My Mother's House Part IV

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As our earth-sheltered houses is backfilled, it's time to tell you about our natural air conditioning system.

STAFF PHOTOS

The building's natural air conditioning system consists of 15" diameter PVC irrigation pipes buried deep in the cool soil.

The drainage lines for the foundation run through the same trenches as the "cool tubes".

The cooling system pipes enter the house through an opening at each end of the front wall.

The intake ends of the cool tubes are capped with screens and shields to keep rain out.

Fill dirt was added until we reached a level about 1-1/2 feet below the edge of the roof on the back of the building. We then laid a 6'-wide sheet of ymil polyethylene along the entire length of the building, to prevent water draining off the roof from running directly down along the wall.

The aboveground portions of the upper level are insulated with 1/2" polystyrene and 3-1/2" fiber. glass . . . for a combined R-value of over 20.

Gravel is spread around the drainpipes that lie against the back wall.

The greenhouse section of MOM's house nears completion.

With winter upon us, the Eco-Village crew has been hard at work getting "My MOTHER's House" ready to weather the coming storms. And beyond the innumerable seasonal details to be taken care of—which include installing insulation, sealing, shingling, and flashing to name a few—we've had to finish off one component that we really won't be needing all that much until next summer.

Because our building's single most important energy-conserving feature is its earth berming (and, on the front half of the structure, the sod roof), we've been anxious to get on with the necessary backfilling and grading. But to do so, we've also had to go ahead and install the natural cooling system (it consists of a pair of buried 15"-diameter, 60'-long plastic pipes), through which ground-cooled air can be drawn into the house. Now air conditioning may not be at the top of your list of concerns as the snow blows past the living room window, but the tubes had to be installed before the berming could be done. So snuggle up to your woodstove while we tell you about our passive home cooling system.

THE EARTH AS HEAT EXCHANGER

Since soil is far less willing to conduct heat than is air, the temperature of the earth below the frost line remains comparatively constant throughout the year. At 25 feet down there's essentially it change in the ground temperature . . . though at shallower depths the tempering effect is weaker. In general, however, the earth six feet or more below the surface will stay fairly close to the average annual air temperature for the area.

And that stability of ground temperature is, as many of you know, the key to the energy efficiency of earth-sheltered homes. The soil surrounding such structures is likely to remain in the 50°F to low 60°F range, so the buildings lose less warmth in the winter, and gain less heat in the summer, than they would if their walls were exposed to outside air.