We have weeks where the daytime temps don't get above 0F more winters than not.
Insulation is a given. Windows alone aren't practical for the layout of the building (monitor barn). The middle bay would be dark and thus cold.
Solar is a strong possibility. I've measured 132F at 4" beneath the sheathing in our roof with "weathered wood" asphalt shingles when the temp was in the mid 60's outside, so there's certainly some potential there to be captured. The vacuum tube solar collectors are also interesting (as was the pop can heater). We did parabolic mylar hotdog cookers in 8th grade and I knew even then that such a technique had more useful applications than bursting the edges on Oscars wieners. :laughing:
I'm looking at roughly 5000sf with a nominal 12' ceiling for the main floor for the shop, and something around 2-3K for the house. So roughly 10Ksf of heated floors between the two buildings. So by using the slab to take the bottom edge off the heating needs, and then also using it to help chill the area when the outside temps are high, I think there's possibly some merit in exploring that. Ground loops are only one technique. You could have buried heat exchangers with barrels of water acting like a water body. It's entirely possible I'll hit the water table too, as I have a spring fed seep maybe 400' from the house site and it's only about 20' lower in elevation.
What'd be sweet, but completely impractical would be to drill down deep enough to get 100F core temps and place an exchanger there.
Honestly, reading about the costs of short lived geothermal pumps makes buying propane and simply having 2000 gallons of it on hand while buying in the summer when prices drop a better solution than doing GT heating at all. I'll be encasing the whole exterior in 2" of high density foam and sealing it again. My current shop has 1.5" pink foam and R19 in the cavities and it's pretty darn efficient even given the fact I made it drafty intentionally so I could get air moving when I'm welding. The new shop won't be drafty, I'll have some make up air ducting in place instead.