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re: first attempt at solar air heater
4 feb 2002
bill kreamer  wrote:

>...in situations with lots of wall space, low cost reigns as the most 
>sensible strategy.  this is only overridden by lack of available wall
>space (situation in most houses).

new houses can be different, or houses with occupants willing to look
through an extra layer of glazing and window screen...

>> thermostats with motorized dampers or fans might be nice for
>> better room temp control.
>
>thermostats work until the weather gets really warm, then thermosypnoning
>tends to overheat you.

you mean thermosyphoning vs thermostats?

>at that point you cover the collectors for the remainder of the summer.

or block the inside vent and open an outside vent, a la morse? those $11
8"x16" automatic foundation vents with bimetallic springs might do summer
venting as well as control the room temp. we might move the louvers with
a $50 honeywell 6161b1000 damper motor (2 watts moving and 0 watts stopped.)
or build a small insulated box around the springs with a resistor in series
with a thermostat to sharpen the temperature threshold. or let the damper
admit room air or collector air to the box, like a trimtab, but then, one
might as well build the whole damper with a large piece of foamboard.

>simplify, but don't eliminate the furnace filter.  it is by far the best
>commonly available absorber...

>> some black window screen might be useful as a mesh absorber, with no need
>> for a fan to protect it from high summer temps. or use plastic shadecloth
>> inside the glazing, and vent the box and hang another layer of shadecloth
>> over the outside in summer to keep the inner shadecloth from shrinking.
>
>use black window screen if its very much cheaper.  it's just not as
>efficient as one-pass furnace filter.

black window screen doesn't seem cheaper, at 50 cents/ft^2 in 4'-wide
rolls, vs say grainger's 4'x90'x1" 4wz73 for $99.54 ($0.276/ft^2), but
it may be easier to attach and more heat-tolerant during stagnation,
withstanding umpteen degrees vs 180 f. it might also work better with
thermosyphoning vs fans. what do you think? 

>storage is a bottom-tier strategy, behind direct online use.  reason:
>storage loses a portion of what was collected.

maybe not, if it's inside the house. collecting heat at a higher temp
lowers the storage cost but it can also lower collection efficiency.
one exception might be some thermal mass inside a glazed box behind
a window. no loss of efficiency there. the inside of the box stays hot
until air flows through to provide room heat on a cloudy day...

>use storage if you are overheating the room in december...

sounds like a good rule of thumb.

>...in the northern usa, one 4x8 collector will heat a well-insulated
>10x15 room without storage.

this won't work on cloudy days for solar fanatics :-) 

nick




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