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Originally Posted by stevehull
As for the DIYer - I have a lot of faith in direct exchange (DX) applications. You can increase the heat flow by using copper.
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In the studies I have done, the copper/DX advantage is around 15%. Intuition would suggest it would be far greater, but in the grand scheme of things, the thermal resistance phenomenon is very much like several resistors placed in series, and the resistance of the pipe wall turns out to be one of the smaller resistors, so radically changing its value doesn't have a radical effect on the whole system. Personally, I think that most of the DX advantage comes from eliminating a HX (the rule of thumb is 10% per HX).
Quote:
Originally Posted by stevehull
And a LOT of soft thin wall copper can be put in a small volume. But to do this, you need to build several heat exchanger "nests" that reside in the bore hole pipe. Lots of parallel tubes with 180 degree soldered bends also assists with turbulence.
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Is this your own hunch, or is there more to this story? I'd like to know your experience or references or studies about this. My own experience is that heat movement in ground is much more like molasses. Prove me wrong, Steve.
I was surprised to read in the IGSHPA manual that putting in two (HDPE) loops in a borehole increased heat transfer by only 4%... I would have expected 40%.
Quote:
Originally Posted by stevehull
Copper is simple to solder... You have to know your soldering technique...
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Are you suggesting that refrigerant pressure and temperature cycling can be effectively contained by solder joints? In the trade, they braze. They might call it soldering, but it is brazing, using phosphor/bronze + silver.
Quote:
Originally Posted by stevehull
...use a fluid that is close to neutral pH...
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Depending on the locale, ground PH can eat copper pretty quick. In Norway, they were figuring a copper loop life of about 30 to 40 years. They also studied using stainless instead, but decided that an inexpensive, very long lived, but somewhat less efficient loop was best.
Quote:
Originally Posted by stevehull
But all this can be done by the careful DIYer. There is a lot of resistance from water quality people that are scared that aquifers will be contaminated if a loop installation goes bad. But a monitoring situation is easy to set up (detect loss of loop pressure for example).
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If you're doing Direct Expansion, a loop faillure means you have contaminated your soil with refrigeration lubricant. If you live in an area where it is just fine to contaminate soil with compressor lubricating oil, I guess it's only your conscience you'd have to deal with. In areas like Oregon, with a strong Department of Environmental Quality, you'd have to deal with your conscience and also the fury of the State.
So, when there is a copper DX loop field failure, what exactly is the procedure to remedy the situation? I mean... location of the leak, how would that proceed... and remediation of contaminated soil, what would that look like?
I think HDPE has a lot going for it, a 'guaranteed' life of 50 years, and a more realistic life of 200 is pretty darn good. I mean if our forebears had put in HDPE loop fields all across America in 1813, we'd still be able to use them today.
Best,
-AC