Heat Recovery System for Discharged Hot Water into the Sewer System

Water heating accounts for approximately 16% of primary residential energy consumption in the U.S. Some water heating energy can be recaptured from the drain water system, but costs and space requirements limit the marketability of existing products. The subject of this proposal is a more compact, lower- cost drain water heat recovery (DHR) device that expands DHR market potential. The technology can include a heat storage capability to recover heat from fixtures that fill and drain asynchronously, such as dishwashers and clotheswashers. Preliminary analysis suggests that an advanced unit can be manufactured with installed costs of $190 to $225 in preferred applications, and can achieve performance that will yield payback periods under three years when paired with electric resistance water heaters. The proposed project is structured to maximize system performance and market potential through analytical studies, engineering design, and product cost reduction. Phase I work will create a sound foundation for subsequent development work by verifying the viability of the design concept, identifying preferred applications and their impact on the design, and providing more detailed evaluations of economic viability.