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Query about Heathing a Swimming Pool

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Posted by Don on October 18, 2007, 10:23 pm
 
I have a new swimming pool heating system installed professionally in
Columbia SC.  It is HOT here and we wanted a thermal solar heating
system to broaden the period that we could enjoy the pool.  The panels
are Heliocol and the ratio of panels to pool volume was calculated to
heat the pool for 80% of the year.  We have almost total southern
exposure with very little shade.  During the first summer there was no
challenge to the heating system; we were using it to cool the water at
night.  Now in October the temperatures at night are dropping into the
50s while the daytime temperatures vary from 70s to 80s.  We have no
pool cover by the way.  After a long hot day in the mid to high 80s
I'm thinking that the water coming into the pool with the heating ON
ought to be warm.  Instead it feels like about the same temperature as
the water already in the pool.  Indeed the temperature of the pool is
in the low to mid 70s while the daytime temperature was in the mid
80s.  Next door the neighbors' pool, with less direct sun, i.e., more
shade, is about 4 or 5 degrees cooler.  It seems like we should be
getting more heat for our investment.  When I feel the large pipes
going into and out of the panels they feel the same in temperature.
I've spoken to the installer who seemed a little uncertain about what
kind of performance I should be getting.  She suggested I might slow
down the water coming OUT of the solar panels.  That makes sense to
me: the water is going into the panels and coming out.  We have no
leaks.  If it goes slower, it should heat more.  Does this sound like
a plausible diagnosis and remedy?

I welcome your advice.
  --Don


Posted by Don on October 19, 2007, 1:00 am
 
Uhh, make that Heating not heathing.


Posted by Jeff on October 19, 2007, 1:52 am
 Don wrote:

   I'm not a pool owner or a solar expert.

   It shouldn't matter if it is raising the temperature only slightly.
Generally it's more efficient to keep the collector closer to ambient. A
better question is how much heat are you getting. Can you measure the
temperature of both the incoming and outgoing water? Then get some idea
of the volume of water, perhaps by filling a container and counting the
time. It takes one BTU to heat one pound of water one degree F, and
there are about 7 lbs in a gallon.

   Then we can tell if the solar collector is underperforming or whether
you need to consider more carefully controlling pool heat losses.

   My own suspicions are that those 50F nights are overtaking what you
add in the day. It takes an awfull lot of BTUs to heat a pool a few
degrees, you should consider a cover. I think there are some ideas for
very  easy and cheap covers. Nick?

   I'd say get us some stats. The morning pool temp just before the
heater goes on, the evening, just after it shuts off and the amount of
heat the collector is making (see second paragraph). Also, the size of
the pool and the area of the collector. If nothing else, get the temps
of the pool...

   Jeff





Posted by gary on October 19, 2007, 2:05 pm
 Hi,
As Jeff said, high flow with a low temperature rise is the efficient
way to go, so the panels may be fine.  You need to measure
temperatures and the flow to know for sure.

But, the big problem is that you don't have a cover.  About half of
your pool heat loss (maybe more) is from surface evaporation, and a
cover will stop this.  Heating a pool without a cover is like trying
to air condition a house with all the doors open.

Have a look at the FSEC material and some of the basics articles on
pool heating here:
http://www.builditsolar.com/Projects/PoolHeating/pool_heating.htm

Gary



Posted by thedoc on October 23, 2007, 7:54 pm
 Don wrote:

I would suggest you invest in a pool cover.. I have one that is like a
very thick
bubble wrap and it reduces heat loss considerably... that combined with
a solar array should extend your swimming season..

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