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High temperature or high flow?

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Posted by Lawrence on November 6, 2004, 7:46 am
I have a solar setup feeding my pool. At full flow, there is a marked
difference between in/out, but not more than a few degrees. Decreasing
the flow increases the temp, but it all still flows into the main flow
into the pump before going into the pool. Not the best design, but the
plumbing was concreted in that way...

Anyway, my thought is that, all things being equal, it doesn't make much
of a difference, since lowering the flow only through the solar cuts the
percentage of mixture with the main flow, too., meaning, I think, that
the pool still reaches the same temperature, in about the same time,
either way...

I know there are quite a few math-oriented minds out there, and I'm just
going by the seat of my pants in my assumptions...

Any thoughts?


Posted by Robert Morien on November 6, 2004, 8:53 am

Lower flow = lower pump pressur = longer pump life

Posted by Bert Menkveld on November 6, 2004, 12:45 pm
 The higher the temperature of your solar collector, the less efficient it
will get.  Though it may seem a bit counter-intuitive, you will collect more
heat by keeping your solar collector as cool as possible.  This is
especially important for unglazed collectors (which are typically used for
pool heating).  Of course, there is a point of diminishing returns, and I
certainly wouldn't shoot for even less than "a few degrees", which sounds
like a reasonably low temperature rise.

Bert Menkveld

Posted by daestrom on November 6, 2004, 4:55 pm

Well, here are several.... :-)

1) Higher flow through heat-exchanger tubing means better heat transfer.
This includes the tubing in a collector. (good)
2) Higher temperatures (caused by low flow) in the collector and return
piping means more losses to ambient before the return water mixes with the
rest of the pool flow (bad).
3) Higher flow means more pumping power needed.  This is bad if the energy
to pump the water is expensive (separate solar powered pump for example).
But the energy of the pumping ends up in the water as heat, so it isn't like
its completely wasted.


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