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re: air panel questions
15 mar 2001
m russon wrote:
>whats your thoughts on shadecloth use in a solar air collectors?
adding some sort of mesh to a bare black box can a) help keep cooler
air near the cold glazing, which reduces the heat loss to outdoors, and
b) increase the heat transfer surface, which keeps the absorber cooler
and lowers reradiation loss, and c) reduce the reradiation loss by
blocking some outwards radiation from an absorber behind the mesh.
did bill measure the solar collection efficiency of a bare black box?
geometry matters too. windows can be very efficient solar collectors,
with 70 f still air inside and an "absorber" a few feet away, so its
reradiation mostly hits the inside walls of the house, vs the window...
>panels are 4x8 feet in size, and there are 4 of them. roof mounted
>at a tilt of 55 degrees (40 degrees latitude +15 degrees) i am at
>the point of installing absorber into the boxes and i am weighing
>the shadecloth idea over bill kreamers furnace filter idea.
if you put some shadecloth into boiling water, it might shrink 30%.
furnace filter may be a safer absorber for these panels, or maybe black
window screen, in case the fan fails. i see bill's furnace filter also
comes in 4' widths., grainger's 4wz73, $94.35 for a 4'x90'x1" roll, with
an upper temp limit of 180 f. what happens to it in boiling water? does
it work a lot better than the 1/2" material, at 18 vs 26 cents/ft^2?
>bill states an increase in surface area of over 50 times using
>filter media compared to a rigid absorber plate...
that's good, altho it can also increase the airflow resistance,
and increased surface is only 1 of 3 benefits i see when using
a mesh absorber.
nick
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