July 3, 2002

A Place in the Sun

- from the summer issue of New Homes & Ideas magazine

By Kelly McCall Branson, staff reporter
© Copyright 2002 Lone Wolf Publishing, Inc.

Do you love open airy rooms filled with sunlight? Natural materials like brick and stone? How about low low utility bills? Then the NC State University Solar House has some great ideas for you. Located on the university’s South Campus (adjacent to the McKimmon Center), this 1,700-square-foot home is one of the most visited solar buildings in the United States—logging more than 250,000 visitors over the past two decades. It is a model of solar and energy-efficient technologies, both active and passive. But this house is no sterile laboratory specimen. It’s designed to appeal to the average homeowner. “We wanted a house about which people would say, ‘Hey, I’d like to live there!’,” says Carole Coble, Solar House Manager.

The dominant feature of this three-bedroom, transitional-style house is the two-story sunspace, around which the rest of the house wraps on three sides. This glassed-in greenhouse room at the back of the house collects solar heat during the day, storing it in its masonry walls and floors. The brick and tile act as a valuable form of thermal mass, helping to stabilize sunspace temperature variations. A spiral staircase leads from the lower level to a balcony where a sweeping view of the south lawn can be viewed. All of the surrounding rooms have operable doors or windows into the sunspace, in wintertime allowing warm sunspace air to flow into and heat the entire second floor. As warm air gives up its heat, it cools and falls down the northern stairwell, returning to the lower sunspace, where it is reheated. During extreme summer temperatures, the windows and doors are used to isolate the sunspace from the conditioned space in the house.

A trellis shades the front of the sunspace to buffer the strong summer sun and keep the space from overheating. Deciduous vines completely cover the trellis during the summer, but are cut back to the ground in winter, allowing for maximum solar gain in the sunspace. “Even in the sunspace, with this shade buffer,” says Coble, “the temperature in the summer is eight to 10 degrees cooler than that outside.”

Two thermal storage walls, called, Trombe walls also act as passive solar collectors in the east and west lower bedrooms. These 12-inch thick masonry walls are covered with glass and act as a conduit for solar heat into the house.

The house also collects energy from the sun via two photovoltaic (PV) arrays. These roof-mounted PV modules collect and convert sunlight into DC electricity, which is then converted to the AC electricity, required by household appliances. A battery bank stores excess energy for future use. The system is connected to the utility grid, so that when the PV array is receiving more energy from the sun than is required by the household, excess power can be sold. This system can supply an average of 60% of the energy required in a newly constructed, energy-efficient home. Another added feature is its emergency backup capability. During power outages, critical elements in the house (the refrigerator and several key receptacles) can be powered for up to two days with no sun and, with only average winter sunshine—indefinitely.

A roof-mounted solar collector also provides some 60% of the hot water required by the average family of four. And a water source heat pump, coupled to a septic field heat exchanger provides efficient backup heating and cooling.

Exterior elements also contribute to the energy efficiency of the house. Earth berming on the lower level north and west sides reduce both winter heat loss and summer heat gain. And a south-facing porch acts as a barrier to excess summer heat gain, as do the extended rooflines (three feet rather than the standard two feet). Landscaping, too, plays its part. In addition to the shading trellises, deciduous maple trees are planted around the house. “Maples are excellent trees,” says Coble, “because they produce a shading canopy in summer, and lose their leaves in winter. They also have a fairly small trunk.”

The house’s windows are double-paned casement windows, which seal tighter than double-hung windows. East and west-facing windows are limited to reduce summer heat gain, and smaller windows are used on the house’s north side to reduce winter heat loss. And inside, thermal shades perform the same function.

Ceiling fans are employed to promote air movement and provide cooling in summer months. And fluorescent light bulbs are used throughout the house. Several 10 to 14-inch natural light fixtures (reflecting tubes, mounted in the attic) collect and disperse sunlight.

And just how well is all of this technology working? Well, the NC State Solar House has more than 250 solar and temperature measuring devices embedded throughout—all connected to the computer-operated data acquisition system located in the lower level. But we think just a few facts and figures might say all that you need to hear to believe in its technologies. The total summertime cooling bill for the solar house is in the neighborhood of $250 to $300. And the heating bill? A mere $70 for the entire season!

If you are interested in learning more about solar and energy-efficient technologies, the NC State Solar House is open to the public Monday to Friday from 9 a.m. to 5 p.m. and Sundays from 1 to 5 p.m., or you can visit it on the web at www.ncsc.ncsu.edu. An extensive resource library is located on the lower level, and their staff of engineering graduate students is available to answer questions.

Kelly McCall Branson is a freelance writer living in Raleigh.

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