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Polyester felt material.

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Posted by M Russon on September 20, 2003, 3:35 am
Dear group,
  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.  

M Russon

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
  extended periods.

  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, nick@acadia.ee.vill.edu (Nick Pine) wrote:

Hi Nick,

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
 Hi all,

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.

M Russon

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