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Old 11-14-16, 10:07 AM   #1
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Default What underground insulation for hdpe pipe???

OK you ravagers of window units, I'm about to bury 3 or 4 pairs of 3/4" hdpe in/out lines in 1 trench about 75' from my basement to the same # of vertical heat pump utube bores in the yard. Trench depth about 2 or 2.5 ft. Earth is clay/loam.
My first thought was to use the fat pool noodles that are on sale cheap at end of summer at the big box stores to insulate each line as their id seems about right but wondered if they would deteriorate or saturate underground?? Maybe food for earthworms?
Other idea was to get some 8ft sheets of 1" pink foam board, line the trench bottom with it and the sides maybe 6" up from the bottom. Then gang all the cold lines on one side, hot on the other, separate them with a foam piece dividing the hot gang from the cold, the top it with a sheet across both rectangular alleys - think a rectangular cold pipe alley beside a rectangular hot pipe alley extending along the bottom of the trench then and shovel in the dirt??
Not too cold here maybe lows of 5 - 10F and high of 95 in summer.
Then i wondered if these are commonly insulated or even separated in the trench since they are sort of married anyway in the bore holes?
Anyone with any experience on these?

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Old 11-14-16, 06:08 PM   #2
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Lots of details to address, but the short answer to your question is the pro's use armaflex on every pipe above frost line. I don't see why the pool noodles wouldn't work, as they are closed cell also.

Yes, the pipes will interfere with each other if you lay them close eough together. Whether that will make a difference depends on lots more details.

As always, proper preparation prevents poor performance. Keep on with the planning and asking questions. There are many successful DIY geothermal builders just waiting for you to get interesting.

Last edited by jeff5may; 11-14-16 at 09:23 PM..
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Old 12-13-19, 08:45 AM   #3
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Hello Alexandra
I ended up laying all the hot runs side by side in the trench bottom, then a sheet of foam over that, then the side by side row of cold pipes over that with a final sheet of 1" pink foam over those. Didn't use the pool noodles. If nothing else the foam protects the pipe if you have to dig it up.
I left some overhang of foam on the sides so the earth weight bent that down to sort of cover the sides and finally took a lot of pics of the trench and measured its location from other landmarks and put a length of wire on top of everything to maybe be able to find it with a metal detector.
Seems to work well but I really don't have anything to compare it to and after all the hot and cold runs are close to each other all the way down the vertical holes anyway!
Good luck, how cold does it get in Rumania?

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