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re: low cost solar powered water pump
9 oct 2000
darrell thomas wrote:
>hello all.
hi darrell,
>...i have built a green house with 30 degree slope on the glazed south
>side and insulated roof, side and back walls. i would like to store
>enough heat to keep it from freezing in the tennessee winters. right now
>the design is like a walk-in solar collector. i currently have 5 each
>55 gal. drums filled with water...
you might put 2 layers of plastic film over the glazing with a fold
at the bottom to make a trough for a 10% detergent solution with some
antifreeze and a 2" horizontal pvc pipe with lots of 1/16" holes in the
bottom, and use a shop vac to push air into the pipe to fill the space
between the films with a foot of soap bubble foam at night. an opening
at the top (at least 2") might collect the air from between the films.
some window screen over the opening might push on a microswitch when
the bubbles reach the screen, to turn off the shop vac.
one 12,000 ft^2 tomato greenhouse in calgary worked well like this,
even at 20 below zero. tiny cold soap bubbles are almost as good as
fiberglass insulation... 5 25ft^2 80 f drums with a slow-moving air
film conductance of 1.5x5x25 = 187.5 btu/h-f can supply (80-32)187.5
= 9k btu/h to the greenhouse. if, say, 16'x8' of foamed glazing has
a thermal resistance of r30/(16'x8') = 0.234 "ohms," the drums can
keep the greenhouse from freezing until the outdoor temp drops to
about 32 - 0.234(9000) = minus 2077 degrees :-)
nick
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