Near-zero-energy buildings blessing to owners, environment

An electricity meter that sometimes runs backwards is just one of the cool aspects of Department of Energy near-zero-energy homes.

While low or no electric bills are an obvious benefit, high energy efficiency homes and businesses also reduce the amount of electricity that needs to be generated, thus reducing pollution, said Jeff Christian of DOE’s Oak Ridge National Laboratory.

In Tennessee, air pollution is of special concern as the state ranked third behind California and Texas for smog, according to a September 2003 Environmental Protection Agency report. And in June 2003, ozone alerts were in place 25 of 30 days in the Smoky Mountains, the most heavily visited national park in the United States.

Christian, director of ORNL’s Buildings Technology Center, believes he and colleagues have at least part of the answer. “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 boast 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, adaptive mechanical ventilation, cool roof and wall coatings with infrared reflective pigments and solar integrated raised metal seam roofs.

Construction of the house, located in Lenoir City, was quick and the cost was less than $100,000. 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 a mere three hours.

The houses also provide high indoor air quality and mold, mildew and moisture control. In fact, 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 huge 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. 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 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.

ORNL, which is managed by UT-Battelle, employs 1,500 scientists and engineers and is DOE’s largest multipurpose science and energy lab. Funding for this effort is provided by DOE’s Office of Energy Efficiency and Renewable Energy Building America Program and TVA.