A stable transcritical cycle method and system for a CO2 air source heat pump for heating

Abstract

The present invention relates to a stable transcritical circulation method and system for a CO2 air source heat pump for heating. The method divides the heating return water into three branches, and by arranging a stable transcritical circulation heat exchanger and a temperature-raising efficiency-enhancing heat exchanger before the compressor and evaporator inlets, respectively, the CO2 working medium exchanges heat with the heating return water as needed. According to the stable transcritical circulation criterion, when the system cannot perform a transcritical heating cycle under low-temperature working conditions, the heating return water is used to heat the CO2 working medium before the compressor inlet to increase the suction pressure and mass flow before the compressor inlet, thereby increasing the compression ratio and exhaust temperature. Ultimately, the transcritical heating cycle of the CO2 working medium is always ensured under low-temperature working conditions, thereby ensuring the stable operation of the system and improving the heating performance. In addition, according to the temperature-raising efficiency-enhancing criterion, the heating return water is used to heat the CO2 working medium before the evaporator inlet to increase the evaporation temperature and optimize the heating efficiency. The system can ensure that the CO2 air source heat pump heating system operates stably and efficiently under low-temperature working conditions.

Description

Technical Field

[0001] The present invention relates to a stable transcritical circulation method and system of a CO2 air source heat pump for heating, belonging to the technical field of air source heat pump heating. Background Art

[0002] CO2 air source heat pumps are not only energy-saving and environmentally friendly, but also have excellent heating performance and high outlet water temperature when performing transcritical heating cycles. They are considered to be an ideal alternative to traditional heating methods such as coal-fired and gas-fired boilers. CO2 has unique thermophysical properties, with a low critical temperature (31.1°C) and a high critical pressure (7.38MPa). Since the physical parameters of CO2 change very dramatically with temperature and pressure near the critical point, the use of a transcritical cycle can greatly enhance the heat transfer performance and significantly increase the heat exchange rate. At the same time, the temperature glide characteristics of CO2 in the supercritical heat release process of the transcritical heating cycle match the temperature rise process of water, thereby effectively increasing the outlet water temperature and reducing irreversible heat transfer losses on the high-pressure side. Therefore, the CO2 air source heat pump can significantly improve the heating performance when performing a transcritical heating cycle.

[0003] However, when a CO2 air source heat pump provides heating under low-temperature conditions, as the ambient temperature decreases, the compressor suction pressure and suction mass flow rate decrease accordingly. When the excessively low suction pressure causes the compressor exhaust pressure and exhaust temperature to fall below the critical value, the CO2 air source heat pump will be unable to perform a transcritical heating cycle, resulting in a sharp drop in the system's heating performance, unstable operation, or even failure to operate normally, making it impossible to meet the user's heating needs. Although some scholars have proposed using heat recovery cycles, introducing ejectors, and low-pressure air supply to solve this problem, these methods have limitations such as the lack of significant effect in increasing the suction pressure, high processing precision requirements, and energy consumption. In addition, when a CO2 air source heat pump is used for heating under low-temperature conditions, there are also problems with the evaporation temperature dropping as the ambient temperature decreases, the evaporator fin surface is prone to frost, the heating return water temperature and the air cooler CO2 outlet temperature are high, and throttling losses increase, resulting in a continuous decline in the energy efficiency ratio and heating capacity of the CO2 air source heat pump. Therefore, in a low-temperature environment, increasing the system suction pressure to ensure stable transcritical circulation of the CO2 working fluid, effectively reducing the heating return water temperature, reducing throttling losses, and increasing the evaporation temperature are key issues affecting the promotion and application of CO2 air source heat pumps in the heating field. Summary of the Invention

[0004] The purpose of the present invention is to address the deficiencies in the prior art and provide a stable transcritical circulation method and system for a CO2 air source heat pump for heating, which can ensure that CO2 undergoes a transcritical heating cycle in a low-temperature environment, while increasing the evaporation temperature, reducing the return water temperature and throttling loss, thereby improving the efficient and stable operation performance and low-temperature performance of the CO2 air source heat pump heating.

[0005] The purpose of the present invention is achieved through the following technical solutions:

[0006] A method for stabilizing transcritical circulation of a CO2 air-source heat pump for heating: a stabilizing transcritical circulation heat exchanger 15 is provided before the inlet of a compressor 1 of a CO2 air-source heat pump unit for heating; when the system cannot perform a transcritical heating cycle under low-temperature conditions, heating return water is used to heat the refrigerant before the compressor inlet on demand, thereby increasing the suction pressure and mass flow before the compressor inlet, thereby increasing the compression ratio and exhaust temperature, and always ensuring the transcritical heating cycle of the CO2 working medium and the stable operation of the system under low-temperature conditions, while improving the heating performance; a temperature-raising and efficiency-enhancing heat exchanger 7 is provided before the inlet of an evaporator 4 of the CO2 air-source heat pump unit for heating; under low-temperature conditions, heating return water is used to heat the refrigerant before the inlet of the evaporator 4 on demand, thereby increasing the evaporation temperature and optimizing the heating efficiency of the system, thereby ensuring the stable and efficient operation of the CO2 air-source heat pump heating under low-temperature conditions;

[0007] The water temperature of the heating return water is reduced after heat exchange with the refrigerant before the inlet of the compressor 1 and before the inlet of the evaporator 4, thereby reducing the water temperature at the inlet of the air cooler, reducing throttling losses, and improving the heating coefficient and heating capacity; based on the particle swarm algorithm and multi-objective function optimization, a heating efficiency criterion and a stable transcritical cycle criterion are established to control the heating return water flow rate flowing into the heating efficiency heat exchanger 7 and the stable transcritical cycle heat exchanger 15, and the response surface method RSM is used to optimize this flow rate to obtain the optimal heating return water flow rate; the heating efficiency heat exchanger 7 and the stable transcritical cycle heat exchanger 15 adopt a three-dimensional internal and external rib heat exchange tube upper end spray cross flow heat exchange structure.

[0008] Furthermore, the heating return water is divided into three branches, namely branch I 27, branch II 11 and branch III 13; a stable transcritical cycle heat exchanger 15 is set at the front end of the compressor 1 inlet, and the heating return water is transported to the stable transcritical cycle heat exchanger 15 through branch III 13 to moderately heat the CO2 working medium before the compressor 1 inlet to ensure a transcritical stable heating cycle of the low-temperature working system; the controller 25 controls the opening of the electric regulating valve III 20 according to the stable transcritical cycle criterion to adjust the heating return water flow into the stable transcritical cycle heat exchanger 15 as needed.

[0009] Furthermore, the suction temperature T of compressor 1 is obtained in real time. i , suction pressure P i , compressor exhaust temperature T c , exhaust pressure P c , heating power W, coefficient of performance COP, compression ratio E and heating return water temperature T s , considering the changes of these parameters with the ambient temperature T under low temperature conditions a The changes during the descent and the compressor exhaust temperature T c and exhaust pressure Pc The stable transcritical cycle criterion is established by determining whether the CO2 value is lower than the critical value. The particle swarm algorithm, which has been well applied in multi-objective optimization of coupled variables, is used to take the heating power W, coefficient of performance COP, and compression ratio E as the control targets of the stable transcritical cycle criterion, and the weights m1, m2, and m3 are taken respectively. The opening K of the electric control valve III20 is determined by optimizing the multi-objective function {m1W, m2COP, m3E}. c , thereby determining the heating return water flow Q flowing into the stable transcritical cycle heat exchanger 15 c ', to ensure that the system performs a transcritical stable heating cycle so that the system can operate stably and efficiently under low temperature conditions; K c Is with T i ,P i ,T c ,P c ,W,COP,E,T s ,The quantity related to the T parameter can be specifically expressed by the function as follows:

[0010] K c =f(T i ,P i ,T c ,P c ,W,COP,E,T s ,T a )

[0011] Q c '=K c Q c

[0012] Where Q c It is the water flow rate when the electric regulating valve III 20 is fully opened.

[0013] Furthermore, when heating in a low-temperature environment, as the ambient temperature decreases, the compressor suction pressure and temperature decrease accordingly, the compressor suction mass decreases, and the compressor exhaust pressure and temperature also drop below the critical value. When the CO2 working medium cannot undergo a transcritical heating cycle, the electric regulating valve III 20 opening is controlled by the stable transcritical heating cycle criterion (judging whether the CO2 working medium can stably undergo a transcritical heating cycle) to allow the heating return water to flow into the stable transcritical cycle heat exchanger 15, so that the heating return water heats the CO2 working medium at the front end of the compressor inlet as needed. On the one hand, it can maximize the suction temperature, suction pressure and suction mass flow of the CO2 working medium at the compressor inlet, and the compressor exhaust temperature and exhaust pressure will rise to above the critical state point, thereby ensuring that the CO2 working medium undergoes a transcritical thermodynamic cycle and improving the system operation stability; on the other hand, it can further improve the heating performance under low-temperature conditions, so that the system has better low-temperature performance; at the same time, without consuming additional energy, it can prevent the lubricating oil temperature in the compressor from being too low and avoid refrigerant migration when the compressor is shut down.

[0014] Furthermore, a temperature-raising and efficiency-enhancing heat exchanger 7 is provided at the front end of the inlet of the evaporator 4, and then the heating return water is transported to the temperature-raising and efficiency-enhancing heat exchanger 7 through the branch line II11 to moderately heat the CO2 working medium before the inlet of the evaporator 4, so as to increase the evaporation temperature and slow down the frosting of the evaporator; the controller 15 controls the opening of the electric regulating valve II21 according to the temperature-raising and efficiency-enhancing criterion to adjust the flow rate of the heating return water flowing into the temperature-raising and efficiency-enhancing heat exchanger 7 as needed.

[0015] Furthermore, the frost frequency F and evaporation temperature T of the evaporator 4 are obtained in real time. e , heating power W, coefficient of performance COP, compression ratio E and heating return water temperature T s , considering the changes of these parameters with the ambient temperature T under low temperature conditions a The temperature rise efficiency criterion is established based on the change of the temperature when the temperature decreases; the particle swarm algorithm with good application in multi-objective optimization of coupled variables is used, and the heating power W, performance coefficient COP, and compression ratio E are used as the control targets of the temperature rise efficiency criterion, and the weights m4, m5, and m6 are taken respectively. The opening K of the electric control valve II21 is determined by the optimal multi-objective function {m4W, m5COP, m6E} e , thereby determining the required heating return water flow Q flowing into the temperature-increasing efficiency heat exchanger 7 e ', to increase the evaporation temperature, reduce the frequency of evaporator frosting, and thus improve the heating efficiency of the system under low temperature conditions; K e Is with F,T e ,W,COP,E,T s ,T a The quantity related to the parameters can be specifically expressed by functions as follows:

[0016] K e =f(F,Te ,W,COP,E,T s ,T a )

[0017] Q e '=K e Q e

[0018] Where Q e It is the water flow rate when the electric regulating valve Ⅱ21 is fully opened.

[0019] Furthermore, when heating in a low-temperature environment, as the ambient temperature decreases, the evaporation temperature decreases, the defrosting frequency of the evaporator increases, the suction volume ratio increases, the heat absorption of the evaporator decreases, and the compression ratio becomes larger, resulting in a decrease in unit heating capacity, an increase in unit power consumption, and a decrease in energy efficiency. The opening of the electric regulating valve Ⅱ21 is controlled by the temperature increase efficiency criterion (determining whether the CO2 working medium at the front end of the evaporator 4 inlet needs to be heated and increased) to make the heating return water flow into the temperature increase efficiency heat exchanger 7, so that the heating return water can moderately heat the CO2 working medium at the front end of the evaporator 4 inlet. On the one hand, the low-grade heat of the heating return water can be used to increase the evaporation temperature and evaporation pressure of the evaporator without consuming additional electricity. On the other hand, after the evaporation temperature and evaporation pressure increase, the surface temperature of the fin of the evaporator 4 increases accordingly, thereby achieving the effect of slowing down the frosting on the evaporator coil surface, reducing the defrosting frequency and extending the system operation time; at the same time, after the evaporation temperature increases, the system heating coefficient and heating power increase accordingly.

[0020] Furthermore, during the actual operation process, the response surface method (RSM) is used to optimize the heating return water flow rate flowing into the warming efficiency heat exchanger 7 and the stable transcritical cycle heat exchanger 15, and the optimized flow rate is used as the optimal heating return water flow rate flowing into the warming efficiency heat exchanger 7 and the stable transcritical cycle heat exchanger 15.

[0021] Furthermore, the temperature-raising and efficiency-enhancing heat exchanger 7 is respectively composed of a temperature-raising and efficiency-enhancing heat exchanger CO2 working medium heat exchange pipe 8, a hot water spray port 9 at the upper end of the temperature-raising and efficiency-enhancing heat exchanger, and a hot water outlet 10 at the lower end of the temperature-raising and efficiency-enhancing heat exchanger; the temperature-raising and efficiency-enhancing heat exchanger CO2 working medium heat exchange pipe 8 adopts a three-dimensional internal and external rib form heat exchange pipe to enhance heat exchange, and the heating return water is sprayed downward from the hot water spray port 9 at the upper end of the temperature-raising and efficiency-enhancing heat exchanger and flows out from the hot water outlet 10 at the lower end of the temperature-raising and efficiency-enhancing heat exchanger, and the CO2 working medium and the heating return water are subjected to reverse cross flow exchange. Heat; This type of temperature-raising and efficiency-enhancing heat exchanger 7 not only has good heat exchange performance, but also can prevent hot water from freezing inside the heat exchanger; the structure of the stable transcritical cycle heat exchanger 15 is the same as that of the temperature-raising and efficiency-enhancing heat exchanger 7, and is composed of a stable transcritical cycle heat exchanger CO2 working medium heat exchange tube 16, a hot water spray port 17 at the upper end of the stable transcritical cycle heat exchanger, and a hot water outlet 18 at the lower end of the stable transcritical cycle heat exchanger. The working principles of the two are also the same, so the heat exchanger also has good heat exchange performance and anti-freezing function.

[0022] The temperature-raising and efficiency-enhancing heat exchanger 7 and the stable transcritical cycle heat exchanger 15 adopt a structure of three-dimensional inner and outer rib heat exchange tubes with upper end spray cross-flow heat exchange, which also has the advantage of cost saving, because the use of antifreeze for antifreeze not only affects the heat exchange performance, but is also expensive.

[0023] Furthermore, in order to ensure thermal comfort at the heating end, the heating return water temperature increases with the decrease in ambient temperature. Excessive heating return water temperature not only reduces the heat release of the air cooler but also increases the throttling loss. Therefore, the heating return water with higher water temperature exchanges heat with the CO2 working medium of the warming efficiency heat exchanger 7 and the stable transcritical cycle heat exchanger 15, and the air cooler inlet water temperature is reduced, which is conducive to solving the problem of the high heating return water temperature causing the heating capacity to decrease in low temperature environment. Specifically, after the air cooler inlet water temperature is lowered, countercurrent heat exchange is carried out with the air cooler CO2 working medium, and the outlet specific enthalpy of the air cooler CO2 working medium is greatly reduced. The heat exchange efficiency between the CO2 working medium and the low-temperature heating return water in the air cooler is improved, thereby increasing the heating capacity of the air cooler. After the CO2 working medium is fully condensed in the air cooler, the irreversible throttling loss in the throttle valve 3 can be reduced. Finally, the heating capacity and heating performance coefficient of the system are improved, thereby ensuring the stable and efficient operation of the CO2 air source heat pump heating under low temperature conditions.

[0024] Furthermore, a CO2 air source heat pump stable transcritical circulation system for heating includes the following main components: a compressor 1, an air cooler 2, a throttle valve 3, an evaporator 4, a temperature-raising efficiency-enhancing heat exchanger 7, a stable transcritical circulation heat exchanger 15, an electric regulating valve I 22, an electric regulating valve II 21, an electric regulating valve III 20, a water distributor 23, a controller 25, a water collector 29, etc. The compressor 1, the air cooler 2, the throttle valve 3, the temperature-raising efficiency-enhancing heat exchanger 7, the evaporator 4 and the stable transcritical circulation heat exchanger 15 are connected in sequence through the CO2 working medium circulation pipeline 5; the heating return water is connected to the inlet of the water distributor 23 through the return water main pipe 24, and the water distributor 23 divides the heating return water into three branches, namely branch I 27, branch II 11 and branch III 13, and the water distributor 23 is connected to the water collector 29, The temperature-increasing efficiency heat exchanger 7 and the stable transcritical cycle heat exchanger 15 are connected through branch I 27, branch II 11 and branch III 13 respectively. The water collector 29 is connected to the temperature-increasing efficiency heat exchanger 7 and the stable transcritical cycle heat exchanger 15 through branch V 28 and branch IV 19 respectively. After the water collector 29 merges the return water of branch IV 19, branch V 28 and branch I 27, the water outlet of the water collector 29 is connected to the gas outlet through branch VI 30. The water inlet of the air cooler 2 is connected, and the heating return water is heated by the air cooler 2 and then flows out through the water supply main 31 to provide heat to the user; the electric regulating valve I 22, the electric regulating valve II 21, and the electric regulating valve III 20 are respectively installed on the branch I 27, the branch II 11, and the branch III 13, and the electric regulating valve I 22, the electric regulating valve II 21, and the electric regulating valve III 20 are connected to the controller 25 through a control circuit; the branch I 27, the branch II 11, and the branch III 13 are respectively equipped with flow sensors I 26, flow sensors II 12, and flow sensors III 14, and the flow sensors I 26, flow sensors II 12, and flow sensors III 14 are also connected to the controller 25 and used in combination with the electric regulating valves I 22, the electric regulating valve II 21, and the electric regulating valve III 20 to control and detect the heating return water flow of these three branches;

[0025] The compressor 1 inlet, compressor 1 outlet, CO2 working medium outlet of air cooler 2, throttle valve 3 outlet, evaporator 4 inlet, and evaporator 4 outlet are all equipped with pressure sensors and temperature sensors, the water separator 23 inlet, the temperature increasing efficiency heat exchanger 7 outlet, the stable transcritical cycle heat exchanger 15 outlet, the air cooler 2 water inlet, and the air cooler 2 hot water outlet are all equipped with temperature sensors, the air cooler 2 hot water outlet and the air cooler 2 CO2 working medium outlet are both equipped with flow sensors, a temperature and humidity sensor is installed at the air inlet of evaporator 4, and smart meters are installed on the compressor and evaporator to measure the input power. The flow sensor, temperature sensor, pressure sensor, temperature and humidity sensor and smart meter are all connected to the controller 25.

[0026] Furthermore, the controller 25 adopts a PLC controller, which is composed of a CPU module (including a CPU chip and a memory), an input module, an output module and a programming device module; the input module can have multiple inputs and has 22 analog inputs: compressor suction temperature, compressor suction pressure, compressor exhaust temperature, compressor exhaust pressure, evaporator inlet temperature, evaporator inlet pressure, evaporator outlet temperature, evaporator outlet pressure, air cooler CO2 working medium outlet temperature, air cooler CO2 working medium outlet pressure, air cooler CO2 working medium outlet flow, throttle valve outlet temperature, throttle valve outlet pressure, heating return water temperature, ambient temperature, air cooler water inlet temperature, The program module programs the temperature-elevating efficiency criterion, the transcritical cycle criterion, and the particle swarm algorithm. The CPU module receives and stores the input control variables, performs the particle swarm algorithm calculations with the multi-objective function to optimize the multi-objective function, and then outputs two standard voltage signals for controlling the openings of the electric control valves II21 and III20.

[0027] The beneficial effects of the present invention are:

[0028] 1. Under low-temperature working conditions, when the ambient temperature decreases and the compressor exhaust temperature and exhaust pressure are lower than the critical value, resulting in the CO2 working medium being unable to undergo transcritical thermodynamic circulation, the CO2 working medium before the compressor inlet is appropriately heated by the heating return water through the stable transcritical cycle heat exchanger and according to the stable transcritical cycle criterion, thereby increasing the temperature and specific enthalpy of the CO2 working medium at the compressor inlet to ensure that the CO2 working medium undergoes transcritical thermodynamic circulation and ensure the efficient and stable operation of the CO2 air source heat pump heating system in low-temperature environments;

[0029] 2. Under low-temperature conditions, as the ambient temperature decreases, the evaporation temperature decreases, the evaporator defrost frequency increases, the suction volume ratio increases, and the evaporator heat absorption decreases, the heating efficiency heat exchanger is used, and the heating return water is used to heat the CO2 working medium before the evaporator inlet as needed based on the heating efficiency criterion, thereby increasing the evaporation temperature, heating operation time, and system heating performance without consuming additional energy or affecting indoor thermal comfort;

[0030] 3. After the heating return water and CO2 working medium exchange heat, the water temperature at the air cooler inlet is reduced, which enhances the heat exchange efficiency between the air cooler and the heating return water, thereby increasing the heating capacity. After the CO2 working medium is fully condensed in the air cooler, the irreversible throttling loss of the CO2 working medium during the throttling process can be reduced. The heating capacity and heating performance coefficient of the system under low temperature conditions are further improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 It is a structural schematic diagram of the present invention.

[0032] Figure 1 The numbers in the figure are: 1-compressor, 2-air cooler, 3-throttle valve, 4-evaporator, 5-CO2 working medium circulation pipeline, 6-smart meter installed on the compressor, 7-temperature-increasing heat exchanger, 8-CO2 working medium heat exchange pipe of temperature-increasing heat exchanger, 9-hot water spray port at the upper end of temperature-increasing heat exchanger, 10-hot water outlet at the lower end of temperature-increasing heat exchanger, 11-branch II, 12-flow sensor II, 13-branch III, 14-flow sensor III, 15-stable transcritical cycle heat exchanger, 16 -CO2 working medium heat exchange tube of stable transcritical cycle heat exchanger, 17-hot water spray port at the upper end of stable transcritical cycle heat exchanger, 18-hot water outlet at the lower end of stable transcritical cycle heat exchanger, 19-branch IV, 20-electric regulating valve III, 21-electric regulating valve II, 22-electric regulating valve I, 23-water distributor, 24-return water main pipe, 25-controller, 26-flow sensor I, 27-branch I, 28-branch V, 29-water collector, 30-branch VI, 31-water supply main pipe. DETAILED DESCRIPTION

[0033] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0034] Example 1, a method for stabilizing transcritical circulation of a CO2 air source heat pump for heating: a stabilizing transcritical circulation heat exchanger 15 is provided before the inlet of the compressor 1 of the CO2 air source heat pump unit for heating; when the system cannot perform a transcritical heating cycle under low-temperature conditions, heating return water is used to heat the refrigerant before the compressor inlet on demand to increase the suction pressure and mass flow before the compressor inlet, thereby increasing the compression ratio and exhaust temperature, and always ensuring the transcritical heating cycle of the CO2 working medium and the stable operation of the system under low-temperature conditions, while improving the heating performance; a temperature-raising and efficiency-enhancing heat exchanger 7 is provided before the inlet of the evaporator 4 of the CO2 air source heat pump unit for heating; under low-temperature conditions, heating return water is used to heat the refrigerant before the inlet of the evaporator 4 on demand to increase the evaporation temperature and optimize the heating efficiency of the system, thereby ensuring the stable and efficient operation of the CO2 air source heat pump heating under low-temperature conditions;

[0035] The water temperature of the heating return water is reduced after heat exchange with the refrigerant before the inlet of the compressor 1 and the inlet of the evaporator 4, thereby reducing the water temperature at the inlet of the air cooler, reducing throttling losses, and improving the heating coefficient and heating capacity; based on the particle swarm algorithm and the multi-objective function optimization, a heating efficiency criterion and a stable transcritical cycle criterion are established to control the heating return water flow rate flowing into the heating efficiency heat exchanger 7 and the stable transcritical cycle heat exchanger 15, and the response surface method (RSM) is used to optimize this flow rate to obtain the optimal heating return water flow rate; the heating efficiency heat exchanger 7 and the stable transcritical cycle heat exchanger 15 adopt a three-dimensional internal and external rib heat exchange tube upper end spray cross flow heat exchange structure.

[0036] Furthermore, the heating return water is divided into three branches, namely branch I 27, branch II 11 and branch III 13; a stable transcritical cycle heat exchanger 15 is set at the front end of the compressor 1 inlet, and the heating return water is transported to the stable transcritical cycle heat exchanger 15 through branch III 13 to moderately heat the CO2 working medium before the compressor 1 inlet to ensure a transcritical stable heating cycle of the low-temperature working system; the controller 25 controls the opening of the electric regulating valve III 20 according to the stable transcritical cycle criterion to adjust the heating return water flow into the stable transcritical cycle heat exchanger 15 as needed.

[0037] Furthermore, the suction temperature T of compressor 1 is obtained in real time. i , suction pressure P i , compressor exhaust temperature T c , exhaust pressure P c , heating power W, coefficient of performance COP, compression ratio E and heating return water temperature T s , considering the changes of these parameters with the ambient temperature T under low temperature conditions a The changes during the descent and the compressor exhaust temperature T c and exhaust pressure P c The stable transcritical cycle criterion is established by determining whether the CO2 value is lower than the critical value. The particle swarm algorithm, which has been well applied in multi-objective optimization of coupled variables, is used to take the heating power W, coefficient of performance COP, and compression ratio E as the control targets of the stable transcritical cycle criterion, and the weights m1, m2, and m3 are taken respectively. The opening K of the electric control valve III20 is determined by optimizing the multi-objective function {m1W, m2COP, m3E}. c , thereby determining the heating return water flow Q flowing into the stable transcritical cycle heat exchanger 15 c ', to ensure that the system performs a transcritical stable heating cycle so that the system can operate stably and efficiently under low temperature conditions; K c Is with T i ,P i ,T c ,P c ,W,COP,E,T s ,T aThe quantity related to the parameters can be specifically expressed by functions as follows:

[0038] K c =f(T i ,P i ,T c ,P c ,W,COP,E,T s ,T a )

[0039] Q c '=K c Q c

[0040] Where Q c It is the water flow rate when the electric regulating valve III 20 is fully opened.

[0041] Specifically, the heating return water flow Q flowing into the stable transcritical cycle heat exchanger 15 c 'As shown below:

[0042]

[0043] The T a When the temperature is higher than -10℃, the electric regulating valve Ⅰ22 is fully opened, otherwise it is closed.

[0044] Furthermore, when heating in a low-temperature environment, as the ambient temperature decreases, the compressor suction pressure and temperature decrease accordingly, the compressor suction mass decreases, and the compressor exhaust pressure and temperature also drop below the critical value. When the CO2 working medium cannot undergo a transcritical heating cycle, the electric regulating valve III 20 opening is controlled by the stable transcritical heating cycle criterion (judging whether the CO2 working medium can stably undergo a transcritical heating cycle) to allow the heating return water to flow into the stable transcritical cycle heat exchanger 15, so that the heating return water heats the CO2 working medium at the front end of the compressor inlet as needed. On the one hand, it can maximize the suction temperature, suction pressure and suction mass flow of the CO2 working medium at the compressor inlet, and the compressor exhaust temperature and exhaust pressure will rise to above the critical state point, thereby ensuring that the CO2 working medium undergoes a transcritical thermodynamic cycle and improving the system operation stability; on the other hand, it can further improve the heating performance under low-temperature conditions, so that the system has better low-temperature performance; at the same time, without consuming additional energy, it can prevent the lubricating oil temperature in the compressor from being too low and avoid refrigerant migration when the compressor is shut down.

[0045] Furthermore, a temperature-raising and efficiency-enhancing heat exchanger 7 is provided at the front end of the inlet of the evaporator 4, and then the heating return water is transported to the temperature-raising and efficiency-enhancing heat exchanger 7 through the branch line II11 to moderately heat the CO2 working medium before the inlet of the evaporator 4, so as to increase the evaporation temperature and slow down the frosting of the evaporator; the controller 15 controls the opening of the electric regulating valve II21 according to the temperature-raising and efficiency-enhancing criterion to adjust the flow rate of the heating return water flowing into the temperature-raising and efficiency-enhancing heat exchanger 7 as needed.

[0046] Furthermore, the frost frequency F and evaporation temperature T of the evaporator 4 are obtained in real time. e , heating power W, coefficient of performance COP, compression ratio E and heating return water temperature T s , considering the changes of these parameters with the ambient temperature T under low temperature conditions a The temperature rise efficiency criterion is established based on the change of the temperature when the temperature decreases; the particle swarm algorithm with good application in multi-objective optimization of coupled variables is used, and the heating power W, performance coefficient COP, and compression ratio E are used as the control targets of the temperature rise efficiency criterion, and the weights m4, m5, and m6 are taken respectively. The opening K of the electric control valve II21 is determined by the optimal multi-objective function {m4W, m5COP, m6E} e , thereby determining the required heating return water flow Q flowing into the temperature-increasing efficiency heat exchanger 7 e ', to increase the evaporation temperature, reduce the frequency of evaporator frosting, and thus improve the heating efficiency of the system under low temperature conditions; K e Is with F,T e ,W,COP,E,T s ,T a The quantity related to the parameters can be specifically expressed by functions as follows:

[0047] K e =f(F,T e ,W,COP,E,T s ,T a )

[0048] Q e '=K e Q e

[0049] Where Q e It is the water flow rate when the electric regulating valve Ⅱ21 is fully opened.

[0050] Specifically, the heating return water flow Q flowing into the temperature-raising efficiency heat exchanger 7 is e 'As shown below:

[0051]

[0052] The T a When the temperature is higher than -10℃, the electric regulating valve Ⅰ22 is fully opened, otherwise it is closed.

[0053] Furthermore, when heating in a low-temperature environment, as the ambient temperature decreases, the evaporation temperature decreases, the defrosting frequency of the evaporator increases, the suction volume ratio increases, the heat absorption of the evaporator decreases, and the compression ratio becomes larger, resulting in a decrease in unit heating capacity, an increase in unit power consumption, and a decrease in energy efficiency. The opening of the electric regulating valve Ⅱ21 is controlled by the temperature increase efficiency criterion (determining whether the CO2 working medium at the front end of the evaporator 4 inlet needs to be heated and increased) to make the heating return water flow into the temperature increase efficiency heat exchanger 7, so that the heating return water can moderately heat the CO2 working medium at the front end of the evaporator 4 inlet. On the one hand, the low-grade heat of the heating return water can be used to increase the evaporation temperature and evaporation pressure of the evaporator without consuming additional electricity. On the other hand, after the evaporation temperature and evaporation pressure increase, the surface temperature of the fin of the evaporator 4 increases accordingly, thereby achieving the effect of slowing down the frosting on the evaporator coil surface, reducing the defrosting frequency and extending the system operation time; at the same time, after the evaporation temperature increases, the system heating coefficient and heating power increase accordingly.

[0054] Furthermore, during the actual operation process, the response surface method (RSM) is used to optimize the heating return water flow rate flowing into the warming efficiency heat exchanger 7 and the stable transcritical cycle heat exchanger 15, and the optimized flow rate is used as the optimal heating return water flow rate flowing into the warming efficiency heat exchanger 7 and the stable transcritical cycle heat exchanger 15.

[0055] Furthermore, the temperature-raising and efficiency-enhancing heat exchanger 7 is respectively composed of a temperature-raising and efficiency-enhancing heat exchanger CO2 working medium heat exchange pipe 8, a hot water spray port 9 at the upper end of the temperature-raising and efficiency-enhancing heat exchanger, and a hot water outlet 10 at the lower end of the temperature-raising and efficiency-enhancing heat exchanger; the temperature-raising and efficiency-enhancing heat exchanger CO2 working medium heat exchange pipe 8 adopts a three-dimensional internal and external rib form heat exchange pipe to enhance heat exchange, and the heating return water is sprayed downward from the hot water spray port 9 at the upper end of the temperature-raising and efficiency-enhancing heat exchanger (although the hot water spray port 9 at the upper end of the temperature-raising and efficiency-enhancing heat exchanger and the hot water outlet 10 at the lower end of the temperature-raising and efficiency-enhancing heat exchanger are in the Figure 1 The positions in the figure are below and above respectively, but in actual application they are respectively at the upper and lower ends of the temperature-increasing and efficiency-enhancing heat exchanger. Figure 1 The figure is only drawn for the convenience of drawing and does not limit the position), and the CO2 working medium flows out from the hot water outlet 10 at the lower end of the temperature-raising and efficiency-enhancing heat exchanger, and the CO2 working medium and the heating return water perform reverse cross-flow heat exchange; this temperature-raising and efficiency-enhancing heat exchanger 7 not only has good heat exchange performance, but also can prevent the hot water from freezing inside the heat exchanger; the structure of the stable transcritical cycle heat exchanger 15 is the same as that of the temperature-raising and efficiency-enhancing heat exchanger 7, and is respectively composed of a stable transcritical cycle heat exchanger CO2 working medium heat exchange tube 16, a hot water spray port 17 at the upper end of the stable transcritical cycle heat exchanger, and a hot water outlet 18 at the lower end of the stable transcritical cycle heat exchanger. The working principles of the two are also the same, so the heat exchanger also has good heat exchange performance and anti-freezing function.

[0056] The temperature-raising and efficiency-enhancing heat exchanger 7 and the stable transcritical cycle heat exchanger 15 adopt a structure of three-dimensional inner and outer rib heat exchange tubes with upper end spray cross-flow heat exchange, which also has the advantage of cost saving, because the use of antifreeze for antifreeze not only affects the heat exchange performance, but is also expensive.

[0057] Furthermore, in order to ensure thermal comfort at the heating end, the heating return water temperature increases with the decrease in ambient temperature. Excessive heating return water temperature not only reduces the heat release of the air cooler but also increases the throttling loss. Therefore, the heating return water with higher water temperature exchanges heat with the CO2 working medium of the warming efficiency heat exchanger 7 and the stable transcritical cycle heat exchanger 15, and the air cooler inlet water temperature is reduced, which is conducive to solving the problem of the high heating return water temperature causing the heating capacity to decrease in low temperature environment. Specifically, after the air cooler inlet water temperature is lowered, countercurrent heat exchange is carried out with the air cooler CO2 working medium, and the outlet specific enthalpy of the air cooler CO2 working medium is greatly reduced. The heat exchange efficiency between the CO2 working medium and the low-temperature heating return water in the air cooler is improved, thereby increasing the heating capacity of the air cooler. After the CO2 working medium is fully condensed in the air cooler, the irreversible throttling loss in the throttle valve 3 can be reduced. Finally, the heating capacity and heating performance coefficient of the system are improved, thereby ensuring the stable and efficient operation of the CO2 air source heat pump heating under low temperature conditions.

[0058] Furthermore, a CO2 air source heat pump stable transcritical circulation system for heating includes the following main components: a compressor 1, an air cooler 2, a throttle valve 3, an evaporator 4, a temperature-raising efficiency-enhancing heat exchanger 7, a stable transcritical circulation heat exchanger 15, an electric regulating valve I 22, an electric regulating valve II 21, an electric regulating valve III 20, a water distributor 23, a controller 25, a water collector 29, etc. The compressor 1, the air cooler 2, the throttle valve 3, the temperature-raising efficiency-enhancing heat exchanger 7, the evaporator 4 and the stable transcritical circulation heat exchanger 15 are connected in sequence through the CO2 working medium circulation pipeline 5; the heating return water is connected to the inlet of the water distributor 23 through the return water main pipe 24, and the water distributor 23 divides the heating return water into three branches, namely branch I 27, branch II 11 and branch III 13, and the water distributor 23 is connected to the water collector 29, The temperature-increasing efficiency heat exchanger 7 and the stable transcritical cycle heat exchanger 15 are connected through branch I 27, branch II 11 and branch III 13 respectively. The water collector 29 is connected to the temperature-increasing efficiency heat exchanger 7 and the stable transcritical cycle heat exchanger 15 through branch V 28 and branch IV 19 respectively. After the water collector 29 merges the return water of branch IV 19, branch V 28 and branch I 27, the water outlet of the water collector 29 is connected to the gas outlet through branch VI 30. The water inlet of the air cooler 2 is connected, and the heating return water is heated by the air cooler 2 and then flows out through the water supply main 31 to provide heat to the user; the electric regulating valve I 22, the electric regulating valve II 21, and the electric regulating valve III 20 are respectively installed on the branch I 27, the branch II 11, and the branch III 13, and the electric regulating valve I 22, the electric regulating valve II 21, and the electric regulating valve III 20 are connected to the controller 25 through a control circuit; the branch I 27, the branch II 11, and the branch III 13 are respectively equipped with flow sensors I 26, flow sensors II 12, and flow sensors III 14, and the flow sensors I 26, flow sensors II 12, and flow sensors III 14 are also connected to the controller 25 and used in combination with the electric regulating valves I 22, the electric regulating valve II 21, and the electric regulating valve III 20 to control and detect the heating return water flow of these three branches;

[0059] The compressor 1 inlet, compressor 1 outlet, CO2 working medium outlet of air cooler 2, throttle valve 3 outlet, evaporator 4 inlet, and evaporator 4 outlet are all equipped with pressure sensors and temperature sensors, the water separator 23 inlet, the temperature increasing efficiency heat exchanger 7 outlet, the stable transcritical cycle heat exchanger 15 outlet, the air cooler 2 water inlet, and the air cooler 2 hot water outlet are all equipped with temperature sensors, the air cooler 2 hot water outlet and the air cooler 2 CO2 working medium outlet are both equipped with flow sensors, a temperature and humidity sensor is installed at the air inlet of evaporator 4, and smart meters are installed on the compressor and evaporator to measure the input power. The flow sensor, temperature sensor, pressure sensor, temperature and humidity sensor and smart meter are all connected to the controller 25.

[0060] Furthermore, the controller 25 adopts a PLC controller, which is composed of a CPU module (including a CPU chip and a memory), an input module, an output module and a programming device module; the input module can have multiple inputs and has 22 analog inputs: compressor suction temperature, compressor suction pressure, compressor exhaust temperature, compressor exhaust pressure, evaporator inlet temperature, evaporator inlet pressure, evaporator outlet temperature, evaporator outlet pressure, air cooler CO2 working medium outlet temperature, air cooler CO2 working medium outlet pressure, air cooler CO2 working medium outlet flow, throttle valve outlet temperature, throttle valve outlet pressure, heating return water temperature, ambient temperature, air cooler water inlet temperature, The program module programs the temperature-elevating efficiency criterion, the transcritical cycle criterion, and the particle swarm algorithm. The CPU module receives and stores the input control variables, performs the particle swarm algorithm calculations with the multi-objective function to optimize the multi-objective function, and then outputs two standard voltage signals for controlling the openings of the electric control valves II21 and III20.

[0061] The working principle of the present invention is:

[0062] Water distributor 23 divides the heating return water into three branches: branch I 27, branch II 11, and branch III 13. Under low-temperature operating conditions, as the ambient temperature decreases, the compressor exhaust temperature and pressure fall below critical values, preventing the CO2 working medium from undergoing a transcritical thermodynamic cycle. Based on the stable transcritical cycle criterion, the heating return water is transported via branch III 13 to the stable transcritical cycle heat exchanger 15 to moderately heat the CO2 working medium before the compressor 1 inlet, thereby increasing the temperature and specific enthalpy of the CO2 working medium at the compressor inlet, ensuring the CO2 working medium undergoes a transcritical thermodynamic cycle. This ensures efficient and stable operation of the CO2 air-source heat pump heating system under low-temperature conditions. Under low-temperature conditions, as the ambient temperature decreases, the evaporation temperature decreases, the evaporator defrost frequency increases, the suction volume ratio increases, and the evaporator heat absorption decreases. Based on the heating efficiency criterion, the heating return water is transported via branch II 11 to the heating efficiency heat exchanger 7 to heat the CO2 working medium before the evaporator inlet on demand. This increases the evaporation temperature, heating operation time, and system heating performance without consuming additional energy or compromising indoor thermal comfort. Manifold 29 combines the return water from branch IV 19, branch V 28, and branch I 27, which then flows into air cooler 2. The heating return water is heated by the CO2 working medium in air cooler 2 and then flows out through the water supply main 31 to provide heat to users. After the heating return water exchanges heat with the CO2 working medium in the stable transcritical cycle heat exchanger 15 and the temperature-raising efficiency heat exchanger 7, the water temperature at the air cooler inlet is reduced, which enhances the heat exchange efficiency between the air cooler and the heating return water, thereby increasing the heating capacity. After the CO2 working medium is fully condensed in the air cooler, the irreversible throttling loss of the CO2 working medium in the throttling process can be reduced, and the heating capacity and heating performance coefficient of the system under low temperature conditions are further improved.

[0063] The specific embodiments of the present invention are described in detail above with reference to the accompanying drawings. However, the present invention is not limited to the above embodiments. Various changes can be made within the knowledge of ordinary technicians in this field without departing from the scope of the present invention.

Claims

1. A method for stabilizing transcritical circulation of a CO2 air source heat pump for heating, characterized by: The method adopts a CO2 air source heat pump stable transcritical circulation system for heating, which includes: The invention comprises a compressor (1), an air cooler (2), a throttle valve (3), an evaporator (4), a temperature-raising and efficiency-enhancing heat exchanger (7), a stable transcritical cycle heat exchanger (15), an electric regulating valve I (22), an electric regulating valve II (21), an electric regulating valve III (20), a water distributor (23), a controller (25), and a water collector (29); the compressor (1), the air cooler (2), the throttle valve (3), the temperature-raising and efficiency-enhancing heat exchanger (7), the evaporator (4), and the stable transcritical cycle heat exchanger (15) are connected in sequence through a CO2 process. The heating return water is connected to the water distributor (23) through the return water main (24). The water distributor (23) divides the heating return water into three branches, namely branch I (27), branch II (11) and branch III (13). The water distributor (23) is connected to the water collector (29), the temperature-increasing heat exchanger (7) and the stable transcritical cycle heat exchanger (15) through branch I (27), branch II (11) and branch III (13). The water collector (29) is connected to the temperature-increasing heat exchanger (7), the stable transcritical cycle heat exchanger (15) through branch I (27), branch II (11) and branch III (13). The fixed-span critical cycle heat exchanger (15) is connected through branch V (28) and branch IV (19) respectively. After the water collector (29) collects the return water of branch IV (19) and branch V (28) and branch I (27), the water outlet of the water collector (29) is connected to the water inlet of the air cooler (2) through branch VI (30). The heating return water is heated by the air cooler (2) and flows out through the water supply main (31) to provide heat to the user; the electric regulating valve I (22), the electric regulating valve II (21) and the electric regulating valve III (20) are respectively installed on branch I ( On branch line 27, branch line II (11) and branch line III (13), electric regulating valve I (22), electric regulating valve II (21) and electric regulating valve III (20) are connected to the controller (25) through a control circuit; branch line I (27), branch line II (11) and branch line III (13) are respectively equipped with flow sensor I (26), flow sensor II (12) and flow sensor III (14), and flow sensor I (26), flow sensor II (12) and flow sensor III (14) are also connected to the controller (25); A stable transcritical cycle heat exchanger (15) is provided at the front end of the inlet of the compressor (1), and heating return water is transported to the stable transcritical cycle heat exchanger (15) via the branch line III (13); a controller (25) controls the opening of the electric regulating valve III (20) according to the stable transcritical cycle criterion to adjust the flow rate of the heating return water flowing into the stable transcritical cycle heat exchanger (15) as needed; Real-time acquisition of compressor (1) suction temperature T i , suction pressure P i , compressor exhaust temperature T c , exhaust pressure P c , heating power W, performance coefficient COP, compression ratio E, heating return water temperature T s , considering the changes of these parameters with the ambient temperature T under low temperature conditions a The changes during the descent and the compressor exhaust temperature T c and exhaust pressure P c Whether it is lower than the CO2 critical value is used to establish a stable transcritical cycle criterion; using the particle swarm algorithm, the heating power W, performance coefficient COP, and compression ratio E are used as the control targets of the stable transcritical cycle criterion, and the weights m1, m2, and m3 are taken respectively. The opening K of the electric control valve III (20) is determined by the optimal multi-objective function {m1W, m2COP, m3E}. c , thereby determining the heating return water flow Q flowing into the stable transcritical cycle heat exchanger (15) c '; A temperature-raising and efficiency-enhancing heat exchanger (7) is provided at the front end of the inlet of the evaporator (4), and the heating return water is then transported to the temperature-raising and efficiency-enhancing heat exchanger (7) via the branch line II (11); the controller (25) controls the opening of the electric regulating valve II (21) according to the temperature-raising and efficiency-enhancing criterion to adjust the flow rate of the heating return water flowing into the temperature-raising and efficiency-enhancing heat exchanger (7) as needed; Real-time acquisition of the frost frequency F and evaporation temperature T of the evaporator (4) e , heating power W, coefficient of performance COP, compression ratio E and heating return water temperature T s , considering the changes of these parameters with the ambient temperature T under low temperature conditions a The temperature increase efficiency criterion is established by the change of the temperature when the temperature decreases; the particle swarm algorithm is used to take the heating power W, the performance coefficient COP, and the compression ratio E as the control targets of the temperature increase efficiency criterion, and the weights m4, m5, and m6 are taken respectively, and the opening K of the electric control valve II (21) is determined by the optimal multi-objective function {m4W, m5COP, m6E}. e , thereby determining the required heating return water flow Q flowing into the temperature-raising and efficiency-enhancing heat exchanger (7) e '.

2. The method for stabilizing transcritical circulation of a CO2 air source heat pump for heating according to claim 1, characterized in that: During actual operation, the response surface method (RSM) is used to optimize the heating return water flow rates flowing into the temperature-raising efficiency heat exchanger (7) and the stable transcritical cycle heat exchanger (15), and the optimized flow rates are used as the optimal heating return water flow rates flowing into the temperature-raising efficiency heat exchanger (7) and the stable transcritical cycle heat exchanger (15).

3. The method for stabilizing transcritical circulation of a CO2 air source heat pump for heating according to claim 1, characterized in that: The temperature-raising and efficiency-enhancing heat exchanger (7) is respectively composed of a temperature-raising and efficiency-enhancing heat exchanger CO2 working medium heat exchange pipe (8), a hot water spray port (9) at the upper end of the temperature-raising and efficiency-enhancing heat exchanger, and a hot water outlet (10) at the lower end of the temperature-raising and efficiency-enhancing heat exchanger; the temperature-raising and efficiency-enhancing heat exchanger CO2 working medium heat exchange pipe (8) adopts a three-dimensional internal and external rib form heat exchange pipe to enhance heat exchange, and the heating return water is sprayed downward from the hot water spray port (9) at the upper end of the temperature-raising and efficiency-enhancing heat exchanger and flows out from the hot water outlet (10) at the lower end of the temperature-raising and efficiency-enhancing heat exchanger, and the CO2 working medium and the heating return water perform reverse cross-flow heat exchange; the structure of the stable transcritical circulation heat exchanger (15) is the same as that of the temperature-raising and efficiency-enhancing heat exchanger (7), and is respectively composed of a stable transcritical circulation heat exchanger CO2 working medium heat exchange pipe (16), a hot water spray port (17) at the upper end of the stable transcritical circulation heat exchanger, and a hot water outlet (18) at the lower end of the stable transcritical circulation heat exchanger.

4. The method for stabilizing transcritical circulation of a CO2 air source heat pump for heating according to claim 1, characterized in that: The controller (25) adopts a PLC controller, including a CPU module, an input module, an output module and a programming device module. The CPU module includes a CPU chip and a memory; the input module can input multiple channels and has 22 analog inputs: compressor suction temperature, compressor suction pressure, compressor exhaust temperature, compressor exhaust pressure, evaporator inlet temperature, evaporator inlet pressure, evaporator outlet temperature, evaporator outlet pressure, air cooler CO2 working medium outlet temperature, air cooler CO2 working medium outlet pressure, air cooler CO2 working medium outlet flow, throttle valve outlet temperature, throttle valve outlet pressure, heating return water temperature, ambient temperature, air cooler water inlet temperature, air cooler Hot water outlet temperature, hot water outlet flow of air cooler, compressor input power, evaporator input power, outlet temperature of heating efficiency heat exchanger, outlet temperature of stable transcritical cycle heat exchanger; the analog output of the output module is two standard voltage signals for controlling the opening of electric control valve II (21) and the opening of electric control valve III (20); the heating efficiency criterion, stable transcritical cycle criterion and particle swarm algorithm are programmed in the programming device module; the CPU module receives and stores the input control variables, completes the particle swarm algorithm operation with the optimal multi-objective function, and then outputs two standard voltage signals for controlling the opening of electric control valve II (21) and the opening of electric control valve III (20).

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