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re: solar pool heating
6 jan 2006
ct wrote:
>i have a nw facing roof (46 deg n of west), i live in central fl, the
>roof pitch is 6" drop for every 1'. i would like to put about 225 sq
>ft of panels on that roof. how can i figure how effective they are
>going to be? i have a potential to add another 225 sq ft on the nw
>patio roof as well. in addition i could add about 100 sq ft of panels
>to a sw facing roof.
nrel says 1020 btu/ft^2 of sun falls on the ground and 1280 falls on
a south wall on an average 59.9 f january day with a 69.8 f daily max
and a 0.0083 humidity ratio in tampa. deep ground is 72.3 f. a square
foot of flat r1 glazing with 90% transmission over 80 f water might
collect 918 btu and lose 6h(80-65)1ft^2/r1 = 90, for a net gain of 828.
with ambient vapor pressure 29.921/(1+0.62198/0.0083) = 0.394 "hg and
80 f water vapor pressure e^(17.863-9621/(460+80)) = 1.047 "hg, 1 ft^2
of uncovered pool might lose 24hx100(1.047-0.394) = 1568 btu/day.
>i am not looking to add much temp in the winter, most of the swimming
>is from apr to oct. gas heater takes the spa up during the winter. i
>would perfer to leave the panels flat on the roof and not on a rack.
you might trickle water over the roofs with 1 or 2 layers of greenhouse
polyethylene film suspended above. or put a plastic film greenhouse over
the pool for the winter, which would reduce the heat loss by evaporation.
nick
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