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Solar air heating

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Posted by Frontier on December 11, 2010, 4:10 pm
I havent read alt.energy.homepower in years but have been doing some
research regarding solar air heaters. We live 100% off grid solar PV and
small wind generator but have a custom wood shop that is on the grid. It has
a nice south facing wall that gets good sun in the winter months and has 3
large overhead doors (12x10) on that wall which we are planning to frame in
2 of the three as they are no longer needed and are huge heat loss openings.

I got to thinking and remembered hearing here years and years ago (perhaps
10) about building solar collectors out of things like aluminum cans and 2
liter bottles and so on. I was wondering if any who read the group had toyed
around with this or perhaps built one/some. I would like to try to keep it
passive (no fans) but fans are not out of the question. My initial thoughts
were to build a box to fit the opening with 2" foam on the back so it would
have an R15 at night with the collector being a simple box with perhaps
aluminum cans epoxy'd to the back wall and painted flat black. An inlet at
the bottom and outlet at the top.

The only thing I didn't like about the passive is the system wont really be
automated and we would likely have to close dampers/gates at night and open
them in the morning.

Just kicking it around and wondering what others may have done especially
with regards to glazing. This would be the hardest part I assume. Trying to
find a cost effective material for 120sq' could get pricey. Lexan and
similar products would be pretty costly for that size opening.

I am thinking however that a collector this size may heat our 4000sq' shop
any time the sun is out which would cut down on the gas bill.

Any input is appreciated,

Posted by clare on December 11, 2010, 5:46 pm

 Go to your local window/door contractor and offer to take all his
take-out patio doors. Tempered glass panels for free if you strip off
the aluminum frames for him and allow him to scrap the aluminum.
Normally they need to pay their guys to strip them, and they shatter
the units and trash them.

Posted by vaughn on December 11, 2010, 6:54 pm

You need to talk to Morris, a semi-regular here.  His passive solar system:


Posted by Morris Dovey on December 11, 2010, 7:52 pm
 On 12/11/2010 10:10 AM, Frontier wrote:

You haven't provided any clues as to your location or shop dimensions,
but your 240 ft^2 of collector capture area would be enough to slightly
overheat approximately 30,000 ft^3 of shop air in central Iowa. If the
shop floor were a 6-inch slab and you installed a pair of slow-turning
ceiling fans, that would provide a couple of weeks worth of heat storage
to make up for periods of lousy weather.

How frequently (and for how long) you open the remaining door will have
a significant effect.

I have a strong bias toward passive systems - and I've built more than
just a few. As far as I've been able to determine, a well-designed
passive panel will always outperform a same-size panel that needs a blower.

Forget the old black-painted aluminum can approach - it's only good for
heating the aluminum cans.

It's possible to build a really good no-moving-parts passive system that
regulates its own airflow so as to prevent reverse operation when the
sun isn't shining. Baffles/gates simply aren't needed.

There are always trade-offs. If the object is to replace fuel/electric
heat with solar heat, then even the short-term (2 - 3 year) trade-off
will favor spending on something like twinwall polycarbonate glazing.

A lot depends on things you haven't talked about - but yes, at the very
least you should be able to substantially reduce your gas bill.

If you follow the link in my sig, you can see a photo of a smaller shop
heated with a pair of 8x6 passive panels - and if you click on the photo
you can see more of the installation.

Hope this helps...

Morris Dovey


Posted by Frontier on December 11, 2010, 8:43 pm
I have seen your site before I think via Sawmill Creek perhaps? I think you
may have sold a unit to a member there but not positive. I want to say he
was a custom counter top manufacturer.

Our shop is 4000 sq' metal sided structure which use to be the town fire
station. Its fairly poorly constructed with regards to insulation though we
are improving on that as much as possible. Concrete slab is no where near 6"
thick in the few places I have had to cut it to install dust collection.
Very poor ceiling insulation though we will be improving that once we get
all the bad wiring fixed up and can blow in 12" of cellulose or fiberglass.

The only reason I was talking 10x12 is that is the size of the overhead door
opening that is going to be framed in. It doesn't need to be that big and
being smaller would be much better with regards to the cost of glazing. I
have looked into patio door panels and often have them ourselves as we are
contractors however the double insulated panels often come apart over time
especially once removed from the frames. I had just quickly looked into
single panel polycarbonate from companies like US Plastics and the price on
a 4x8 is reasonable at 200+freight. I may be able to find it locally as
well. I know I can get polycarbonate greenhouse style panels as we use to
have a nursery business and have ready access to that material.

I guess I will have to re-think the metal can idea which was only because I
had seen it before and then of course they are virtually free. What other
material do you recommend inside the collector?

I seem to remember at the time I saw your site last you were not in
production or in limited production and were recommending people to build
their own collectors or something to that effect.

Anyway, thanks a lot for your time and reply. I use to be one
alt.energy.homepower almost daily when we were getting this off-grid
property underway and on line but havent been on in ages.


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