Underground Heat Storage - The Storage Zone

Still, the most advanced book available on the subject is Passive Annual Heat Storage - Improving the Design of Earth Shelters. This 1983 text is still quite up to date as it teaches the basic methods of understanding natural heat flow methods that never change. Other supplementary materials, home plans and instruction videos are available.

You can order books, videos, and papers on a large variety of topics which are available from the Rocky Mountain Research Center.

The storage zone is that body of earth which will be warmed to room temperature, so that the stored heat will conduct its way back into the home in the winter. When this underground heat storage mass finally becomes climatized, it will function at or near the desired interior temperature.

The storage zone is quite large. First of all, it includes that portion of earth which is on top of the roof and under the umbrella. Not all home designs will have the capability of supporting more weight than just the 2 foot (.6 m) deep moderation zone. In that case, only the roof itself will store heat at room temperature. Secondly, it includes the warm earth to the sides, rear and front of the home, under the umbrella, out to within 7 to 10 feet (2 3 m) of the uninsulated surface. That is, out to the isolation zone.

The largest body of earth that is available as warm underground heat storage zone is underneath the home. This earth is very well isolated from the out of doors and can be climatized for a great distance. Over a very long time, the actual warm temperatures may extend 40 or more feet into the earth. However, the six month delay through the first 20 feet (6 m) prevent any of the heat that may be further away from entering the home. It will, though, maintain a very small temperature differential over very long conductive paths, so that essentially no more heat will be lost into this very deep earth.

One limiting factor may be moving ground water. This water will carry the heat away, and thus will limit the extent of deep earth temperature modification. However, very few homes should be built very close to flowing ground water, and water that comes down from the surface will be taken care of by the water control methods discussed in the next two chapters (Chapters 3 and 4 of the book, Passive Annual Heat Storage Improving the Design of Earth Shelters).

A new thermal environment, under this umbrella, can now come into existence as the underground heat storage mass is climatized to achieve a new constant temperature, which it and the home together, will maintain year round within very narrow limits, on the order of 3 to 5F (2 -3C) from the average.