DIY Geothermal Heat Pump

Dig a large hole in the ground near the building using the shovel, or a backhoe if it is available or even necessary to use a large piece of machinery. The hole needs to be roughly one-half of the building's footprint and two feet deeper than the local frost line. In most of the continental U.S., the frost line varies from 3 to 4 feet below the surface, but it's advisable to contact your local governmental agency to check the average depth for your area.

Lay out the flexible steel tubing in a zig-zag manner along the dirt at the bottom of the hole. Parallel portions of the tubing should be kept two feet apart from each other. The bottom of the hole should be dirt. Clay and sand are fine, but if the bottom is rock, you should find a new location or you will have to add 2 feet of earth before laying the tube, and still cover it later with 5 to 6 feet of dirt.

Run one end of the flexible tubing up to the building and then inside to the ventilation system. Attach the expansion port on the other end and attach another piece of tubing to run to the ventilation system. The ventilation system is often located in a storage room for commercial buildings, while a home generally has its ventilation fan located in the basement or an attic. If you can't find it, trace the duct work from the vents to find the fan.

Place the heat exchanger in front of the ventilation fan. The heat exchanger should fit just over the duct work in front of the fan without any gaps. Connect the duct work to the heat exchanger to form an air-tight system again.

Connect the tube running to the expansion port to the output of the heat exchanger.

Connect the other tubing to the refrigerant filling port and then to the input of the compressor.

Connect the output of the compressor, using a short piece of tubing, to the input of the heat exchanger. The compressor will compress the refrigerant, which makes it hot. The heat will be dumped to the building, via the heat exchanger, then the refrigerant will be allowed to expand, cooling it below the ground's temperature.

Solder every joint in the system's tubing using the solder and blow torch. If you are using pressure-lock joints, they do not need to be soldered shut.

Add refrigerant through the filling port and fill in the hole in the ground. The refrigerant will flow through the tubing in the ground, being warmed to the ground temperature. It will then be compressed, heating up the liquid. The hot liquid will be cooled by the fan blowing over the heat exchanger into the rest of the building. The cooled liquid will depressurize, cooling it below the ground temperature; the process is repeated, forming a continuous closed loop.