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Glazing Materials?

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Posted by schooner on October 6, 2005, 10:19 am
I see most people are using lexan, Plexiglas, or similar rigid plastic for
glazing.  What about Mylar or the shrink materials for windows?  Would they
be good or would they give up too much heat through them?  Would the heat
cause them to overtighten?  Looking for something that is easy to install
but that does not expand and buckle in the heat.

Posted by Steve Spence on October 6, 2005, 2:33 pm
schooner wrote:

We use old windows, already framed.

Steve Spence
Dir., Green Trust, http://www.green-trust.org
Contributing Editor, http://www.off-grid.net

Posted by Gary on October 6, 2005, 5:44 pm
 schooner wrote:

I like the polycarbonate (Lexan) materials.  They have a good
temperature capability (about 270F), and they are easy to work with.
The buckling tendency can be easily controlled by just properly
supporting them.

I would not use acrylic (Plexglass) or PVC glazings -- they will
deform permanently from the heat when used in solar collectors -- I
have some well deformed samples to prove this :-)  A thin film glazing
MIGHT be OK for the inside layer of a double glazed arrangement, but I
doubt it would hold up well on the outside.  Some of the commercial
collectors use a thin film of Teflon for the inner glazing layer -- I
doubt they would go to this expense if there were a cheaper film
material that would hold up?

As Steve points out, glass is good.  Our local glass supplier has a
whole stack (I'm guessing more than 500 sqft) of double glazed glass
that was cut wrong or has blemishs that he is willing to sell very
cheap -- maybe your local dealer does to?

On your question in the other post about arranging ducts and air
passages for the collector.  The link that I provided earlier to the
book you can download for free has a lot of material on this subject
-- these guys built dozens and dozens of air collectors -- use their
experience!  If you want a forced air collector to work well, the
internal passage sizes and path need to be well thought out to make
sure all of the absorber surface gets swept and the air velocity is in
the right range for good heat transfer.  Relying on a large fan (to
me) is not a good idea -- the power consumption of the fan can be



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Posted by schooner on October 6, 2005, 5:57 pm
 Gary - What is the material you used in your barn wall for the glazing?
I've seen those panel before but not clear ones.

Posted by Gary on October 6, 2005, 6:38 pm

It is SunTuf corrugated polycarbonate.  It has a "co-extruded" UV
absorbing coating on one side, and is guaranteed for "life".  My Home
Depot sells it in 8ft and 12 ft lengths at 2 ft wide.  It is also made
in a 4ft(?) wide version that would be easier to use, but I can't
easily get it here.
Its only $ per sqft at HD.
In loose terms, I'd say that if you support it every two feet in the
direction of the corrugations (ie at the panel edges), then a light
support is needed about every 3 ft in the other direction.  If the
main supports are running along the corrugations, the supports in the
other direction can be very light weight -- just enough to control the
tendency to buckle as it warms up.  Using this system, it stays very flat.

The SunTuf website has some material on it, including this greenhouse
plan that uses it:

www.SundanceSupply.com sells both the corrugated and the twinwall
polycarbonate, and has a some design information.

Morris -- if you are watching, maybe you can provide a little insight
on using the twinwall polycarbonate glazing??


schooner wrote:

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