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Approach
Utilize a demand hot water system to bring hot water to a faucet without waste as a simple and efficient alternative to three-pipe re-circulation domestic hot water systems.
Technology Description
The Hot Water Demand system (HWDS) is an electric water pumping system that quickly (typically within 30 seconds) brings hot water to the fixture by drawing water from the hot water tank and returning ambient house temperature water back to the hot water tank where it is heated. The HWDS is usually installed under the sink farthest from the water heater. At the push of a button, it circulates the ambient house temperature water normally discarded down the drain, back to the water heater through the cold water line. At the same time, the HWDS pumps hot water rapidly from the hot water heater to the fixture. When a predetermined set point temperature (usually 5°F above room temperature) in the line near the fixture is reached the pump stops automatically and hot water is subsequently available at the faucet. The pump may be operated by a switch placed next to the fixture or by a remote control.
Technology Improvements
Water savings for a household of four occupants varied from about 900 gallons to about 3000 gallons per point of use, per year. Point of use is a single location at a home, for example a faucet where hot water is available. The water savings in a home with four points of use, on the average, would be 3,600 to 12,000 gallons per year.
Electricity savings for a household of four occupants varied from about 200 kW-h/year to 400 kW-h/year for a single point of use. Extrapolation to a home with at least four points of use would imply electricity savings from 800 kW-h/year to 1600 kW-h/year.
Scope
The U.S. Department of Energy's Emerging Technology Program and City of Palo Alto Public Utilities Commission teamed together to estimate the potential of saving potable water and electrical energy that is lost directly to the drain while occupants wait for hot water to arrive at the faucet (point of use). The amount of water wasted down the drain depends upon the distance between the point of use and the hot water tank, the hot water temperature setting, the location, type, internal diameter, effective length and insulation level of the pipes and other factors such as the consciousness of the user in regulating the flow of water. This daily wastage of potable water, endemic in every home, can be eliminated by installing a simple recirculation device, available widely from retail stores or purchased on-line via the internet. Such a device, the Metlund® Hot Water D'MAND® System, was retrofitted in each participating home and offered both convenience as well as water savings. The City of Palo Alto Utilities (CPAU) selected single family homes in Palo Alto, California and provided free installation and service to them for the duration of the study.
Partners
The City of Palo Alto Public Utilities Commission and Oak Ridge National Laboratory which is administering the project for the DOE Buildings Technologies Program.
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