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An improved solar attic - Page 5

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Posted by nicksanspam on December 23, 2005, 1:12 pm
 

... $45 for a 9'x100' roll.


If 1 cfm = 16.6Asqrt(HdT) = 16.6Asqrt(dP) in a 1' chimney with a 1 F temp diff
and dP = 0.075x(1/460-1/461) = 3.54x10^-7 psi and a 0.01"H20 fan pressure makes
dPf = 3.61x10^-4 psi, it might push 0.01 cfm through an A ft^2 hole in a 1 ft^2
surface if 0.01 = 16.6Asqrt(dPf/dP) = 531A, so A = 1.88x10^-5 ft^2, ie 0.0027
in^2, ie a 0.059 inch diameter hole, about 1/16".

So we might put up an 8'x40' 32 cfm Typar wall with 2x4 studs on 4' centers and
poke big nailholes on a 1' grid from the south. With luck, the edges will open
more at higher flows, keeping the pneumatic resistance low. A layer of black
window screen might make it last longer and reduce the heat loss by radiation.

Nick


Posted by nicksanspam on December 23, 2005, 8:04 pm
 

Oops. That's a 3.2 cfm wall. For 32 cfm, we might poke 0.59" holes, or
0.29" pencil-sized holes with 0.04 "Hg. For uniform air distribution,
we might make the pneumatic resistance of the mesh large compared to
the pneumatic resistance of the stud cavity.

Nick


Posted by Jeff Thies on December 24, 2005, 5:13 am
 nicksanspam@ece.villanova.edu wrote:


What's wrong with felt or multiple layers of black screen (could be
fiberglass). Seems to me that you don't want much distance between
holes. Surely the thermal conductivity of Typar is not that great. I'm
think of getting the heat off the collector...

   Cheers,
Jeff


Posted by nicksanspam on December 24, 2005, 8:55 am
 

The tiny airflow (32 cfm for an 8'x40' wall) just provides insulation,
eliminating convection heat loss from the mesh to the glazing, as in
a Scandinavian breathing wall. The fin tubes collect the heat, which
moves from the south to the north side of the Typar by conduction and
up to the fin tubes by convection.

Nick


Posted by Abby Normal on December 23, 2005, 2:28 pm
 
nicksanspam@ece.villanova.edu wrote:

Perhaps, then do not crosspost the spew if you cannot handle the
critcism.


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