Glenn,
Thank you for your interest...
> You estimate in the Oregon area that two 200-ft wells would be
> required.? I assume, alternatively, four 50-ft wells.? Putting these
> in line with a simple header arrangement would allow the wells to
> be easily connected together.?
Thanks for spotting my error...
In western Oregon where I live:
1 Ton (12,000BTU/jhr) = 200 ft borehole
(or)
2 each 100 ft boreholes
(or)
4 each 50 ft boreholes
(etc)
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[UPDATE: When I first wrote this, I thought it was correct, but experience has shown that the idea needs modification. The deeper you go, the less seasonal temperature fluctuations will affect the temperature of the earth. The opposite is also true, and the shallower, the more seasonal temperature shifts will affect the temperature of the earth. The following picture illustrates this principle:
In my case, I ended up drilling 16 holes, with an average depth of 17 feet each. The top of each borehole was 2 feet under the surface of the earth, so the effective depth of each borehole was 15 feet. So my total borehole length was 16 X 15 = 240 feet. But since this was close to the surface of the earth, it was certainly not as effective as a 240 foot deep hole. During the winter of 2010-2011, I ran a very small heat pump 24 hours a day. I was able to extract useful heat but I was not able to log so much useful data.
Nonetheless, it is clear to me that the idea works. It is also clear to me that drilling shallow holes, as I did, will require that more holes must be drilled.
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In the part of Oregon where I live, temperature swings are not as large as they are in many other parts of the country, so the heating and cooling load is generally less than in many other places. The information I have gotten from quite a few local sources is that the rule of thumb, when estimating the amount of borehole required here is 200 ft. of borehole for every Ton (12,000 BTU/hr) of cooling/heating required. Because my house is small and well insulated, my design heat load is somewhat less than 12,000 BTU/hr. I have found that respectful conversation with GSHP installers and water well drillers who also drill wells for GSHP installations (most do), will readily yield this rule-of-thumb information for your particular area. Also, I show how you can experimentally derive this information for your own specific location yourself at this URL:
http://ecorenovator.org/forum/introd...nifesto-2.html. The blog posting also cites a document that I took as the source for my test. You would do well to read and understand that document before you do your own test.
One aspect of my test that may appear as a source of error is that the test hole I used was only 12 ft. deep. It would likely give you misleading results to only use a 12 ft. test hole in your location. As the source document points out, your test hole should be as close in size and construction detail as the actual boreholes you plan to use. In my case however, I live in a very small house, which I have re-insulated very well, and I live in a relatively mild climate, and most importantly I am actually planning to use many 12 to 15 foot deep boreholes. So in fact, the borehole I used does resemble the boreholes as they will finally be constructed.
The rest of your thinking is correct regarding using a branching loop field.
> ...where the piping could easily be lifted out and replaced if necessary...
Generally, the piping is designed to go in the ground and to stay in the ground.
> ...considering adapting my Bobcat (since I have one) to do vertical
> drilling to 50-ft.? And, I imagine the adaptation could be done for
> less than the $10k price that somebody quoted me)?
This sounds great! I wish you the best on this one. Please post photos as this progresses. I guarantee that you will have considerable respect for loop field installers when your own loop field is complete and working!
But if you're actually thinking about doing this yourself, you need to give yourself the benefit of all the information you can lay your ambitious hands on. So if you're expecting to save the better part of $10,000 you'd be well advised to spend $100 and go straight to the source of information:
Publications | Manuals. In fact, they offer a ground source installer course at a pretty reasonable cost. My advise is to go for it!
> I would assume maintenance, in event of leaks, would present no
> particular problems with the more conventional methods of
> pipe connection.?
I think that there's probably a good reason why most states require fusion welding and pressure testing of GSHP loop fields. I'm not saying that you're incorrect, but I'd advise you to do more research.
There are also other issues such as being able to achieving flow turbulence and minimizing friction losses, etc. that might not be apparent at this stage of your thinking.
GSHP_guide
> ...the rest of the installation...could be handled by most any qualified
> HVAC installer.? Am I right??
There's probably less cost and drama in the HVAC portion of the project, but your best bet would be to hire someone with successful experience in GSHP installation.
But overall, you have correctly identified that the majority of the cost & work is in the loop-field.
But Glenn, if you are going to go to this length, I would advise you to also consider abandoning forced air and going with hydronic radiant floor heating. Not 'staple up', not the panels that go on top of the floor, but what's known as 'wet system' where the PEX is embedded in a 1.5 inch layer of concrete. When properly done, this offers substantial advantages over forced air, as the heat pump is not called on to raise the working fluid (water) to as high a temperature.
hydronic-heating
Hope this has answered your questions.
Regards,
AC_Hacker