Pex for SDHW [RE-wrenches]

[Ken Schaal]

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This pertains to drainback systems----no pressure on the return line !
I would certainly agree that plastics have to be used carefully, especially
for interior runs, where failure may have consequential damage.
The standard figure for selective flat plate max stagnation temp is 350*F ,
but I don't think that means we'll see 350* steam , because of the large
change of phase energy requirement, for very long. Of course this is for
residential 1-3 collector arrays. The larger the array the more this risk of
steam- and at what temp and pressure- becomes a significant issue.
For instance one system I did in 1984  [ 2 - 4x8 ] has poly bute piping for
the 30' run to the roof. I'm sure it has occasionally started up after a
power interruption during stagnation conditions, but the piping is fine. I
just last month remounted the collectors after the porch roof they're
mounted on was rebuilt. Of course, the poly is not connected directly to the
collector. Only copper for that !

For current systems, I'm using a control from Thermo Technologies that has a
high limit for collector temps as an option. BTU meter built in too! And I
generally use Kitec, which is a pex/al/ pex composite. I do have to account
for movement due to expansion/ contraction .
 Despite the cost of copper, I do believe that durability is vital to SHW,
although I'm finding some customers, especially new owners, who think that
any equipment 20 yrs old, must be ready for the landfill.   [ If they
thought of recycling, they'd probably keep the system ! ] I guess because
I've used polyethylene tanks for 25 years, I trust it. Also, the  ' lifetime
' electric water heaters are poly lined.
I also limit storage water temps to 150*

Ken
CommonWealth Solar,LLC






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Hi Kurt,
I think that you will find an overwhelming consensus to not use any kind of
plastic tubing for SDHW.  There will be a situation sooner or later where
you will get live steam in the loop as hot as 350 F.
Conrad Geyser
Cotuit Solar

> Has anyone tried Rehau Insulpex for SHW?  PEX tubing surrounded by
polyurethane insulation and covered with an LDPE jacket.  They make it in
larger diameters that are looking like a possible solution for a commercial
project.
>
>
<http://www.rehau-na.com/construction/heating...plumbing/energy.transfer.pip
ing..shtml>


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