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Passive Solar Heating Panels

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Posted by Morris Dovey on January 23, 2013, 10:14 pm

Over the past month I've put together a web page describing a passive
solar heating panel capable of providing 100% of the heat needed to
maintain a comfortable temperature 24/7 in a conventional structure with
reasonably good insulation and which is reasonably snug. The panels need
to be installed in unshaded south-facing walls.

These panels work reasonably well in overcast conditions and will
produce heat whenever there's enough sunlight to read a newspaper. They
work unreasonably well in clear-sky direct sunlight.

Five years' experience in central Iowa indicates that each square foot
of panel area can heat approximately 125 cubic feet of air with enough
additional heat for storage to maintain that much air at a comfortable
temperature for more than a week of completely dark days.

My plan is to add both English and metric 3-D DXF/DWG files and an
assembly animation, and to clean up some of the stuff that I don't think
I presented as well as I might have. I didn't hold off because I have
friends outside the US who need the info now.

The web page will remain a work in progress for some time. If you find
the content interesting, I suggest linking to the page rather than
downloading a snapshot - and I ask that you not re-publish the page or
any of the content until I have it in final form.

The page is at http://www.iedu.com/Solar/Panels

Morris Dovey

Posted by Jim Wilkins on January 24, 2013, 1:24 pm

The local plastics supplier wanted nearly twice this price:

My experiments seem to show that one layer of treated polycarbonate
over a cheaper clear PVC sheet is adequate to withstand storms and
falling branches. The PVC is stiffer and sags less under a snow load.
They are the corrugated sheets from HD and Lowes, so I can quickly
replace a damaged panel without having to store spares. The rounded
PVC and trapezoidal polycarbonate corrugations make only intermittent
line contact, with mostly thin insulating airspace between them. They
make good roofing but I don't think they look good enough for the wall
of a home.

Do you know of a decent-looking durable reflective material besides
plywood siding to replace or cover the panels with during the summer?
Large painted panels are difficult to store densely without scratching
them, as I know from managing theatre scenery. The volume the flats
took up would be excessive for a home.

Posted by Morris Dovey on January 24, 2013, 5:10 pm
 On 1/24/13 7:24 AM, Jim Wilkins wrote:

The retail price of a 6mm sheet was ~$0 when I began the project.

As you probably figured out, aesthetics was not one of my primary design
considerations - and cost was only a secondary consideration. Some
people don't like /black/ panels. :-)

My experience with vertically-installed panels has been that snow load
considerations don't apply.

The vertical orientation and flat surface appears adequate to minimize
summer heating in at least northern US and southern CA.

I think your covers need only be opaque (not reflective) if you provide
an adequate air space between cover and glazing - but it makes more
sense to me to eliminate the need for them.

Morris Dovey

Posted by j on January 25, 2013, 4:30 pm
 On 1/24/2013 8:24 AM, Jim Wilkins wrote:

Very nicely done. The part about air flow characteristics is fabulous

The Lowes product is different than the HD.The HD SunTuff has a UV
coating while the Lowes does not need it. I could never get thin flat
polycarb here, which surprised me. It all had to be shipped.

  so I can quickly

I'm less concerned about conventional appearance, which is fortunate for me.

I've been using mylar as the interior glazing. I have a variety of ways
I've tried this. The UV coating on the SunTuf protects the mylar.

  Currently I'm redoing the solar hot water.  A frame cut from sheet
polyiso is covered on both sides by 1 mil mylar. This sits inside the
collector and is then covered by SunTuf. Typically the corrugated Suntuf
is shortly above that. About a half inch air space is about right, which
is the thickness of the polyiso. In the home,the storm frames are also
1/2", but made of wood.

The aluminized heavy duty tarps from Northern Tool might work, I'm well
pleased with the durability of them.

As far as sun temps the vertical orientation plus summer foliage is all
I need. Site specific, of course.


Posted by j on February 3, 2013, 5:53 pm
 On 1/23/2013 5:14 PM, Morris Dovey wrote:

I've had a bit more time to go through this, although I haven't absorbed
it all.

It seems to me that you must be close to optimum, as far as getting the
amount of heat out of this. That you can generate heat with so little
light is striking.

A few notes.

I notice that you said a thin coat of gloss worked better than flat
black. This strikes me as similar to the way selective coatings work.
The absorption is slightly lower but the re-radiative losses are much
less. Certainly important in a cold climate.

I note the distance from the absorber fins to the glazing and the back
is on the order of a half inch. Larger distance seem to create their own
air currents and are counter productive, that was not obvious to me!

I also note your point that the object is to heat the air and not the
absorber! I've made some progress here, IR measurements of my absorber
(black felt) show it be a good bit cooler than the air between it and
the glazing. In my collector I'm pulling air from the collector and
pushing it into the old air vents.

The fin rolling "machine" is very interesting. I made a series of jigs
to form aluminum around the copper risers. That and riveting it all
together was extremely exhausting. Perhaps some details of the machining
would be useful.

I've altered my own solar air collector several times as money and
experience has allowed. The current geometry is too much depth, but that
was largely determined by the geometry of the house and the jalousie
windows. On the plus side the cats love to spend time inside the
collector (the house side).


f that I don't think

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