Water and Energy Savings From On-demand and Hot Water Recirculating Systems

Electric hot water recirculation and on-demand instant hot water systems have been identified as “green” water systems due to purported energy and water savings, and some municipalities and districts even require green systems in residences. The performance of these devices have never been rigorously tested and evaluated. This work aims to address that gap by conducting a comparative, head-to-head study evaluating energy efficiency, temperature profiles and consumer issues such as cost and quality of system for two “green” water heating systems as compared to a standard water heater. Not only did the standard system outperform the hot water recirculation system with respect to temperature profile during flushing, but the standard system also operated with 32–36% more energy efficiency. Although the recirculation system did in fact save some water at the tap, when factoring in the energy efficiency reductions and associated water demand, recirculation systems actually consumed up to 7 gallons more water per day and cost consumers more money. On-demand systems operate with virtually 100% energy efficiency, but cannot be used in many circumstances dependent on scaling and incoming water temperature, and may require expensive upgrades to home electrical systems and use of low/ultra low flow showerheads. Although additional research is necessary to better understand nuances of electric water heating in the context of the water-energy nexus, this research provides a first step for rational decision making by regulators, public health officials, manufacturers and consumers.