A semi-experimental method for evaluating frosting performance of air source heat pumps

Frosting has always been a crucial problem for air source heat pumps (ASHPs) operated in heating mode. Quantitative evaluation of frosting is of vital importance to the development of technologies against frosting. Although frosting maps have been developed in many studies, they are specific for unique systems. To evaluate the frosting performance of arbitrary system, a semi-experimental method, to depict frosting evaluation plot, was proposed in the present study. In the frosting evaluation plot, frosting region was clarified, and the frosting driving forces with the effect air temperature and relative humidity (RH) were evaluated, through theoretical calculation of Gibbs free energy change. After that, experiments were conducted to verify the frosting evaluation plot, and the results demonstrated the present method was feasible. In some experimental cases, the inlet segment of the heat exchanger escaped from frosting but the outlet segment frosted. As implementation of the semi-experimental method, the methodology was utilized to clarify the air temperature and RH ranges causing uneven frosting. In addition, the frosting evaluation plot with impact of air velocity was drawn. The results suggested that, increased air velocity restrained frosting, and reduced the chance of uneven frosting.