The rest of garden and Geothermal plan for the tiny urban greenhouse. 42sq/ft. 0 AC power, 220 c/ft

Cost so far about $300 less time and trees. I have a rigid 100w solar panel as well as back up. New fan running about 180 cfm for 220 c/ft room. If I make a 3d printed splice I could run 1" tubing through potted soil inside before existing ground battery. This would keep roots well above freezing maybe.
100% off grid so as a test of whether you could have a closed system on say Mars you could raise valuable citrus and add a bit of home to the Mars base. I doubt Elon the Wizard Musk has a 6 year running citrus experiment so he will have to get Tang flavor crystals from NASA.

[@rjung_ch]

Coming along, you're going for the natural heat exchanger method, was wondering about any vacuum effect, you are on it.
👍💪✌

[@441rider]

Thanks, The greenhouse is around 250 cubic feet less pots etc making it closer to 200 c/ft. The inline fan produces 180cfm So in theory when 0c 32f comes I can turn over the whole space with 60 c/f of hose in 2 minutes to fight off the cold or make the terra cotta crisco or DC inline heater circulate faster. I am mentally preparing for the flash dig next week. 3hrs estimate I hope. Be interesting to see how much heat gets stored down there detachable probe lead installed already.