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re: ...geodesic dome questions
9 nov 2003
alec chiasson wrote:
>i am thinking of using concrete piles at the vertices for footings, with
>a wooden main floor... i've modelled what i think is what you mean...
http://www.chebucto.ns.ca/~ba325/solar.html
nice drawing, with the air heaters in the right place, but it looks like
the dome starts 7' vs 3' or 4' above the ground and the concrete block
"column" is turned sideways as a shoebox under the floor, and there's no
solar attic.
a column might operate with natural thermosyphoning air flow, with no fans
or blowers, absorbing heat in the afternoon as warm air near the top flows
into the column and cools and sinks, and providing heat in the morning as
cool room air near the bottom enters the column near the bottom and warms as
it rises and exits near the top.
but water is cheaper than concrete and stores more heat by volume, often
with less thermal resistance, and a warmer ceiling with a larger temp swing
requires less mass to store the same heat, so why not put about 1" of water
in poly film ducts under the first floor, on top of a plywood ceiling? you
might drape another layer of poly film over the ceiling first, to avoid leaks.
with a central post and 10 14' radial beams and a 4' stemwall and a
pi(14^2-4^2) = 565 ft^2 ceiling, each wedge only needs to support 3500/10
= 350 pounds of water, with m = wl/8 = 350x14x12/8 = 7350 in-lb and s = m/f
= 7.35 and d = sqrt(6s/b) = sqrt(44.1/1.5) = 5.4", so it looks like you can
do this with 2x6s, ignoring the plywood strength.
you might store cloudy-day heat in a 70 ft^3 ~4' cubical tank under the floor
that cools from 130-80 f over 5 cloudy days, and warm the dome on a cloudy day
by pumping some water up through the ceiling. the attic floor needn't contain
much water, just enough for solar collection during the day. it would have
insulation underneath, and maybe a few transparent patches for daylighting.
with separate average and cloudy day tanks, you might avoid the air heaters.
nick
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