Clay tiles (tubes) could be a possibility, ground is red clay/dirt composition, maybe someone makes them locally ? Ground temp possibly around 55 deg @5' depth ? Haven't tested yet.
Not trying to heat or cool directly, just integrate as much as possible to lessen expensive means to heat or cool. Closing doors to bedrooms, bathrooms will lessen amount of CFM to be treated and still, "creepage" or cooler/warmer air under doors etc. should still help somewhat. Addition of solar power to cut electric bills should also help greatly.
Solar panels on roof might shade the "vaulted" roof/ceiling inside, but, a fitted second roof of 1x6 rafters, as such, and sheetmetal, insulated on underside would prevent excess heat and help longer lasting asphalt shingle roof deterioration.