Study On The Defrosting Of The Air Source Heat Pumps With Large Heat Exchanger

Air source heat pump(ASHP)is a large-scale promotion as a highly efficient way of heating.However,at low temperature condition,the frosting on the surface of the heat exchanger will greatly reduce the thermal efficiency of the heat pump,which will seriously affect the reliability of the heat pump.Recently,with the continuously increasing requirement of the heating capacity,the area of the outdoor heat exchanger is also increasing,so does the difficulty of defrosting.There are few researches on the work process of large heat exchanger in the defrosting operation,especially with the increasing of the heat exchanger;the study on the longitudinal temperature variation of the heat exchanger is much fewer.This paper makes a concrete analysis of various factors affecting frosting,and the design for the retard frost accumulation based on the wind field and structure of large heat exchangers.Meanwhile,the effects of air flow rate,temperature,humidity and other factors in the frosting process of outdoor heat exchanger were compared.Firstly,The most widely used reverse cycle defrosting operation is studied.Through the experiment,the trend of the key temperature points in the defrosting process was recorded.Secondly,the effect of the starting conditions on the defrosting effect,the trend of each branch's temperature during defrosting process,and the determination of the defrost exit conditions were tested and compared.In the defrosting process,the temperature change of the inner chamber heat exchanger and the control function of improving the indoor comfort were tested.Finally,the incompleteness of large area heat exchanger's defrosting is analyzed,based on the raise of the temperature of outdoor heat exchanger and the change of the direction of ice water mixture,several corresponding solutions are proposed.According to the analysis of the practical application,the optimal method is used to improve the existing defrosting method,which has been confirmed by experiments.The improvement of defrosting effect of large heat exchanger in low temperature condition has been realized,ensuring the efficiency of the heat pump unit in extreme conditions,and improved the reliability of heat pump unit.