just thought of the coolest thing ever and this gave me the inspiration.

ok things you will need shovel and lots of PVC

k so dig a big hole in your yard about 2 meters by 2 meters and about 1 meter down
then lay pvc tubing down in a back and forth pattern
then rig it up to your WC loop

i think this will work cause ground temp is about 7-21 degrees Celsius 1 meter down