I found some links to get you started. Has been several years since my schooling, and most of it is sketchy now as they failed to tell me at the time I was to old to actually get work in the field, lol.

One of the things to remember is the principle behind an ac unit (which is what the heat pump uses). Most people assume they function by pushing cold air into the room, but what they are actually doing is extracting the heat from the room, making it boil (changing the saturation point) through manipulation of pressure in the refrigerant and then throwing that heat outside.

https://www.doityourself.com/stry/4-things-to-know-before-you-build-your-own-heat-pump-system

http://www.madehow.com/Volume-3/Heat-Pump.html

http://www.refrigerationbasics.com/RBIII/heat_pumps1.htm

This video made me laugh. He stripped what he needed from an old refrigerator. My instructor was an old HVAC contractor who advised us to do the same to save money on a pump when we were starting out.

This video is intricate, as the guy makes solar panels to make his more diverse in functionality. The one takeaway I got from it though was he appears to only go under the house and hot down into the ground as many heat pumps do, as the temperature remains more constant (and warmer in the winter) the further down you go.

https://www.architectmagazine.com/technology/going-underground_o

https://www.physicsforums.com/threads/temperature-for-3-or-4ft-underground.826193/

https://courseware.e-education.psu.edu/courses/egee101/L01_plug/L01_05.html

It appears that at 8 feet or so down that despite being freezing temp on the surface the temp will be somewhere around 50 degrees. Hope this gives you a good place to start.