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Ethyl from propyl..... how to differentiate.

kcoppkcopp Member Posts: 3,514
I was working on a Solar thermal evac tube system yesterday. The system pressure was down around 10 psi. So I wanted to add some more pressure into the system and bring it up to 25 psi. (prv is set to pop at 45psi.)
I added about a 2 gallons of solar propylene glycol.
In removing a 1/2 gallon on the other side of the system it certainly looks like the original installer used Ethylene glycol in the system.
How do you tell the difference between the toxic and non toxic stuff?


  • hot_rodhot_rod Member Posts: 13,528
    You would need to send it to a lab to determine if it is PG or EG. Once it is blended, it's a tough nut to crack.

    The two can mix and work together without problems, however you end up with an unknown toxicity. EG really should not be allowed to work near potable water without a double walled HXer, from what the Dow engineers tell me. No doubt from a liability standpoint.

    Much of the automotive antifreeze is switching to PG based. When it is flushed and recycled at the auto and truck repair shop, or lube places PG and EG all goes into the same recycle barrel, as they have no way of knowing what is in the engine. The recycler filters and RO the fluid, add new inhibitors and color and then sell it as reclaimed fluid.

    Realistically that evac tube system may only hold a few gallons of glycol, so a leak or mix with 50- 80 gallons of DHW in the tank would hardly be noticed. Not that I suggest EG, just saying.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
  • kcoppkcopp Member Posts: 3,514
    I saved the stuff into a separate jug...I mean, it is greenish yellowish, fluorescent. Sure looks and smells like Prestone to me.
    There is a brazed plate HX between the two. Its in one of the Purist sps-2ac pumping stations.
    Its prob best to pump it out and start again in the near future.
    There is little documentation left on the job.
    Thanks HR.

  • hot_rodhot_rod Member Posts: 13,528
    if you want piece of mind, I agree, flush it all out, clean the system with a hydronic cleaner, and start over. especially if it is harsh smelling and has been overheated numerous times. Eva tube systems can really cook glycol, stagnation in excess of 500F under no flow conditions.

    Color really doesn't tell you anything. I've used PG that is red, yellow, green, pink, etc. The Rhomar I use now is blue.

    If you knew the brand, the color could help determine. Dow uses different colors for the various fluids. Dow frost HD is fluorescent yellow, DowFrost is clear for example.

    The Caleffi Solar fluid is a corn based product, if that helps, as are some others. But when they start adding all the inhibitor chemicals that is where the toxicity creeps in. The higher temperature fluids generally have more or stronger inhibitors and toxicity goes up. I'm not sure all the imports glycols are FDA accepted GRAS (generally regarded as safe).

    DowFrost is USDA approved for food application, immersion freezing where the fluid contacts the food, for example.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
  • kcoppkcopp Member Posts: 3,514
    From your description it may indeed be Dowfrost HD.
    I tested the Ph and it was just a hair above 8.
    Considering the system has been out of commission for most of the summer (bad connection to the sensor) that pretty good.
  • hot_rodhot_rod Member Posts: 13,528
    Any solar should use a HD heavy duty fluid. Some swear by the high temperature Tyfocor versions, but I'm not sure they all pass the FDA requirements.

    The bio or corn based tend to have higher operating temperature also.

    There are special fluids for high temp vac tubes the XT or HTL. Also a special fluid for steam back type systems.

    As you can see a wide variety of colors also :wink:
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
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