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re: heating a pool?
12 sep 1996
wrote:
>nick@ufo.ee.vill.edu (nick pine) wrote:
>>steve wrote:
>...... 500 feet of hose to glue a 6 foot diameter flat coil.
>>28 ft^2? how much does the hose cost?
>$30 per 6ft diameter coil
6 cents/foot...?
>plus $10 worth of hot melt; and 4 hours of my time.
another $14 :-) hmmm. $44/28 ft^2 = 1.57/ft^2. not bad, but...
>dang, how cheap do you want?
i still like the south roof idea. 10 cents/ft^2 for the two layers of poly
film, another 75 cents/linear foot for the extrusion clamps to hold it (or
maybe some cheaper 1x3s or aluminum strips with screws), and another $1/ft
for the 1 1/2" pvc pipe along the top edge? $60 + $75 + $30 = $165 for a
30' long x 20' slant height 600 ft^2 roof, ie 28 cents/ft^2?
>>. . .freestanding north wall, with polyethylene film glazing?
>this assumes you have the funds and space for a north wall, of course.
funds may be easy, vs. space. that wall might cost 10 cents/ft^2 for the
beadboard back, another 10 cents/ft^2 for the concrete, another 10 cents
for the chicken wire, 18 cents for the tubing on 4" centers and 5 cents
or so for the poly film cover, ie 43 cents/ft^2, not counting labor. more
than the roof, but swimming pools often need walls around them anyway.
>how about a comment on pulling heat from a hot attic?
good idea. especially if you make the south roof transparent, like mine. ed
palmer of solar attic in minnesota (612) 441-3440 sells something like this
for use with an ordinary attic. you might start with a used auto radiator
with its attached 12 v fan, like the $35 1984 dodge omni radiator in my
living room floor. ed charges more than that for his version, $1500 or so
in the tax credit era, $500 or so now :-)
or you might use a duct heat exchanger like the $139 all-copper 2' x 2'
shw 2347 unit made by magic aire, which transfers 45k btu/hour between
125 f water and 68 f air, ie about 800 btu/hr-f at 1400 cfm, with a 0.1"
h20 air pressure drop. the $12 chinese-made holmes (800)-5-holmes 20"
box fan moves about 1000 cfm, whilst consuming about 100 w.
>how big a radiator?
how big an attic? how big a pool? where i live, a 24'x32'x6' deep pool at
72 f might lose 24(72-36)768ft^2/r10 = 66k btu/day of heat through its
floating 2" styrofoam cover, another 24(72-45)672ft^2/r10 = 44k btu from its
r10 sides, if any, to the warmer ground, and another 24(72-55)768/r10 = 31k
through its uninsulated bottom, ie 141k btu/day in december. a 150 ft^2 $50
solar collector could keep it heated in december, if it were mostly covered.
>>>water entering at 82 degrees came out at 96 degrees at 2 gpm flow.
>
>>sounds like (96 f - 82 f)(8 lb/g)(2 g/m)(60 m/hr) = 13,440 btu/hr
>>out of 300 btu/ft^2/hr x 51 ft^2 = 15,300 btu/hr in full sun.
>>88% efficient, as a solar collector! :-)
>...isn't 8lbs/gal for water a bit high?
heavy water.
8 is a nice binary number, no? as is 64 pounds for a cubic foot.
>anyway, what efficiency can a simple open air collector hope
>to get on a windless day in full sun?
it can hope for 100%, or more, if the air is warmer :-)
nick
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