Posted by M Russon on September 20, 2003, 3:35 am
Has anyone other than Bill Kreamer used polyester felt material as
an absorber in a solar air heating panel? I am interested in real life
performance over time. Thanks in advance.
Posted by Nick Pine on September 22, 2003, 10:51 am
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
Posted by bherms on September 22, 2003, 1:50 pm
On 22 Sep 2003, email@example.com (Nick Pine) wrote:
I'm repainting some and cleaning my first floor furnace filter
collector material which worked well last year. I'll put 1/2"
polyiso' board behind that (with the black or silver side to the
sun?), as last year the plastic got sucked into the frame a little.
My collector is between the salvaged storm glass windows and the
inside of 2x6 framing.
Is there an ignition point for bugs? I had quite a few in the system
that seemed to fall down to between the filter material and the glass.
I'm considering some sort of automatic sprinkler system for fires.
I'm almost always there and haven't had a problem yet, but did melt
some black plastic onto some clear and warped some extruded
polystyrene. I insulated around the metal frames some with polyiso'
and wrapped heavy baking foil over the framing, thinking that would
make it less likely to ignite. The air is blown to my walkout
basement through a 10" insulated duct. My top temp was 120F with
intake at 70F. My guess was around 350cfm.
I'm running the 2nd floor system now (same setup) to start heating up
my concrete and water in the basement.
I have a large duct across the top of my five large windows with a fan
at one end (same at the bottom with intake at opposite end of the
fan). Opposite the fan on the top duct, I have a plastic film damper
in case power goes off. The fan sucks it closed normally.
west central Illinois
Posted by Bill Kreamer on September 22, 2003, 5:33 pm
Some reminder caveats on using black polyester felt for the absorber:
Don't stop up the inlet and/or outlet in the summer.
Instead, cover the collector.
Use white or light colored polytarp or thick canvas cover material, with
a hem all around containing a 1/8" braided nylon drawstring.
You must use a freely thermosyphoning collector design.
The most trouble free concept is a point-of-use design, not connected to
The inlet and outlet should be at nearly the same height, with a
descending cool air leg situated within the collector.
Such a design will not backsyphon at night, but will thermosyphon
vigorously during collecting hours if the fan power is interrupted.
The absorber will run at less than 160 degF avoiding any meltdown.
Email me to receive a free pdf file of a really good design.
- Bill Kreamer
Posted by M Russon on September 23, 2003, 8:40 pm
On Mon, 22 Sep 2003 17:33:07 GMT, "Bill Kreamer"
Is this the wall mounted heater you posted several years ago? If so,
i would love to see some pictures of a home built version somewhere.
Anyone you know have some images of your heater on the web somewhere?
I was actually reading your instructions for building one this week.