Mr. Willy, Hopefully I can add some infomative infomation. I am a home builder here in Ohio and have reseached geothermal heating. Depending on your well output and other variables such as summer water tables etc. I have found that an open loop system is very effective. Basically you "pump and dump". You pump the water out of your well and it goes through the geo and discharges into your pond. I have a well that produces 25 gal/min. I have 2 hvac contractors that I use and they both have the same system at their own homes. They have told me that anti freeze coolant lines have some problems such as the longevity of the antifreeze producing cooling and heating returns over a long period of time. Both of my contractors recomended a pump and dump (open loop system) vs. a closed loop.

Another advantage that I have with my system is that when my geo is running, I have 4-10 gal./ min. emptying in to my pond to keep it full during drought.

It all depends on what kind of well water you can produce. Here in my area it is not a problem. Hope this may help.