Heat exchanger applications in wastewater source heat pumps for buildings: A key review

•The first comprehensive study on wastewater heat exchangers was done.•Wastewater heat exchangers were reviewed with types and commercial applications.•Classification of wastewater heat exchangers was done.•Utilization of wastewater heat exchangers in heat pump systems was presented.

Wastewater heat recovery applications are becoming widespread in energy saving applications. A sustainable and low emissions operation in air conditioning and heating processes is achieved by harvesting the otherwise wasted energy in wastewater through specially designed heat exchangers, lying at the core of heat pumps. This combined system is called wastewater source heat pump. In this study, a review of wastewater heat exchangers in wastewater source heat pump applications is presented, and wastewater heat exchangers are classified in detail based on multiple features, including utilization and construction methodology. Also, the potential of wastewater, types of wastewater source heat pumps, and their applications are briefly discussed.