I read your geo adventure. Quite interesting. Your comment about direct exchange vs. water loops is not quite accurate. Rather than being "old" systems, the majority of all geo systems sold today are water loop systems. They have improved over the years with better heat exchangers, etc. Actually the thermal conductivity of the plastic pipe is not a major issue, as the heat flow through the earth is much lower and the limiting factor. Many of the companies offering direct exchange have have dropped the product. The two major issues were corrosion of the copper pipe in the ground, and too much heat flow from the direct exchange loop. This causes a greater amount of heat flow than the ground can handle. Using a smaller copper line (to minimize the problem) creates too much flow loss for the compressor, and in some in some installations a "perma frost" effect occurs as the ground freezes locally around the coils. Also the losses for the water circulator are very small, and not much of a consideration.
Sounds like yours was a better design than some of the older units. From the pictures, it looks like you don't have one of the great features with a geo unit - ahot water generator. The waste heat from the system is recovered and preheats water for the domestic hot water. 2000-3000 BTU/hr can be claimed from each unit, and typically 40%-50% of the hot water energy can be realized. Hope it does well for you. Keep your site updated with the performance.
paul
