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Working in California, we have never had to use glycol on any of our systems, but a customer has asked me to take care of his solar system; monitor the pH and replace the glycol as necessary.

I haven't the foggiest idea how to do this. Any suggestions, youtube videos or products recommendations are welcome.

Come to think of it, I don't see it discussed here on The Wall very often. Is it that simple?


Often wrong, never in doubt.


  • heatpro02920
    heatpro02920 Member Posts: 991

    get a total amount that the system holds and do the math to get your gycol percent, I would use your refractometer to test what is there... best bet would be to check with the manufacturer to see what and how they want it done..
  • Harvey Ramer
    Harvey Ramer Member Posts: 2,217

    Most Glycol's contain phosphates and nitrates. In about 5 years it starts decaying and as it does the PH level starts dropping. When that happens it will attack any ferrous materials in the system. It can become quite corrosive.

    One option would be to flush the system and replace the Glycol. Bad part about that is every time you do it you bring in all that oxygen with the fresh water. When ever I encounter a system that has Glycol in it, first thing I do is check the PH level. If it is below 7 I put in this cleaner

    After the cleaning cycle is complete I thoroughly flush the system and then refill and add the proper quantity of this Glycol/Inhibitor

    It is a non-phosphorous based Glycol and is premixed with an Inhibitor to prevent corrosion. It is not supposed to go bad. You may still want to check the Glycol and or the Inhibitor levels during annual service.

  • TeeSee
    TeeSee Member Posts: 10

    First thing does this system have any aluminum components? If so, you must use an antifreeze that is safe for aluminum.

    I check antifreeze with a refractometer and ph test strips. Antifreeze goes basic, ph 8+, when it goes bad and it loves to disolve rubber gaskets. HeatPro is right where you need to get the manufactuer's literature to know your concentration ratios. Never mix more than 75% antifreeze to water. The mixture could possilble froth/ cavitate when passing through circulators and it will have a terrible heat transfer ratio. Most manufacturers recommend 50% mix. Just a note, wear rubber gloves with antifreeze...the chemicals, phospates, will dry your hands out with prolonged contact.
  • hot_rod
    hot_rod Member Posts: 14,865
    Use only

    Solar rated fluids for solar. Take a sample in a clear glass, it should not be dark colored or have a sharp smell. Ph as it comes from the container is usually 10.5 - 11. If it drops into the 8 range it's time to buffer or replace.

    It is a small system, under 10 gallons flush and replace. It if flushes really dark you might run a cleaner like Rhomar or fernox, before re-filling.

    A small electronic "stick meter" is the best way to check ph, and a refractometer for concentration level.

    Rare to ever need over a 45- 50% mixture! even in the coldest climates. Use a pre-mixed fluid instead of blending on the job site.

    Many of the solar glycols are now a corn based fluid, better for the environment and high operating temperatures for solar.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Mark Eatherton
    Mark Eatherton Member Posts: 5,837
    Pumpin' the hump...

    Alan, If you don't know for sure how much fluid is in the system, it is best to purge with compressed air into buckets, keeping an inventory of what comes out. As HR said, use only glycols developed for solar thermal applications. Glycol, when exposed to stagnation conditions (350 F ) breaks down into a glycolic acid. It likes to eat copper at that point, which is not good. Solar fluid has a more robust corrosion inhibition package than conventional hydronic glycnoids. Use the lowest ambient temperature, and add 20 degrees F to that for proper freeze protection, but don't go less than 30% in order to provide minimum corrosion inhibition. The less glycol the better, to a certain point (30%)

    You will need a pump with enough head to get the fluid to the top of the system, and maintain enough velocity at the return to develop a siphon on the downcomer. I find that a sewage lift station/foundation dewatering type of pump has this capacity and won't cost an arm and two legs… Velocity needs to be above 5 FPS at the top of a system, and that depends upon the size of pipe the downcomer is.

    Once you know capacity, premix your glycol at a slightly stronger rate than you want to see, and when you have the system filled with the premix, you can use city water pressure to top off the system to its normal operating pressure. Dilution due to the use of straight water for pressurizing is negated by the fact that you overcompensated glycol concentration in the first place. If you have a good hand powered hydrostatic pump, then go in at recommended concentration and use hand pump to top off.

    Don't even think about doing this process during full sun. Or you will learn the steam generating potential of stagnated solar panels, and having been there and done that and still having scars to prove it, you do not want to go there. If need be, cover the array with tarps to keep it from seeing the sun.

    If there is an automatic air vent on the top of the system, make sure it is closed tight during the filling operation or the bubbles will NEVER come out of suspension, and establishing a siphon will be next to impossible. Learned that trick the hard way as well…

    When pumping fluid in, run the system pump, and it will add its capacity to your charge pump, making filling, establishing siphon and sweeping air back down to your charging buckets much easier.

    Lots of buckets filled with premix will keep you form having to start and stop. Once through, in and out, and get 'er done. And use short washing machine hoses for making the connections between the pump, the system, the system and the buckets. Keep the return hose submerged in the bucket, and during post fill circulation, when the bubbles stop rising up from the end of the return hose, you are completely filled and ready to top off. Once completely charged, open AV on top, and start and stop pump numerous times, giving any air you missed to vent thru the AV. I've put a ballon on the outlet of the AV so I can see how much air is still coming out.

    Don't forget your safety gear whilst on the roof :-)

    It's not so much a case of "You got what you paid for", as it is a matter of "You DIDN'T get what you DIDN'T pay for, and you're NOT going to get what you thought you were in the way of comfort". Borrowed from Heatboy.
  • psb75
    psb75 Member Posts: 433
    solar system glycol use

    Great summary Mark. Some invaluable nuggets in there. Can we put this in the "Solar" section?
  • Mark Eatherton
    Mark Eatherton Member Posts: 5,837
    Fine with me...

    It's not so much a case of "You got what you paid for", as it is a matter of "You DIDN'T get what you DIDN'T pay for, and you're NOT going to get what you thought you were in the way of comfort". Borrowed from Heatboy.
  • Alan (California Radiant) Forbes
    Alan (California Radiant) Forbes Member Posts: 2,901
    edited April 2014
    Thanks everyone

    for your input. It helps me a lot.

    Often wrong, never in doubt.