Greywater source heat pump system for heating purposes in a newly built Dutch dwelling

Around 15% of the thermal energy delivered to buildings is lost through the drain and ends up warming wastewater in the sewer system. A promising solution in reducing the energy consumption of buildings is to recuperate heat from wastewater and using it to produce space heating & domestic hot water by means of heat pumps. Wastewater source heat pumps (WWSHPs) have been largely discussed in existing literature, although a lack of scientific studies in small-scale applications such as detached dwelling has been noted. The purpose of this study is to design a wastewater source heat pump system able to satisfy both space heating & domestic hot water demands. The present work proposed a fully greywater source heat pump and a greywater-air dual source heat pump for heating purposes in a newly built Dutch dwelling. Ten different configurations have been modelled, evaluated, and finally compared to a fully air source heat pump. More specifically, the yearly performances were evaluated hour-by-hour taking into account the climate data from the Dutch reference year with the aid of CoolPack and Microsoft Excel. Methods for the COP enhancement have been proposed, the effects of the variations in size of the greywater storage tank have been evaluated, and the optimal control strategy has been found. Results in seasonal COP obtained from the fully greywater source heat pump systems are lower than the ones obtained from fully air heat pump systems. Instead, greywater-air dual source heat pumps perform better than fully air source heat pumps. On the other hand, the introduction of a secondary heat source would increase the cost and the complexity of the system. Nevertheless, several systems present, albeit slight, saving in energy consumption. In particular, up to 1.10 GJ per year can be saved developing this kind of heat pump system.