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DC circulator pump question

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Posted by ouioui on September 21, 2003, 10:45 pm
To get my feet wet in solar heating I'm building a hot water solar collector
from plans I got from www.JC-SolarHomes.com <http://www.JC-SolarHomes.com> .
I'd like to use it to solar assist my hot tub. I'm planning on drilling two
ports on opposite sides of the 500 gallon tub. One port for in and the other
for out.
I'd pipe it to the collector on the roof (about 10 feet higher then the tub)
in such a way so the water would drain back into the tub (I live in the
north east USA). I'd like to use a circulator pump that is powered directly
from a solar cell so when the sun is out the pump goes.

The collector has sixty feet of 3/8 ID copper tubing in a serpentine
configuration. If I need to build a second collector in parallel I will.

How do I go about sizing a pump and solar cell to match?

Any help you can provide would be greatly appreciated.


 PS: If I like what I see I'd probably start working on solar heat for my
 whole house. The house is currently heated with radiant floor heating. Gas

Posted by Scott Willing on September 26, 2003, 3:18 pm
On Sun, 21 Sep 2003 22:45:32 GMT, ouioui@optonline.net wrote:

Can't really help with your question I'm afraid, but if you don't mind
a question in return...

I gather you actually bought the ($0?) book. What do you think of it?
I've been to the site a few times and often wondered if the book's any


Posted by Lynn Coffelt on October 1, 2003, 4:43 pm

No engineering degree here, but did some 'hands on" work with my solar
powered greenhouse. Operation a little over a year, in northwest Washington
state. Here are a couple of practical issues:

1.   Ivanlabs makes a really great pump (SID20PV) intended for solar
powering, but won't be much good for pumping against a 10' head. I had to
resign myself to a "closed" circulating system, without any provision (at
present) for "drainback" when sun goes down or "away" for days at a time
<grin>.  But circulate it does, 3 or 4 gallons per minute, with no noise at
all, no brushes, no shaft seals to leak. I'm not selling, but a satisfied

2.   Sometimes (actually quite often) solar heated water will be cooler than
that already in the heat sink, hot tub, or whatever, and during those times,
some sort of controls would be a good idea to prevent circulating good hot
water up into a cooler solar collector. or, slowing the circulation some, to
allow the collector water to heat above the temperature already in the heat
sink or hot tub. I'm stuck with doing the controlling manually while control
design languishes on the drawing board.

3.   Although it would detract from the elegant simplicity of the system you
are thinking about, I think there my be some very practical merit in
providing a well insulated hot water storage vessel to slowly bring solar
heated water up to usable temperature while the sun is out, and then release
that water into the hot tub when you need it. Maybe gravity flow from an
insulated vessel mounted less than ten feet below your collector, so a
direct solar powered pump is capable of sufficient heating cycle

     Oh, my heat sink is currently a concrete slab floor with imbedded
copper pipe, so the situation is not precisely the same as yours.


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