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re: alternative uses for grain bin
26 jun 1998
daniel akst wrote:
>...i'm planning to use a grain bin for my home offc in the
>hudson valley of ny state...
albany has an average outdoor temperature of 26.5 f in december,
the worst-case month for solar heating, with an average daily max
of 34.9, and 700 btu/ft^2-day of sun that falls on a south wall...
>my plan, by the way, is to get maybe an 18 ft butler or gsi grain bin,
or maybe something a tad bigger, like 20 or 24 feet?
>maybe put it on a polished concrete slab,
with perimeter insulation, and a small blower,
and some air channels in the slab to store solar heat?
>insulate the inside with standard batt insulation,
with a thermal conductance of 450 ft^2/r20 = 23 btu/h-f
for the 18' version with 6" fiberglass insulation...
>use galvalume for the interior walls,
vertical? i wonder how to install that...
>install heat and air conditioning,
or maybe a 200 ft^2 solar air heater made by wrapping the
dark-painted south quadrant with 2 4' wide x 25' long strips
of clear polycarbonate plastic, 0.020" thick, from a $250 50' roll,
plus $10 ups, from rimol greenhouse systems at (603) 425-6563, to
gather 126k btu/day of solar heat in december while losing about
6h(100f-30f)200/r1 = 84k, for a net gain of 42k btu/day, plus
another 50k/day from body heat and electrical usage.
>drop a sheetrock ceiling for insulation,
24(70f-26.5f)(23+gc) = 92k btu makes the ceiling conductance
gc = 66 btu/h-f = 254ft^2/rv, so the ceiling needs rv = 254/66
= 3.9 to keep the structure warm. let's use r13, so the building's
conductance is 43 btu/h-f, and it needs 24h(70-26.5f)43 = 44k btu
to stay warm on an average december day.
and about 222k btu to stay warm for 5 cloudy days in a row, or
maybe less, if it's only heated during the day. this might come from
the concrete slab's cooling from 100 f to 80 f, if its thermal mass
is 222k/(100-80) = 11k btu/f. concrete and soil have a specific heat
by volume of about 25 btu/f, so that means including 11k/25 = 444 ft^3
of material around the air channels, ie a "slab" thickness of about
254/444 = 7", something like a slab poured 3" over 4" pvc pipes on
2' centers, with a rug on the floor with r-value rf that lets 42k
= 24h(100f-70f)254/rf of heat escape from the floor to the building
on an average december day, so rf = 0.22. the rug might have an inch
of styrofoam underneath if the office is only used during the day.
>cut in a window,
not too big...
>and voila.
100% chauffage solaire.
nick
(alternatively, stack up about 20 55 gallon drums full of water in
a 40 ft^2 solar closet, with some astroturf over poly film over the
ground as an alternative to the floor slab, or put the drums inside
one of bill sturm's specialty cea structures (in calgary alberta,
(403) 274-8800.) he has a 12,000 sf greenhouse that uses soap bubbles
as the insulation/shading method, and they are building a 120,000 sf
greenhouse using this technology now. plastic film greenhouses cost
about $1/ft^2, installed on site.)
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