Oak Ridge In Hot Water

January 01, 2005
January/February 2005
A version of this article appears in the January/February 2005 issue of Home Energy Magazine.
Click here to read more articles about Hot Water

        Scientists at Oak Ridge National Laboratory (ORNL) are taking on the second biggest energy user in the home—hot water. One way to minimize water-heating energy is to combine this technology with other energy-using devices.Two of ORNL’s current projects take this approach. One project uses the heat given off by refrigerators to help heat water and also to cool the house in the summer.The other project combines a water heater with a dehumidifier.A third project is aimed at effectively marketing new technologies, such as ORNL’s heat pump water heater (HPWH). Finally, a project has studied the efficiencies of hot water distribution systems and has made recommendations for improvements.

Heating Water with Waste Heat

         Cleaning the coils on the back of your refrigerator won’t save you any energy (see “Common Energy Myths,”HE Sept/Oct ’01 p. 33).However, researchers at ORNL,working together with Habitat for Humanity, have designed a home in the Harmony Heights subdivision in Lenoir City,Tennessee, that makes use of the heat from those refrigerator coils to heat water and cool a house. The nearnet- zero energy house includes a HPWH,donated by Enviromaster International LLC, that is integrated with the refrigerator as well as with the unvented crawlspace and the heating and cooling system (see “Near-Net-Zero Energy”). Waste heat is used to preheat water in the HPWH.When the home is in cooling mode,waste heat from the refrigerator is directed through motorized dampers to the HPWH situated in a closet behind the refrigerator.The HPWH uses this waste heat and then returns cool exhaust air into the kitchen to lessen the load on the air conditioner.When the heat is on, a fan sends crawlspace air to the HPWH, which then exhausts it to the outside. (This does not take heat from the house and transfer it to the HPWH.There is more heat transfer from the ground to the outside air that is drawn into the crawl space than there is heat transfer from the house to the crawlspace, since the floor is well insulated.) Because the HPWH uses multiple sources of heat,the HPWH coefficient of performance (COP) has ranged from 2.0 to 2.2 during a year of testing.

Water-Heating Dehumidifier

        As new,well-insulated homes become tighter, potential moisture problems arise, especially in homes that bring in humid outside air for fresh air. Humid air can promote the growth of mold, leading to poor indoor air quality and rot.The water-heating dehumidifier (WHD) in development at ORNL is meant to address humidity control. Several configurations will be modeled and tested to identify the most marketable, least expensive, and most energy-efficient device.
        The WHD will include a compressor, two condensers, an evaporator, and an expansion device. One condenser will be used when the WHD is operating as a water heater.When the tank is full of hot water, the WHD changes over to operate as a dehumidifier. In this mode, the second, aircooled condenser becomes operational. The goal is to create a WHD with an energy factor of 1.2 that will remove 10–24 liters of water from the air each day. ORNL estimates that the WHD will cost $400–$600.This price is comparable to that of a 65-pint dehumidifier that costs approximately $250 and that of a 50-gallon electric water heater that costs $200–$300.
          The WHD will be prototyped through a collaborative effort among ORNL,the Education and Research Consortium of the Western Carolinas,Western Carolina University,Asheville-Buncombe Technical Community College, the American Carolina Stamping Company, and Clemson University. The WHD will be marketed by the newly created Western North Carolina Center for Technology Development (a partnership among ORNL, Institute at Biltmore, University of North Carolina at Asheville, Clemson University, and Western Carolina University). Ten or more of the new WHD will be field tested in North Carolina and Tennessee homes in 2005.

Heat Pump Water Heater

        ORNL and Arthur D. Little helped engineers at ECR International, Incorporated, to create a HPWH that could be installed on top of a conventional electric water heater. The drop-in unit is 3 times as energy efficient as the most efficient conventional electric water heater. Since the HPWH draws heat from the surrounding air, it also has the capacity to cool and dehumidify the space where it is installed. (For more on the HPWH, see “All Pumped Up,” HE Nov/Dec ’02, p. 30.)
        Because of the high first cost, and past serviceability issues, the HPWH has made little impact on the water heater market, despite its energy efficiency. ORNL is conducting market research with the hope of integrating what they learn into their research and development efforts. Their goal is to work with industry partners to better market energy-efficient technologies such as the HPWH.

Hot Water Distribution Systems

        ORNL was commissioned by the California Energy Commission to study the impact of various hot water distribution systems on a house’s energy use,water use, and the wait time for hot water to reach the end user.To this end, ORNL created a model to study various configurations of housing type and hot water distribution system.
        For a complete description of the study and its outcomes and recommendations, see “Are You Getting into Hot Water?”HE Sept/Oct ’03, p. 33, and “Hey,Where’s the Hot Water?”HE Sept/Oct ’04, p. 36.

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