Modeling and analyzing of airside heat exchanger under frosting in air source heat pump water chiller/heater

When an air source heat pump water heater/chiller operates under low ambient temperature as a heating source in winter, the formation of frost on the surface of its airside heat exchanger easily leads to the degradation of heating capacity or even the shutdown of a unit. In order to solve the problem, a model of airside heat exchanger under frosting in an ASHPWHC is developed and its operating characteristics are analyzed to improve its reliability. The distributed parameters modeling was used to develop the steady mathematical model, which concerns the characteristics of heat exchange and performance of frosting. According to the solution of the model developed, the frosting under different operating conditions was analyzed and the main factors which have impact on frosting were obtained. The results indicate that the frosting accumulation obviously increases with the increase of relative humidity and varies with different rows of pipes along the direction of airflow. It proves that the model and analyzing results are very useful to optimize the structural layout and improve the operating performance of ASHPWHC units.