Old thread resurrection, but this is also sort of relevant.



There is a little more information if you google Citrus in the Snow, but don't bother paying for the .pdf. It's horribly put together.

The concept is geothermal heating but instead of circulating water, it's circulating air. Simplifies the geothermal design, and works quite well. We implemented a similar plan/system for my brothers house. He keeps his entire 1960's poorly insulated house at 68 degrees all summer long for the cost of moving air through some pipe. We used "free" solar panels to run the fans, so it's basically free, minus all the extra work.