"We have a roadmap for communities to transform their building industry from part of the problem to part of the solution by leading buildings from energy consumers to net energy producers," Christian said.

While DOE's long-term goal is to develop technologies that enable net-zero-energy homes at low incremental costs, today's focus is on leading new home owners and builders toward houses that feature high efficiency and use solar panels to generate some of their own electricity.

"The effort must be all-inclusive, so we're not limiting our approach to space heating, cooling, water heating, lighting, and major appliances," Christian said. "We're also looking at a number of other advanced technologies and we are integrating sensors so the homeowners can monitor their energy usage and savings."

In July, workers completed a fourth Habitat for Humanity DOE Building America Near-Zero-Energy House. These houses feature airtight envelope construction, advanced structural insulated panel systems, insulated precast concrete walls, a heat pump water heater, geothermal systems, grid-connected solar photovoltaic system, adaptive mechanical ventilation, cool roof and wall coatings with infrared reflective pigments, and solar integrated raised metal seam roofs.

Construction of the new house, located in Lenoir City, was quick and the cost was less than $100,000, says DOE. The first floor, a walkout basement, was constructed in six hours with premanufactured insulated concrete panels. The top floor walls, made of structural insulated panels, were installed in five hours, and the insulated cathedral ceiling was installed in three hours.

The houses also provide high indoor air quality and mold, mildew, and moisture control, DOE says. The advanced construction techniques make these houses six times more airtight than similar houses with 2-by-4 wood frame construction. This and mechanical ventilation, which brings outside air into the house, play a major role in making the design effective.

While the fourth Near-Zero-Energy Habitat for Humanity House was just completed, the first house has been occupied by a family of four since November 2002. The daily cost for heating and cooling this house with an air-source heat pump was 45 cents, says DOE. Adding the cost of operating the water heater and all of the appliances brought the total average daily energy cost for this all-electric house to 82 cents. This number takes into account $291 for solar credits that are part of the Tennessee Valley Authority's (TVA's) Green Power Generation program. In comparison, a conventional house in Lenoir City would use between $4 and $5 of electricity per day.

Already, builders and the public are taking notice, said Christian, who noted that many of the energy-saving features are cost-effective for all houses.

Plans call for a true net-zero-energy house to be built by the end of 2005.

Funding for this effort is provided by DOE's Office of Energy Efficiency and Renewable Energy Building America Program and TVA.

Publication date: 08/30/2004