the evaporator 170 are sequentially connected through a first refrigerant pipe to form a first refrigerant cycle. In the secondary heat pump cycle system 200, the second compressor 210, the hot-side passage of the condenser 220, the second expansion valve 230, and the cold-side passage of the cascade heat exchanger 130 are sequentially connected through a second refrigerant pipe to form a second refrigerant cycle. The terminal pipe 300 connects the cold side passage of the gas cooler 120 and the cold side passage of the condenser 220. Along the flow direction of the working fluid in the terminal pipe 300, the cold side passage of the gas cooler 120 is located upstream, and the cold side passage of the condenser 220 is located downstream.

[0023] At runtime, such as Figure 3 As shown, the working fluid flow state in the first refrigerant cycle is as follows: Low-pressure two-phase flow a absorbs heat from its hot-side channel (e.g., air source) as it flows through the cold-side channel of evaporator 170, becoming low-pressure superheated gas b. Low-pressure superheated gas b is compressed by the first compressor 110, becoming high-pressure superheated gas c. High-pressure superheated gas c flows through the hot-side channel of gas cooler 120, transferring heat to the working fluid in its cold-side channel, becoming high-pressure superheated gas d. The pressure of high-pressure superheated gas d is less than the pressure of high-pressure superheated gas c. Continuing, high-pressure superheated gas c flows through the hot-side channel of cascade heat exchanger 130, transferring heat to the working fluid in its cold-side channel, becoming high-pressure subcooled liquid e. High-pressure subcooled liquid e then expands through the first expansion valve 160, becoming low-pressure two-phase flow a again, and flows back into evaporator 170. This cycle continues, continuously transferring heat through gas cooler 120 to terminal pipe 300, and through cascade heat exchanger 130 to secondary heat pump cycle system 200.

[0024] The working fluid flow state in the second refrigerant cycle is as follows: During the process of the low-pressure two-phase flow f flowing through the cold side channel of the cascade heat exchanger 130, it absorbs heat from its hot side channel and becomes low-pressure superheated gas g. The low-pressure superheated gas g is compressed by the second compressor 210 and becomes high-pressure superheated gas h. During the process of the high-pressure superheated gas h flowing through the hot side channel of the condenser 220, it transfers heat to the working fluid in its cold side channel and becomes high-pressure subcooled liquid i. The high-pressure subcooled liquid i is then expanded by the second expansion valve 230 and becomes low-pressure two-phase flow f again, and flows back into the cascade heat exchanger 130. In this way, it continuously absorbs heat from the first-stage heat pump cycle system 100 through the cascade heat exchanger 130 and transfers the heat to the terminal pipe 300 through the condenser 220.

[0025] The working fluid flow in the terminal pipe 300 is as follows: the working fluid w1 in the terminal pipe 300 first flows into the cold side channel of the gas cooler 120, absorbs the heat of the working fluid in its hot side channel and its temperature rises to become the working fluid w2; the working fluid w2 continues to flow into the cold side channel of the condenser 220 through the terminal pipe 300, absorbs the heat of its hot side channel and its temperature rises to become the working fluid w3, and is output to the outside through the terminal pipe 300 to heat the indoor environment or provide hot water to the outside, etc.

[0026] In the cascade heat pump provided in this embodiment, on the one hand, the gas cooler 120 enables the primary heat pump cycle system 100 to preheat the working fluid in the terminal pipe 300, thereby reducing the effective energy loss of the primary heat pump cycle system 100 during the heating process and improving the overall performance coefficient of the cascade heat pump. On the other hand, the working fluid in the terminal pipe 300 is preheated by first flowing through the gas cooler 120 before flowing into the condenser 220 for heat exchange. During the flow of the working fluid in the terminal pipe 300 through the gas cooler 120, it exchanges heat with the working fluid in the first refrigerant cycle. The working fluid in the first refrigerant cycle transfers heat to the working fluid in the terminal pipe 300 to preheat it before the working fluid flows into the condenser 220. While the working fluid temperature inside the condenser 220 increases, the working fluid temperature flowing into the cascade heat exchanger 130 decreases. Consequently, the heat transferred from the primary heat pump cycle system 100 to the secondary heat pump cycle system 200 through the cascade heat exchanger 130 decreases, resulting in a decrease in the working fluid temperature flowing into the condenser 220 from the secondary refrigerant cycle. As the working fluid temperature in the hot-side channel of the condenser 220 decreases, the working fluid temperature in the cold-side channel increases, thereby doubly reducing the working fluid temperature difference between the hot-side and cold-side channels in the condenser 220. This improves the effective energy of the heat exchange process in the hot-side and cold-side channels of the condenser 220 and effectively reduces the heating load of the condenser 220, thereby further improving the overall performance coefficient of the cascade heat pump.

[0027] In this embodiment, as Figure 3 and Figure 4As shown, the terminal pipeline 300 includes a first pipeline 310 and a second pipeline 320. The output end of the first pipeline 310 is connected to the inlet end of the cold side channel in the gas cooler 120. The input end of the second pipeline 320 is connected to the outlet end of the cold side channel in the gas cooler 120, and the output end is connected to the inlet end of the cold side channel in the condenser 220. The second pipeline 320 is equipped with a three-way valve 410. A branch pipeline 340 is connected between the branch interface of the three-way valve 410 and the first pipeline 310.

[0028] The three-way valve 410 has two main ports and one branch port. The two main ports are connected to the second pipeline 320. The section of the second pipeline 320 between the three-way valve 410 and the gas cooler 120 is section A, and the section of the second pipeline 320 between the three-way valve 410 and the condenser 220 is section B. The branch port is connected to the first pipeline 310 through the branch pipeline 340. The valve core of the three-way valve 410 is used to adjust the on / off state and flow area between the two main ports, as well as the on / off state and flow area between the branch port and the main port adjacent to section B. This allows the flow rate of the working fluid in the first pipeline 310 into the cold side channel of the gas cooler 120 to be adjusted according to the actual working conditions, ensuring that the gas cooler 120 effectively heats the working fluid w1 in the terminal pipeline 300.

[0029] Specifically, when the temperature of the working fluid c entering the hot-side channel of the gas cooler 120 in the first refrigerant cycle is higher than the temperature of the working fluid w1 in the first pipe 310, it indicates that heat exchange can occur between the working fluid c in the hot-side channel of the gas cooler 120 and the working fluid w1 in its cold-side channel. The three-way valve 410 is adjusted accordingly to connect the two main interfaces, allowing all the working fluid w1 in the first pipe 310 to flow into the cold-side channel of the gas cooler 120. This increases the temperature of the working fluid w2 entering the cold-side channel of the condenser 220 and decreases the temperature of the working fluid h entering the hot-side channel of the condenser 220. This effectively reduces the temperature difference between the working fluids in the cold-side and hot-side channels of the condenser 220, reduces the heating load of the condenser 220, and improves the heating efficiency of the condenser 220. Effective energy during heat exchange in the internal hot and cold side channels; when the temperature of the working fluid c entering the hot side channel of the gas cooler 120 in the first refrigerant cycle is not higher than the temperature of the working fluid w1 in the first pipeline 310, it indicates that the working fluid c in the hot side channel of the gas cooler 120 cannot effectively heat the working fluid w1 in its cold side channel. Accordingly, the three-way valve 410 is adjusted to connect the branch port with the main port adjacent to the pipeline section B. The working fluid w1 in the first pipeline 310 bypasses the gas cooler 120 and flows directly into the second pipeline 320 through the branch pipeline 340, and then into the condenser 220, so as to reduce the resistance formed by the working fluid in the terminal pipeline 300 flowing through the gas cooler 120 and improve the smoothness of the flow of the working fluid in the terminal pipeline 300.

[0030] In this embodiment, as Figure 6 As shown, a first detection element 420 is provided on the pipe section of the first pipe 310 upstream of the branch pipe 340. The first detection element 420 is used to detect the working fluid temperature at the corresponding position of the first pipe 310. A second detection element 430 is provided on the pipe connected to the exhaust side of the first compressor 110 in the first refrigerant cycle. The second detection element 430 is used to detect the working fluid temperature in the corresponding pipe. Specifically, the first detection element 420 is provided in the first pipe 310 to detect the initial input temperature of the working fluid w1 in the terminal pipe 300. The first detection element 420 can be a temperature sensor. In the first refrigerant cycle, the second detection element 430 is provided in the pipe connected between the first compressor 110 and the gas condenser 220 to detect the temperature of the working fluid c initially entering the hot side channel of the gas cooler 120. The second detection element 430 can be a temperature sensor or a pressure sensor. The temperature sensor can directly detect the temperature of the working fluid at the corresponding position in the pipe, while the pressure sensor can detect the pressure of the working fluid at the corresponding position in the pipe. The temperature of the working fluid is then calculated from the measured pressure.

[0031] In use, the temperatures of working fluid w1 and working fluid c are accurately obtained based on the detection values ​​of the first and second detectors, and the connection state of the three-way valve 410 is adjusted according to the temperature to ensure effective heat exchange of the gas cooler 120 and smooth flow of the working fluid in the terminal pipeline 300.

[0032] In this embodiment, as Figure 7 As shown, the cascade heat pump also includes a controller 500, and a three-way valve 410, a first detection element 420, and a second detection element 430 are all connected to the controller 500.

[0033] This embodiment also provides an adjustment method applied to the above-mentioned cascade heat pump. The adjustment method includes: obtaining the working fluid temperatures of the hot-side channel and the cold-side channel entering the gas cooler 120; determining whether the working fluid temperature of the hot-side channel entering the gas cooler 120 is greater than the working fluid temperature of the cold-side channel; if so, adjusting the three-way valve to allow the working fluid in the first pipeline 310 to flow through the cold-side channel of the gas cooler 120 to the second pipeline 320; if not, adjusting the three-way valve 410 to allow the working fluid in the first pipeline 310 to flow through the branch pipeline 340 to the second pipeline 320.

[0034] During the operation of the cascade heat pump, the first detection element 420 can detect the temperature of the working fluid w1 in real time, while the second detection element 430 can detect the temperature of the working fluid c in real time. Both of them feed back the measured temperature signals to the controller 500 in real time. The controller 500 determines whether the temperature of the working fluid c is greater than the temperature of the working fluid w1 based on the two temperature signals received. If so, it adjusts the two main ports of the three-way valve 410 to connect, and all the working fluid w1 in the first pipeline 310 flows through the cold side channel of the gas cooler 120. If not, it adjusts the branch port of the three-way valve 410 to connect with the main port of the adjacent pipeline segment B, and all the working fluid w1 in the first pipeline 310 bypasses the gas cooler 120 and flows into the second pipeline 320 through the branch pipe 340. The controller 500 makes the adjustment of the three-way valve 410 of the cascade heat pump more precise and convenient.

[0035] In this embodiment, as Figure 4 As shown, the primary heat pump cycle system 100 also includes an internal heat exchanger 150. The hot-side passage of the internal heat exchanger 150 is connected between the hot-side passage of the cascade heat exchanger 130 and the first expansion valve 160, and the cold-side passage of the internal heat exchanger 150 is connected between the cold-side passage of the evaporator 170 and the first compressor 110. In the first refrigerant cycle, the pipeline between the first expansion valve 160 and the cascade heat exchanger 130 is the first refrigerant pipeline, and the pipeline between the evaporator 170 and the first compressor 110 is the second refrigerant pipeline. The internal heat exchanger 150 is installed between the first refrigerant pipeline and the second refrigerant pipeline. The temperature of the working fluid e output through the hot-side passage of the cascade heat exchanger 130 is higher than the temperature of the working fluid b output through the cold-side passage of the evaporator 170. After the internal heat exchanger 150 is installed, the working fluid e first flows through the internal heat exchanger before entering the evaporator 170. The hot-side passage of heat exchanger 150 heats the working fluid b flowing through the cold-side passage of the inner ring heat exchanger by transferring heat to it, thereby increasing the temperature of the working fluid entering the hot-side passage of gas cooler 120. This correspondingly improves the preheating effect of gas cooler 120 on the working fluid w1 in terminal pipe 300, further reduces the temperature difference between the working fluid in the hot and cold-side passages of condenser 220, further improves the efficiency of condenser 220, reduces the heating load of condenser 220, and correspondingly further improves the overall performance coefficient of cascade heat pump.

[0036] In this embodiment, as Figure 7 As shown, a third detection element 440 is provided on the output side of the cold side channel in the condenser 220. The third detection element 440 is used to detect the working fluid temperature output from the cold side channel of the condenser 220. The third detection element 440 can detect the temperature of the output working fluid w3 after heat exchange between the terminal pipe 300 and the condenser 220, and adjust the frequency of the first compressor 110 and the second compressor 210 according to the temperature of the output working fluid w3 so that the temperature of the output working fluid w3 reaches the target temperature.

[0037] In this embodiment, the third detection element 440, the first compressor 110, and the second compressor 210 are all connected to the controller 500. During operation, the third detection element 440 feeds back the measured temperature of the output working fluid w3 to the controller 500. The controller 500 adjusts the frequencies of the first compressor 110 and the second compressor 210 according to the received temperature signal and the set target temperature, so that the temperature of the output working fluid w3 reaches the target temperature quickly and stably. Specifically, the frequency of the first compressor is equal to the frequency of the second compressor.

[0038] The third detection element 440 can be located at the output port of the cold side channel of the condenser 220, or the terminal pipe 300 includes a third pipe 330 connected to the outlet end of the cold side channel of the condenser 220, and the third detection element 440 is located in the third pipe 330; specifically, the third detection element 440 can be a temperature sensor.

[0039] The following is about Figure 1 The cascade heat pump shown and Figure 4 The coefficient of performance (COP) simulation of the cascade heat pump shown is performed under the first operating condition. In the two cascade heat pumps, the working fluid of the first-stage heat pump cycle system 100 is R454B, the working fluid of the second-stage heat pump cycle system 200 is R1234ze(E), and the working fluid of the terminal pipe 300 is water. The outdoor ambient temperature is taken as 7dB / 6WB℃, the initial input temperature of the working fluid w1 in the terminal pipe 300 is 15℃, the target temperature of the working fluid w3 output from the terminal pipe 300 through the condenser 220 is 75℃, and the target upper limit of the high-pressure superheated gas c temperature on the exhaust side of the first compressor 110 is 95℃.

[0040] When the frequencies of both the first compressor 110 and the second compressor 210 are adjusted to 50Hz... Figure 1 and Figure 4 The cascade heat pumps shown can all meet the target temperature of the working fluid w3 output by the terminal pipe 300 to reach 75°C, and the temperature of the high-pressure superheated gas c on the exhaust side of the first compressor 110 can all reach 95°C. Figure 1 The cascade heat pump in the middle operates under the first condition and can obtain Figure 2 The diagram shown illustrates the enthalpy-temperature cycle, where... Figure 2 The enthalpy-temperature values ​​of the working fluid at each location shown are detailed in Table 1; Figure 4 The cascade heat pump in the middle operates under the first condition and can obtain Figure 5 The diagram shown illustrates the enthalpy-temperature cycle, where... Figure 5 The enthalpy-temperature values ​​of the working fluid at each location shown are detailed in Table 2.

[0041] Table 1

[0042] Table 2

[0043] Calculate according to formulas (1)-(5) Figure 1 and Figure 4 The overall coefficient of performance (COP) of a cascade heat pump: (1); In equation (1), W L The power consumed by the first compressor is expressed in kW; m L The working fluid flow rate of a primary heat pump cycle system is expressed in kg / s; w L This represents the compression power of the first compressor, expressed in kJ / kg.

[0044] (2); In equation (2), W H The power consumed by the second compressor is expressed in kW; m H The working fluid flow rate of a two-stage heat pump cycle system is expressed in kg / s; w H This represents the compression power of the second compressor, expressed in kJ / kg.

[0045] (3); In equation (3), Q CAS The heat exchange capacity of the cascade heat exchanger is expressed in kW; h CAS COP represents the enthalpy difference between the working fluid d in the hot-side passage and the working fluid f in the cold-side passage of the cascade heat exchanger, expressed in kJ / kg. H The coefficient of performance (COP) of a two-stage heat pump cycle system.

[0046] (4); In equation (4), Q CND The heat exchange capacity of the condenser is expressed in kW or h. CND The enthalpy difference is the difference between the working fluid i in the hot-side channel and the working fluid w1 in the cold-side channel of the condenser, expressed in kJ / kg.

[0047] (5); In equation (5), Q GC for Figure 4 The heat exchange capacity of the gas cooler in the cascade heat pump shown is expressed in kW / h. GC for Figure 4 The enthalpy difference between the working fluid c in the hot-side channel and the working fluid w1 in the cold-side channel of the gas cooler in the cascade heat pump shown is expressed in kJ / kg; COP L The coefficient of performance (COP) of a primary heat pump cycle system.

[0048] Calculate according to equations (1)-(4) Figure 1 The overall coefficient of performance (COP) of the cascade heat pump shown is: (6); Among them, according to Figure 2 From Table 1, we can obtain: (7); In equation (7), h h h i h g In order Figure 1 The enthalpy values ​​of working fluid h, working fluid i, and working fluid g in the two-stage heat pump cycle system of the cascade heat pump shown are given in kJ / kg. Figure 2 From Table 1, we can find: h h =438kJ / kg, h i =311kJ / kg, h g =411kJ / kg.

[0049] (8); In equation (8), h d h e h b In order Figure 1 The enthalpy values ​​of working fluids d, e, and b in the first-stage heat pump cycle system of the cascade heat pump shown are in kJ / kg; according to Figure 2 From Table 1, we can find: h d =523kJ / kg, h e =271kJ / kg, h b =464kJ / kg.

[0050] The overall performance coefficient COP of the cascade heat pump is calculated to be 2.52 according to equations (6)-(8).

[0051] Calculate according to formulas (1)-(5) Figure 4 The overall coefficient of performance (COP) of the cascade heat pump shown is: (9); Among them, according to Figure 5 From Table 2, we can obtain: (10); In equation (10), h c h j In order Figure 4 The enthalpy values ​​of working fluids c and j in the first-stage heat pump cycle system of the cascade heat pump shown are in kJ / kg; according to Figure 5 From Table 2, we can find: h c =539kJ / kg, hj =481kJ / kg.

[0052] (11); In equation (11), h d for Figure 4 The enthalpy of the working fluid d in the first-stage heat pump cycle system of the cascade heat pump shown is expressed in kJ / kg; according to Figure 5 From Table 2, we can find: h d =475kJ / kg.

[0053] (12); In equation (12) h h h i h g In order Figure 4 The enthalpy values ​​of working fluid h, working fluid i, and working fluid g in the two-stage heat pump cycle system of the cascade heat pump shown are given in kJ / kg. Figure 5 From Table 2, we can find: h h =439kJ / kg, h i =309kJ / kg, h g =407kJ / kg.

[0054] (13); In equation (13) h e for Figure 4 The enthalpy of the working fluid e in the first-stage heat pump cycle system of the cascade heat pump shown is expressed in kJ / kg; according to Figure 5 From Table 2, we can find: h e =258kJ / kg.

[0055] Calculated according to equations (9)-(13) Figure 4 The overall coefficient of performance (COP) of the cascade heat pump shown is 2.73.

[0056] As can be seen, in this embodiment, the working fluid is preheated by first flowing through the gas cooler 120 and the terminal pipe 300, and an internal heat exchanger 150 is installed to increase the temperature of the working fluid c entering the gas cooler 120. As shown in the simulation calculation above, the working fluid W1 at 15°C in the terminal pipe 300 becomes the working fluid w2 at 26°C after being preheated by the gas cooler 120, an increase of 11°C, in order to reduce the effective temperature of the first-stage heat pump cycle system 100 during the heating process. This reduces energy loss; simultaneously, the heating load of condenser 220 changes from a 60°C temperature difference (inlet 15°C, outlet 75°C) to a 49°C temperature difference (inlet 26°C, outlet 75°C), a reduction of approximately 82%. Furthermore, the inlet temperature of the hot-side channel of condenser 220 decreases from 76.7°C to 75.4°C, doubly reducing the temperature difference between the working fluid in the hot-side and cold-side channels of condenser 220. This improves the effective energy of the heat exchange process in the hot-side and cold-side channels of condenser 220, thus enhancing the efficiency of this embodiment. Figure 4 The cascade heat pump shown is compared to Figure 1 The overall coefficient of performance of the cascade heat pump shown is improved by approximately 8%.

[0057] In this embodiment, as Figure 7 As shown, the pipeline for the first refrigerant circulation located between the hot side channel of the internal heat exchanger 150 and the hot side channel of the cascade heat exchanger 130 is equipped with a third expansion valve 140, which is connected to the controller 500. In the primary heat pump cycle system 100, a third expansion valve 140 is added to the pipeline between the internal heat exchanger 150 and the cascade heat exchanger 130. By adjusting the opening of the third expansion valve 140, the exhaust temperature of the first compressor 110 can be adjusted to ensure that the exhaust temperature of the first compressor 110 is at the target upper limit. This ensures that the preheating capacity of the gas cooler 120 is maximized while preventing damage caused by excessively high exhaust temperature of the first compressor 110. Specifically, the high-pressure subcooled liquid e output from the hot side channel of the cascade heat exchanger 130 is compressed by the third expansion valve 140 and becomes an intermediate-pressure two-phase flow l before entering the internal heat exchanger 150. This intermediate-pressure two-phase flow l heats the low-pressure superheated gas b in the internal heat exchanger 150 while condensing. By adjusting the opening of the third expansion valve 140, the condensation temperature can be adjusted, thereby controlling the heat exchange capacity of the internal heat exchanger 150 to maintain the exhaust temperature of the first compressor 110 at the target upper limit.

[0058] Accordingly, this embodiment also provides an adjustment method applied to the above-mentioned cascade heat pump, which obtains the working fluid temperature discharged by the first compressor; compares the working fluid temperature discharged by the first compressor with a target upper limit value; if the working fluid temperature discharged by the first compressor is greater than the target upper limit value, then the opening of the third expansion valve is reduced; if the working fluid temperature discharged by the first compressor is equal to the target upper limit value, then the third expansion valve is controlled to maintain its current opening; if the working fluid temperature discharged by the first compressor is less than the target upper limit value, then the opening of the third expansion valve is increased.

[0059] Specifically, such as Figure 7 As shown, the controller 500 may include a first control unit 510, a second control unit 520, and a third control unit 530. A first detection element 420, a second detection element 430, and a three-way valve 410 are all connected to the first control unit 510. The first control unit 510 adjusts the connection state of the three-way valve 410 based on temperature signals received from the first detection element 420 and the second detection element 430. A second detection element 430 and a third expansion valve 140 are both connected to the second control unit 520. The second control unit 520 adjusts the opening degree of the third expansion valve 140 based on temperature signals received from the second detection element 430. A first compressor 110, a second compressor 210, and a third detection element 440 are all connected to the third control unit 530. The third control unit 530 adjusts the frequencies of the first compressor 210 and the second compressor 210 based on temperature signals received from the third detection element 440.

[0060] As mentioned above Figure 4 The simulation calculation of the cascade heat pump shown shows that when the outdoor ambient temperature is 7dB / 6WB℃, the high-pressure subcooled liquid e with a temperature of 33.7℃ output from the hot side channel of the cascade heat exchanger 130 flows entirely into the hot side channel of the internal heat exchanger 150; the low-pressure superheated gas b with a temperature of 2℃ output from the cold side channel of the evaporator 170 flows into the cold side channel of the internal heat exchanger 150. Therefore, the working fluid temperature difference between the hot side channel and the cold side channel of the internal heat exchanger 150 is 31.7℃. This temperature difference serves as the heat transfer driving force and determines the heat transfer capacity of the internal heat exchanger 150. Correspondingly, the low-pressure superheated gas j on the suction side of the first compressor 110 rises to 18.5℃, and the temperature of the high-pressure superheated gas c on the discharge side of the lower-stage compressor reaches the target upper limit of 95.0℃ for the discharge temperature of the first compressor 110.

[0061] However, when the outdoor ambient temperature decreases, the temperature drop of the low-pressure superheated gas b output from the evaporator 170 is greater than the temperature drop of the high-pressure subcooled liquid e output from the cascade heat exchanger 130. Consequently, the working fluid temperature difference between the hot and cold channels in the internal heat exchanger 150 increases, and the heat exchange capacity of the internal heat exchanger 150, the temperature of the low-pressure superheated gas j on the suction side of the first compressor 110, and the temperature of the high-pressure superheated gas c on the exhaust side all increase, resulting in the temperature of the high-pressure superheated gas c on the exhaust side of the first compressor 110 exceeding the target upper limit of 95.0°C.

[0062] As mentioned above Figure 4 In the simulation calculation of the cascade heat pump shown, with other conditions remaining unchanged, the outdoor ambient temperature is reduced to -15dB / -16WB℃ as the second operating condition, and the calculation is performed according to the second operating condition. Figure 4 The cascade heat pump shown can obtain Figure 6 The diagram shown illustrates the enthalpy-temperature cycle, where... Figure 6 The enthalpy and temperature of the working fluid at each location shown are detailed in Table 3.

[0063] Table 3

[0064] See Figure 6 As shown in Table 3, when the outdoor ambient temperature drops to -15dB / -16WB℃, the temperature of the low-pressure superheated gas b output from the evaporator 170 is -22℃, and the temperature of the high-pressure subcooled liquid e output from the cascade heat exchanger 130 is 15℃. Therefore, the working fluid temperature difference between the hot and cold side channels in the internal heat exchanger 150 increases to 37℃. This temperature difference serves as the heat transfer driving force, increasing the heat exchange capacity of the internal heat exchanger 150. Correspondingly, the low-pressure superheated gas j on the suction side of the first compressor 110 rises to 2.3℃, and the temperature of the high-pressure superheated gas c on the discharge side of the first compressor 110 rises to 98.4℃, which is higher than the target upper limit of 95.0℃ for the temperature of the high-pressure superheated gas c on the discharge side of the first compressor 110.

[0065] When a third expansion valve 140 is installed in the pipeline between the hot side channel of the internal heat exchanger 150 and the hot side channel of the cascade heat exchanger 130, the temperature of the high-pressure superheated gas c on the exhaust side of the first compressor 110 can be detected by the second detection element 430. When the temperature of the high-pressure superheated gas c is higher than the target upper limit value, the opening of the third expansion valve 140 is reduced, so that the high-pressure supercoolant e flowing through the third expansion valve 140 is thermally expanded and its temperature is reduced, becoming a two-phase flow l at intermediate pressure. This reduces the working fluid temperature difference between the hot side channel and the cold side channel in the internal heat exchanger 150, thereby reducing the heat exchange capacity of the internal heat exchanger 150. Consequently, the temperature of the low-pressure superheated gas j on the suction side and the high-pressure superheated gas c on the exhaust side of the first compressor 110 is reduced, so that the temperature of the high-pressure superheated gas c on the exhaust side of the first compressor 110 drops to the target upper limit value.

[0066] Specifically, adopt Figure 6 The corresponding operating conditions Figure 7 The cascade heat pump shown was simulated, and the opening of the third expansion valve 140 was reduced so that the temperature of the high-pressure superheated gas c on the exhaust side of the first compressor 110 was 95℃, thus obtaining... Figure 8 The diagram shown illustrates the enthalpy-temperature cycle, where... Figure 8 The enthalpy and temperature of the working fluid at each location shown are detailed in Table 4.

[0067] Table 4

[0068] See Figure 8 As shown in Table 4, when the outdoor ambient temperature drops to -15dB / -16WB℃, the opening of the third expansion valve 140 is reduced, causing the high-pressure supercoolant e flowing through the third expansion valve 140 to be thermally expanded into an intermediate-pressure two-phase flow l with a temperature of 4.1℃. The temperature of the low-pressure superheated gas b output through the cold side channel of the evaporator 170 is -22℃. Then, the working fluid temperature difference between the hot side channel and the cold side channel of the internal heat exchanger 150 is reduced to 26.1℃, thereby reducing the heat exchange capacity of the internal heat exchanger 150. Correspondingly, the temperature of the low-pressure superheated gas j on the suction side of the first compressor 110 is reduced to -1.1℃, and the temperature of the high-pressure superheated gas c on the discharge side of the first compressor 110 is reduced to the target upper limit of 95℃.

[0069] Figure 9 This is a first flowchart of an adjustment method provided according to an embodiment of the present invention. Figure 9 As shown, the adjustment method includes: S902 obtains the working fluid temperature in the hot-side and cold-side channels of the gas cooler.

[0070] S904 determines whether the working fluid temperature in the hot-side channel of the gas cooler is greater than the working fluid temperature in the cold-side channel. If yes, proceed to step S908; otherwise, proceed to step S906.

[0071] The S906 adjusts the three-way valve to allow the working fluid in the first pipeline to flow through the branch pipeline to the second pipeline.

[0072] The S908 adjusts the three-way valve to allow the working fluid in the first pipeline to flow through the cold side channel of the gas cooler to the second pipeline.

[0073] Figure 10 This is a second flowchart of an adjustment method provided according to an embodiment of the present invention. Figure 10 As shown, the adjustment method includes: S101 obtains the temperature of the working fluid discharged from the first compressor.

[0074] S102 determines whether the temperature of the working fluid discharged from the first compressor is greater than the target upper limit. If yes, proceed to step S103; otherwise, proceed to step S104.

[0075] S103 reduces the opening of the third expansion valve.

[0076] S104 determines whether the temperature of the working fluid discharged from the first compressor is equal to the target upper limit. If yes, proceed to step S105; otherwise, proceed to step S106.

[0077] S105 controls the third expansion valve to maintain its current opening.

[0078] S106 increases the opening of the third expansion valve.

[0079] Finally, it should be noted that in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element. The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A cascade heat pump, characterized in that, include: The primary heat pump cycle system (100) includes a first compressor (110), a hot-side passage of a gas cooler (120), a hot-side passage of a cascade heat exchanger (130), a first expansion valve (160), and an evaporator (170) connected in sequence to form a first refrigerant cycle. A secondary heat pump cycle system (200) includes a second compressor (210), a condenser (220), a second expansion valve (230), and a cold-side passage of the cascade heat exchanger (130) connected in sequence to form a second refrigerant cycle; and, The terminal pipe (300) is connected sequentially to the cold side passage of the gas cooler (120) and the cold side passage of the condenser (220) along the conveying direction.

2. The cascade heat pump according to claim 1, characterized in that, The terminal pipeline (300) includes a first pipeline (310) and a second pipeline (320). The output end of the first pipeline (310) is connected to the inlet end of the cold side channel in the gas cooler (120). The input end of the second pipeline (320) is connected to the outlet end of the cold side channel in the gas cooler (120), and the output end is connected to the inlet end of the cold side channel in the condenser (220). The second pipeline (320) is provided with a three-way valve (410). A branch pipeline (340) is connected between the branch interface of the three-way valve (410) and the first pipeline (310).

3. The cascade heat pump according to claim 2, characterized in that, The first pipeline (310) is provided with a first detection element (420) on the section upstream of the branch pipeline (340). The first detection element (420) is used to detect the working fluid temperature at the corresponding position of the first pipeline (310). The pipeline connected to the exhaust side of the first compressor (110) in the first refrigerant circulation is provided with a second detection element (430). The second detection element (430) is used to detect the working fluid temperature in the corresponding pipeline.

4. The cascade heat pump according to claim 3, characterized in that, The cascade heat pump also includes a controller (500), and the three-way valve (410), the first detection element (420) and the second detection element (430) are all connected to the controller (500).

5. The cascade heat pump according to any one of claims 1-4, characterized in that, The primary heat pump cycle system (100) further includes an internal heat exchanger (150), the hot side passage of which is connected between the hot side passage of the cascade heat exchanger (130) and the first expansion valve (160), and the cold side passage of which is connected between the cold side passage of the evaporator (170) and the first compressor (110).

6. The cascade heat pump according to claim 5, characterized in that, The first refrigerant circulation pipeline located between the hot side channel of the internal heat exchanger (150) and the hot side channel of the cascade heat exchanger (130) is equipped with a third expansion valve (140).

7. The cascade heat pump according to any one of claims 1-4, characterized in that, The condenser (220) is provided with a third detection element (440) on the output side of the cold side channel. The third detection element (440) is used to detect the working fluid temperature output by the cold side channel of the condenser (220).

8. The cascade heat pump according to any one of claims 1-4, characterized in that, The frequency of the first compressor (110) is equal to the frequency of the second compressor (210).

9. An adjustment method, characterized in that, The adjustment method is applied to the cascade heat pump according to any one of claims 2-4, and the adjustment method includes: Obtain the working fluid temperature in the hot-side and cold-side channels of the gas cooler (120); Determine whether the working fluid temperature in the hot side channel of the gas cooler (120) is greater than the working fluid temperature in the cold side channel; If so, adjust the three-way valve (410) so that the working fluid in the first pipeline (310) flows to the second pipeline (320) through the cold side channel of the gas cooler (120). If not, adjust the three-way valve (410) so that the working fluid in the first pipeline (310) flows to the second pipeline (320) through the branch pipeline (340).

10. An adjustment method, characterized in that, The adjustment method is applied to the cascade heat pump according to claim 6, and the adjustment method further includes: Obtain the temperature of the working fluid discharged from the first compressor (110); The working fluid temperature discharged by the first compressor (110) is compared with the target upper limit value. If the working fluid temperature discharged by the first compressor (110) is greater than the target upper limit value, the opening of the third expansion valve (140) is reduced. If the working fluid temperature discharged by the first compressor (110) is equal to the target upper limit value, the third expansion valve (140) is controlled to maintain the current opening. If the working fluid temperature discharged by the first compressor (110) is less than the target upper limit value, the opening of the third expansion valve (140) is increased.

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