A couple of months ago, the zero-energy house became a reality.

The house, in Tucson, Ariz., was the result of a collaboration by the NAHB Research Center, based in Upper Marlboro, Md., and John Wesley Miller Co., a Tucson residential builder whose namesake president is a pioneer in solar-energy design and development.

After all, it is Tucson, where the sun shines just about 365 days a year. In addition, the electric company has meters that run backward, so the search for the ultimate in energy efficiency is nothing new there.

The Tucson project is a prototype for other zero-energy houses that Miller will build in Armory Park del Sol. (Sol is Spanish for sun.)

"What we are doing here is building one small power plant, one house at a time," Miller said. "Once we monitor the success of this home, it is likely that we will build more in this community."

Such houses cost about 15 percent more. Simply add that to the prices of the two- and three-bedroom houses he is now building and the asking price at the higher end will be about $333,000, Miller said.

The 15 percent estimate does not figure in incentives that could come from the utility and the state of Arizona, he said.

Miller already built energy-efficient houses. Daily heating and cooling costs for the models at Armory Park del Sol range from 78 cents to $1.18.

The houses are designed to satisfy the voluntary requirements of the Tucson Sustainable Energy Code, which reduce heating, cooling and water-heating energy to half that of houses built under the Model Energy Code or the International Energy Conservation Code.

The costs are still too much, by zero-energy standards, even though the typical homeowner would do handstands over them.

Because a zero-energy house is designed to produce as much energy as it consumes, Tucson Electric Power Co. is running the house meter backward and credit the homeowner when he or she puts power back into the grid, resulting in a net zero energy bill over the year.

The zero-energy project was part of a national initiative funded by the federal Department of Energy through the National Renewable Energy Laboratory. The Energy Department's "Million Solar Roofs Initiative," announced in June 1997, is an effort to install solar-energy systems on one million buildings by 2010.

The initiative includes two types of solar technology: solar electric systems (or photovoltaics) that produce electricity from sunlight; and solar thermal systems that produce heat for domestic hot water, space heating, or heating swimming pools.

"This is the future for the American home," said David Garman, the department's assistant secretary for energy efficiency and renewable energy. "Solar-energy technologies are affordable and practical today. Combined with off-the-shelf energy-efficiency products and proven construction techniques, solar energy can make houses zero net users of electricity, while staying competitively priced."

The goal of the initiative is to introduce the zero-energy concept to the mainstream home-building industry, where some progressive builders are already producing energy-efficient housing in concert with local utilities.

The Energy Department wants to see a 30 percent to 60 percent reduction in residential energy use in the next 10 to 15 years.

To make the zero-energy house a reality, research center engineers, Miller's staff, and architects Devereaux & Associates, of McLean, Va., designed the house, which the center's staff is monitoring for a year after completion, and make those results available to the public.

This house is solid masonry construction, which takes advantage of thermal mass to buffer daily temperature swings in the desert climate.

Insulation includes R-14 polystyrene in the exterior walls and R-38 in the ceilings.

Many of the products used in the house have been donated to defray the costs of construction, Miller said. Among them is radiant-barrier roof decking from LP Corp. in Roaring River, N.C., designed to reduce air-conditioning cooling loads in warm or hot climates.

When radiant energy from the sun strikes the surface of a roof, the roof heats up. The heat radiates into the attic, where it is conducted through the attic floor into the living areas. Air-conditioning ductwork in the attic is also heated, further decreasing cooling efficiency.

A radiant barrier reflects radiant heat and does not emit it to the cooler surfaces around it.

The effectiveness of a radiant barrier is determined by how much radiant heat it reflects and how little heat energy it transmits, which is known as emissivity.

The lower the emissivity, the more effective the radiant barrier.

Other features of this house include a 3.5-kilowatt photovoltaic array to generate electricity from the sun - the typical Tucson house needs about 4 kilowatts at the hottest part of a summer’s day - as well as an integrated solar water- and space-heating system.

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