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ClearDome Solar Heat products?

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Posted by rolandda@emporia.edu on January 26, 2005, 3:29 pm
I was considering purchasing an indoor/outdoor solar forced air heater
from ClearDome Solar.  They sell their products through Amazon.com,
which surprises me a bit.  Anyway, the product I wanted is currently
out of production for upgrading.  I was just wondering if anyone has an
opinion on this company and its products?


Posted by Anthony Matonak on January 26, 2005, 5:25 pm
rolandda@emporia.edu wrote:

My opinion is that their products are OK but highly overpriced.
Everything they produce can be knocked together in a garage out of
relatively common materials.

Is a 2x8 foot solar air heater worth $170 ($95 +275 shipping)?
I haven't done a materials cost review but I would think that you
could build one yourself in a few hours for less than a quarter
that price.


Posted by Gary on January 27, 2005, 2:07 am
 rolandda@emporia.edu wrote:

There is an awful lot of exaggeration in their writeup -- as just one
example, they say:

"Home heating bills can be slashed even when using house current to
power the fan on the 2X4  heater. It costs less than 25 cents per
month to operate six hours every day! Compare that to a standard
800-1000 watt space heater, which costs about $2-$0 per month for
the same usage."

The implication here is that their 2X4 heater costing 1 cent a day to
run will produced about as much heat as a 1kw electric heater costing
about a $ a day to run.  This is no where near true:

If you are paying 10 cents per kwhr, then the electric heater at $0
per month it it is producing ($0/ $.1 per kwh) /(30 days per month)
= 10 kwhr/day of heat.

The 2X4 solar heater on a FULL SUN day might produce:

    (1600 BTU/day -ft^2) (2ft)(4ft) (0.6 efic)/(3412 BTU/kwh)
    = 2.3 kwhr/day

Where 1600 BTU/day-ft^2 is approximately what one square foot of well
aimed collector will collect over a full winter day.  The 0.6 is 60%
efficiency, which is about what a good air collector does with
moderate outdoor temperatures.  So, they are comparing the cost of
something that produces 10kwhr of heat per day to the cost of
operating their panel that produces about 2 kwh of heat per day -- not
exactly a fair comparison.

They also seem to endorse the idea of locating a solar collector
inside of a room.  This seems completely pointless to me in that the
solar energy coming through the window is going to be absorbed inside
the room whether you put one of their solar collector there or not.

It seems to me that the collector sizes that they promote are too
small unless you 1) have very little area to heat, or 2) live in a
very moderate climate, or 3) you expect to save very little on your
heat bill.  A very rough rule of thumb is that you can have collector
area of 10% to 20% of the floor area to be heated without overheating
the area -- this depends on your climate, insulation levels etc.
Using more collector area than this would require adding thermal storage.

This is not at all to say that solar air collectors are a bad idea.
They can be very effective heaters, and can be very cost effective --
I have two of them totaling about 270 sqft -- they work great.

I think Anthony is correct in saying that you would be much better off
to build one from locally available materials.  You should be able to
do this for somewhere between $ to $0 per square foot, depending on
how fancy you get.  If your situation allows, thermosyphon collectors
are simpler than forced air collectors in that no fan or control
system is required.

As alternatives: Increased south facing window area is just as
effective as adding air collectors if you provide a way of insulating
them at night to prevent the large night time heat loss.  Or, building
an attached sunspace can provide house heating and some added living
or plant growing space.

Here are some sites with plans:
http://users.montanadsl.net/~reysa/  (this is my workshop air collector)
I have seen more plans out there, so, if you search around you can
probably find additional plans.

Here is a pretty good book on the subject that is out of print, but is
usually available used at Amazon.com used books:
"Solar Air Heating Systems", Kornher and Zaugg


Posted by rolandda@emporia.edu on January 27, 2005, 9:47 pm
 Thanks for the links and the book recommendation!

Posted by Morris Dovey on January 27, 2005, 2:33 am
 rolandda@emporia.edu wrote:

If Cleardome is selling at the prices Anthony posted, I'd be
inclined to look around a bit more. Fifty-five dollars/ft seems
pretty steep to me.

Gary has some good pictures and good ideas on his web site.

If you follow the link in my sig, you can some that I build,
sell, and use.

[Going off by myself to ponder selling panels on Amazon for
outrageous prices...]

Morris Dovey
DeSoto Solar
DeSoto, Iowa USA

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