SB: Re: strawbale Digest 23 Sep 2002 16:59:11 -0000 Issue 301

[Rene Dalmeijer <rened@cistron.nl>]

Chuck,

Besides the already mentioned shrinkage the loam will be detrimental to 
performance for 2 reasons lower density and lower specific thermal 
capacity. The difference is not that big maybe about 10%-20%. Loam differs 
so the best indication of the difference is in specific density. Measure 
the weight of a bucket of sand and loam the difference is roughly 
equivalent to the difference is storage capacity.

I just wrote the following to John Glassford:

A primer 1m^3 of water with a higher specific heat capacity then earth will 
store 4200000 J/K (joule/Kelvin) Which is equivalent to roughly 50W per C 
for 24 hours.
The 4" slab will store an equivalent of 142800 J/K which is roughly 1.7W 
per C for 24 hours. Which might seem little but if the floor is 50m^2 and 
its end of day temperature is about 6K higher than the interior air 
temperature it does amount to roughly 1000W over 12 hours which is a 
serious amount of heat. (The 6K is a bit optimistic) Therefor the slab is 
fine for daily storage but not long term. Long term heat storage is not 
very feasible because the same floor will only produce 73W for a period of 
1 week which is negligible.

The preceding is a gross simplification which also errs to the optimistic. 
In actual fact the amount of attainable heat storage will be much less due 
to losses. Another very strong negative effect on storage efficiency is the 
increasing and decreasing temperature differential while respectively 
heating and cooling the mass.

An addition to the above which I didn't send to John is that the heat box 
you are talking about is not going to give you seasonal heat storage but 
will add some buffering capacity to bridge short (a few days) grey overcast 
spells. Seasonal heat storage requires huge buffers.

At 06:59 PM 9/23/02, you wrote:
>The solar designer has always used sand inside the heat box/floor. Well to
>fill this two feet deep will cost about $1800 in sand or rock. Meanwhile I
>am sitting with huge mounds of loam and wondering about incorporating the
>loam. Again the idea is to use part of Aug and Sept and October to charge up

Greetings,

Rene Dalmeijer


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