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Old 07-15-15, 01:51 AM   #2
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Originally Posted by MEMPHIS91 View Post
Greetings and welcome to my largest project yet, and by far the most expensive. I currently have a old 10 seer 4 ton air source heat pump that is on its last leg. I had plans to replace with a new unit but considering the cost and how doable this build looks I plan to build a DX (thats right no water pumps) geothermal heat pump (R290 of course) that uses a 3 acre, 17 feet deep pond/lake that is 40 feet from the edge of my house.
Oh boy! One amazing project after another!!

Personally, I think that the pond scheme could put you right up against the maximum limits of DX feasibility, what with lubrication issues, etc.

I have seen schemes where GSHP systems of the size you are talking about have worked.

Here is how they do it:

The advantages are that all of the copper loops, return to a central manifold. Also, since they are on a slant, the vertical distance (head loss) is reduced, while the linear exposure to the earth (water) is the same.

You might be able to use parts of this general scheme for your mega project.

If it were me, I would go with HDPE piping, which is not such a beast to weld as it might first appear.

In the grand scheme of things, going from copper to plastic results in about 15% reduction of heat transfer per linear foot. The remedy is to put in more plastic pipe.

Once welded, HDPE is eternal. It is very tough, and totally immune to corrosion.

You could run your HDPE up to your compressor shed, and go through a HX. Since it will be closed loop, a correctly sized brazed plate would be a perfect choice.

Also, please note that a 4-Ton compressor unit (and associated copper if you go this route) will contain a non-trival amount of propane and you do not want that to be in, or even up-hill of your house. Definitely outside, definitely downhill, preferably at a modest distance.

Them's my thoughts...

Go for it, however you will.

Best of luck,

I'm not an HVAC technician. In fact, I'm barely even a hacker...
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