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re: newbie solar pool heating question (long).
5 dec 2003
mark wrote:
>what i have is an 11 x 24 fiberglass pool in a 20x30 greenhouse type
>structure located in central massachusetts. the pool is about 7000 gallons.
>the pool is currently heated as a zone on an oil boiler...
bad.
>the greenhouse structure has a bronze tinted twinwall polycarbonate roof
>so although the room is warmer during the day it's not hot in there by
>any means.
what's the solar transmission? you might replace the bronze with clear.
>currently with the outside temps averaging in the 30's i'm experiencing
>about a 4 degree temperature drop in water temp at night...
so it's losing 4x7000x8 = 224k btu at night, the heat equivalent of
about 2 gallons of oil, with a water to air thermal conductance of
about 224k/(87-30) = 3930 btu/h-f, like 10 houses. wow.
>i just have a cheapy solar cover and going to get a better thermal cover
>which may help minimize the temp drop.
i'd get a non-tinted clear cover.
>i like the water warm, 86 to 88 degrees f.
ok. insulate the walls of your pool and greenhouse and cover the twinwall
with two layers of greenhouse polyethylene plastic film with 10 gallons of
10% detergent solution and 2" holey pvc pipe in film troughs at the eaves,
and turn on a shop vac blower to fill the space between films with soap
bubble foam at night. put an air return at the ridge and use a microswitch
and some window screen in the return to turn off the vac when bubbles begin
to push on the screen.
nrel says 480 btu/ft^2 of sun (270 diffuse) falls on the ground on
an average 27.4 f december day with an average daily max of 34.7 in
worcester, ma. if the modified roof has 50% solar transmission and
you unfoam it for an hour a day on average, the pool might collect
11x24x0.5x210 = 28k btu and the rest of the greenhouse might collect
20x30x0.5x210-28k = 35k btu. an r1 roof for an hour a day and average
r20 insulation at night (6" of 1/16" bubbles at a mean 50 f) makes
28k+35k = (t-27.4)20x30(1h/r1+23h/r20), ie t = 76 f greenhouse air.
how much insulation does the pool need to be 87 f?
as a loyal member of the order of hvac criminals, i am required
to bill you $12,621.87 for this consultation. please remit.
nick
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