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poor man's trombe wall

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Posted by vmpolesov on September 20, 2008, 11:24 pm


I am interested in passive solar.  I am a renter.  I have approx 7 m^2
of south-facing windows in one room.  My location is the cloudy
pacific northwest USA, approx 47.5 degrees north latitude.  I am
thinking of conducting an experiment by putting some landscaping
blocks, painted black, near the window.   Obviously I am not going to
go all out here, just a few hundred pounds worth.   I know this is not
the same thing as a trombe wall because it will not be large enough to
have convective airflow, but there are the same basic concepts at
work.  I will take unscientific measurements with an IR thermometer to
see how long the blocks retain their heat in the evening.

Will this have any effect at all or should I find something else to
waste my time on?



Posted by Morris Dovey on September 20, 2008, 11:54 pm
vmpolesov@gmail.com wrote:

It will have /some/ effect - but what effect and how much is difficult
to predict from here. :-)

The only you'll ever find out is to give your idea a try and take the
measurements. Good karma accrues to those who try their ideas and share
the results with others.

Don't forget to take a few photos so we can see...

Morris Dovey
DeSoto Solar
DeSoto, Iowa USA

Posted by vmpolesov on September 21, 2008, 12:54 am
Morris thank you.  I can start with one block and just see how it
goes, does it get above and remain above ambient temp on a typical
cloudy day and if so how much.  With the IR thermometer I can
determine this.   The heat capacity of concrete is listed as 0.88
joule g^-1 deg. C^-1 by wikipedia.  Let's say a 40 kg block, about as
heavy as I care to pick up and move around unassisted.  35.2 kJ/deg.
C.  per block.

Let's pick 2 deg C for the block's temperature above ambient after a
sunny day.  I don't know if this is realistic or not, I'll find out.  .
074 MJ/day/block.

At my current gas rate of $.03/MJ and let's say $0 per block ($42/
MJ/day), payback is 138 sunny heating season days.  This does not
include amortization of fixed costs for the furnace, etc.

If I were building my own place I would design to make maximum use of
passive solar.  I think that by working with  the forces of nature
instead of in opposition there is savings to be had, whatever one's
political position on environmental questions.  But for now I am a
tenant in an over-inflated housing market.  So I adapt and do things
on a small scale to learn.


Posted by Morris Dovey on September 21, 2008, 1:55 am
 vmpolesov@gmail.com wrote:

Well, one block is a start. If you're going to paint the sunward face
flat black, I'll suggest Rustoleum flat black aerosol paint. It's
available at most hardware stores and works better than the same paint
in a can. Use just enough to completely blacken the concrete - I've
found that too much paint can work as insulation...

...and for the sake of interest, you might buy two blocks and leave one
unpainted as a control.

I suggest putting your blocks on something that'll insulate them from
the floor so that your results aren't skewed by heat flowing to/from the


Sounds like a good plan to me. The experiment is simple, inexpensive,
and safe - and might provide a good learning experience.

Morris Dovey
DeSoto Solar
DeSoto, Iowa USA

Posted by Malcolm \"Mal\" Reynolds on September 21, 2008, 3:42 am

If you are the curious type, you might try a 5 gallon bucket of water.

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