[Sneap] De-ionized water

[kerna]

Dear SNEAPer's,

 

A few years ago, after being in service for almost 30 years, a heat
exchanger in our closed loop chilled water system sprung a leak.  Because
the system was woefully energy inefficient, the entire system was replaced
(It was calculated that the energy savings over 5 years would pay for the
system replacement costs which was $125,000).  We were instructed by the
project engineer to add a water treatment solution to the system.

 

Last year a problem developed in our magnet power supplies.  Some of the
brass fittings (where the rubber hoses are attached that route the water
from heat sink to heat sink) began leaking.  After some investigation, we
discovered that the water treatment solution, which contained Sodium
nitrate, was making the water very conductive.  This conductivity was
causing oxidation and reduction to take place between heat sinks in the
power supply where there was a voltage difference.  The fittings were being
etched away wherever current flowed through the water.  After this
discovery, we flushed out all of the water in the system, replacing it with
water from our municipal water source.  Fortunately the damage to the power
supplies could be repaired before this etching phenomena ruined them.  

 

At the last SNEAP Symposium I was talking to Nathan Jones about chilled
water in the equipment that he works with.  He told me that they used
de-ionized water in their equipment.  I found an article on the internet
that talked about advantages and disadvantages regarding using de-ionized
water.  Here is an excerpt from that article that addresses disadvantages:

 

"The disadvantage of de-ionized water is that it is very corrosive to metal.
Since it has no dissolved solids in it, water will seek equilibrium with
whatever it contacts.  So water with a pH of 7.0 can dissolve metal pipe.
Especially yellow metals like copper and brass.  It is also very aggressive
to mild steel or "black" iron, and forget about galvanized pipe.  Piping is
best as PVC or glass."

 

I ask Nathan Jones to review and comment about the article.  His comments
were:

 

"We have a simple go-nogo cell in our system that lights a neon glow lamp as
long as the conductivity is less than 1micro mho / cm. Our system also
contains a sacrificial anode of zinc rod to prevent galvanic corrosion due
to dissimilar metals (the zinc corrodes instead). The only time that I have
heard of one of the sacrificial anodes being attacked was when a customer
let their deionizer run for three years without replacement (supposed to be
replaced annually) and then over-temped the system resulting in the
deionizer dumping all that it had collected back into the system at once.
They had a zero ohm short on everything and gray slime circulating in the
system. The anode was 50% consumed in just a few hours. Luckily for them
they were able to flush the system, install a new deionizer, and return to
operation in just a few days with no damage. I would have volunteered to go
help them recover - it was at Queen's Hospital in Honolulu!"

 

Additionally, I talked to several local companies that are in the water
treatment business.  They hold the same view with regard to the
corrosiveness nature of de-ionized water

 

My question to the SNEAP community is:  What do you do regarding maintenance
of the water in your closed loop chilled water systems.

 

Thank you taking the time to read this very lengthy email.

 

 

Allan Kern

Western Michigan University, Kalamazoo, MI

269-387-4958

 

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