12 VOLT controller [RE-wrenches]

[sunwise]

It is my understanding that it is never a good idea to stagnate a
collector.  High heat build up will at the very least reduce the useful
life of the propylene glycol.  The mixing valve is a good way to go, or
for very large systems, a shunt loop.

Kurt Nelson

-----Original Message-----
From: Pat Redgate [mailto:solarpro at aol.com] 
Sent: Monday, October 13, 2003 10:59 PM
To: RE-wrenches at topica.com
Subject: Re: 12 VOLT controller [RE-wrenches]


In a message dated 10/13/2003 7:17:47 PM Pacific Standard Time, 
allan at positiveenergysolar.com writes:

  "The problem I see with the approach you have described is that it
allows 
the> PV pump to        shut off at high storage tank temperature"

        Preventing overheat problems is, has and ever shall be a
problem.  It 
is best solved by proper sizing, orientation and tilt.  This is the best

reason for elevating panels to a higher angle (to stop overheating,
rather than to 
be enhancing performance).   Also, black chrome kills.
 
        "I would rather see no high-limit shutoff, and rather a
thermostatic 
mixing valve to prevent overheating. How do you handle this?"
        
       
       To set an upper limit or not to set an upper limit; that is the 
question...   What fails on a solar water heater first?  It seems, much
to my 
surprise, to be the tank.  The panels can take the heat, so can the
copper tubing 
and pump; but the tank goes into hyper-oxidation above 165F.  Maybe your
fluid 
needs replacing more often, but it sure beats rolling out a new tank
every five 
to ten years.  BTW, how does a thermostatic mixing valve prevent
overheating 
IN the tank?  Tempering valves are required in our part of the world -
they 
prevent scalding water from entering the household.  The guts of the
valve need 
periodic maintenance and most fail by mixing in too much cold water,
thus 
diminishing the solar contribution.  But they do work well as hot water
extenders 
when they are new.  

As far as the PRV is concerned...  You do not need one (I know, code) if
the 
system is sized correctly.  If you do use one, DO NOT install it
anywhere near 
the solar collector.  If you must, put it in the loop downstream and
vent it 
to grade.

But, every SHW solution is site specific.  I am lucky, with 95% of our 
systems located within 75 miles of the coast and the BEST weather in the
world, I 
have very little to worry about.

Surfs up.

Patrick A. Redgate
AMECO
Long Beach, CA
(562) 595-9570
www.amecosolar.com

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