Attached is a rather long description of the ground source heatpump that I built at the end of 2021.  It's completely diy - two 2nd hand fridge compressors(one for vacuuming down, one for the HP itself), bits of bent copper pipe, etc.  I've encapsulated it as a pdf so that it hangs together in one thread, and should be an easier read.  Thanks buildhub for a big filesize limit! I started out knowing vaguely what I wanted to do, then watching every youtube on R290 compressor systems several t