Would it be reasonable to install ground loops and simply circulate water through radiators in a building or greenhouse? I have a building that I need to maintain between 50 and 80 deg F. Most of the time in the winter the building requires no additional heat other than what radiates from the foundation and sunshine on the exterior. I'm wondering if I could adequately cool the building in the summer, or if the thermal transfer to the ground would be insufficient due to a low differential. I expect the water returning to the loop would be something less than 80F (since my goal is max 80 inside) and the soil temperature is probably 70F. With <10F differential, my gut tells me it would require a huge amount of loop piping. I know there is no such thing as free lunch, but a cheap one might be good enough Thanks in advance.