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Looking for 12 Volt pump in closed loop from collector. - Page 2

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Posted by Brian Graham on March 22, 2006, 6:36 pm
 
A friend of mine is running that same pump in his system. He has 2 flat-plate
collectors. It pumps it quite well. He was running from a 15 watt 'Crappy Tire'
panel. It didn't work well in lower light conditions. Now he's running from a BP
20 Watt panel (Toronto Canada region). Now his problem is that the panel is
still providing 25%+ power on very overcast days when the panel is not really
collecting much heat. Forced thermosiphoning. lol I see a control system coming!

And before anyone says its too much power hooked up to the pump, he spoke
directly with the guy who actually designed the pump. For us guys up North, no
problem. Further south it may well be.

Anyway, a great pump.

Personally, I'm using a 3-speed Grundfos but I'm heating the water on my wood
stove in the winter. Day & night, sunny and cloudy, I've got LOTS of HOT water
all winter. Come spring, I'll have to settle for collecting on sunny days only.
Oh well. Its all $$$ saved!
--
Brian

Hello All,
I've seen some great ideas on the heat exchanger tank and now have some
questions on the pump. I would like to keep it 12 Vdc as my hot air
solar setup now has a solar photovoltaic charger / battery and AC
charger. I have been finding some really nice pumps on the internet
that are made for this application in 12 volt but are a little pricey.
I got my heat exchanger for free so $ 220 US isn't all that bad for a
pump.  I have a link for one of the pumps :
http://shop.solardirect.com/product_info.php?products_id63  


Anyone have any ideas or sources for a 12 Vdc pump / low power that can
handle the temperature / pressure of a solar collector ?  Thanks, Kevin




Posted by Steve Shantz on March 26, 2006, 11:37 pm
 
Brian,


collectors. It pumps it quite well. He was running from a 15 watt 'Crappy Tire'
panel. It didn't work well in lower light conditions. Now he's running from a BP
20 Watt panel (Toronto Canada region). Now his problem is that the panel is
still providing 25%+ power on very overcast days when the panel is not really
collecting much heat. Forced thermosiphoning. lol I see a control system coming!



directly with the guy who actually designed the pump. For us guys up North, no
problem. Further south it may well be.



I would heartily agree that the El SID is a good pump.

As for your problems with the pump starting too early, causing
thermosyphoning...
You should be drawing water from the bottom of your DHW tank to go into
your heat exchanger.  This water naturally is the coldest in the tank
due to the natural density driven stratification of water.  As long as
the glycol is even a bit warmer than your water at the bottom of the
tank, it is not thermosyphoning.  My system runs even on cloudy days,
and I'm always quite suprised to see the return glycol return
temperature  1 - 3 degrees F warmer than what went out.  Even if it the
outside air temperature is only 25 - 30 degrees F.  Is it making much
heat? Definitly not!  Is it loosing heat? No.

One could argue that on some really cold cloudy days, you may return
the glycol colder than it goes out.  However, in this case, the cold
water will mostly fall to the bottom of your DHW tank.  Some mixing
will happen as the water falls to the bottom.  The extent of this
depends on where you return your heated (or occasionally cooled) water
back into your DHW tank.  This would suggest some good reasons why the
return water line to the DHW tank should not be at the top of the tank,
but rather, in the middle or even near the bottom.  Hot water from a
nice sunny day will naturally rise to the top.

If the premature startup really is a problem, could one put a resistor
in parallel across the pump?  This would draw some of the current, and
prevent premature startup.  For a 12 V system, a resistance of 29 Ohms
would draw off about 5 Watts.  Standard resistances are 22 and 33 Ohms.
 You would need a power resistor, likely about 10 W.  These
calculations assume 12 V.  In reality, at startup or for cloudy days,
under low current conditions, I'm not sure you will have 12 V coming
from your PV panels.  You would likely have to experiment some to find
the best value for your system.


Best regards,

Steve

P.S.   It's a good thing I grew up in Ontario, 'cause not many people
will know what 'crappy tire' is!


Posted by Brian Graham on March 27, 2006, 6:07 pm
 
the
tank, it is not thermosyphoning. <<

Therein lies his problem. His tank is insulated to about R400, if you take my
meaning. ;-) On a cloudy day his ElSid 10 with a BP panel pumps, even though the
clouds are heavy enough to keep the panels from producing. So the heat in being
transferred from the tank into his coil and out to the collector to dissipate.


will know what 'crappy tire' is! <<

LOL  ..and everyone in Canada recognises it instantly!
--
Brian




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