All efforts like this should be encouraged and applauded. I especially like the geothermal design. I have wondered why no one was using that idea as a heat-exchanger ever since I've thought about passive energy building design. They have been. I just wasn't aware of it.

I think an underground building makes that process even more direct and efficient. Something cave-dwellers would know. Probably the biggest problem/downside to earth dwellings (other than caves in a mountain side; although they might be too) is water leakage and being flood prone in flash-flood conditions. The idea of living in a cave in the side of a mountain is very appealing. Applying current knowledge and technology to the idea would be interesting and challenging -- a reliable water source would be a major issue, for starters. On second thought, doing this on more level ground makes more sense. Much harder to garden on a mountain side.

Looks like some good ideas and conversations here.

Passerby, geothermal energy is used in Iceland and northern New Zealand to great success, but these places sit on top of very hot thermal vents, or volcanic activity, so it is not possible to do this cheaply at other locations!

Spencer.

Thanks for the comment, xanasax (aka Spencer).

I was under the impression that geothermal can be used for both cooling and heating, or at least using ground temperatures (beyond 30ft. according to the info. at one link) to stabilize the fluctuations of building air at ground level. Since I don't personally know anyone with a geothermal cooling or heating system, I don't have any personal accounts to rely on or examples to sample physically. But there seem to be people online who have systems for both cooling and heating and also endorse the idea.

The word thermal has the connotation of "heat." I can see how heating would seem the easier, more obvious case. I'm sure geography does influence the practical application. And cost does seem to be a limiting factor in the practical use. I think that is because heat is considered the primary reason for using geothermal as implied in this article. I think the emphasis on heat is because "we" are looking for it to also generate electricity.

Here's one person's attempt to not be limited by cost. (Surely his "method" could be automated and not require manual monitoring and switching. His solution isn't practical for someone who isn't home during the day -- especially in hot areas. But mainly it demonstrates why passive design of human occupied spaces, in the beginning, is a better solution.)

The basement temperature used for cooling in the above "story" lends support for underground dwellings to be considered as part of the solution to energy conservation planning. Overall, this is why I think energy efficient design of buildings is very important to curtailing non-renewable energy needs. It begs for creativity AND implementation.

I'll try to educate myself more, starting here. (Although, the emphasis there still seems to be on seeking "heat" sources within the earth. To me, it's definition and use is more versatile than just a heat source and shouldn't be limited in that way.)