[Greenbuilding] Power Vent for Solar Air Heater

[LarenCorie]

From: "conservation architect" <elitalking at rockbridge.net>

> Can any on the list recommend a through the wall power vent to
> achieve active flow in air heater. If not satisfied with the production,
> I will remove and reuse the materials.  I would like it to activate when
> 80F is achieved that reduces the outward heat losses of increasing
> to 90F before passive flaps can work.  Motorized damper for
> return air may also be useful.

Hi Eli;

  You do not want the fan to activate at 80F.  When the fan starts
its will lower the collector temperature. You are better to have it start
at 90F (or more) and have the fan drop the collector temperature to
80F or so. Use a cooling snap switch. It will have an on temperature
that is higher than its off temperature, so that when the fan drops the
temperature, it will not turn it off until it truly can not supply useful 
heat.
Use the fan on the lower end, so that it remains cool. If you can put
a passive backflow damper there too, fine.  But, if you have to fit it
all within the depth of a wall, you might need to put the backflow
damper in the top vent.  Depending on the collector size and the
capacity of the air mover, you might use a bathroom or kitchen
vent fan, that has a noise rating.    Noise can be an important
aesthetic and customer satisfaction factor, for simple, through
the wall type, Solar air heater.

> I am putting plastic over the parts of the South wall that are
> not windows.  Because I live on a steep hill in a wooded site,
> I am not sure about the reduction in solar available.   However,
> from my South windows, I know that I feel that warmth.  I am
> framing such that if it proves affective, I can replace plastic with
> permanent glass when plastic wears out. If it proves not adequately
> productive, I will dis-assemble materials to repurpose.

Okay....So you may not be building a Solar air heater.  What will
you be using as your absorber?  What kind of "plastic" will you be
using?  Polyethylene is transparent to IR, so only has an Rvalue of
around 0.83   TwinWall polycarbonate (also "plastic") can have
an Rvalue of R2.  With your partial sunny situation, that can
make the difference between heat and no heat.

 -Laren Corie-
 Natural Solar Building Design and
 Solar Heating/Natural Cooling/Energy
 Efficiency Consultation Since 1975
 www.ThermalAttic.com  (many new
 photos and pages, coming soon)

Read my Solar house design articles in:
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www.essnmag.com

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