“A simple underground house design uses a novel insulating/water-shedding blanket that covers the structure and surrounding soil. The umbrella creates a huge subterranean thermal reservoir that soaks up the sun’s energy during summertime and stores it for winter heating.”
Umbrella Homes – Sustainable house with passive annual heat storage By JOHN HAIT My first earth-sheltered house, an underground geodesic dome was partially complete when the truckload of insulation my colleagues and I had ordered arrived. Right away, we knew we had a problem: How do you put flat, rigid polystyrene insulation on a round house?
We called housing experts all over the country, but no one had any ideas. Finally, Ray Sterling at the University of Minnesota’s Underground Space Center suggested that we place a flat, insulating “umbrella” in the earth above the building. This, he said, would keep the domelike house warm by insulating the soil around it.
“What a marvelous idea!” I thought when I heard his advice. After two weeks of rigorous examination, I realized that the concept was even more promising than I’d supposed. By then I was convinced that the dry earth under an insulating/water-shedding umbrella could store enough free solar heat from the summertime to warm the house through the entire winter (see diagrams above). This meant that a house could actually be constructed with an unchanging built-in temperature, which would make heating and cooling equipment unnecessary. Now, five years later, I still think it’s a marvelous idea. The Geodome, the house we built in the cold and cloudy climate of western Montana, remains at 66 to 68 degrees F, even through the coldest winters.
The success of the Geodome led to the establishment of the Rocky Mountain Research Center, a nonprofit organization dedicated to the development of what is now called the passive annual heat storage (PAHS) approach to free year-round passive-solar heating. Four basic points make PAHS different from techniques used in conventional solar-heated earth-sheltered houses:
“Geodome, the first umbrella home (in idealized form), maintains a 66° to 74° temperature year-round without heating equipment in western Montana’s cold climate. In summer, solar heat radiates in, falls on internal surfaces, and is absorbed into the surrounding soil. The umbrella traps heat in the dry soil until winter, when it migrates back into the house. Adding convection-driven earth tubes would modify the internal temperature by conveying outside air in.”
Twenty feet under the surface, the soil temperature reflects the average ambient air temperature during the year. In effect, the umbrella raises this constant temperature zone to the surface and allows the house to warm it further.
In summer, air enters the house through an earth tube and is warmed by the sun; moving through the second tube, it warms the cooler soil.
In winter, cool air enters, is heated by the warm earth, and passes to the house
Second generation umbrella home in Missoula, Montana was constructed by Tom Beaudette, the engineer of Geodome.
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