Recently rated the most energy efficient home in Colorado by ENERGY STAR auditors by achieving 97 out of 100 points, Solar Harvest stands ahead of the pack of homes seeking Zero-Energy status. It is the first in Boulder, Colo. – and perhaps the nation – to pass construction and heating codes without being required to have an electric or gas backup heating system.

Eric Doub, the designer and builder of Solar Harvest and president of award-winning contracting firm Ecofutures Building, Inc., remarks that since the beginning, the design goal was clear: to achieve a net-zero energy use. “By meeting this net-zero energy goal, we are striving to build a house that will be affordable and viable 100 years from now, when who knows how much natural gas – and electricity – will cost.”

The wood-framed, two-story, 4,700-square-foot house combines energy efficient design with renewable energy technologies and energy conservation to have a final net-zero energy use. Beyond exceptional energy-related performance, the home also serves as a showcase of the luxury and comfort possible by building with predominantly green materials. To achieve a net-zero rating, the grid-tied home uses a 6.84kW photovoltaic array by Sharp Electronics Group (Huntington Beach, Calif.) in two mounts connected to two Fronius IG (Santa Barbara, Calif.) inverters. The panels provide enough electricity to go above and beyond meeting all of the home’s energy needs.

At the core of the superinsulated house rests a 6,000-gallon superinsulated tank designed by Doub that stores hot water at 170 to 190 degrees Fahrenheit, fed by 12 salvaged Novan (Denver, Colo.) solar thermal flat-plate collectors set up in a drainback system to serve essentially as a thermal battery. The tank is constructed with Greenblock (Stuart, Fla.) ICF walls, Icynene (Mississauga, Ontario) insulation and recycled polyiso foam. Coils of copper tubing act as heat exchangers, transferring heat to a domestic hot water, staple-up radiant floor space heating system, and the 360-gallon outdoor hot tub kept at 103 degrees F. When fully “charged,” the water tank can heat the house to 68 degrees F for eight consecutive days.

Fresh air entering the house is also pre-warmed or pre-cooled seasonally as it passes through 260 feet of PVC pipes buried up to 8 feet below ground. An Ultimate Air RecoupAerator ERV (Athens, Ohio) functioning at 96 percent heat recovery efficiency ensures continuous fresh air exchange into the airtight building with 0.1 natural air changes per hour or lower. Air is also circulated from the sunspace through distribution ducts to provide 100 degrees F air to northern reaches of the home during winter months.

cost and payback

The home showcases the luxury and comfort possible when building with predominantly green materials.

A frustration with net-zero energy homes is a tendency for critics to inquire about the payback period of the home. Answering this question requires resolving two crucial issues: accurately predicting actual rising energy costs; and, including externalities into the energy costs. “What are the energy costs in terms of healthcare, the environment and the climate?” asks Doub. Like builders of other zero-energy homes, Doub agrees that the benefits are greater than simple payback economics of energy costs. The home provides a greater benefit to the family as a healthy living space that functions without depleting natural resources.

Until the home has a track record of energy use and production, it is difficult to begin to set numbers into assessing how long it will take for greater efficiencies to cover the extra costs. Regardless of exact numbers, Doub contends, “Sometime in the future, when energy bills are $500 or $600 a month, this place will still be chugging along with no costs and sending excess power back to the grid.”

Alison Ray, assistant project manager at Ecofutures Building, is a recent graduate from the University of Vermont with a B.S. in Environmental Studies. With Ecofutures, she is helping to research and develop ecological design techniques for residential home construction.

SIDEBAR: solar harvest house

designer and builder: eric doub, ecofutures building, inc.
location: boulder, colo.
size: 4,700 square feet
building products: wood frame; 6.84kw photovoltaic array by sharp electronics group; fronius ig inverters; 6,000-gallon superinsulated tank designed by doub; salvaged novan solar thermal flat-plate collectors; tank: greenblock icf walls, icynene insulation and recycled polyiso foam; ultimate air recoupaerator erv.