CO2 mixed working fluid variable concentration air source heat pump system in high-altitude and cold regions

Abstract

The application relates to a CO2 mixed working medium variable-concentration air source heat pump system in an alpine region. The system is composed of a high-low compressor, a variable-concentration mixing chamber, a variable-concentration liquid storage tank and the like components which are connected through pipelines. The system can realize the optimal mixed ratio adjustment of the CO2 mixed working medium in different working conditions in the alpine region through the frequency conversion of the compressor and the cooperation of the variable-concentration liquid storage tank and the like components, so that the system can be efficiently and stably operated in the heating season. The device has wide popularization and application space and energy-saving significance when used in a room in the alpine region.

Description

Technical Field

[0001] This invention belongs to the field of refrigeration and air conditioning technology, and relates to a CO2 mixed working fluid variable concentration air source heat pump system for high-altitude and cold regions, and particularly to a heat pump system that utilizes the cooperation between various devices to adjust the concentration of CO2 mixed working fluid in high-altitude and cold regions. Background Technology

[0002] Traditional vapor compression cycle air source heat pumps have become the most suitable method for promotion due to their advantages of high efficiency, energy saving, and cost-effectiveness, and have been widely used in Beijing and areas south of North my country. However, when used in cold regions, air source heat pumps face challenges such as low ambient temperature, large intake specific volume, small system working fluid circulation volume, high pressure ratio, high exhaust temperature, poor lubrication, and frost formation on the evaporator surface, which limit their widespread application in cold regions.

[0003] By purposefully mixing pure working fluids, mixed working fluids with excellent thermodynamic properties can be obtained. Excellent mixed working fluids generally have lower energy consumption, lower pressure ratio, lower exhaust temperature, and lower standard evaporation temperature than their pure components. Among these, the refrigerant substitution method combined with air-source heat pumps exhibits good low-temperature adaptability. Comparative studies have shown that CO2 mixed working fluids can improve the low-temperature performance of heat pumps and increase the seasonal energy efficiency of air-source heat pumps. Simultaneously, two-stage compression can alleviate the problems of high compressor pressure ratio and high exhaust temperature under low-temperature conditions with CO2 mixed working fluids. Domestic and international scholars have attempted to mix other working fluids with CO2 to form CO2 mixed working fluids to reduce system operating pressure and improve system performance by utilizing the temperature glide characteristics during heat exchange. Furthermore, if other component working fluids are flammable or explosive, mixing them with CO2 can utilize CO2's fire-extinguishing properties to suppress their flammability and explosiveness.

[0004] Studies by scholars from various countries have shown that system performance exhibits a nonlinear characteristic with changes in the composition of the mixed working fluid. The operating parameters and optimal performance of the system under different operating conditions are closely related to the working fluid composition. In existing two-stage compression cycles, the mixed working fluid ratio is often fixed, making it impossible to change the mixed working fluid ratio according to changes in operating conditions to obtain the optimal performance of the system. Summary of the Invention

[0005] The purpose of this invention is to provide an air source heat pump system with variable concentration of CO2 mixed working fluid in high-altitude and cold regions, which solves the defect of constant mixed working fluid concentration in the cycle under variable operating conditions in high-altitude and cold regions, and achieves high performance of the system.

[0006] The specific technical solution of the present invention is as follows:

[0007] The CO2 mixed refrigerant variable concentration air source heat pump system provided by this invention includes a CO2 mixed refrigerant two-stage compression circulation loop consisting of a low-pressure compressor, a high-pressure compressor, an evaporator, a heating device, a variable concentration mixing chamber, a first electronic expansion valve, a second electronic expansion valve, and refrigerant connecting pipelines. The connection method of each device in the CO2 mixed refrigerant two-stage compression circulation loop is as follows: the upper refrigerant pipeline of the low-pressure compressor is connected to the left end of the high-pressure compressor; the upper refrigerant pipeline of the variable concentration mixing chamber is connected to the refrigerant pipeline connecting the low-pressure compressor and the high-pressure compressor; the upper refrigerant pipeline of the high-pressure compressor is connected to the lower end of the heating device; the upper refrigerant pipeline of the heating device is connected to the upper end of the variable concentration mixing chamber via the first electronic expansion valve; the lower refrigerant pipeline of the variable concentration mixing chamber is connected to the lower end of the second electronic expansion valve; the left end of the second electronic expansion valve is connected to the upper end of the evaporator; and the lower end of the evaporator is connected to the left end of the low-pressure compressor.

[0008] A variable-concentration refrigerant storage tank with a sight glass, a first solenoid valve, a second solenoid valve, and a third solenoid valve are added between the variable-concentration mixing chamber and the second electronic expansion valve to form a variable-concentration refrigerant storage charging circuit. The connections of each device in the variable-concentration refrigerant storage charging circuit are as follows: the refrigerant pipeline on the right side of the first solenoid valve is connected to the lower left port of the variable-concentration mixing chamber; the refrigerant pipeline on the left side of the first solenoid valve is connected to the lower part of the second electronic expansion valve; the upper refrigerant pipeline of the second solenoid valve is connected to the refrigerant pipeline between the first solenoid valve and the variable-concentration mixing chamber; the lower refrigerant pipeline of the second solenoid valve is connected to the lower right port of the variable-concentration storage tank; and the lower left port of the variable-concentration storage tank is connected to the refrigerant pipeline between the first solenoid valve and the second electronic expansion valve via the third solenoid valve. The variable-concentration refrigerant storage charging circuit... When the second solenoid valve is energized and open, and the first and third solenoid valves are de-energized and closed, a variable concentration liquid storage circuit is formed. The connection method of each device in the variable concentration liquid storage circuit is as follows: the refrigerant line at the upper end of the second solenoid valve is connected to the refrigerant line connecting the variable concentration liquid storage tank and the first solenoid valve, and the refrigerant line at the lower end of the second solenoid valve is connected to the lower right port of the variable concentration liquid storage tank. When the first and second solenoid valves are de-energized and closed in the variable concentration refrigerant storage charging circuit, the third solenoid valve is energized and open, forming a variable concentration charging circuit. The connection method of each device in the variable concentration charging circuit is as follows: the refrigerant line at the lower end of the third solenoid valve is connected to the lower left port of the variable concentration liquid storage tank, and the refrigerant line at the lower end of the third solenoid valve is connected to the refrigerant line between the first solenoid valve and the second electronic expansion valve.

[0009] The variable concentration mixing chamber in this system has one inlet and two outlets. The inlet is located at the top center of the variable concentration mixing chamber. The inlet pipe extends into the mixing chamber at an angle, and after forming a "V" shape, the end of the pipe stops at the upper left part of the mixing chamber. One outlet is located at the upper part of the variable concentration mixing chamber, and the other outlet is located at the lower part of the variable concentration mixing chamber. A sight glass is also located on the left side of the mixing chamber.

[0010] In the variable concentration control strategy, when it is necessary to increase or decrease the concentration of the circulating working fluid in the system, the frequency of the low-pressure compressor and the high-pressure compressor can be changed, and the variable concentration storage tank and the coordination of various valves can be used to achieve the variable concentration of the system.

[0011] In the above technical solution, the refrigerant in the system can be replaced according to the working environment.

[0012] The present invention has the following beneficial effects:

[0013] The effects and benefits of this invention are: the CO2 mixed working fluid variable concentration air source heat pump system in high-altitude and cold regions utilizes a variable concentration mixing chamber, a variable concentration storage tank, and other components to adjust the intermediate pressure to achieve changes in the mixed working fluid ratio under different operating conditions, thereby improving the system's circulation performance and enabling it to operate efficiently and stably during the heating season. Attached Figure Description

[0014] Figure 1 This is a schematic diagram of the structural principle of an air source heat pump system with variable concentration of CO2 mixed working fluid in high-altitude and cold regions.

[0015] The reference numerals in the figure are:

[0016] 1-Low-pressure compressor; 2-High-pressure compressor; 3-Evaporator; 4-Heating equipment; 5-Variable concentration mixing chamber; 6-First electronic expansion valve; 7-Second electronic expansion valve; 8-Variable concentration storage tank; 9-First solenoid valve; 10-Second solenoid valve; 11-Third solenoid valve. Detailed Implementation

[0017] The specific embodiments of the present invention will be described in detail below with reference to the technical solutions and accompanying drawings.

[0018] Increase the system's CO2 concentration mode

[0019] Increase the frequency of low-pressure compressor 1, energize and open the second solenoid valve 10, and de-energize and close the first solenoid valve 9 and the third solenoid valve 11. The refrigerant is compressed by the low-pressure compressor 1 into a high-temperature, medium-pressure superheated gaseous refrigerant. The high-temperature, medium-pressure gaseous refrigerant from the top of the low-pressure compressor 1 mixes with the saturated gaseous refrigerant from the top of the variable-concentration mixing chamber 5 and enters the high-pressure compressor 2. After being compressed by the high-pressure compressor 2 into a high-temperature, high-pressure superheated gaseous refrigerant, the refrigerant enters the heating equipment 4 for heat exchange and cooling. After heat exchange, it is throttled by the first electronic expansion valve 6 into a medium-temperature, medium-pressure mixture of gaseous and liquid refrigerant and enters the variable-concentration mixing chamber 5 for gas-liquid separation. The saturated gaseous refrigerant mixes with the superheated refrigerant from the outlet of the low-pressure compressor 1 and enters the high-pressure compressor 2. The saturated liquid refrigerant in the variable-concentration mixing chamber 5 enters the variable-concentration storage tank 8 through the lower left port and the second solenoid valve 10. The liquid level in the sight glass of the variable-concentration storage tank 8 is observed. After the required liquid level is reached, the first solenoid valve 9 is energized and opened, while the second solenoid valve 10 and the third solenoid valve 11 are de-energized and closed. The frequency of the low-pressure compressor 1 is returned to its original position, and the system operation ends with an increase in CO2 concentration.

[0020] Reduce system operating CO2 concentration mode

[0021] The frequency of high-pressure compressor 2 is increased, the third solenoid valve 11 is energized and opened, and the first solenoid valve 9 and the second solenoid valve 10 are energized and closed. The refrigerant is compressed by low-pressure compressor 1 into a high-temperature, medium-pressure superheated gaseous refrigerant. The high-temperature, medium-pressure gaseous refrigerant exiting from the upper end of low-pressure compressor 1 mixes with the saturated gaseous refrigerant exiting from the upper part of variable-concentration mixing chamber 5 and enters high-pressure compressor 2. After being compressed by high-pressure compressor 2 into a high-temperature, high-pressure superheated gaseous refrigerant, the refrigerant enters the heating equipment 4 for heat exchange and cooling. After heat exchange, it is throttled by the first electronic expansion valve 6 into a medium-temperature, medium-pressure mixture of gaseous and liquid refrigerant and enters the variable-concentration mixing chamber 5 for gas-liquid separation. The refrigerant mixes with the superheated refrigerant at the outlet of the low-pressure compressor 1 and enters the high-pressure compressor 2. The saturated liquid refrigerant in the variable concentration mixing chamber 5 is stored in the variable concentration mixing chamber 5. The liquid refrigerant in the variable concentration storage tank 8 enters the second electronic expansion valve 7 through the third solenoid valve 11. The liquid level in the sight glass of the variable concentration storage tank 8 is observed. After the required liquid is filled, the first solenoid valve 9 is energized and opened, while the second solenoid valve 10 and the third solenoid valve 11 are de-energized and closed. The frequency of the high-pressure compressor 2 is adjusted back to its original position, and the system operation ends with a decrease in CO2 concentration.

[0022] The CO2 mixed working fluid variable concentration air source heat pump system of the present invention, based on the characteristics of a CO2 two-stage compression heat pump system, through the variable concentration storage tank and the cooperation between various valves, can realize the change of the mixed working fluid ratio under different operating conditions in high-altitude and cold regions by adjusting the high and low compressor frequencies, thereby improving the system circulation performance.

[0023] Obviously, the examples above are merely illustrative and not intended to limit the implementation. Those skilled in the art will recognize that many other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom remain within the scope of this invention.

Claims

1. A variable concentration air-source heat pump system for CO2 mixed working fluid in high-altitude and cold regions, characterized in that: A two-stage compression loop for CO2 mixed working fluid is formed by a low-pressure compressor (1), a high-pressure compressor (2), an evaporator (3), a heating device (4), a variable concentration mixing chamber (5), a first electronic expansion valve (6), a second electronic expansion valve (7), and refrigerant connecting pipes. The connection method of each device in the two-stage compression loop for CO2 mixed working fluid is as follows: the refrigerant pipe at the upper end of the low-pressure compressor (1) is connected to the left end of the high-pressure compressor (2), and the refrigerant pipe at the upper end of the variable concentration mixing chamber (5) is connected to the low-pressure compressor (1) and... On the refrigerant pipeline connected to the high-pressure compressor (2), the upper refrigerant pipeline of the high-pressure compressor (2) is connected to the lower end of the heating equipment (4), the upper refrigerant pipeline of the heating equipment (4) is connected to the upper end of the variable concentration mixing chamber (5) via the first electronic expansion valve (6), the lower refrigerant pipeline of the variable concentration mixing chamber (5) is connected to the lower end of the second electronic expansion valve (7), the left refrigerant pipeline of the second electronic expansion valve (7) is connected to the upper end of the evaporator (3), and the lower refrigerant pipeline of the evaporator (3) is connected to the left end of the low-pressure compressor (1). A variable concentration refrigerant storage tank (8) with a sight glass, a first solenoid valve (9), a second solenoid valve (10), and a third solenoid valve (11) are added between the variable concentration mixing chamber (5) and the second electronic expansion valve (7) to form a variable concentration refrigerant storage charging circuit. The connection method of each device in the variable concentration refrigerant storage charging circuit is as follows: the refrigerant pipeline on the right side of the first solenoid valve (9) is connected to the lower left port of the variable concentration mixing chamber (5), the refrigerant pipeline on the left side of the first solenoid valve (9) is connected to the lower part of the second electronic expansion valve (7), the refrigerant pipeline on the upper part of the second solenoid valve (10) is connected to the refrigerant pipeline between the first solenoid valve (9) and the variable concentration mixing chamber (5), the refrigerant pipeline on the lower part of the second solenoid valve (10) is connected to the lower right port of the variable concentration storage tank (8), and the lower left port of the variable concentration storage tank (8) is connected to the refrigerant pipeline between the first solenoid valve (9) and the second electronic expansion valve (7) via the third solenoid valve (11). When the second solenoid valve (10) in the liquid filling circuit is energized and opened, and the first solenoid valve (9) and the third solenoid valve (11) are not energized and closed, a variable concentration liquid storage circuit is formed. The connection method of each device in the variable concentration liquid storage circuit is as follows: the refrigerant pipeline at the upper end of the second solenoid valve (10) is connected to the refrigerant pipeline connected to the variable concentration liquid storage tank (8) and the first solenoid valve (9), and the refrigerant pipeline at the lower end of the second solenoid valve (10) is connected to the lower right port of the variable concentration liquid storage tank (8). When the first solenoid valve (9) and the second solenoid valve (10) in the variable concentration refrigerant liquid filling circuit are not energized and closed, the third solenoid valve (11) is energized and opened, forming a variable concentration filling circuit. The connection method of each device in the variable concentration filling circuit is as follows: the refrigerant pipeline at the lower end of the third solenoid valve (11) is connected to the lower left port of the variable concentration liquid storage tank (8), and the refrigerant pipeline at the lower end of the third solenoid valve (11) is connected to the refrigerant pipeline between the first solenoid valve (9) and the second electronic expansion valve (7). The variable concentration mixing chamber (5) has one inlet and two outlets. The inlet is located in the middle of the top of the variable concentration mixing chamber (5). The inlet pipe extends into the mixing chamber at a 45° angle. After forming a "V" shape, the end of the pipe stops at the upper left of the mixing chamber. One outlet is located at the upper part of the variable concentration mixing chamber (5), and the other outlet is located at the lower part of the variable concentration mixing chamber (5). A sight glass is also located on the left side of the mixing chamber. The system operates the CO2 concentration regulation module; the mode to increase the system's operating CO2 concentration is: increase the frequency of the low-pressure compressor (1), the second solenoid valve (10) is energized and opened, and the first solenoid valve (9) and the third solenoid valve (11) are de-energized and closed; the mode to decrease the system's operating CO2 concentration is: increase the frequency of the high-pressure compressor (2), the third solenoid valve (11) is energized and opened, and the first solenoid valve (9) and the second solenoid valve (10) are de-energized and closed. The refrigerant in the system can be replaced according to the working environment.

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