A Wastewater Heat Recovery System as a Solution to Improve the Energy Efficiency of Buildings and Reduce Greenhouse Gas Emissions: Technical, Financial, and Environmental Aspects

Greywater can be a valuable energy source in buildings. Its advantages over other renewable energy resources include its daily availability, regardless of weather conditions. Consequently, wastewater heat exchangers are increasingly used in domestic hot water preparation systems. This article presents the results of tests on three DHW installation variants, including two integrated with various drain water heat recovery exchangers. A horizontal DWHR exchanger (a prototype of a new exchanger design) reduced the energy demand for hot water preparation by up to 29.6%, while a commercially available vertical DWHR unit (“tube-in-tube”) reduced this demand by up to 64.7%. This reduction was primarily influenced by the flow rate from the shower head and the mixed water temperature. Furthermore, a Life Cycle Cost analysis showed that, despite the additional costs associated with implementing DWHR exchangers, the traditional water heating method was the least cost-effective solution in all calculation cases. Furthermore, the tested wastewater heat exchangers significantly reduced CO 2 emissions compared to traditional water heating. This indicates the great potential of wastewater heat recovery systems in decarbonizing the building sector.