One of the largest players in the metro Atlanta area market changed owners a while back (they used to have most of the 40+ HD stores). The previous owner offered 10yrs parts&labor for years... then sold the co. The new owners do NOT honor the warranty from the old owners customers.
Guess who lost (and who won)... :whistle:
This shows the install of the ground loop, shows grouting and back fill with neutral PH sand. http://www.youtube.com/watch?v=FC69Vc-mcaQ
This would slow down or stop the corrosive effects of the soil. I would still clean and coat the manifold braze connections.
In 85 I repiped my Grandparents house in Jacksonville FL. Did it under a Great-Uncles plumbing license. I used K from the meter to the Main shut-off at the house. Within eight years it had been replaced. I went down deeper than the original, so it didn't freeze. So this is a universal problem.
Only noble metals (like gold) appear in pure form since they don't corrode (at least not with just oxygen). therefore all geothermal systems use some plastic piping. If you don't trust plastic for 4 billion years, you could use schedule 80 gold as well... if you can afford it :)
The 50 year warranty is only good if the contractor stays in business that long :) chose the right contractor and the right design and material and you don't need the warranty. I'm sure there are certain certifications in your area to find a good contractor.
Gross: I'm not a mining expert. But a copper deposit in the earth is not just a cubic mile or pure copper with just the edges corroded and pure copper inside. It is copper-oxide mixed with all type of "dirt". I don't know exact %, but iron ore has maybe 5% iron to be worthwhile being dug up, copper may be even less. Even gold deposits or diamonds have much dirt around them. the erath didn't specifically separate metals for us to just dig up. there are just areas with higher concentrations. Maybe copper in normal earth is 0.00001% and in a copper mine it is 3%. (don't quote me on the numbers, I'm just illustrating). I've seen the copper mine by SLC (the largest in the world) and didn't see any copper at all, it all just looks like dirt before being smeltered and elctrolytically concentrated.
I would think that a direct earth contact DX system would be cheaper to install, and more efficent. In 20 years the technology will have changed enough to warrant installing a totally new system. Even though I have an acre and quarter of yard, I really don't want a very large area dug up for the horizontal loops. I thinking next Fall installing a new system, my mortgage should be paid, off and I can use the rather large escrow to pay for it.