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re: looking for photos/schematics
15 mar 2005
john wrote:
>i have had an interest in building a pool heater for too long...
where do you live? is your pool shaded? indoors? covered when not in use?
>lowes sells galvanized corrugated roofing, they have one that you can order
>that has a center to center distance of just 1.5 inches. if memory serves it
>is 24 inches by your length and a 15 footer ran about 22 dollars. an array
>of these painted black, mounted on the roof with piping and holes drilled on
>center so the water leaks into each valley of the corrugated...
harry thomason heated hundreds of houses that way.
>drawback is evaporation, what amount i do not know...
about 0.1(pw-pa) lb/h-ft^2, where pw = e^(17.863-9621/(tw+46)) and
pa = 29.921/(1+0.62198/w), where tw (f) is the average collector temp and
w is the outcoor humidity ratio in pounds of water per pound of dry air.
for instance, w = 0.050 on average in april in phila, so pa = 0.239 "hg.
if tw = 80 f, pw = 1.047, so the collector would lose 0.1(1.047-0.239)
= 0.081 pounds of water and 81 btu/h per square foot.
nrel says 1520 btu/ft^2 falls on the ground and 950 falls on a south wall
on an average 52.4 f april day with an average daily max of 62.6 in phila,
so sqrt(1520^2+950^2) = 1792 btu/ft^2 would fall on an atn(950/1520) = 30
degree sloped roof. in 8 hours, it might lose 8x81 = 648 btu/ft^2 and
collect 1144 btu/ft^2, net. a 24x32' = 864 ft^2 uncovered 80 f pool would
lose about 24hx864x81 = 1680k btu/day (and 202 gallons of water), so you
might heat it with a 1680k/1144 = 1468 ft^2 roof which loses another
8x1468x0.081/8.33 = 114 gallons per day.
so, you _could_ do without covers in phila, but...
>...it could be glazed, i can get clear 5 mil mylar for free so i was
>thinking of covering with that to prevent contamination (leafs, dirt, etc).
in narrowish widths? how long would it last in the sun?
>my mental scheme is to secure galvanized piping near the ridge line serving
>as both as mount and water delivery plumbing, another run of galv to mount
>the bottom of the galv to. water pumped up 24 feet, drains down to gutter
>and into pool. a diverter at the gutter allows it to be a regular gutter in
>the event of rain.
or refill the pool...
>if you find the magic bullet, please post it.
you might use greenhouse polyethylene plastic, which costs about 5 cents/ft^2
and comes in wide folded rolls, up to 40x150', with a 4-year guarantee. it
won't last very long if it touches a hot dry roof you might stretch it over
shallow doubled 1x3 roof bows or inflate it over the roof with a small blower
or suspend and contain it with ropes or straps under and over.
a 24'x36' shaded 80 f pool with an r1 cover would lose about 24h(80-52.4)864
= 572k btu on an average april day in phila. a square foot of covered roof
might gain 0.9x1792 = 1613 btu and lose 8h(80-57)1ft^2/r1 = 184 over a day,
ie 1429 net, so you might heat the pool with a 572k/1429 = 400 ft^2 roof.
an unshaded pool with an r1 cover with 90% solar transmission might collect
1613 btu/ft^2-day and lose 24h(t-52.4), so t = 52.4 + 1613/24h = 120 f,
theoretically-speaking.
nick
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