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Old 05-01-15, 10:05 AM   #9
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Originally Posted by MEMPHIS91 View Post
...What would be the advantage of top vs bottom?
I don't have any experience with DX, so I'm trying to imagine what the behavior of the vaporized refrigerant would be, based on what I have witnessed so far...

I initially imagined that there might be a condensation problem, but then I realize that condensation will not happen in the low pressure side. Another aspect would be that the temperature of the liquid-flashed-to-gas that is exiting from a high-pressure tube into a low pressure area will be the very lowest in it's trip back to the the compressor, so the delta-T will be greatest and the heat migration into your vaporized refrigerant will be maximum at that point. The delta-T will decline as the vaporized refrigerant gathers more heat. So there could be an advantage to having all that take place at the deepest, most wet, most temperature-stable part of the bore hole.

The opposite scenario would be that if the liquid-to-gas transition happened at the top of the hole, the vapor would have a longer distance, and longer time to gather heat. The construction and maintenance would be much easier. Also, if you went for a TXV, it would need to be at the top of the hole. But I think that a TXV for such a tiny compressor would be just too much techno for what should be a simple, elegant project.

Originally Posted by MEMPHIS91 View Post
I now have an idea to run 2 loops of 1/4 tubing 30 deep feet coming off a common manifold at the top, both sharing the same bore hole. It might be a bit trickier to get all that in 2-2 1/2 inch bore hole, but it will completely solve the lubricant issue.

In the IGSHPA manual (CLGS Installation Guide (#21020)), in the section on the loop fields, it looks at various ways of doing loop fields, both trenches and boreholes. There was even a small discussion on putting two loops in the same hole, and I believe that the performance increase was about 3% to 5%.

I'm afraid I don't understand how two loops would remedy the lubrication issue?


P.S.: This manual is a tad expensive ($45.00), but it is so amazing in the breadth and depth of information regarding Ground Source heating and cooling, that you should seriously consider getting a copy. It can sometimes be found used, sometimes in libraries. But considering the information, it is a miracle. As I recall, the manual does not directly address DX, but most of the principles are the same.
I'm not an HVAC technician. In fact, I'm barely even a hacker...

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