An experimental study on the operating performance of a novel reverse-cycle hot gas defrosting method for air source heat pumps

This paper reports on an experimental study on the operating performance for a novel reverse-cycle hot gas defrosting method for air source heat pumps (ASHPs). Firstly, a description of both an experimental prototype ASHP unit where the novel reverse-cycle hot gas defrosting method may be realized, and its operating modes are presented. This is followed by reporting an experimental set up for testing the defrosting performance of the prototype ASHP unit using the novel thermal energy storage (TES) based reverse-cycle hot gas defrosting method. Finally, experimental results are presented and discussed. The experimental results suggested that the use of the novel reverse-cycle hot gas defrosting method for the experimental ASHP unit was able to help shorten the defrosting time by ∼3 min or 38%, and minimize the risk of shutting down the ASHP unit due to low suction pressure through increasing the compressor’s suction pressure by about 200 kPa, when compared to the use of the traditional standard reverse-cycle hot gas defrosting method. In addition, when the TES based reverse-cycle hot gas defrosting method was used, the mean indoor coil surface temperature during defrosting was about 25 K higher than that when the traditional standard reverse-cycle hot gas defrosting method was used. These results suggested that as compared to the use of the traditional standard reverse-cycle hot gas defrosting method, the use of the novel TES based defrosting method would enable a quicker space heating resumption, impacting less on indoor thermal environment due to defrosting. Hence, the novel TES based defrosting method was proven to be effective in reducing the current problems in ASHPs using standard reverse-cycle hot gas defrosting method, such as a longer defrosting time and a poor system reliability.