The Homemade Heat Pump Manifesto

[AC_Hacker]

Originally Posted by superlen

I seem to recall that you can't fuse pex so I would be left with a mechanical connection that most likely will cause some issue sometime in the future. I thought about bringing the 3/4" up nearer the surface (18-20") at the connection point to the supply/return and making that connection in a box so that I could easily inspect/repair if necessary. 95% of the loops would still be at 6' of course. This would require 5 boxes and a small portion of the supply/return lines to be at 20" depth. I would then drop back to 6' deep on the 200' way out and back to the loop field from the house to pick up whatever additional heat transfer I could gain in transit. That amount of heat exchange might be small due to laminar flow in the larger pipe.

That's right, can't fuse PEX. I even tried... will not work.

So that leaves you some kind of physical connections. Whatever you use will most likely go inside of the piece(s) of PEX so you don't want to reduce the diameter any more than needed. I've seen brass barbed connectors that might do it. The more acidic your soil, the faster the corrosion, so if you know the pH it could help. Also, if it is possible to obtain (make) stainless steel barbed connectors, that would give you a chance. I used some stainless steel hose clamps on some very wet-duty applications, and the clamp itself was resistant to corrosion, but the screw was the problem. If you can get 100% SS hose clamps you might be OK.

As to the rest, it looks like you did your homework, so your guess will be an educated one.

-AC

[jeff5may]

Please flog me if I am wrong, but this would seem to be a good fit for shark bite fittings. They are not as cheap as irrigation-style clamp or crimp fittings, but they are dead easy to install and come in either plastic or brass. The connection is repairable if it leaks.

[superlen]

Jeff,

If I made the connections inside the access boxes I think sharkbites would be fine, although I'd probably still just use typical crimp rings. If I opt to bury I think sharkbites would bite it. (I don't know if they are underground rated, but I suppose they could be)

Truthfully I'm a bit leery of any connection 6' underground. The hassle to dig up and repair is just too much risk. I'd much rather just bring them up to the near surface at those 5 locations and make the connections there. I do like how easy sharkbites are to replace/repair.

Len

[AC_Hacker]

Other than the fact that PEX is not a thermoplastic (weldable) like HDPE is, it's great for Ground loops.

It might more expensive than PEX, but PEX actually starts out life as HDPE.

Regarding shark bite vs. barbs & rings, I have tried barbs and rings, both compression copper rings, and stainless steel 'clinch' rings. I think the clinch rings are superior in every way... even to corrosion.

-AC

[jeff5may]

Originally Posted by AC_Hacker

Other than the fact that PEX is not a thermoplastic (weldable) like HDPE is, it's great for Ground loops.

It might more expensive than PEX, but PEX actually starts out life as HDPE.

Regarding shark bite vs. barbs & rings, I have tried barbs and rings, both compression copper rings, and stainless steel 'clinch' rings. I think the clinch rings are superior in every way... even to corrosion.

-AC

I agree. The stainless "pinch or cinch clamps" are much stronger than the copper crimp rings. If a pipe freezes, the stainless clamps are strong enough that the fitting will pop open and leak before the clamped end. With the copper rings are used, a lot of times the ends leak when the pipe thaws out. However, It's not a good idea to use the stainless clamps with plastic fittings. They tend to squeeze hard enough on the fittings to deform them.

[rvCharlie]

I've never tried it for a PEX application, but electrical workers have several solutions for permanent protection of buried electrical joints. There's liquid that's painted on, but I have no idea about whether it will adhere to PEX. There are also tapes that seal to typical insulation used on direct burial cable.

This
http://www.permatex.com/products-2/p...ne-tape-detail
might be an option to apply over whatever connector/crimp is used for the splice. The tape would only serve to keep ground water away from the outside of the joint. (There are lots of other brands; I just picked this link because Permatex has a good reputation for their other products, in my experience.)

I even wonder if a pvc compression splice would fit over the crimp rings of a standard PEX splice. Almost 20 years ago, I trenched through a 1/2" plastic (polyethylene) medium pressure natural gas line (that fed my gas meter). The service guy for the tiny community gas company showed up (without any tools or supplies) and asked if I had a plastic PVC splice. I did; he installed it; it's still in the ground, about 20 feet from my gas meter.

Last, those direct burial polyethylene natural gas lines have their own connectors, too. Link to one source:
https://www.gastite.com/us/products/...nd/couplings/#

FWIW....

Charlie

edit: I'd probably still bring the splices to somewhere near the surface, but I have little risk of freezing where I live. Perhaps a 90 degree splice would make the rise & fall easier.

[AC_Hacker]

All of these considerations are reminders of the wisdom of using weldable HDPE for Ground Loops.

-AC

[superlen]

Originally Posted by AC_Hacker

All of these considerations are reminders of the wisdom of using weldable HDPE for Ground Loops.

-AC

Give me a backhoe and some free time & wisdom goes out the window.

If I had started the project, 6 months later I would have been golden. About 6 months after I finished my system, I started manufacturing the control electronics (day job) for the pipe fusion equipment manufacturer, McElroy. When I met with their engineers to start the project, I starting telling them about my homebrew system (& in particular the pex/pvc setup). They shook their heads and laughed. I believe the comment was something like "keep the backhoe handy".

Len

[jeff5may]

Some engineers just don't like to think out of the box. I live there.

On that bombshell, let me plug my latest thread:

http://ecorenovator.org/forum/geothe...onversion.html

Dirt cheap and recycled as usual. Guaranteed to work when it wants to.

[stevehull]

Jeff, - how about "some" engineers don't think out of the box and "some" engineers want to pull things inside the box . . . .

I often point to the Apollo project and engineers who not only thought out of the box, but thought out of this world. Simple mission statement in 1963; go to the moon, pick up some rocks and return to earth. No technology to do this, but physics that dictated limits. Six years later (1969), this mission was accomplished - all done by engineers.

All that said, there are a LOT of middle level engineers who can't/won't think. Upper level engineer types have to constantly pry them out of complacency and comfort.

One modern company that does think out of the box - GE.

OK AC, you can now delete these posts as they do not follow your thread . . . .

Steve