Sounds great! I wonder: Why is sand better than the dirt that’s already on site? Dirt, after all, contains water, which I believe should have an even higher th

Sounds great! I wonder: Why is sand better than the dirt that’s already on site? Dirt, after all, contains water, which I believe should have an even higher thermal capacity, or not? Also: How about combining this approach with a heat pump instead of resistive heating?