Wastewater Heat Recovery System as a Source of Affordable and Clean Energy in Buildings: Multi-Factor Assessment of an Innovative Shower Drain Water Heat Exchanger

Greywater can be a valuable source of energy, which is often wasted when discharged into the sewer system. The use of drain water heat recovery (DWHR) exchangers in buildings allows for the recovery of this energy. With this in mind, a new horizontal shower heat exchanger solution was developed, and a prototype was built. This device was tested in the laboratory under conditions similar to those of normal shower use. The obtained results allowed the determination of the temperature-based effectiveness for a wide range of variables. The experimental results also formed the basis for a Life Cycle Cost analysis of various domestic hot water system variants and for determining the environmental impact of implementing the tested exchanger. Depending on the system configuration, the DWHR temperature-based effectiveness ranged from 24% to 29% (Configuration 1), from 29% to 40% (Configuration 2), and from 38% to 57% in Configuration 3. The tests also confirmed that the new exchanger solution is financially viable. For two-person households with average water consumption per bath, the payback period does not exceed 7 years, and for a four-person family, it is reduced to approximately 3 years. A key aspect of the research was the demonstration of a significant reduction in operational CO2 emissions resulting from the implementation of this DWHR exchanger in the building. This study highlights the importance of selecting the optimal configuration for connecting the exchanger to the sanitary system and confirms the need for continuous development and research into wastewater heat recovery technologies.