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Solar DHW: Copper or PEX - Page 2

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Posted by greif on October 19, 2007, 12:35 am
 
pex is only rated for 180-200 degrees and summer temps could reah that
high. one way to help is to put collectrs at 60 degree angle, they
will get less direct summer sun angle but it will be a better angle
for winter sun


Posted by Loren Amelang on October 20, 2007, 6:53 pm
 


Back when I chose it, the Tern TD40 was near the top of the list,
competence wise; now it is nearer the bottom:
<http://www.tern.com/portal/content.asp?contentid4>
I do still like everything of theirs I've used, though.

It does have lots of digital I/O, 12-bit ADC, two RS-232, and a real
time clock, all of which are heavily used here. But today it really
needs to be a web server, integrated WiFi would be nice, and very soon
the ease of integrating ZigBee will become an issue. If I wasn't
off-grid, I'd probably use an old notebook with USB I/O modules, but
24/7 that seems like too much power stolen by the control system.

If you already know a particular chip family or compiler/development
system, that's a powerful reason for choosing a board that uses what
you know. Dealing with the internal complexity makes up far more of
the job than figuring out which hardware terminal to hook your sensor
to.

Loren

Posted by Brian Graham on October 23, 2007, 5:38 pm
 A friend of a friend - no, not me! - used PEX. There was a power failure and
his AC pump (as opposed to a PV powered one) was off for a duration. The sun
was shining. Then the power was restored. The superheated fluid burst the
PEX line directly over his pool table, sending hot propelyne glycol
everywhere.

IMHO, stick with copper!
--
Brian




Posted by Steve Shantz on October 23, 2007, 9:08 pm
 Brian,

This is exactly the scenario I'm afraid of.  Nobody can absolutely
guarantee flow when it is needed.  Even PV powered pumps fail.  My own
El-SID 20PV had a premature failure and let the smoke out of the
driver.  Fortunately I have all copper!  Just because a system runs
fine for 1 or 3 or 5 years isn't good enough.  IMHO, a good solar DHW
system must be designed to gracefully handle this highly probable
event.

I think I'm going to compromise and have PEX on the cold line to the
collectors, and 3/4" copper on the all-important return line.


Thanks for the input!

Steve


Posted by daestrom on October 25, 2007, 11:21 pm
 

ISTR that even copper systems can have a problem in direct sun with no flow.
If the water/glycol gets too hot it can melt the solder used in the
connections.  (or maybe that is only concentrating collectors...?)

daestrom


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