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Query about Heathing a Swimming Pool - Page 2

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Posted by Christian Kaiser on October 24, 2007, 3:52 pm
 

No. I's not that easy.

The energy gain is smaller the hotter the water coming out of the panels
is. Reason: When the water/the system is hotter, there's more thermal
(radiation) loss at the panels and lines.

On the other hand, the pumps need more energy if it comes out colder for
more turnover, but the energy will add to the water temperature, so
there's no real loss, it's just an additional, more expensive heating.

I would suggest adding a small controller that controls the pump so that
the water temperature coming into the pool is just a little warmer than
the wanted temperature of the pool.

Anyway, an "installer" should know the "performance" you should be
getting, and the system should be designed good enough for your 80%
coverage. Possibly it isn't.

Christian

Posted by Don on November 6, 2007, 1:36 am
 
As we move into November the thought of going swimming is less
appealing with every day.  I understand the need for a pool cover, but
I just don't want to have an ugly pool cover and reel at the end of
our great looking pool.  Are there any good looking solutions?  We
have a "double roman" shape with half circles on each end and that
seems like it would make it harder to cover.  I still don't understand
why the water is not warmer coming into the pool on a clear sunny
day.  That seems pretty basic and whatever the ratio of pool volume to
panel area, the water ought to be warm.  Why isn't it?

--Don




Posted by Morris Dovey on November 6, 2007, 10:11 am
 Don wrote:

| I
| still don't understand why the water is not warmer coming into the
| pool on a clear sunny day.  That seems pretty basic and whatever
| the ratio of pool volume to panel area, the water ought to be warm.
| Why isn't it?

At this time of year the daily heating period is shorter and the
cooling period is longer, so you're getting less heat into the pool
and losing more to evaporative cooling, direct transfer to air, and
radiation into the night sky.

--
Morris Dovey
DeSoto Solar
DeSoto, Iowa USA
http://www.iedu.com/DeSoto/



Posted by Morris Dovey on November 6, 2007, 10:17 am
 Morris Dovey wrote:
| Don wrote:
|
|| I
|| still don't understand why the water is not warmer coming into the
|| pool on a clear sunny day.  That seems pretty basic and whatever
|| the ratio of pool volume to panel area, the water ought to be warm.
|| Why isn't it?
|
| At this time of year the daily heating period is shorter and the
| cooling period is longer, so you're getting less heat into the pool
| and losing more to evaporative cooling, direct transfer to air, and
| radiation into the night sky.

I hit 'send' too soon.

...So every day you're heating cooler water. If you're not seeing
close to the same difference (in full sun) between panel input and
output temperatures, you may need to adjust panel orientation.

--
Morris Dovey
DeSoto Solar
DeSoto, Iowa USA
http://www.iedu.com/DeSoto/



Posted by nicksanspam on November 8, 2007, 1:33 pm
 

A pool cover that sinks vs rolls up when you want to swim?


Physics :-) NREL says the outdoor temp on an average November day in Phila
is 46.4 F, with a 9.7 mph wind and 680 Btu/ft^2 of sun on the ground and
a humidity ratio of 0.0048 pounds of water vapor per pound of dry air.

20 TAF.4'ambient air temp (F)
30 WA=.0048'ambient humidity ratio (lb water/lb dry air)
40 PA).921/(1+.62198/WA)'vapor pressure ("Hg)
50 VW=9.7'windspeed (m/h)
60 SUNh0'sun on pool (Btu/ft^2-day)
70 GP=2+VW/2'water-air conductance (Btu/h-F-ft^2)
80 TMAX=TA+SUN/24/GP+100*PA+460
90 TWE=TA+460'uncovered water temp estimate (R)
100 TW21/(22.47-LOG(TMAX-TWE))'new water temp (F)
110 IF ABS(TWE-TW)>.01 THEN TWE=TW:GOTO 100'iterate
120 TWC=TA+.8*SUN/24*(1+1/GP)'water temp under cover (F)
130 TWF=TA+.8*SUN/(8/(1+1/GP)+16/(6+1/GP))'water temp under foam (F)
140 PRINT TW-460,TWC,TWF

no cover      R1 cover     +R5 foam

44.03232      72.37567      103.16 F

An R1 pool cover with 80% solar transmission would raise the water temp
from 44 to 72. R5 foamboard under the cover would raise it to 103.
The cover might sink to the bottom for swimming.

Nick


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