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re: storing solar heat
26 feb 1997
greg burgin wrote:
>i have an idea! build a modified ice house. superinsulate it and fill it
>with plastic 55 gal drums full of water and maybe some antifreeze.
sounds economical, if you need an ice house anyway. otherwise it sounds like
an interesting hobby, perhaps not too expensive if its a commerical plastic
film greenhouse with some strawbales stacked inside, and the drums are free.
(like the 300 drums i collected from a local food processing plant, who were
used to paying to have them hauled away.) you might put an epdm rubber liner
under the drums with about 3" of antifreeze in it...
>maybe a couple thousand pounds of water would be enough.
let's see... suppose your house were 30x30x16' tall, with average r10 walls
and r20 ceiling, eg walls with 6" of fiberglass insulation, along with some
r3 thermal bridging from studs and some r3 windows, and it had only 1 air
change per hour... its thermal conductance would be about 2000 ft^2/r10 for
the walls, 1000 ft^2/r20 for the ceiling, and 30x30x16x1/55 for the air
infiltration, about 500 btu per hour per degree f, so on a 90 f day when it's
70 f inside, it would need about 10,000 btu/hr to stay cool. it takes about
144 btu to melt a pound of ice, so 2,000 pounds of ice would keep the house
cool for about 2,000x144/10,000 = 29 hours. philadelphia has about 1,100 (f)
heating degree-days (and about 5,000 cdd) so cooling a house like that would
take at least 24x500x1100 = 13 million btu, or about 90k pounds or 1400 cubic
feet of ice, eg a 30x30' a crawl space with a layer of ice 1.6 feet thick.
>through the winter a damper would open and perhaps a fan would circulate
>outside air into the ice house whenever the outside air is cooler.
it might be simpler to bury the ice store, and let cold outside air flow
downwards into it when it's cooler than the store, and stay there when the
outside air is warmer. an ice store might live under the crawl space of a
house, with some foil insulation under the house floor. it might have a vapor
barrier on the ground, then some canvas to protect the vapor barrier, then
a foot or two of fine-grained soil, then a layer of epdm rubber or pond liner,
with the edges of soil under it somehow exposed to cold winter air but not
summer air, to keep it dry. can this be done with a perimeter sewer pipe
under a vapor barrier with holes in the bottom, and a fan in series with
a humidistat and thermostat? humid air rises...
>it should get very cold in the ice house.
sure. you might use a temperature sensor to pump more water up on top of
the ice whenever the temperature near the surface is less than freezing,
or perhaps a bunch of dallas semiconductor 1820 sensors daisy-chained in a
vertical array.
>in the summer, circulate air between the ice house and your house.
if it's any distance, it may be easier to move water or antifreeze, which
has about 4,000 times the heat capacity rate.
>even if the ice house warms it will always be cooler than peak summer!
you could cool it with night air in a dry place like abilene, texas, and
combine it with evaporative cooling. perhaps you could make and store ice in
abilene. the 24 hour average air temp is 43 f in january, with an average
daily minimum of 30.8, but record lows for october through march are 28, 14,
-7, -9, -7, 7 and 25 f. seems like ice would work best in places with not-
too-cold winters and not-too-warm summers. for instance, international falls,
minnesota has
avg air temp, t inches of ice per day = 24(32-t)1.5/144/64x12
november 24.9 f 0.33" which comes out to a layer of
december 7.2 f 1.16" ice more than 11 feet thick,
january 1.0 f 1.45" altogether...
february 7.7 f 1.14"
march 22.1 f 0.46"
but the hottest month there is july, with an average air temperature of 66.7 f
and an average daily minimum of 54.6 f. hmmm. can we freeze ice barges in
minneapolis and float them down the mississippi to new orleans basements?
nick
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