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An Affordable Heat-Pump Water-Heater Retrofit

07/30/08

By Alex Wilson

The engineers at AirGenerate (previously Beyond Pollution) appear to have done something remarkable: create an affordable, effective, heat-pump water heater that can be retrofit onto a conventional gas or electric water heater, more than doubling the energy performance compared with a standard electric water heater.

Air Tap Heat Pump
Photo © AirGenerate
Standard fittings and simple connections are used to install an AirTap heat pump unit onto a standard electric or gas-fired water heater.
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The AirTap A7 water heater has a rated output of 7,000 Btu/hour, a first-hour rating of 42.5 gallons, a maximum water temperature of 135°F, an efficiency of 240% (coefficient of performance of 2.4), and an energy factor of 2.11. (Energy factor is a standardized measure of performance of water heaters; the higher the number, the better.) All this is in a unit that measures only 18" wide by 14" deep by 14" high, weighs only 48 pounds, and sits on top of a standard water heater. The list price is $499. The energy factor and first-hour rating of the AirTap are certified by GAMA (previously the Gas Appliance Manufacturers Association and now a broader association of appliance and equipment manufacturers).

Heat-pump water heaters have always been a good idea, but most efforts to design, build, and market them have failed. With today’s high energy prices, however, consumers should be more receptive to heat-pump water heaters, according to Harvey Sachs, Ph.D., the buildings program director at the American Council for an Energy-Efficient Economy. “The economic savings potential is so much greater than before, with the run-up of energy prices,” Sachs said.

AirGenerate initially produced its AirTap A7 water-heater kit in Houston, Texas. After selling a few hundred units in late 2007, the company began sourcing the product from an offshore supplier. The outsourcing of production will allow the company to significantly ramp up production. The first of the new (offshore-manufactured) AirTap units were received in January 2008, and about 200 had been sold through May 2008. Of 400 units scheduled to arrive in June, almost all were pre-sold by the end of May, according to Sunil Sinha, chief scientist at AirGenerate.

Skyland Falls, a Tennessee developer, has installed 30 AirTap units since January 2008 in a 70-unit subdivision currently under construction. Houses in the subdivision are 2,000 ft2 (190 m2) each and sell for an average of $230,000.
 
“The AirTap is doing a fantastic job,” according to Skyland Falls president Gary Alexander, who said that he also intends to use the product in a 100-unit subdivision that is in the works. Skyland Falls is installing the AirTap units on new 40- and 50-gallon electric water heaters, set up so that the standard electric element provides a backup. The controls on the water heater are set so that the standard element will come on at 100°F, while the AirTap is set to heat water to 130°F. If the heat-pump module stops working for some reason, the conventional electric-resistance element will still keep the water warm, but homeowners will notice the problem and contact Skyland Falls. The company will go out and troubleshoot the problem—but it probably won’t be an emergency call, since the water will remain at least warm.

“Since this is a new system, we wanted a backup,” Alexander said. With some units in place for four months, Skyland Falls has yet to receive a call. Installation is fairly easy—even feasible for skilled do-it-yourselfers. According to Alexander, one of his employees can install three AirTap units in a day. Skyland Falls installs the water heaters in utility closets with the outflow air from the AirTap heat pump vented into the adjacent garage; this setup provides some cooling to the garage, which is beneficial in the summer.

Of the 30 units so far installed, only one unit has had a problem—a loose bolt that Skyland Falls easily fixed. In late spring 2008, the all-electric homes were using less than $2 per day for energy, according to Alexander, though how much of this is for water heating is not known.

Other heat-pump water heaters will be coming along soon. General Electric expects to introduce its Hybrid Electric Water Heater in late 2009. The model will sell for about $400 more than a standard, 50-gallon (190-l) electric water heater but save an average family $250 per year with electricity at 10 cents per kWh, the company claims.

 According to Sachs, a second major player is likely to soon announce another heat-pump water heater. Having major manufacturers enter the heat-pump water-heater market, according to Sachs, will give this sort of product legitimacy. “[AirTap] may be able to ride the wake instead of having to break through the ocean waves,” he said.

In addition to the AirTap A7 model, AirGenerate is introducing a larger 12,000 Btu/hour model in August 2008, according to Sinha. This model will offer the same energy factor of 2.11 but will have a first-hour rating of 60 gallons (230 l).

This article was produced by BuildingGreen, LLC.- www.buildinggreen.com

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