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PV Powered Drainback Control

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Posted by Jeff Butera on April 18, 2006, 2:36 am
I'm considering installing a PV powered drainback DHW system. I
understand how PV runs the 12/24V DC pump, but how do I incorporate high
temp shutoffs should water in the storage tank exceed 165F?  I don't
seem to find anything written about how to deal with this issue for PV
drainback systems...but I'm sure there's a simple temp-based switch
which could open the circuit, stopping the pump.

Jeff Butera

Posted by DJ on April 19, 2006, 2:33 am

Jeff Butera wrote:

A simple off-the-shelf bimetallic thermostat would do it. Make sure you
get one rated for the amperage of the panel, though. Many thermostats
out there are used to interrupting milliamp control wiring, and running
a couple of amps through them can cause a meltdown.


Posted by louie on April 19, 2006, 12:11 pm
 I don't know much about PV or solar hot water systems, but it seems to
me that DJ's idea of a bimetalic thermostat would be fine.  Instead of
having the thermostat rated for the pump circuit (which is probably
much too high a current for most 'stats), use the thermostat to control
a relay.  Finding a relay to carry the necessary current shouldn't be
too hard.

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