Heat Transfer Performance Of An Integrated Solar-air Source Heat Pump Evaporator

China’s primary energy reserves and per capita possession are far below the world’s average,and the resource utilization rate is low.However,China’s solar and air energy reserves are abundant and the degree of availability is high.There are certain problems with the use of air or solar energy alone.For instance,the heat pump’s heating efficiency decreases when the condensing temperature is high or the ambient temperature is low,and the evaporator is prone to frosting in winter,the solar energy has low energy density,unstable energy intensity,etc.which are still important problems to be solved.Therefore,the application of solar energy to an air source heat pump has a positive effect on improving the energy efficiency of the air energy and the solar energy.This study investigated the research status of solar air energy integrated heat pump in domestic and abroad,and designed a dual heat source integrated heat pump system using solar energy and air energy as the heat sources.The evaporator coil consists of three rows of tubes.Out of these three rows,one is of hot water tube,while the other two are of refrigerant tubes.The hot water tube is installed on the upwind side of the refrigerant tube,whereas the air flowing through the evaporator is first heated by hot water tube.The heated air then exchanges heat with the refrigerant coil.Experiments and simulations were carried out on the heat transfer performance of the evaporator and the energy efficiency of the heat pump system.The minimum heat transfer unit model of the integrated solar air source heat pump evaporator was established,and the feasibility of the simulation was verified.The factors affecting the evaporator structure and heat pump energy efficiency were further analyzed.The results showed that: 1)Evaporator’s hot water supply can effectively increase the evaporator’s heat transfer performance and heat pump’s COP,and when the average temperature of the evaporator water supply is higher than the ambient air temperature,the refrigerant evaporation temperature can be effectively increased to prevent the evaporator coil from frosting.When the evaporator’s water temperature increased from 14.6 °C to 39.5 °C,the COP of heat pump gradually increased from 3.87 to 4.45.2)The simulation study of the minimum heat transfer unit model of the evaporator has little error between the simulation results and the experimental results.The model can be used for parameter research.3)Comparing the refrigerant-water-refrigerant type evaporator with the water-refrigerant-refrigerant type evaporator,the former is more capable of gaining heat from low temperature water than the latter,and is more conducive to the comprehensive utilization of air and solar energy by heat pump in the cold season.Additionally,the refrigerant-water-refrigerant type evaporator has better anti-frosting capability under lower water temperatures.