[stevehull]

I am assuming that a peripheral heat exchanger be put in water contact in a bore hole and not in the ground (as in buried in soil). I do not have a lot of faith in a flat copper plate, buried in the ground, absorbing/radiating many BTUs.

My mistake to use the work DX as in direct exchange. I would replace the vertical loop with a loop with a "nest" of copper tubes in parallel, with several of these exchange nests located in the vertical bore hole each suspended in the static water column.

This replaces the long vertical loop, and does NOT contain refrigerant.

The above is a low pressure application and conventional soldering techniques can be used as there is NOT high pressure refrigerant. If a blow out occurs, yes, you do have to deal with a fluid in the aquifer, and that is why so much research is going on to prevent this and also to have a biologically compatible fluid.

The question I am relying to is "what can the DIYer do?" They can build, rather inexpensively, a set of copper based heat exchangers that sit in a deep bore hole of water. These can be built with simple techniques to accelerate turbulence (dimples) to maximize heat transfer.

The use of thin wall type L copper pipe can be used in water situations where water quality will permit.

The industry is trying hard to come up with other solutions. There are ceramics that are being looked at (tremendous heat transfer capabilities) and other exotic metals, but it is hard to compete with HDPE. It is quite inert, takes a lot of pressure, inexpensive, long lived, flexible and simple to fuse.

But conventional bore holes with HDPE vertical loops are expensive . . . and are curtailing the acceleration of the industry.

Steve