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swimming pool solar covers vs. "pills" - Page 3

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Posted by mm on April 18, 2007, 2:52 am
On Mon, 16 Apr 2007 22:36:50 -0500, Richard J Kinch

Does this mean that one woudln't have to put on skin oil after
swimming.  I'm not talking about sunburn protection, just oil that
some peopel use.  Otherwise, might not be so good, depedning on how
much there is.

Posted by Richard J Kinch on April 18, 2007, 4:07 am
mm writes:

The layer is pretty thin, so you won't get much.  But not unlike bath oil,

Posted by mm on April 18, 2007, 6:45 am
 On Tue, 17 Apr 2007 23:07:51 -0500, Richard J Kinch

Yeah, when reading my post, I realized I had never heard of skin oil.

Posted by nicksanspam on April 16, 2007, 9:01 am

NREL says 1550 Btu/ft^2 of sun falls on the ground on an average 53.4 F
April day in Baltimore. The average humidity ratio w = 0.0052, with
V = 10.4 mph average windspeed, which makes the airfilm conductance
about 2+V/2 = 7.2 Btu/h-F-ft^2.

ASHRAE says an uncovered A ft^2 pool loses about 100A(Pw-Pa), where Pw
and Pa are pool and air vapor pressures. Pw = e^(17.863-9621/(460+Tp))
"Hg (100% RH at Tp (F)), approximately, and Pa = 29.921/(1+0.62198/w).

Maybe R1 with 80% solar transmission, for a clear vs blue blanket.

You might weigh a pill and chop it up or dilute it several times,
homeopathic-like, to treat water in one dark plastic bucket (does
the coverage formula include depth?), and put a pool cover sample
over another bucket of the same kind...

If the pill completely eliminates evaporation and you wrap both buckets
with a few layers of bubble wrap with black plastic on the outside, the
covered one might gain 1240 Btu/ft^2 = 24h(Tc-53.4)1ft^2/R1, which makes
Tc = 105 F :-) The pill version might have 1550 = 24h(Tp-53.4)1ft^2x7.2,
which makes Tp = 62 F.

These will both work better if you paint your pool black
or let it get muddy, like a natural lake in the sun.


Posted by nicksanspam on April 16, 2007, 10:18 am
It might be about 59 without the pill...

20 W=.0052'humidity ratio
30 PA).921/(1+.62198/W)'ambient vapor pressure ("Hg)
40 FOR TPX.78 TO 58.8 STEP .01'pool temp (F)
50 PW=EXP(17.863-9621/(TP+460))'pool vapor pressure
60 GAIN50-24*(100*(PW-PA)+(TP-53.4)*7.2)'net gain (Btu/day)

58.78         2.795166
58.79         .6347656
58.8         -1.525879


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