re: polyester felt material.
22 sep 2003
m russon wrote:
> has anyone other than bill kreamer used polyester felt material as
>an absorber in a solar air heating panel?
i haven't. perhaps it melts without constant cooling, eg a pv fan...
kornher and zaugg's complete handbook of solar air heating systems says
use high-temperature materials
if a blower quits or the electricity goes off in an active system,
the collector will stagnate and get very hot bcause there is nowhere
for the solar heat to go. although collectors usually operate between
90 and 150 f (and can be subjected to -30 f temperatures at night),
well-built collectors under stagnation conditions can easily reach
temperatures of 350 f. collectors that were built with the wrong
materials have actually ignited. all materials used in active
collectors must be able to withstand temperatures of 350 f for
much more leeway is possible in material selection for convective
collectors. they are by nature, self-ventilating [unless we close all
the vents in summertime] and should never reach temperatures over 180 f.
wood is a reasonable choice for the framework of a passive collector,
but be sure to use fir and spruce rather than pine...
if you are considering using materials that are not discussed in
this book, it is a good idea to test them beforehand. place small
samples of the materials in a covered glass baking dish and bake
them overnight at 350 f. if anything strange happens to them, or
if they give off any gases, they are unsuitable for collector
construction. it is better to stink up the kitchen for a night than
have poor air quality from your collector for the next 20 years.
a word of caution, though: don't bake foam insulation because some
types emit very toxic gases.
shadecloth shrinks dramatically at 212 f. window screen seems more
fail-safe than plastic furnace filters, albeit less efficient, and
it offers a chance to provide daylight and keep most of the air in
a large sunspace close to 70 f.
the most serious mistake was making the outer container of the receiver
of plywood. we thought that the plywood would be sufficiently insulated
from the copper panel which was the receiver proper, that it would not
get too hot. the copper panel was separated from the plywood by 4" of
fiberglass insulation. nevertheless, the plywood caught fire and the unit
was completely destroyed. we suppose this is a success, of sorts...
from "a solar collector with no convection losses," (a downward-facing
receiver over a 4:1 concentrating parabolic mirror) written by
h. hinterberger and j. o'meara of fermilab, ca 1976