Since the temperature of shower drain water (SDW) is relatively high, lots of heat is wasted with the
discharge of SDW. Therefore, the recovery of this unutilized heat from SDW shows great potential in
improving the building energy efficiency. In this paper, a novel heat pump water heater assisted with
SDW for small single family was proposed, which could effectively recover the energy in domestic
SDW. To improve its performance, a shower waste heat extraction device (WHED) with water
pre-heated loops was designed. A prototype of the system was firstly set up, and then the system performances
under different conditions were experimented and discussed. The experimental results showed
that approximately 70% of energy could be saved using this novel heat pump water heater, compared
with the traditional electric water heater. Furthermore, the COP of the system could be improved observable
when using water pre-heated loops