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High-Temp Glycol (Solar)

Carl PE
Carl PE Member Posts: 203
Ok, we all know that regular 250º Ethylene Glycol won't survive collector stagnation at 300º+.

Just wondering if anybody has had any experience with a 350º mix, like Dowtherm 4000 or Interstate OP-100.



  • hr
    hr Member Posts: 6,106
    I use

    Dowfrost HD rated to 325°. The DowTherm products are a bit higher rated at 350° but keep in mind they, DowTherms, are EG and it may be an issue for DHW use. Unless you use a double walled HX or indirect.

    Info I get tells me solar can hit 400- 450° under some conditions. Say Phoenix, mid summer, panel without circulation :)

    If money is no object Dow Slytherm is a low oral toxicity product used in the pharmaceutical industry. It has an operating range of -100- 500°F. Last I priced it it was around $27/ gallon. But it is a one time product!

    Salts, Glycols, Alchols, and Potassiums are other options. Vanguard used to sell potassium acetate for an anti freeze in early PB systems. Plenty of heat pump guys still use methynol!

    Pick your poison :)

    hot rod

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  • Carl PE
    Carl PE Member Posts: 203
    I'm not so worried..

    about poisoning myself. I got some nice double-wall hxers from a guy in MO a couple months ago. You probably know him :)

    I'll fill it up with the high-$ fluid when I get done fiddling around with the piping and get the whole system dialed-in like I want. For now, I'd rather spill the cheap(-er) stuff.

    I guess I'm going to use the EG and see what happens. Sounds like it'll be fine.

    I'm really not expecting that high a temperature in the summer anyway. I've got the collectors jacked up way past my latitude to flatten out the curve.
  • hr
    hr Member Posts: 6,106
    As you noticed

    those panels and HXers had been filled with heat transfer oil. Hense the nice condition of the copper.

    This is the 16 year old pump volute that was on one of those systems. The iron body is like brand new inside. Rare if ever you find a water or glycolled system in that condition.

    EG is the better heat transfer fluid, temperature and viscosity wise. In your case I would feel fine about the EG use.

    hot rod

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