[Greenbuilding] Al Pex for Solar Heating System

[Keith Winston]

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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