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The subterranean heating system is comprised of several hundred feet of thin
walled 4″ perforated drainage tubing buried under gravel. A fan connected to the tubing via a common plenum provides forced flow of greenhouse air through the tubing. Because daytime greenhouse air is warm and humid and the greenhouse base is cool, moisture will condense as the air passes through the buried drainage tubing, thus removing heat from the air. Upon returning into the greenhouse air space, the air is cooler and less humid. In this condition, the returned air can absorb moisture, thus cooling the greenhouse air. The uniqueness of this cooling system lies in the phase change that has occurred in the buried tubing.
Besides cooling the greenhouse air, this process also heats the greenhouse base. At night, the fan can be run to heat air as it again passes through the buried tubing, thus convectional transferring heat stored in the
greenhouse base to the greenhouse atmosphere as the air re-enters the greenhouse.