copper leaching in solar thermal system [RE-wrenches]

[matthew tritt]

Graham,

As luck would have it, this isn't my system, it's Todd Cory's at Mt. Shasta
Energy. Between all of us that have responded to Todd's question, virtually
all the points you mention have been touched on, but I am in the camp of
stray electrical current of some kind, and poor grounding. This kind of
problem is often really tricky to pin down. He did use prop. glycol, not
automotive anti-freeze, and says that the TDS is way down.

This type of problem is why I prefer the Heliodyne system with PV-direct
circ pump. Burying pipes though is something to avoid, no?

Matt
----- Original Message -----
From: "Graham Owen" <graham at solarexpert.com>
To: <RE-wrenches at topica.com>
Sent: Tuesday, October 22, 2002 11:25 AM
Subject: RE: copper leaching in solar thermal system [RE-wrenches]


> Matt,
>
> Is the heat exchanger double walled?  I am wondering if there is any
> chance of the solar loop having higher internal pressure than the
> potable loop?  Did you use clear non-toxic glycol (propylene) or the
> regular toxic green stuff (ethylene) sold at automotive stores?  Has
> there been any pressure drop in the glycol loop?  What size is the
> copper pipe?  The flow rate needs to be less than 5 feet per second to
> prevent corrosion.
>
> The rarely-encountered copper corrosion problems are of five main types:
> (1) aggressive, hard well waters that cause pitting (which contains
> sulfates and chlorides, high total dissolved solids and a pH range of
> 7.3 - 7.8 or carbon dioxide at more than 10 parts per million); (2)
> soft, acidic waters that do not allow a protective film to form inside
> the copper tube; (3) system design or installation which results in
> excessive water flow velocity or turbulence in the tube (burs left
> behind at tube end cuts which upset the streamlined flow resulting in
> localized high velocity and turbulence); (4) lapses in good workmanship
> (too much flux which becomes polymerized) , and (5) aggressive soil
> conditions (most natural soils do not attack copper but "cinders" in the
> soil create acid when it becomes moist.
>
> If the water source is the problem sometimes simple aeration is
> treatment enough.
>
> Graham Owen
> GO Solar
>
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