Can one have a 10 yard x 10 yard x 10 yard water tank under the house, and use it as a massive thermal mass to use summer heat to keep the building warm in winter?
You could, but my intuition for heat storage capacity tells me it wouldn't last more than into mid October, in many places. Also building a foundation that can take the weight of a 10x10x10 tank of water is costly and non trivial, before you buy or fabricate a tank...
