Research On Performance Of Air Source Heat Pump System For Alternate Defrosting With Supercooled Heat

In recent years,the air source heat pump market has developed rapidly in the context of the steady development of the Chinese economy,the government’s continued efforts to promote energy conservation and emission reduction,the development of a low-carbon economy,and the transformation of heat sources.However,the frosting and high-efficiency defrosting of the air source heat pump in the low temperature environment heating operation are the key problems to be solved urgently in its application.The timely defrosting of the air source heat pump unit is the guarantee for the reliable and efficient operation of the unit.Aiming at the problems of high energy consumption,poor stability and low comprehensive performance of the existing defrosting technology,an air source heat pump system with alternately defrosting double evaporators using supercooled heat of liquid refrigerant was proposed.The basic principle is that the two sets of evaporators are operated in sequence and frosted,and the evaporator in the defrosting state is defrosted by the heat mixed by the condenser outlet high temperature and high pressure refrigerant liquid and the bypass compressor exhaust gas.The other set of evaporators continues to function as the original to ensure that the system maintains a stable heating operation while defrosting.First,the thermal process of the double-evaporator liquid refrigerant alternately defrosting air source heat pump system is calculated and analyzed.The calculation results show that in this system,the supercooling and alternating defrosting method can effectively get out of the frost layer on the surface of the evaporator,to achieve efficient and stable operation of the system.Secondly,according to the relevant design requirements of the air source heat pump hot and cold water unit,the various components of the heat pump hot water system under design conditions are selected.Modeling methods such as zone concentrated parameters and distributed parameters are used to establish simulation mathematical models for compressors,heat exchangers,and throttle valves in the system;through the conservation of mass,momentum,and energy,each component model is coupled to establish a double evaporator The system simulation dynamic model of frosting and defrosting of the air source heat pump hot water system,the simulation calculation program is compiled in the MATLAB language environment,and the accuracy of the built model was verified by the relevant experimental data.Finally,using the system simulation mathematical model,the system’s performance parameters such as condensing pressure,evaporating pressure,heating capacity,power consumption and COP are simulated under the system’s heating and frosting and defrosting operation modes.The simulation model is used to calculate the change of the overall performance of the system under the condition of variable inlet air parameters.The results show that,when the inlet air temperature is between5℃and 5℃,the inlet air humidity is between70%and 90%,and the inlet air volume is between 2000 m~3/h and 4000 m~3/h,the heating capacity of the system during the frosting phase of heating operation decreased by 12.8%～15.3%,and the COP decreased by 7.9%～8.9%;during the defrosting operation phase,the heating rate decreased by 4.37%～5%,the COP decreased by 2.87%～4.1%.Compared with the heating operation mode,the defrosting operation mode unit’s heating capacity decreases by 46.16%～46.52%.The system can still guarantee a certain amount of heat supply during the defrosting process,and the COP drop is small,and the system operation stability is well guaranteed.At the same time,the simulation model is used to calculate the change of the unit’s heating capacity during a complete operating cycle under different starting time intervals of the double evaporator.About 10min is a reasonable choice for this conclusion.