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Glycol longevity

mike from pa.mike from pa. Member Posts: 17
I was asked to look at a couple of closed loop solar hot water systems. They want to make sure te system is running properly and if anything should be done to be sure the system will continue to run properly. I am not sure yet what panels or what glycol was used in the systems (haven't been there yet). When I was talking to the customer they said the systems were installed about 6 years ago and nobody has done any work on them since the system was installed. I usually test the glycol with the strips to check its alkalinity and %.

Since the system is this old do you think the glycol should be replaced even if the tests on the glycol show that it is usable?



  • kcoppkcopp Member Posts: 2,746
    This may be...

    best posted in the Solar section... that being said the only real way to test glycol is w/ a refractometer....the test strips are unreliable. How does the system look? Any leaks? Any signs of corrosion
  • hot rodhot rod Member Posts: 7,014
    if it was over heated

    by the collectors going into stagnation, it may be time to drain and re-fill

    Drain some fluid into a glass or clear bottle. Is it dark with a harsh acid smell?

    The best first check would be a ph meter. New glycol reads 10.5 - 11.5. If the ph has dropped into the 7 ph range most manufacturers suggest flush and re fill with new fluid.

    Generally solar systems only hold 1 gallon per collector plus the piping and HX, usually 5-6 gallons for most residential systems, so the cost to refill with new fluid may be good insurance.

    Stagnation is when the pump turns off when the tank reaches temperature. So the glycol sits in the collector and cooks. Temperatures in excess of 300F are common. If the system goes into stagnation often, the fluid breaks down quickly.

    System with light DHW loads, or vacation homes can stagnate frequently and need to be checked yearly for fluid quality.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
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