Posted by Jeff on June 20, 2006, 5:16 am
Oops different computer than last time I saw it. I'm getting a
mscoree.dll can't be found. I'll try to fix this later.
What temps are you thinking about for your "Shed and Collector Wall"?
I notice that you are thinking about baseboards for now and maybe
retrofitting pex floor heating later.
I usually see about 140F (minimum) for baseboards and much less for
floor radiant. The lower temps of the floor heating is certainly a big
plus for heat storeage and collector efficiency. I wonder how car
radiators, perhaps the AC condensor, would do. They usually have a lot
of fin area, and I'm thinking that is what's needed. That and they are
BTW, take a look at using 4" insulation and unselective absorbers (use,
.96 and .88)
vs 2" and selective coating (.88 and .15) usings the CoDePro calculator
They look fairly close. 24 gauge aluminum.
It looks to me that added insulation gives the best return per $
invested in the collector for high delta Ts.
Mike had mentioned using fiberglass along with urethane... Fiberglass
is certainly cheap, I wonder how it handles collector moisture? At any
rate, you may wish to run some numbers on the 4" insulation values. For
delta T/Gt's greater than .3 F Hr Ft2/BTU it makes a noticeable difference.
Posted by Mike on June 20, 2006, 9:06 am
Foil covered fibreglass, sold as ducting insulation in 15M rolls placed over
the urethane foam foil face up has no problems, any condensation forms on
the underside of your glazing material, usually at the bottom of the
collector. Any drips hit the foil and drain off to the side then bottom of
the foam, so the fibreglass itself is isolated from any major condensation
by the impervious foam layer. When the panel heats up any moisture is driven
off, providing you have a 1/2" breather hole at the bottom of the panel.
Water will not travel upwards in fibreglass due to any capillary action but
remain localised at point of entry.
I have made one test panel that has been in use for 2 years and the
insulation backing is 2" of high temperature low binder industrial
fibreglass batting, no foam or foil. The collector fins sit directly on top.
The only moisture problem encountered was when the rear of the wooden casing
developed a leak, after I had fiddled with it, allowing about 1 litre of
water to enter over a very wet weekend. The water sat at the bottom and was
easily removed by lifting up the glazing and squashing the batting down at
the bottom. After about a week of use it had dried out entirely, the wooden
case bottom was not painted so moisture naturally migrated out when it got
In retrospect I would only use entirely fibreglass or foil covered version,
when it sat off the bottom of the panel on some other impervious material
(urethane) or a false raised bottom - say of very thin ply with a 5mm airgap
to the bottom of the panel. If ordinary house batts are used say R3 then
there may be a problem with the binders in the material outgassing in
extreme heat conditions. A layer of non bitumen foil faced building paper
placed on top would fix it.
Posted by Gary on June 22, 2006, 8:47 pm
I am going to try to get the radiant floor heat in for this winter. If
I can't get it done by then, might give the baseboard a try. As you
say, the baseboard is typically used at higher temps. But, I don't see
why the baseboard would not work at lower temps with lower output --
might just take too much of it.
I ran some simulations for my system earlier, and being able to use
lower temp water is a definite advantage.
I'll do that -- I'm away from home now, but will take a look when I get
back. But, I would be hard put to get 4 inches of insulation in.
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