The potential of wastewater heat and exergy: Decentralized high-temperature recovery with a heat pump

Abstract

There is a large potential in the heat losses from the wastewater leaving a building. We present a novel concept for recovering this heat. Instead of recovering it in a mixed state, the recovery immediately after use is evaluated. This allows the exploitation of the higher temperatures found at the points of warm water usage. By integrating a heat pump to utilize this heat, we can produce a higher temperature heat supply while maintaining a low temperature-lift requirement. This leads to the possibility of directly regenerating the hot water supply through wastewater heat recovery. The concept is a result of research into low exergy building systems, and is part of the IEA ECBCS Annex 49. We have modeled the annual performance of two different system scenarios, which result in a potential average annual coefficient of performance (COP) of over 6. The first scenario supplies up to 4400kWh of heat for all hot water events with only 790kWh of electricity, while the second scenario regenerated directly the hot water supply just for bathroom fixtures at 2400kWh with just 410kWh of energy. This is a significant reduction in the demand for hot water supply of a building compared to most modern installations.