Passive Solar House Design Using a Two-Story Trombe Wall

Image Gallery This passive solar home is heated and cooled by a two-story Trombe wall. Sunlight is converted to heat and trapped between the glass windows and the wall and used to heat the house and its attached greenhouse. PHOTO: MOTHER EARTH NEWS STAFF

Up in New Jersey, a guy by the name of Doug Kelbaugh designed (and moved his family into) a passive solar home that's not only cozy in winter and cool in summer, but aesthetically pleasing to boot!

Yes, Virginia, a solar heated and cooled house can be beautiful. That, among other things, was what architect Douglas Kelbaugh set out to prove when he designed and built his family's all-new Princeton, N.J., solar home, and it shows!

The split-level dwelling's major design element — as you can see in the Image Gallery — is a massive, south-facing "collector wall" made of 15-inch-thick poured concrete that has been painted flat black and faced with 600 square feet of double-pane glass. (The two layers of glass are mounted in greenhouse-type aluminum channels, set 6 inches in front of the slab.) This passive collector not only heats the three-bedroom house in winter and helps cool it in summer, but lends aesthetic appeal to the structure as a whole, something that, until recently, has been missing from too many solar home designs.

How the Solar Heated Home’s Collector Wall Works

In the diagram of the house design, the rays of the low winter sun (1) strike the glass surfaces of the collector wall nearly perpendicularly and (2) readily pass through to impinge upon the concrete slab (3), which, because it's painted black, absorbs slightly more thermal energy than it reflects. And, since glass is transparent to light but opaque to heat, about two-thirds of the warmth that is radiated from the slab is retained within the collector.

OK. As the air between the glass and the concrete becomes heated, it rises (4), drawing cool air into the collector wall via floor vents (5) on both of the home's two stories. The sun-warmed air then exits through vents (6) near the ceiling of both stories into various rooms of the house, where it mixes with cooler air, descends, and is ultimately drawn back through the collector again.

(Thanks to an adjustable damper halfway up the solar wall, each floor of the house can be heated independently. Without the damper, most of the warm air generated by the glass-and-concrete "heater" would go straight into the upstairs rooms.)

At night, the massive slab — which has been soaking up the sun's warmth all day — radiates Btu's into all the important rooms of the house, from the upstairs bedrooms and study to the single expansive downstairs "living area." (Doug wisely arranged storage space, a half bath and a formal entrance along the dwelling's "back" — or north — side, to buffer the living quarters from the cold.)