July 2008: Geothermal heating/air conditioning: Using the earth's stable, below-ground temperature to heat or cool a building. This method has been used since as early as the reign of the Roman Empire...and probably earlier. Advances have been made to take advantage of the renewable (and free) resource, but the general concept is the same.
In Minnesota, the temperature of the earth about 7'-10' below ground is a constant 55-60 degrees. Standard geothermal heating and cooling implement the use of long hoses, which contain some sort of antifreeze fluid. The fluid is heated or cooled as it moves through the hose for the purpose of heating or cooling the element in your forced air furnace and/or AC unit.
A somewhat simpler method was bouncing around in my head after a couple casual conversations, then later confirmed by some research. I figured that you could just as easily heat or cool air by running large diameter tubing underground for a specific distance. You'd leave the back end open for incoming fresh air, drawing it into the house with some kind of fan or air pump. The size of the tubing and the distance it would need to run were what I had no idea how to figure. I mentioned this to Roger Kranz, my excavation guy, and he showed me an excellent magazing called "Farm Show". It contained MANY great, low maintenance, economical, energy-efficient, eco-friendly household ideas. Among them was almost exactly the idea that had been bouncing around in my head - but with some specs on diameter and distance to give me a start.
The pictures below are just the beginning, as there are MANY bugs to work out. All I have so far is the tubing - buried and routed into the house, through my workbench and upstairs at the center of the structure. There will be a great deal of experimenting to get this thing to work right. Some of the challenges will be: Selecting the correct fan, ducting for optimal heat/cooling (probably two sets of ducting), moisture (condensation) collection, and filtering impurities out of the incoming air.
Cost: trench excavation (8-10' deep x 125' long) - $600, tubing & accessories (6" I.D. x 200' corrugated plastic pipe, tee, coupling, etc.) - $300