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Commercial Solar Water Heaters ? - Page 4

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Posted by Rob Dekker on September 15, 2005, 5:42 am


I know. But I wonder how important the insulation material is.
Common sense tells that the (single-pane) 3mm glass glazing should loose
a lot more heat by radiation and transmission/convection than even 1/2" of
good insulation material on the backside of the collector..

Mmm. Yeah, that is kind of tightly designed isn't it...

Posted by Christian Kaiser on September 15, 2005, 6:07 am

Sounds sound :) But as I once said here in Germany you only get money for
the collectors from the state if they fulfill that logo program "blue angel"
(who invents these?!), which means they have to be able to produce 525
W/m^2 --- and all of them have at least 6 cm insulation... I don't know
whether that's the reason, but when the collector surface is about 100 to
110 deg C when in operation at noon, there's 80 degrees (to 20 deg C
environment) in temperature difference at the insulation.

I don't know the insulation constants, maybe Polyisocyanurate is so much
better than mineral wool that that makes no difference. But then there's the
problem of temperature stability of that stuff. It seems the manufacturers
don't learn from the experience of others.

I found a few collectors with a layer of mineral or glass wool, backed up by
another layer of polyurethane. But most have one thick layer of mineral


Posted by nicksanspam on September 15, 2005, 9:26 am

When Gary sent me the nice solar pond water heater model he tested in
Montana, I put it together in partial sun with the pump unpowered and
had a meltdown :-) The 2" Styrofoam cover (under a layer of EPDM under
2 layers of polycarbonate) developed multiple 1" hills and 2" valleys.

A 2" double-foil polyiso replacement with foil-taped edges has worked
fine so far. One polyiso ap engineer says it's good to at least 350 F,
when the surface starts to develop cosmetic wrinkles. But I think we
should replace both polycarbonate layers with greenhouse polyethylene
to lower the cost and assembly complexity and stagnation temperature.

I put some polyiso on top of a toaster oven, and it deformed badly...


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Join PE Drew Gillett and PhD Rich Komp and me for a workshop on Solar House
Heating and Natural Cooling Strategies at the first Pennsylvania Renewable
Energy Festival at 9 AM on Saturday September 24, 2005 near Allentown. See


Posted by Gary on September 15, 2005, 9:29 pm
 nicksanspam@ece.villanova.edu wrote:

Here are some additional (unintended) thermal sculptures.

I like polycarbonate on the outside layer for weathering, durability,
impact resistance, AND the dog can't chew a hole through it to get to
a warm spot (like she did on my poly film sunspace) :-)

"Build It Yourself" Solar Projects

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Posted by nicksanspam on September 15, 2005, 10:09 pm

That's OK too. Does your dog get to vote?


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