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re: frugal storm shelters?
4 may 2000
opinionated wrote:
>does anybody have any experience using a septic tank (new and
>empty, of course) as an in-ground storm shelter? i live in
>missouri and checking out commercial storm shelters i find that
>they are very expensive! a friend told me about someone they
>knew who had used a concrete septic tank but i can't figure out
>how that would work...
never done that... sounds a bit cramped. the biggest local version is
"1500 gallons," 5' tall x 6' wide x 12' long, with a lid with a 2' hole.
made of reinforced 5000 psi concrete, about 3" thick and $600, delivered.
i guess it weighs about 9 tons empty, so you might not have to bury it.
hmmm. (v/20)^2 = 18klb/60ft^2 = 300 pounds per square foot, so
a 346 mph wind might tip it over... you might add a couple of log
chains over the lid, attached to a couple of 12' dead men under the
width of the tank, or buy it without the lid and install it upside
down on top of 22 steel 55 gallon water-filled drums to make 8' of
headroom in your small survivalist palace.
with no drums, surrounding the 470 ft^2 of surface and 2800 btu/f of
thermal mass with r50 strawbales makes 470/50 = 9.4 btu/h-f of thermal
conductance and a 13 day time constant. two people could slowly make
it about 600btu/h/9.4btu/h-f = 64 f warmer than the outdoors at about
0.2 degrees per hour. a large dog might keep it comfy in wintertime.
without people or dogs, it only needs 24h(70f-30f)9.4btu/h-f = 9k btu
of solar heat to stay 70 f on an average december 30 f day in phila, when
a square foot of r1 south sunspace glazing with 90% solar transmission
gains 900 btu of solar heat and loses about 6h(100f-30f)1ft^2/r1 = 420,
so we could solar heat it with 18 ft^2 of glass on the south side and
a couple of passive plastic film one-way dampers made from a dry cleaner
bag over a hole at the top and an extra hole near the bottom. (extra
holes are cheap if ordered in advance...) it might cool from 70 f to
30+(70-30)exp(-7/13) = 53 f over a cloudy week.
nick
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