An experimental setup for the analysis of an energy recovery system from wastewater for heat pumps in civil buildings

Despite its low enthalpy content, sewage water from civil buildings could represent an interesting source for energy saving, especially when heating and cooling is supplied by heat pumps. A complete prototype plant was realized to assess the characteristics and performance of heat recovery from civil wastewater, used as ancillary thermal supply to a heat pump heating system; during the experimental analysis, the wastewater discharge cycles estimated from data derived by the most common buildings typologies were applied. The warm water fluids were collected in a purposely-built tank-heat exchanger, which represents the thermal storage aimed at improving the heat pump performance. A dedicated software was created to manage the acquisition of thermal fluid dynamic variables of all hydraulic circuits. Results highlighted the potential of a plant performance enhancement in winter conditions, respect to the common solutions with external air-water heat exchangers, once a correct control system is implemented, needed to automate the decision process of sending the water to be heated to the tank or to the external air-water heat exchanger. The heat pump working conditions could even become close to be independent from external air conditions, if the average wastewater input results high enough during the day. The additional cost of the energy recovery system resulted affordable, achieving a reasonable payback period.