I recently installed a 4 ton Geothermal with a closed loop. From the dual pump I ran 100 feet 1" PVC line to 900 feet 3/4 pvc line 6 feet deep. At the end of the 900 feet I covered it with a 18" of soil. I then made a 360 degree turn and ran another 900 feet of 3/4 to another 100 feet of 1" in the same 18" ditch back to the pumps. It is close to 100 degrees today and my pressures are 210 discharge with a 42* evap. But I'm waiting on the heating season to see where i am with heat. Yo answere your question. It worked for me in the south.
30 to 60 feet drilled at a thirty degree angle the manufactuar should have a distributer that looks like an octopus remember you can incase the pipe in concrete or sand and it wont affect the heat transfer also dont have your loops to close to eachother they will give heat up to eachother or try to obsorb the same heat exelent choice hope your a pro