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re: another solar pool heater q
4 jul 2002
frank martin wrote:
>...a pool can be its own solar collector.
>1/ paint the bottom black.
this could be difficult, but it might be easy to drop
some black epdm rubber roofing material on the bottom.
that could be difficult too, depending on the local
board of aesthetic review.
>2/ enclose the pool in its own 'greenhouse'
fairly easy, with a quonset shape over a rectangular pool or
a round above-ground pool inside a geodesic framework made with 20
2" pvc pipes, with greenhouse polyethylene film attached to the pipes
with sheet metal screws and more pipes slit lengthwise as cap strips.
if the dome is larger, the pool might be surrounded with bags of leaves
for more insulation, with a clear "solar cover" on top and some of the
upper south triangles whitewashed to reflect more sun down into the pool.
would anyone want to swim in something like this? :-)
>the advantages are many:
>no debris in the pool.
fewer unwanted bodies...
>no heat loss from surface (always the chief method of
>heat loss, especially on windy days and nights.)
well, maybe a "greatly reduced heat loss," r1 vs 100(pw-pa) btu/h-ft^2.
consider march in phila, at 42.4 f, with humidity ratio
w = 0.0036 and 1200 btu/ft^2/day on a horizontal surface.
with the greenhouse, a square foot of pool gains 0.9x1200 = 1080
btu/day and loses 24h(t-42.4)/r1. if gain = loss, t = 42.4+1080/24
= 87.4 f, or maybe less, with condensation until the glazing temp
reaches the indoor dew point.
(this might be a hot tub in july, with 76.7 f and 1890 btu and
t = 76.7+0.9x1890/24 = 147.6 f. with a foamed greenhouse, it might
gain 600 btu/day in january and lose 6h(t-30), so t = 30+600/6 = 130.)
with no greenhouse in march, pa = 29.921/(1+0.62198/w) = 0.172 "hg, and
1200 = 24hx100(pw-0.172), so pw = 0.672 = exp(17.863-9621/(460+t)), and
t = 9621/(17.863-ln(pw))-460 = 66.9 f.
>in the depths of winter the pool enclosure might
>function as a greenhouse - if it is made large enough.
sure. make it a lot bigger than the pool, surrounded by dirt, cover the
greenhouse with 2 layers of poly film, fill the space between them with
air during the day and tiny cold soap bubbles at night, and put a poly
film cover over the pool.
nick
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