This is a great topic to begin with, I must say. Using the earth surface as the heat sink or a source of heat is going to benefit human race during both the summer and winter. I believe this ground source to be far better than air source.
Learnt a lot here. Thank you for putting this together.
I am @teekingtv and I write STEM.
It absolutely makes more sense to store our summer heat and reuse it during the winter versus pumping it into the atmosphere and then regenerating it each winter. Air is an extremely poor conductor of heat, indeed. Thank you for checking out my post!
I tell you. Anytime.