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Glycol life

kcopp
kcopp Member Posts: 4,563
in Solar

I was asked to look at a 125 Evac tube solar thermal set up today. System was installed in 2008. The owner did not have the make/ model of the tubes. Overall the system is in decent shape.

The glycol looked a deeper amber color. (I can see through a couple of the flow meters) The installer used Cytotec from Hercules.

Prob not the best choice….

The owner is concerned that the fluid has been compromised and needs replacement.

Can evac tubes stagnate during the summer months and burn?

What is the life of a typical system fluid?

TIA.

Comments

  • hot_rod
    hot_rod Member Posts: 25,123

    Evac tubes are especially hard on glycol due to their high stagnation temperature.

    Does the system have an over-heat dump zone of any sort?

    Do they use a lot of DHW every day? Those are indicators of how often the system stagnates.

    The bio based glycols has a bit higher temperature rating 350 compared to 325° for basic hydronic oil based products.

    There were some high temperature glycols around back when tubes were popular.

    If you can find the TyfoCor HTL that would be my choice. It can be tough on some EPDM gaskets and seals. European made evac tube systems always included or speced the TyfoCor glycols.

    The LS and G-LS fluids were used with the steam-back systems.They are a bit higher temperature than basic hydronic glycols. Steam back systems basically had an oversized expansion tank to allow all the fluid to steam out of the tubes. A cool down tank before the expansion tank was a good idea. I think Zilmet still offers cool down tanks for solar.

    I would do a good flush, run a cleaner if the ph of the old fluid is below 7.

    Screenshot 2025-05-22 at 8.38.30 PM.png Screenshot 2025-05-22 at 8.39.38 PM.png
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • kcopp
    kcopp Member Posts: 4,563

    Thanks.

    The owners are an elderly couple. Just the 2 of them. The system also uses some of the heat generated for space heating. I looked and didnt see a dump zone. There is a very large non pressurized tank in the basement.. Still several days in august could get the system to overheat.

    Unfortunately There were no system design documents around and the HO has some memory issues.

    I asked a bunch of similar questions but didnt get answers.

    Part of me wants to help… part of me wants to not touch it.

  • hot_rod
    hot_rod Member Posts: 25,123

    the good and bad news, a lot of the bargain tubes lost vacuum within a few years, that really cuts down on their output and lessens over-heating 🙃

    Cloudy tubes is an indicator

    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • kcopp
    kcopp Member Posts: 4,563

    Only 2 cloudy tubes out of 125!

  • hot_rod
    hot_rod Member Posts: 25,123

    yikes 125 tubes for DHW for two people?
    it sounds like it was designed for some of the heating load. But what to do with all that solar gain in the summer?

    Approach with caution!

    The Resol controls, sold under many brand names have evac tube settings as well as a few over-heat functions to help with the low summer loads.

    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • kcopp
    kcopp Member Posts: 4,563

    There are 2 of them on this system.

    Thanks.

    kevin

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