Hybrid Car – More Fun with Less Gas

Re: Solar water heating system value - Page 5

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Posted by nicksanspam on March 10, 2006, 10:17 pm

There's no need to go that high. A foot would suffice.


Posted by Doctor Drivel on March 11, 2006, 12:08 am

It "probably" would, but I said "foolproof".

Posted by nicksanspam on March 11, 2006, 12:10 am

No accounting for those who doubt gravity :-)


Posted by daestrom on March 12, 2006, 2:36 pm

Why go all the way up to the panel height?  If you make sure the hole is
always above the water level in the tank, and put a small enough
orifice/restriction in the hole, the flow of water out the hole will be
minimal.  With the pump off, the difference between where the hole is and
the water level in the tank will start the reverse syphon process.  As water
syphons backwards through the collector and pump, the return line will be
more and more air (less and less water) so the dP for the syphon grows and
grows.  Soon the whole pipe and collector will be drained.

Things that can go wrong:  1) If there are any low spots that don't slope
back to the tank, they may hold water that can then freeze.  2) Some fool
puts a check valve in the line.  3) If the orifice/restriction/hole gets
clogged with scale/crud/biofouling, then the system may not drain.  The
first two are avoided by careful installation.  The last, increase the
height above the water line for the hole to provide a stronger dP for
clearing the crud.  Heck, maybe rig a circuit that if the pump is running
but no water out the hole after 60 seconds, sound an alarm.  Scale could be
prevented with a simple mechanical reamer every 3 months or so.

But running a pipe all the way up to panel and pack down creates a
'loop-seal' that will *prevent* drain down, exactly the wrong thing.  Now
you have to 'upside-down U' sections of piping to break the syphon seal on
both to prevent freezing.


Posted by Doctor Drivel on March 12, 2006, 2:46 pm

Because it is "foolproof" and will "always" work, no matter what pump, or
extra panels you insert later.  Just putting the bombproof method forwards,
nothing else.

As the end of the pipe is open to atmosphere in the tank at "all times", it
will not cause a vacuum and lock in the water.  When the pump is on, it will
pump some way up the pipe, how much depends on pump friction, etc.  Once the
pump stops, the water in the pipe will drop back and as it is a open vented
pipe, the water will just fall back.

The last thing you want is water dropping from a small hole inthe wtaer in
the tank, as this aerates the water. Not what you want.

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