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Posted by Jeff on June 13, 2006, 9:17 pm
 
   Best price I can find locally is $1 US for .040" 4' * 8'
polycarbonate sheet.

   So before I buy three sheets ($00 minimum) is there any reason not to ?

   These sheets are not UV coated, and my thoughts are that the UV
coating is not an advantage for solar heating. Am I right?

   The 40 mil seems pretty thin, but thicker than the 1mm that Mike had
mentioned.

  Is there any reason not to make these full size, ie 4' * 8'? That
sounds close to Mike's 2.4 M example.

   Jeff


Posted by Gary on June 13, 2006, 10:55 pm
 
Jeff wrote:

Hi Jeff,

I think the no UV coating may be a bad idea -- I think it will severely limit
the life of the panels.  The UV coating is only partly to protect stuff inside
the glazing, its also protects the polycarbonate itself.  I've not seen numbers
on life of the polycarb with and without the UV coating, but my impression is
that its significantly different -- maybe someone has some data on this?

Around here, the hardware/lumber yards sell corrugated polycarbonate (SunTuf or
the like) for $ per sqft.  Usually its 2 ft wide by 8 or 12 ft long, but I'm
told it can be had in 4 ft wide sheets as well. The stuff I used (SunTuf) is
0.03 inches thick.  Working with the corrugations has its ups and downs, but it
can work well.  I used this on my barn collector, and after 3 seasons it looks
just like the day it first went up.  You need to be careful about how you
support it -- see the barn collector writup on BIS.

Another option would be the twinwall polycarbonate.  You lose about 10% more on
transmitance, but pick up some R value.  Probably a good trade for cold
climates.  I think the twinwall gets down to as little as $.20 per sqft -- it
helps to have a local source so you don't have to pay the shipping.  I think
that it might be easier to work with than the corrugated.

Gary


--


Gary

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









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Posted by Jeff on June 14, 2006, 5:48 am
 <snip>

   Hi Gary,

  This sounds like what I should use. Because it's corrugated I'm
thinking to silicon glue it to the top wiggle strip. It would float
elsewhere held down by flanges. Mike had mentioned 1/2" expansion for 8'
lengths at the temps the collector works at.


Ha ha, I just caught that!


   I just reread this, btw, I like your site's front page redesign!!!

   Cheers,
Jeff


Posted by Mike on June 14, 2006, 5:57 pm
 Hi Jeff

Here in NZ the polycarbonate sheet comes in various thickness's 1.0mm 1.5mm
3mm 5mm etc, they all have one side that is UV resistant. It is essential to
have the UV side facing outwards towards the sun. The manufacturer says they
will last > 10 years without loosing excessive transmission.

If your sheets are not UV treated then they will go opaque and brittle.

The thinner sheets eg 1mm are easily cut with sharp tinsnips, thicker ones
require sawing with a fine tooth saw. Even 1mm wont break if you throw a
brick at the panel, so the stuff is pretty strong.

Over a large area the thinner poly will require some supports glued to the
fins near the centre of the panel, due to the stuff flexing in the wind and
when it gets hot.

Full size panels 8' * 4' or 2440 * 1220mm are damm difficult to man-handle
when walking around on the roof, also it requires a very rigid case to
prevent excessive flexing. If you make them 8' * 2' then the case can be
made from lighter materials and they are easier to manage, also the poly
doesn't flex as much.

Cheers
Mike




Posted by Jeff on June 14, 2006, 5:14 am
 Hello Mike,


  I'm glad I asked!

I find this terribly interesting. It seems to me that this would be just
two finned riser tubes about 12" apart. Since the manifolds are so
short, could I not just make them out of the same diameter pipe (1/2")
and center feed them? I'm thinking a short fat connection (1/2" Tee with
a 1/2" to 1" reducer) out of the box to a large diameter (ABS) manifold
outside the box that ties all the collectors together.  Or have I got
this totally wrong?

   Cheers,
Jeff

  also the poly


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