Hot Showers, Lower Power Bills with Heat Pump Water Heaters

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Newswise RICHLAND, Wash. How much energy was used to heat the water for your morning shower is probably the least of your groggy, uncaffeinated thoughts.

However, some homeowners are discovering they have even less need to think about early-morning energy use thanks to an increasingly popular alternative to conventional electric water heaters - the heat pump water heater. Results from a new field study are challenging an earlier understanding that heat pump water heaters are efficient no matter how theyre installed. It turns out using ducting for air intake and exhaust impacts both the appliances and an entire homes energy use.

Heat pump water heaters can use up to 63 percent less energy than traditional electric water heaters, said the studys lead researcher, Sarah Widder, of the Department of Energys Pacific Northwest National Laboratory. When water heating makes up about 18 percent of U.S. residential energy use, heat pump water heaters offer a real opportunity for energy savings.

Until now, many have thought those savings would be offset by an increased use in heating systems. Thats because heat pump water heaters work by transferring heat from the air into water, which can lower indoor temperatures. This can reduce energy use during the hot summer months, but lead us to heat our homes more in the winter. But PNNLs field tests showed that, depending on how heat pump water heaters are connected to exterior ducting, they can reduce a homes overall power use. The results also showed heat pump water heaters may not affect a homes heating and cooling systems as much as previously thought.

New water heater in town Due to their high efficiency, heat pump water heaters can be much less expensive to operate than electric resistance water heaters, the large, tall cylinders that warm water in 41 percent of U.S. homes. Heat pump water heaters are increasingly being installed in lieu of their conventional electric cousins. Heat pump water heaters make up about 1 percent of new water heater sales nationwide. The total number of units sold increased from 34,000 in 2012 to 43,000 in 2013, according to ENERGY STAR.

Before PNNLs field study, the only data on the impact heat pump water heaters have on whole-home energy use was from an idealized computer model that didnt draw on real-world data. To take a deeper look at total energy consumption, Widder and her colleagues installed heat pump water heaters in the PNNL Lab Homes, two especially equipped manufactured homes used to evaluate energy-efficient technologies.

A heat pump water heater was installed in one of the homes without any ducting whatsoever. Another, identical water heater was installed in the second home with one of two configurations: ducting that only vented the appliances exhaust, or full ducting that both collected outside air and later exhausted used air back outside. Both homes used the same electric resistance heating, cooling and ventilation system.

Sensors placed in each of the Lab Homes measured energy use, indoor and outdoor temperatures, humidity and more. Computers controlling both homes periodically ran hot water and turned on lights to simulate actual occupancy identically in both homes. The PNNL team ran the experiment through the summer and winter of 2013.

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Hot Showers, Lower Power Bills with Heat Pump Water Heaters