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glazing

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Posted by Jeff on October 2, 2007, 3:35 am
 
  I'm ready to reglaze my air collector which is on my south facing wall
and has a double screen "absorber". It's fed from a plenum and the air
returns through windows.

   Currently this is glazed in polyethelene, which enabled me to read
through it to get IR temp readings and poke through to get velocity
measurements.

   I thought I would just glaze this with SunTuf (polycarbonate), but
now I'm thinking of saving a few bucks (13 - 8' sheets) and using Palruf
(acrylic). They have this rated at 150F and it seems I'll certainly be
below this. I'm confused about the UV rating though.  The palruf is UV
inhibited (what is that?), whereas the SunTuf has a UV layer. Now I had
though that acrylic was naturally UV tolerant. Am I wrong here? Will
acrylic deteriorate in the sun/rain or is the concern that it passes UV?
Should I go with the polycarbonate? Is there something else I'm missing?

   Cheers,
Jeff

Posted by gary on October 8, 2007, 1:42 am
 

Hi Jeff,
If it was me, I would not use the Palruf.

I tried it on one little collector I was building just for a quick
test, and within hours there were permanent deformations in the
glazing.

http://www.builditsolar.com/Experimental/CPVCCollector/cpvccollector.htm
Search down the page for "Note on the PVC glazing"

Your collector may run cooler than this one, but it still does not
seem worth taking the chance to me.

It is also much harder to cut without breaking it (its more brittle).


Did you come to any conclusions on the measurements you took through
the polyethylene?
If you have already posted this, just let me know the title of the
post.

Gary



Posted by Jeff on October 8, 2007, 2:13 am
 gary@builditsolar.com wrote:

   Hi Gary,

   The people at Palram told me the same thing. So I think I'll forgo
the PVC. I get the feeling that they like their SunTuf much more!

   The airflow seemed very even, so I probably could up the vent sizes
in the plenum. I want to run some some tests with the black felt in
addition to the double screen, I think I may set up a couple of test
boxes for that.  I don't like the poly as glazing, I had a hard time
finding really clear poly and what I did get I think I was losing a
third to a half or so of the incident insolation  due to 1) loss through
  the hazy poly, 2) reflection off of it 3) IR losses back out. Looking
at it now it looks even hazier.

   The little blower I have seems to have quite a bit of head to it. I
also noted that it drew the same current  no matter what head it was
pushing into. Tiny exit of just 4" by 5" but about 400 CFM.

   Jeff




Posted by schooner on October 8, 2007, 3:28 pm
 That CFM seems really high.  What sort of fan are you using?



Posted by Jeff on October 9, 2007, 3:31 am
 schooner wrote:

   It's an  estimate on my end by filling a large garbage bag and
estimating the time and volume. I suppose that's subject to a large
margin of error! I seem to recall that it filled a large contractor
style bag in about a second. That's probably closer to (but over) 300CFM
than 400.

I don't have the data here now as it is in the duct. Lot of blades
(squirrel cage), draws about 350W or so, came off a very heavy and
expensive print processing unit. I was surprised at how much current it
drew. Not a cheap motor when I looked it up although the HP and name
escapes me at the moment.

   I'll see if I can find my old notes on this...

   Anyone have a rough rule of thumb for power versus CFM for a small
head?  When I was building this last year I found about a 10 different
squirrel cage motors of all different sizes and I thought that was the
best one to  start with.

   Jeff


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