Simulation And Performance Analysis Of Air Source Heat Pump System With A Device For Frost Prevention And Defrosting

There is frosting phenomenon for the operation of air source heat pumps during in winter,so the system performance declines and the heating effect can not meet the requirements of indoor thermal comfort.In this paper,the operating characteristics of common air source heat pump(ASHP)and various air source heat pump with a device for frost prevention and defrosting are compared and analyzed.The air source heat pump with different devices for frost prevention and defrosting has been studied in this paper in order to improve the operating efficiency of the systems under the premise of ensuring the heating effect.Therefore,this paper utilizes the distributed parameter method to establish a modular mathem atical model of these systems,then realizes the dynamic simulation and programming of the model through C language.The formula of dynamic minimum supplementary heat of defrosting of ASHP is established based on the ideal minimum supplementary heat of defrosting and dimensionless defrosting rate model.The model has been verified according to the existing experimental data,and the operation status of four ASHP systems under the frosting condition has been analyzed.Simultaneously,the influence of differe nt devices(traditional electricity auxiliary heat,front type,rear type and leap-over type)on the system characteristics are discussed.The results show that under the same operating condition,the rear type system has the best performance,but the frosting is the highest.Un der the influence of frosting,the air volume of the four systems decreased significantly after 40 minutes of operation,and the defrosting prevention quantity first decreased and then increased with the change of time.The heat transfer coefficient of evaporator of the rear type and the leap-over type is greater than that of the front type and the non-defrost type.With the operation of the system,the evaporator heat transfer coefficient of the four kinds of systems decreases gradually.When the total thi ckness of the evaporator frost layer on both sides of the fin reaches 40% of the fin spacing,the tube segment here cannot exchange heat because of the frost layer blocking the air passage.The influence of different environmental parameters on the evapora tor is also discussed.The results show that the higher the initial temperature and relative humidity,the better the heat transfer performance of the evaporator.Relative humidity is certain,the higher the temperature,the greater the evaporator heat tra nsfer coefficient.The air temperature is constant,and the heat transfer coefficient increases with the increase of humidity.The lower the humidity,the more evenly the frost layer is distributed.Finally,this paper discusses the influence of different environmental conditions on the air source heat pump system.The study shows that when the relative humidity is constant,the increase of air temperature at the initial moment will lead to the increase of evaporation temperature and COP of the system.Afte r 40 minutes of operation,the performance degradation of the three systems decreases first and then increases with the increase of air temperature.When the air temperature is constant,the system performance parameters increase with the increase of relat ive humidity at the initial time.After 40 minutes of operation,the rear-mounted system works efficiently and performs best at 70% relative humidity.