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Originally Posted by Mobile Master Tech
...you made a post in this manifesto considering extra pipe surface area in your ground loops by having the pipe make an inverted U at the top, sending the pipe back down the borehole again to a second U at the bottom of the borehole before returning to the top. I don't think that will work well at all-you will never be able to purge all the air out, and even if you did, any future entrained air or gases that come out of solution will form a bubble that will act like a reverse plumbing trap, stopping or severely limiting flow in that loop!
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The IGSHPA manual actually had a section on the advantage of an extra loop in the hole. They said that the advantage was small, on the order of 5% advantage. With regards to purging, I don't think that would be an issue once purging velocity was reached. If my memory serves me right, the velocity was about 3 ft/sec... at that point, bubbles don't stand a chance. But your other point is a correct one. There are air separators that are used in hydronic floor installations, you probably have one in yours, that do a good job of getting rid of micro-bubbles before they become bigger bubbles. There would be another way this could be done, and that would be to have a mini-manifold in each hole, so there was no bubble trap. It's all a lot of work for 5%. But I was struck by the wetness of my soil (in mid-August), starting at about 8' down... and I know that wet soil is a much better conveyor of heat than dry soil.
Quote:
Originally Posted by Mobile Master Tech
After realizing just how versatile PEX is while purposely torture testing then reheating it during my radiant floor installation (details HERE ), I think a better idea is to have a form, such as 2" thinwall PVC, that can be lowered into the borehole. Slip the appropriate return length through the center, heat the pex to make a Ubend at the bottom, then wrap the PEX barberpole style along the outside of the form. Space it out as there is no need to wind it tight-1/2' pex could wrap about 575 times around a 30' length of 2" PVC for a loop length of 480 feet!!! This would be an easy way to avoid pipe welds or connections down the hole while increasing pipe surface area and effective heat transfer due to turbulence in the pipe. Regular 3/4 poly flow is pretty stagnant at the boundary layers because the flow is slower. You can flow almost 1gpm through a 1/2" Pex loop before you get significant head loss if your loops are less than around 300ft. |
You may be on to something... or, you may also be over-thinking a simple problem. If you're convinced that your idea is a good one, make two test holes and do an A-B test, find out for sure.
But one of the big lessons I learned is how slowly heat travels through the ground. It's flow is not like water, it's much more like "molasses in January". It may be that you have created a much more effective HX, but if the heat will not move fast enough for your system to realize that advantage, then you're just not very far from where you started.
But don't take my word for it. I think you already said you had a post hole digger... dig some holes and do some small tests, that's what I did. If they look promising, carry on, if not try something different.
Quote:
Originally Posted by Mobile Master Tech
I feel this will work for depths up to 50 feet before handling the pipe gets unwieldy.
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If your heat transfer is significantly better, unwieldy won't be such a problem, because gravity will be on your side.
Quote:
Originally Posted by Mobile Master Tech
Looks like most of us doing boreholes without a professional well driller won't be going deeper than that.
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I have heard of amazing holes being dug with the gas engine type drilling rig, in the sandy southern states. You would want a frame for your rig and a power winch because the drill string + power head will get pretty heavy. Don't be too quick to limit your thinking to a 50 foot hole at your location. You just may be a lot more fortunate than those of us in other areas. Have you talked to well drillers yet? They can be a great source of info, especially after lunch.
Good luck,
-AC