An experimental study on the effects of downwards flowing of melted frost over a vertical multi-circuit outdoor coil in an air source heat pump on defrosting performance during reverse cycle defrosting

A previous related study has indicated that for an air source heat pump (ASHP) unit having a vertically installed multi-circuit outdoor coil, during reverse cycle defrosting, downwards flowing of melted frost over the outdoor coil surface could affect the defrosting performance, without however giving a detailed quantitative analysis. Therefore an experimental study has been carried out and the study results are reported in this paper. Firstly, a detailed description of a specially built experimental ASHP unit having a vertical multi-circuit outdoor coil is presented. This is followed by reporting the experimental results. Finally, a detailed quantitative analysis is presented. The experimental results and the corresponding analysis demonstrated that allowing downwards flowing of the melted frost over a vertical multi-circuit outdoor coil would result in a longer defrosting duration and more energy consumption. The study results also suggested that the use of water collecting trays can help mitigate these negative impacts on defrosting performance.