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re: solar hydronic greenhouse questions
11 jan 2001
rick solinsky wrote:
>...if i was to use water storage in my (9x16) greenhouse, i would need
>over 700 gallons of water storage to passively heat it- which would in
>effect make me fill the greenhouse up with a bunch of 50 gallon drums...
i tried that, adding 200 55 gallon drums to a 20x100' greenhouse. at least
it never froze :-) you need less mass if you insulate the glazing at night.
you might fill the space between two layers of poly glazing with 12" of
tiny soap bubbles at night, and put an 18"x16' $6 water-filled round poly
duct on the ground under a bench inside a 24" air-filled duct, and blow
warm air from the peak down through the 24" duct during the day to warm
the water and dehumidify the greenhouse. at night, with about r20/400ft^2
of greenhouse-to-outdoor glazing resistance in series with r0.66/75ft^2 of
water-duct-to-greenhouse resistance, and 70 f water, the duct can supply
i = (70-32)/(0.66/75) = 4280 btu/h of heat, so the greenhouse won't freeze
until the outdoor temp t reaches 32-20i/400 = -182 f :-)
i --> 32 f
70 f ---www---|---www--- t
0.66/75 20/400
at t = 10 f, with the glazing foamed, the 40 f greenhouse would lose
(32-10)/(20/400) = 440 btu/h. the 1800 pounds of water stores about
1800(70-40) = 54k btu of useful heat, so it could keep the greenhouse
at 40 f for about 54k/440 = 123 hours or 5.1 days.
nick
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