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Aquacaresolar Member Posts: 2
What is the favorite glycol - brand and model - for a solar steam-back system?

Tyfocor is looking good up to 338 F. Any others?


  • Aquacaresolar
    Aquacaresolar Member Posts: 2
    Steam-back (Steam -out) glycol system

    I'm still interested if anyone has installed a steam-out/ steam-back system and what glycol was installed. A chemist I spoke with in Denver said is regular glycol would go to 380 F for brief periods without serious damage. He did not have an answer for how it would put up with the steam out activity.

    Anyone got any experience or insight here?
  • Fortunat
    Fortunat Member Posts: 103
    glycol choice


    We've used Dowfrost HD, Tyfocor and others in systems with 'steamback' stagnation control and so far they've all held up well. Some have been in for years and the heat transfer fluid still looks as good as new.

    One of the keys is in the near collector piping arrangement, which should be laid out so that it is forced easily back to the expansion tank when the system is in stagnation. If it does then only a very tiny percentage of the system's glycol actually ever sees the high temperature. When boiled at moderate pressure, about a teaspoon of water will make enough steam to completely fill a typical flat plate hot water collector so in a system that has 5 gallons of glycol in it maybe 1/3840th of the fluid is actually boiled or exposed to high collector temperature during a stagnation event.

    Furthermore, in most PG/Water mixes you will find that it is the water that boils first, forcing the remaining fluid out of the collector before the glycol even reaches 300 degrees so I'm not sure that much if any of the PG ever actually changes phase.

    hope that is helpful.


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