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Polycarbnate at high humidity and temperature conditions

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Posted by Gary on December 15, 2005, 7:10 pm
 
Hi,
There has been some discussion on whether polycarbonate
sheet would be OK for collectors in which it would be exposed
to both high temperatures and high humidities -- as in glazing
for a trickle collector.


I asked GE (maker of Lexan polycarbonate) if they recommended
the use of Lexan in conditions where it would be exposed to
high humidity and temperatures up to 160F.

The response from the GE product engineer was:

- They do not recommend the use of Lexan under these conditions.
- They have test data for Lexan sheet exposed to 80C and 100%
humidity for a period of 4 weeks -- its elongation to failure
went down from 120% to 8%.
They usually consider the material to have failed when material
properties drop to about half their original values -- so by
their working definition of failure, 4 weeks of exposure was
well beyond failure.

He guessed (based on his test data) that the life of the product in service
would be in months rather than years.

This is basically the same information that Nick got when
he talked to GE a while back.
So, I'd say this is not a good application for polycarbonate.

The GE product engineer also said that Lexan is used successfully in air
collectors, and
in water collectors in which there is exposure to high temperature, but
not simultaneously to high moisture.

--


Gary

www.BuildItSolar.com
gary@BuildItSolar.com
"Build It Yourself" Solar Projects










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Posted by perri_mike on December 15, 2005, 8:37 pm
 
Thanks Gary and Nick for showing this flaw of polycarb.   How about
this way of avoiding the problem.   A thick airspace  twinwall
polycarbonate panel (paint the northside black and add foamboard) with
clear plastic tubing running down each channel to avoid water contact
with the polycarbonate and get some higher insulation value than a
single layer tricke panel.  Inside each plastic tubing could be a small
strip of black furnace filter material or screen material to help with
the heat transfer.  The top of the panel would need a good manifold to
disburse the water and avoid water leaking into the polycarbonate
channels.  The bottom of the panel would be cut to drain to a recieving
pipe and be insulated.  Drainsback at night.  Not sure if there is a
tubing material cheap enough and durable enough.  I'm thinking that
making the panel out of twinwall polycarbonate would be attractive and
easy.

Mike


Posted by Gary on December 16, 2005, 2:59 pm
 perri_mike@yahoo.com wrote:

Seems a bit complex to me?
I think the small diameter tubes might not drain down well -- they like
to have half inch ID for draindowns.
Its also an awfully lot of tubes?



--


Gary

www.BuildItSolar.com
gary@BuildItSolar.com
"Build It Yourself" Solar Projects









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Posted by Jeff Thies on December 16, 2005, 3:02 pm
 perri_mike@yahoo.com wrote:

Seems to me the advantages of trickle collectors was simplicity and
cost. Why complicate this (the "details" make this very hard to
construct and get right with lots of gotchas) when other methods are
simpler and, more efficient and probably cheaper?

YMMV,

   Jeff

    A thick airspace  twinwall


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