I'd like to make some forced air panels cheaply - hopefully the cost
can be recovered by the amount of heat they produce.
The most basic design I can think of is a flat piece of 10mm chipboard,
painted black, with sidewalls and baffles about 100mm high and then
covered with a single layer of polycarbonate. The cross sectional area
of each air run would be the same as the the area of the tubes feeding
Would any of the following enhancements improve the efficiency of the
panel enough to justify the extra expense?
- Extra insulation - thicker board or some other material?
- Double glazing - an extra layer of polycarbonate with (say) a 10mm
- A black painted metal mesh attached to the backing board - this would
cause better heat conduction becase a) metal is a better conductor than
wood and b) it would also cause more turbulance in the air passing over
the collector surface.
The sides and back are usually insulated to about 1 inch. You won't
gain a great deal by going to more insulation. If the back is
integrated with a house wall, then you don't gain a great deal by
insulating it at all.
Double glazing and/or selective coating on the absorber both help by
reducing losses out the glazing. But, both also add to the cost.
You may be just as well off keeping the collector simple and making it
a bit larger to make up for the lower efficiency.
As you can see from looking at the links below, the two most common
designs are the flow through absorber in which the air enters the
collector on the south (glazing) side of the absorber, and flows
through the absorber to pick up heat. Absorber materials for this
type range from expanded metal mesh, window screen, polyester felt,
furnace filter media... -- there is some active discussion on which
works the best, but they all probably work OK. In the other design, a
solid metal absorber is used, and air flows on the back (non-glazed)
side of the absorber picking up heat from it. Again, there is some
discussion on which design is better -- I think most favor the flow
I think that if an air collector works for your house geometry, that
it can be very good choice. It is simple, inexpensive, easy to build,
little maintenance... The payback period for a build-it-yourself air
collector can be as little as a couple years.
There has been a lot of work done on air collectors, you might take a
look here for some of the designs that have been developed:
Here is a book on air collectors of various types you can download for
free (courtesy of the authors) -- it has a lot of hands-on information:
Make sure you do some type of solar site survey to make sure that you
really get sun on the collector during the times of year you want it
to work -- here is one:
"Build It Yourself" Solar Projects