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stagnation...

kcoppkcopp Member Posts: 3,538
Have a solar install.... good sized 8 flat panels... My only install. Noticed that the solar fluid was not moving... alarmed when I saw the temp @ the panels was 320F!  I started changing settings thinking that someone had messed w/ the control... looking @ the literature states that when high temps were present that no circulation takes place. 



Question. Would it not make sense that when high temps were present that the best thing to do would get the fluid moving and heat transfer going on?



ty,kpc

Comments

  • hot_rodhot_rod Member Posts: 13,892
    some solar controllers

    have a collector cooling function. OCC (option collector cooling) It allows the pump to run to keep the collector in a "safe" temperature (adjustable), even after the tanks reaches setpoint most are factory set at 140F.



    However you may (will) overcharge the tank (setpoint) temperature. Adjusting the setpoint temperature higher may buy a little time, or space to store excessive energy.



    OCC will allow the tank to run up to 200F, then it shuts down, period.



    Next you could use "system cooling" OSYC (option system cooling) function. This allows the pump to run after the solar gain stops to drag the tank back down to setpoint.



    If you are seeing this overheat condition on a daily basis you may need more storage, a dump zone.. Or less collector area :)



    You need to use it or lose it when it comes to solar energy. Store it in additional tanks, or install a dump zone.



    Or a drainback system.



    hr
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
  • BobbyGBobbyG Member Posts: 79
    good problem to have

    Do you think this will be overheating on a regular basis?  I'm curious to know how you sized the tank.  I haven't sold a job yet, but there's always a nagging concern about properly sized tanks that I quote.

    Just looking for some valuable in-the-field experience.

    Thanks!

    Bob
  • rt_2rt_2 Member Posts: 86
    my controller

    Hot Rod.

    My controller has the OSYC (option system cooling) function. What temp would you set it at? I currently have it set at 170 degrees. The highest I've seen so far with my 80 gal storage tank has been 167 degrees with 50 evac tubes in New Hampshire.

    rt
  • hydronoidhydronoid Member Posts: 2
    high temp solutions

    Pressurized glycol systems need to have work to stay cool. Cooked glycol becomes acidic and requires replacement, it doesn't take long either. Many controls have night-time cooling and other tank heat management functions.

    You might consider larger storage if that works for your winter scenario and you might consider heat dumping. Use the heat elsewhere like a hot tub or pool. You can also divert heat to some soft copper in the ground outside the structure or run some fin tub mounted outside where it wont bother anyone. With the help of your panel manufacturer you can figure out your panels output in high summer and size your heat dump accordingly.

    Expansion tanks should be sized to accept the volume of fluid in the panels so that in the event of overheating during stagnant periods or pump or control failure the h2o in the glycol can flash to steam and push back into the expansion tanks without popping off on high pressure. Popping off creates a cascading set of problems. DOW makes a highly resilient glycol.

    For your next system you might consider piping for "drain-back" and you would avoid all these concerns and collect at a higher efficiency as well. We service a number of four panel drain-back systems with small fan-coils that have been plugging away for thirty years making dhw and space heating with barely any maintenance other than monitoring storage water levels and replacing thermistors and one or two pump cartridges.
  • kcoppkcopp Member Posts: 3,538
    There are 2 tanks.

    1- 80 gallon w/ 2 coils and a 120 gallon storage tank. The Glycol is Tyfocor which is what Buderus reccom. for the job. Yes it was my 1st job.... and yes it was a learning one. I would do a number of things diff. The customer is happy, as they saved $1500+ dollars last yr on the fuel bill.
  • CC.RobCC.Rob Member Posts: 128
    collector:storage

    8 flat panels is 256 sq ft of collector if 4x8 panels. But with only 200 gal storage, you seem to be under the rule of thumb of 1-1.5 gal for every sq ft collector. At least here in the Northeast. Might perform better with more storage (e.g., 300-400 gal), less collector (e.g., 5 panels), or dump it as Hot Rod says. 12-16 ft of MP-80 fintube would probably cover it.
  • kcoppkcopp Member Posts: 3,538
    panels are....

    25 sq. ft. panels... puts me dead on... all was confirmed by Buderus. Yes I do wish there was a pool to heat! kpc
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