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
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...
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. .
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
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.
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.