Numerical investigation on the defrosting performance of an ASHP unit with frost evenly accumulated on the surface of its multi-circuit outdoor coil

Air source heat pump (ASHP) units have found wide applications due to their distinguished advantages of high energy performance and system operation safety in recent decades. Governmental subsidy policies also promote their development due to the environmental friendly performance. For an ASHP unit, frost accumulated on its outdoor coil is an undesired and unavoidable phenomenon, which always results in a lower operation efficiency, or even an unexpected suddenly shutdown. Although this fundamental problem was widely investigated, few of models were developed around reverse cycle defrosting due to its complex process involving spatial and time variations in limited time. Consequently, based on a previously developed and validated semi-empirical defrosting model, the frost was further considered as evenly accumulated on the surface of multi-circuit outdoor coil. Firstly, the model and assumptions were shortly introduced. This is followed by the equations used during different physical stages of defrosting. Then, the simulation results w ere shown, which are parameters hardly possible to measure by experiment. A short conclusion is finally given. Contributions of this work could be used to optimize the intelligent control strategy of an ASHP unit, as well as saving energy for buildings.