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What happened to the TDS?

Zman
Zman Member Posts: 7,611
in THE MAIN WALL
I am overseeing the construction/commissioning of a large commercial snowmelt system.

The piping system breakdown by volume is:
40% new Pex-a
35% new steel pipe
25% copper
About half of the copper was piping previously installed and used by the original system.

The design specs did not call for any specific water treatment aside from a thorough flushing of the pipes and a fill with 50% water and 50% polypropylene glycol.

The contractor cleaned the system with a commercial borax/nitrate cleaner and let it run for about a week.
The system was then flushed until the PH and TDS where the same as the local tap water.
The pex tubing was not flushed as contamination was a concern.

The system was then filled with tap water and glycol.
The Tap water had a PH of 7.5 and TDS of 120. Both well within the boiler manufactures spec. The glycol PH and TDS where similar.

The system was fired up and running happily for about a month.
I went back to check the water and it has a PH of 7.1 and a TDS over 500.

Any ideas what happened?
"If you can't explain it simply, you don't understand it well enough"
Albert Einstein

Comments

  • kcopp
    kcopp Member Posts: 4,472
    Sometimes runtime will stir up stuff and make a second cleaning needed. Was there enough cleaner added? Maybe a second type would have helped...

    Did you see the most recent Coffee w/ Calleffi.?

    https://www.youtube.com/watch?v=Wgxaox_2Id8
  • Zman
    Zman Member Posts: 7,611
    I did see that one. With over 10k worth of glycol in the system, the only option appears to be demineralizing.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • kcopp
    kcopp Member Posts: 4,472
    One thing they mentioned at the end of the Webinar if that you will lose the inhibitors.
  • Zman
    Zman Member Posts: 7,611
    kcopp said:

    One thing they mentioned at the end of the Webinar if that you will lose the inhibitors.

    Yes, it is a bummer. The only way it could have been avoided would have been to run it super hot for a long period of time.
    Wasn't really an option with winter coming.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
    kcopp
  • hot_rod
    hot_rod Member Posts: 23,396
    The TDS goes up due to the inhibitors in the glycol. So it is usually a good increase

    In the Dow engineering handbook they show continuity for various % mixes

    I think it is in metric units, you'll need to convert to ppm

    Typically new glycol runs 10 or so ph. Could be the blend water had something to do with that decrease?
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream

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