Smart Appliances for a Sustainable Smart Grid: Hot Water Hybrids Save Energy and Conserve Water

To conserve water and save energy, professionals can now choose an ENERGY STAR electric hybrid heat pump water heater that will work with new smart grid and smart meter technologies.
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Sponsored by GE Appliances
Celeste Allen Novak, AIA, LEED AP

In a 2008 report, standard electric resistance water heaters were not eligible for an ENERGY STAR label. According to ENERGY STAR stakeholders "electric resistance technology is highly inefficient over the fuel cycle and it potentially increases total energy consumption and emissions." Although typical electric resistance heaters have energy factors up to .95 percent, the additional energy savings of the perfect resistance water heater would only provide a savings of electricity between 4.8 and 8.7 percent and consume 4,622 kilowatt-hours per year. This did not offer enough savings to meet the new ENERGY STAR challenge for rating hot water heaters. Electric Resistance storage hot water heaters represent about half of all hot water heating appliances and the DOE wanted to drive the largest energy savings possible by creating incentives for new technology.

As part of a national strategy to conserve water and save energy as fuel costs rise, the DOE challenged manufactures to develop new products with much more aggressive energy targets. The DOE provided research grants as an incentive. Some manufacturers entered into a Cooperative Research and Development Agreements (CRADA) with Oakridge Laboratories in Oakridge, Tennessee and the DOE. A CRADA is a written agreement between a federal research organization and one or more federal or non-federal parties to work together as partners on a research project of mutual interest.


Annual Energy cost comparison between standard electric heaters and ENERGY STAR qualified heat pump heater

Chart courtesy of GE Appliances

 

As a result of the ENERY STAR incentives and discussions with stakeholders, on April 1, 2008, Richard H. Karney, P.E. ENERGY STAR Products Manager, reported the new criteria for energy efficient heat pump water heaters that use vapor compression refrigeration systems to transfer heat from the surrounding air. DOE includes residential as well as commercial drop-in or integrated heat pump water heaters in the program. The final criteria for these systems are:

  • A minimum Energy Factor of 2.0.
  • A minimum First-Hour Rating requirement of 50 gallons-per-hour.
  • A minimum six-year limited warranty on the sealed system.
  • Compliance with UL 174 and UL 1995.

ENERGY STAR requires that the heat pump unit has a maximum current rating of 24 amperes, with voltage no greater than 250 volts. In addition, these units must have the heat pump integrated into the storage tank as a stand-alone unit. Units must have extended warranties that can be as high as ten years for some products.

Using the DOE test procedure for calculations, a fifty-gallon heat pump water heater with a 2.0 Energy Factor would consume an estimated 2,195 kilowatt-hours per year. This is a savings of nearly 55%, or 2,662 kilowatt-hours, in comparison to the typical electric resistance water heater." Some manufacturers have already surpassed this goal hitting as high as 2.4, or 240% efficient, with a 50-gallon water heater. This equates to about a 62% savings as compared to a standard resistance electric water heater and can mean cost savings of up to $325 per year or $3,250 over the 10 year life of the unit. Even more amazing is the DOE report that "If just 10% of the nation's 4.8 million electric water heater shipments were heat pump water heaters with an Energy Factor of 2.0 instead of conventional models with an Energy Factor at the Federal standard, the aggregate energy savings would amount to nearly 1.3 billion kilowatt-hours per year.

Sustainability: Using nature as a heat source


ENERGY STAR approved water heaters are designed to fit in the same locations as a traditional water heater.

Photo courtesy of GE Appliances

Designed to work with the natural process of heat exchange, an electric hybrid heat pump water heater has at least two modes of operation. It can either work through traditional electrical resistance heaters drawing 4500 watts, or in the heat pump mode drawing as little as 550 watts of electricity. This new product may appear in size, shape and installation requirements, to be similar to the typical family water tank however, it operates on very different principles.

Janine Benyus, author of Biomimicry, discussed the study of nature to find solutions for new technology. She asks designers to think about how to use nature as a resource. Heat pumps extract heat, energy savings and peak load reduction literally from the surrounding thin air. Engineers use the thermodynamic properties of nature to compress air through an environmentally safe refrigerant, capturing residual heat and creating condensate. Through heat transfer, whether from the earth as in a geo-thermal heat pump or from air temperature used for the opposite effect in air conditioning and refrigeration systems, heat pumps use nature as a source for this technology.

This electric hybrid heat pump water heater is designed to absorb heat from the ambient air to transfer it into stored water to a desired temperature for home or commercial heating. It uses less energy to transfer heat than it does to generate heat, thus creating energy savings. A smart meter monitors the flow of electrical consumption across the grid to maintain the temperature at the most efficient price to the consumer. A combination of thermodynamics and economic planning makes this system work for energy savings.

 

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Originally published in Architectural Record
Originally published in June 2012

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