July 2008

Volume 17, Number 7

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An Affordable Heat-Pump Water-Heater Retrofit

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Standard fittings and simple connections are used to install an AirTap heat pump unit onto a standard electric or gas-fired water heater.

Photo: AirGenerate

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. The AirTap A7 water heater has a rated output of 7,000 Btu/hour (7.4 MJ/hour), a first-hour rating of 42.5 gallons (160 l), a maximum water temperature of 135°F (57°C), 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 (460 x 360 x 360 mm), weighs only 48 pounds (22 kg), 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 told EBN.

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 told EBN 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 (150 and 190 l) 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 (38°C), while the AirTap is set to heat water to 130°F (54°C). 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 told EBN. 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).

– Alex Wilson

For More Information:

AirGenerate, LLC

Houston, Texas



Comments (2)

1 Heating water = cooling air posted by Ethan Goldman on 07/01/2008 at 07:37 am

Because this is an air-source heat pump, the heat it's "pushing" into the water in the tank is extracted from the air. Their web site mentions that you can use the cool, dry air during summer months. However, during the winter this could increase the heating load if the AirTap is installed in a conditioned space, or in a basement that is not well-isolated from conditioned spaces.

If the heat pump used the home's drain-water as a heat source instead, this problem would be avoided. As an added benefit, the efficiency of the heater would be much higher, as the source temperature would be higher. However, I suspect they avoided this configuration to simplify retrofits. There would also be some control logic issues, for example if the tank temperature dropped during a period of disuse and the drain-water was not running.

2 Heating Water by Energy from posted by sunil sinha on 07/03/2008 at 07:43 am

AirTap Heat Pump Water Heater is installed in the places like garage, basement, attic which are mostly not directly heated by conventional sources of energy. The heat comes from the heat loss from the walls and roofs of the living space and from the nearby furnace. The heat draw for AirTap from air is about 5000 BTU per hour for average 4 hours a day which comes from the lost heat from walls and roof.

Following is the calculation of the heat loss to the basement from the living space. I found the reference data about heat loss from:http://umt.edu/geosciences/faculty/sheriff/Sheriff_Vita_abstracts/Baseme...

Heat losses: BTU/hour = Area (ft2) * (T1 - T2)(oF) / R (hour*oF*ft2/BTU)

Assumptions: - 6" thick with R value of 0.08/inch - Area: 15'x15' = 225 (ft2.) - Temperates: T1, in living space=76(oF) and T2, in basement = 45(oF)

Heat Given to basement from living space = 225(ft2) * (76 - 45)(oF) / (0.08/inch * 6") (hour*oF*ft2/BTU) = 14,531 BTU /hour

It is evident that even smaller basement of 15'x15' would provide enough heat for AirTap Heat Pump Water Heater to heat the water at about 200% efficiency. AirTap would take roughly 5000BTU from Air and 2000 BTU from electricity to give 7000BTU of heating. This is in line with our customers' experience during winter season.

If the water heater is in the room which is directly heated by electric heat, we don't recommend using AirTap heat pump water heater. However, we have not come across any homeowner who was heating his water heater room with electrical heat.

Generally basement, garage or attic is isolated from the heated living spaces. We recommend ducting out the cooled air from the enclosed space during winter season and enjoy free cooled air during summer using our AirVent. The same is true for AirTap installed in a closet.

Many of our customers in colder places have realized the free dehumidification of basement from AirTap while reaping the benefit of more than 50% energy saving in water heating.

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