Study On Frosting Characteristics Of Ultra-low Temperature Heat Pump Air Conditioning System For Pure Electric Bus

Due to the increasingly prominent energy crisis and environmental protection issues,the state has issued a series of policies to promote the development of new energy vehicles.People are demanding more and more comfort.Air conditioning has become an indispensable electrical appliance in people’s daily life.Air conditioning of heat pump bus is the most power-consuming component of auxiliary equipment of pure electric bus,which seriously affects the range of pure electric bus.The heat pump air conditioning system is easy to frost under low temperature and high humidity in winter.Frost will increase the heat resistance of heat exchanger and reduce the heat transfer coefficient,which will damage the heat transfer system seriously.The frost condition of heat pump air conditioning system of pure electric bus in winter is one of the main reasons affecting its promotion.Aiming at the frosting and defrosting of heat pump bus air conditioning system under the condition of low temperature and high humidity,based on the theory of quasi-secondary compression,an experimental platform was set up for experiment.By changing the outside environment temperature,relative humidity,compressor speed,air supply mode and fan air volume,the effects on frosting regularity and defrosting time were studied.Frosting experiments show that:(1)Under different outdoor ambient temperature(< 2℃),the frosting rate increases with the increase of outdoor ambient temperature,but when frosting is completed quickly,if the outdoor temperature is lower,the degree of heat transfer reduction of evaporator will be smaller,and the normal operation of the system will be longer.(2)Under the condition of different relative humidity,the frosting speed increases with the increase of relative humidity,and the frosting period of the heat exchanger outside the vehicle decreases.(3)Under the condition of different air volume of the outdoor fan,the frosting rate decreases with the increase of the air volume of the outdoor fan,and the larger the air volume,the longer the frosting period.(4)Heat transfer increases with the increase of compressor speed,which leads to a faster decrease of evaporator surface temperature,thus accelerating the frosting rate.(5)The method of supplementing air can effectively reduce the frosting rate and increase the frosting cycle.The frosting period of medium pressure air supplement is 14.3% higher than that of no air supplement,and that of low pressure air supplement is 25% higher than that of no air supplement.The defrosting experiment shows that the average condensation temperature of defrosting process can be increased by using reverse cycle defrosting mode,when the temperature of outside environment is higher,the relative humidity of outside environment is lower,the compressor speed is increased,and the air supplement system is adopted,so that the defrosting time is shortened and the defrosting efficiency is increased.The condensation temperature of low pressure air supplement is higher than that of non-air supplement vehicle heat exchanger,and the defrosting time is shortened by 12.9%.The condensation temperature of medium pressure air supplement vehicle heat exchanger is higher than that of non-air supplement vehicle heat exchanger,and the defrosting time is shortened by 22%.