I apologize if this is a dumb question, but I can't find an answer elsewhere.... I understand that water is a much better conductor of heat than air, but I was just wondering if a geothermal system could be practical if it consisted only of pipes (your choice) looped around in the ground and connected to the living space by only an intake and exhaust fan - no heat exchanger, no water, etc. How much more pipe would be necessary? I'm thinking besides the poorer K (air vs. water) another problem would be the compressibility of air would be a major factor in actually getting the heat to move in a much longer array of pipes. But maybe just a simple air pump would be sufficient? thanks for considering the question.