Design For Limited Planet Living With Natural Energy

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The house conforms to McMullen's—and a growing number of other architects'—concept of energy-saving design: that the right combination of materials for thermal mass, siting, and fenestration will keep a house significantly warmer in winter regardless of climate, without having to install expensive solar hardware. A design change advocated by engineers and architects concerned about fuel waste is incorporated in the Davis house: instead of conventional two-by-fours, the building is framed with two-by-eight studs to make a deeper recess for wall insulation. The house is insulated with 7 inches of fiberglass batts in the walls and 9-1/2 inches in the ceiling.

McMullen's solar design combines features of the basic water, air-to-rock, and greenhouse solar heat systems. The roof-mounted collector is composed of corrugated aluminum sheeting under fiberglass. Water is piped up to a feeder pipe at the top of the corrugated sheeting, where it trickles down the gullies and is heated by the sun to 120 degrees. The water collects in a trough at the bottom of the collector, and from there it flows down into a 2,000-gallon water storage tank that is embedded in a rock bin below the house. Beneath the rock bin is a manifold constructed out of standard concrete block. Air is circulated through the manifold, picking up heat from the rock bin, and then distributed through ducts to the rooms. The hot water supply is also tied into the solar system.

The Davises found that a larger-capacity storage tank would have given the house more heat. Their 2,000-gallon tank was supposed to store enough heat for three successive cloudy days—but they forgot to take into account Maine's strong coastal winds.

"If we have sunny winter days that aren't too windy, with temperatures around 30 degrees, we can just get by on the solar heating system. If it starts to go below 30 degrees and the wind picks up, we have to resort to our wood-burning furnace," Davis explains.

"We have adjusted to the fact that a solar house isn't capable of responding rapidly to changes in temperature," he adds. "For instance, if we come home at night and the inside temperature has dropped to the mid-50's, it takes a while for the stored heat to warm the house up to the 60's. In early winter, we keep the house at 70 degrees, but as it gets colder, we feel comfortable at 65 degrees. You live differently in a solar house," he says. "We are much more aware of what the weather is doing."

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