copper leaching in solar thermal system [RE-wrenches]

[solarpro at aol.com]

Todd, you wrote....


> The rest of the loop is copper, stainless and brass (all
> compatible). The water has very low total dissolved solids and is not 
> acidic
> (anodes last forever). There are 2 homes on this well and only the home 
> with
> the solar thermal is making the shower green, so I know that is the cause,
> for some unknown reason.
> 
Todd
If you have isolated the collector glycol loop from your potable storage by 
means of a stainless steel heat exchanger, how is it that the "solar" is 
contributing copper ions?  Is the potable side of your exchanger made of 
copper or cuprous nickel?  Are you running a long length of soft copper from 
your potable storage to and from the heat exchanger?  Is your system 
overheating?  High heat accelerates and can induce all kinds of chemical 
reactions.  Have you confirmed the fact that the solar is making this copper 
by bypassing the system for a few months?  Are you sure it's copper?  Of the 
hundreds of dhw systems (active, passive, open & closed) we have installed 
over the last twenty-five years, the only time we have had problems with 
excessive Cu in the water is when soft copper is coiled within a holding tank 
and reaches excessive (>F 160) temps.  I have also seen stray currents at the 
holding tanks when dielectrics are used.  You may want to attach a conductor 
between the tank nipple and the piping which would allow any current to go 
around the dielectric, and also on the SS HX if you have also installed 
dielectrics on it.  Then make sure your tank or its piping is grounded.  At 
least this will theoretically eliminate any potential that is being created 
by local appliances (such as pumps and controls).  After witnessing the 
disintegration of dielectric unions and the nipples they were married to, we 
now only install brass between steel and copper.  Its lower reactivity with 
respect to ferrous and cupric combos makes it a much better choice, and our 
record with stainless steel ANYTHING in solar dhw has been dismal.  We have 
had to replace all of our SS exchangers with copper units.
Also, how are the dip tubes in the solar tank?  Five to ten (or so) years ago 
all of the dip tubes in new tanks were crumbling which caused a lot of 
systems to super heat at the top of the tank.  I know you installed a 
magnesium rod, but did you also remove the old one, which may have been 
Aluminum?  I've often wondered if Mg and Al ions might wreak some mischief 
(probably not)   Despite all the copper flat plates we've got on our roof 
(open loop) the only time we have people getting green hair around here is 
when the pool is over chlorinated or my teenage niece visits. 

Just thought I add two cents.


Patrick A. Redgate
AMECO
www.amecosolar.com
(562) 595-9570

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