[Greenbuilding] Al Pex for Solar Heating System

[Dusch, Jim E]

If that first 6-10 feet (or more) of copper is in an unheated space,
what's the best practice for freeze protection?  Up here in Maine the
high has been a sunny beautiful 5 degrees today (which is balmy compared
to what it'll be tonight) -- which is obviously one of those worst case
situations that demands realistic proven technology, built bulletproof.

-----Original Message-----
From: greenbuilding-bounces at listserv.repp.org
[mailto:greenbuilding-bounces at listserv.repp.org] On Behalf Of Keith
Winston
Sent: Thursday, January 03, 2008 2:25 PM
To: Sacie Lambertson
Cc: Greenbuilding
Subject: Re: [Greenbuilding] Al Pex for Solar Heating System

Hi Sacie,

First, Pex-Al-Pex has much higher burst pressures/temps than Pex, so is 
much more suited to solar. It is still necessary to provide some buffer 
so it doesn't get heated to stagnation temperatures ever. 6 or more feet

of copper is an option, as is (I suspect) a foot or two of a higher-temp

lower-conducting plastic tubing, which I am exploring on a job. There is

also a big difference with different solar collectors: evacuated tubes 
might stagnate to 340F, whereas flat plates are unlikely to surpass 250F

or so. In any case, as soon as water is flowing these temps very very 
quickly diminish, typically into the 120-160F range, though that depends

on insolation, collector, flow rate, fluid, etc. The only thing about 
mixing tube types is, connections are where leaks most commonly occur, 
so you'd like to either or both minimize them, keep them accessible, and

put them where leaks won't ruin your house. As is so often the case, 
reality is likely to involve compromise. Good luck.

Keith




Sacie Lambertson wrote:
> When we built our house we plumbed it for a back-up solar water
heating
> system.  Unfortunately this was before I learned that PEX could not be
> used.  Now I'm ready to complete the job (our propane bills have gone
from
> $350/yr to $750/yr) but I'm told that AL PEX should NOT be used
either, that
> it can't take the extreme heat of the glycol coming out of the solar
panel.
> I would appreciate hearing some opinions and best advice on this.
Copper is
> the only recommended carrier this knowledgeable source told me (though
he
> had heard of using copper for the first six feet, with an alternative
after
> that, but didn't think this a good idea either).  I really don't want
to use
> copper if I can help it.
>
> A follow up question: what is the best insulator for the
copper/alternative
> line which will have to be buried for 20 ft before it enters the
house?  Yes
> I know that copper must be contained if it is going to be buried in
the
> ground.
> Thanks
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