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Solar DHW: Copper or PEX - Page 4

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Posted by gary on October 29, 2007, 2:55 pm
 

I understand where you are coming from, but one thing to bear in mind
is that if the PEX is rated for 200F it won't fail at 201F. -- there
would typically be some margin -- possibly a fair bit of margin.  For
example the actual burst pressure on HDPE pipe is typically several
times the rated pressure.
Since the stagnation situation would untypical, I'm not sure you would
have any problems going a few percent over the ratings on rare
occasions.

Just trying to make your decision harder :)

Gary




Posted by TomGocze on October 30, 2007, 12:45 pm
 

Gosh, you guys are over-engineering this thing! In the eighties, when
I was a solar contractor, we usually used polybutylene tubing for
solar loops for vacuum tube systems and had very little problems. The
key was to get off the collector with about 10 feet of copper and then
transition to PB or Pex today! PB was very soft and had a much lower
strength rating compared to PEX. If you are paranoid about the
strength (I would not be) I would use Kitec or some other PEX/AL/PEX
tubing.

If you are using copper, just use a high strength non-silver solder.
The only time we used silver solder is when we did high pressure
refrigerant systems.

I have never seen a melting failure in hundreds of systems! I did have
one polybutylene failure with a vacuum tube system on a sunny day when
the power went out, but that tubing was directly connected to the
collector! (sometimes stupid things happen! One of my installers was
in trouble for that one!)

You are not building a nuclear submarine here, just do it with PEX and
be happy.
Tom In Maine


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