Study On Performance Of Active Anti-frosting Air Source Heat Pump

Air source heat pump has the characteristics of high efficiency,energy saving and dual-use of cooling and heating,which is widely used in heating,air conditioning and other fields.But in winter heating operation,there will be frosting phenomenon,the growth of frost layer leads to the deterioration of heat transfer effect and the attenuation of heating performance,which seriously restricts the application and development of air source heat pump.The current defrosting methods are widely used in reverse cycle defrosting and hot gas bypass defrosting.However,in unfavorable winter conditions,the operation of these two defrosting methods is unstable,the defrosting efficiency is low,and the heating effect and heating time are difficult to guarantee.In order to slow down the frosting phenomenon of air source heat pump in low temperature areas and ensure the efficient and stable operation of air source heat pump units,it is of great significance to explore a reasonable and effective anti-frosting method to improve the heating performance of air source heat pump units in low temperature areas and the promotion of air source heat pump technology.Aiming at the problem that air source heat pump is prone to frosting in low temperature environment,a new method of active anti-frosting with electric auxiliary heating at the evaporator inlet is proposed based on eliminating the harm of frosting fundamentally,and constructs an active anti-frosting air source heat pump experimental device,the thermal performance of the method is analyzed through numerical simulation and experimental research,and the effect of suppressing frosting and the heating performance under low temperature environment are analyzed.The main research contents and conclusions are as follows:(1)Based on the analysis of the defects of traditional defrosting methods and frosting formation mechanism,an active anti-frosting air source heat pump system is proposed.The system consists of refrigerant electric auxiliary heating device,compressor,evaporator,condenser,throttle valve and other main components.The working principle and thermodynamic cycle process of the system are analyzed,and the thermodynamic calculation of the system is carried out according to the pressure enthalpy diagram.(2)According to the thermodynamic cycle principle of heat pump,the steady-state mathematical model of active anti-frosting air source heat pump system is established.The mathematical models of compressor,evaporator,condenser,throttle valve and electric auxiliary heating device are established respectively.According to the coupling relationship between certain parameters,a complete heat pump system model is formed.Using MATLAB software programming,simulation study of its low-temperature heating characteristics,and the influence of outdoor environment temperature and the temperature of the outlet water on the condenser side on the heating performance of the system was calculated and analyzed,and compared with ordinary air source heat pumps.The results show that when the temperature of the refrigerant at the inlet of the evaporator is appropriately increased by electric heating,the system heating capacity increases significantly,and the compressor discharge temperature decreases significantly.The heating capacity of the system is better than that of ordinary air source heat pumps,but the COP of the system is lower.With the decrease of environment temperature,the heating capacity,COP and power consumption of the active anti-frosting heat pump system decrease,while the compressor discharge temperature increases;when the outlet water temperature increases,the heating capacity and COP of the system decrease,while the power consumption and discharge temperature increase.(3)The experimental platform of active anti-frosting air source heat pump system was built,and the adjustable electric auxiliary heat was used to heat the refrigerant temperature at the inlet of evaporator.The defrosting and low temperature heating performance of active anti-frosting air source heat pump system was tested and analyzed.The experimental test results show that the calculated results based on the established mathematical model are in good agreement with the experimental results.In addition,the use of electric auxiliary heat to increase the temperature of the refrigerant at the inlet of the evaporator can effectively anti-frosting on the surface of the evaporator fin tube.The defrosting interval is extended by about 22 minutes on average,and the defrosting frequency is reduced.At the same time,the heating capacity of the system increased significantly,but the cop of the heating system decreased,so the electric auxiliary heat should not be too large.Considering the heating capacity and COP of the system,when the environment temperature is-15℃and the outlet water temperature is 55℃,the suitable electric auxiliary heat is500～750W.(4)Using the orthogonal test method,the environmental dry bulb temperature,condenser side outlet water temperature and electric auxiliary heat are determined as the influencing factors,and the heating capacity and COP of heating were determined as evaluation indexes.The low-temperature heating performance of active anti-frosting air source heat pump system was tested and analyzed,and the main operating parameters of active anti-frosting air source heat pump system under low-temperature conditions were optimized.