Case study: Zero-energy home

By on 02/01/2008

Wouldn’t it be nice if the power company sent you a check every month?

Duke Energy actually does send Hickory resident Frances Thompson a partial reimbursement for her monthly bill. Thompson’s house has a solar-photovoltaic array on its rooftop. Because the solar-electric system is tied in with the power grid, Duke pays her 5 cents per kilowatt-hour for the electricity generated, while she pays the utility fees (at a rate of 8 cents per kwh) for using the traditional power like any other consumer. Thanks to N.C. GreenPower, a statewide nonprofit dedicated to promoting clean energy, her grid-tied solar house amounts to a sweet deal: N.C. GreenPower sends Thompson an additional monthly check at a rate of 18 cents per kwh for using clean energy.

“Even during the hot snap, around July, she still came out a couple bucks ahead,” notes Rob Howard, who oversaw the construction of Thompson’s home. The house was built in 2005 by Habitat for Humanity of Catawba Valley, with the help of the Appalachian State University Energy Center. It was designed to be a “zero-energy home”: a house that consumes roughly as much energy as it produces. Thompson, like all Habitat for Humanity home recipients, was selected after an application process demonstrating her need for affordable housing and ability to keep up with a low-end, no-interest mortgage. Thompson is battling medical issues that make it difficult for her to work full time, so low housing payments and low utility bills are a major help, she says.

The project combined expertise from ASU, grant money from the N.C. State Energy Office, the services of affordable-housing nonprofit Advanced Energy, generous donations from renewable-energy and green-building companies and the hard work of some 100 Habitat for Humanity volunteers. The result? An innovative dwelling that stands as proof of what can be achieved when the twin ideals of affordability and energy efficiency are combined.

The zero-energy home might be easy to miss if it weren’t for the rooftop photovoltaic panels. At a modest 1,200 square feet, with three bedrooms and two baths, the house is designed to blend in with the bungalow-style residences in its suburban Hickory neighborhood, and like the other homes, it fits snugly into a tiny lot.

But the sunny little bungalow is anything but average. The heating and cooling system, for instance, is fueled by a geothermal system donated by WaterFurnace. Depending on the season, the system is supposed to circulate warm or cool air from underground to the interior of the house, taking advantage of constant subterranean temperatures.

Solahart, a solar-technology manufacturing company, donated a solar water heater for the project, which consists of a pair of solar panels and a tank mounted on the roof.

The design of the house, meanwhile, is meant to take full advantage of the sun’s energy. A row of windows in the south-facing living room allow for sunlight to stream in fully during the winter. The sun’s rays are absorbed by an insulated concrete slab overlaid with recycled tiles, which naturally lets off heat as a supplementary heating system.

Energy efficiency was the deciding factor behind many aspects of the design, from insulation to lighting systems. Icynene, a type of foam insulation that seals off every nook and cranny for an optimally airtight building envelope, was used in the exterior walls.

The home is certified Gold by the N.C. HealthyBuilt Homes program, and ASU continues to monitor its performance.

The project demonstrates what is possible when resources are combined with high ideals and green design. Still, it’s not perfect: Thompson says that it is often uncomfortably hot in her home, a signal that the carefully planned heating system is working over time.

Nor can this affordable green model be realistically implemented on a mass scale — at least not yet. Catawba County recently suffered major job losses, and Howard says his Habitat for Humanity chapter is having a difficult time finding home recipients who would be able to keep up with the inexpensive, no-interest mortgage payments that the nonprofit offers to low-income families. For many, simple home ownership — let alone a green home — remains out of reach. A substantial grant from the State Energy Office provided for the solar array on the Hickory zero-energy house, but in most cases, solar is out of the question due to cost. “The big key is going to be reducing the price of photovoltaics,” notes Howard. “It’s going to take something creative to reach the masses.”