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Singing Snowmelt

JMA
JMA Member Posts: 1
Long time reader, first time poster. Have a commercial snowmelt system served by 8 150,000 BTU wall hung, fin tube, mod/con boilers. The boilers are cascaded together and individual units come online and drop off as necessary according to system demand. After two months of operation each boiler sings - high pitched harmonics - as soon as it hits approx 90% firing rate - outlet temps are around 80 to 90 degrees at this point. Once the set point of 130 degrees is reached the boiler modulates down past 90% firing rate to maintain a 20 degree delta and the noise goes away. System was thought to be mixed to 30% glycol but one last zone has not been brought online so it was discovered that the mix is around 45%. We were able to make the noise go away using larger more expensive boiler pumps but the calculated flow rate difference between pumps was minimal - approx 11gpm with the smaller and approx 16 gpm with the larger. We are in the process of lowering the glycol mix for the current system - last zone won't go online until next winter - and hope that helps because the cost for 8 of the larger pumps is not pretty and not sure we want even more flow going through the boilers. Thoughts?

Comments

  • DZoro
    DZoro Member Posts: 1,048
    Are you sure the singing is from the pumps/fluid? Almost the way you describe seems like a possible combustion sounds. Did it just develop, or has it always done this from the get go. How much glycol does the MFR suggest in there boilers?
    Steve Minnich
  • kcopp
    kcopp Member Posts: 3,990
    What boiler? Any possibility of a HX that would allow you to not have to run glycol through the boilers?
  • HomerJSmith
    HomerJSmith Member Posts: 1,567
    I assume all the boilers had a combustion analysis done on them.
  • Mark Eatherton
    Mark Eatherton Member Posts: 5,839
    Sounds like whales in heat?

    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.
    kcopp
  • Henry
    Henry Member Posts: 995
    Sounds like steam is being made or no combustion test. Who designed the system including the loops, boilers, piping and pump selection?
  • hot_rod
    hot_rod Member Posts: 16,327
    Are the boilers piped via a hydraulic separator or Primary secondary. Each boiler needs to have adequate flow, and use the glycol derate info, usually no the bucket, to select the circ.

    With a high glycol% you could require 30% more circ compared to water.

    Or it could be a combustion noise. Check venting lengths, was a combustion analysis done?
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    Steve Minnich
  • Steve Minnich
    Steve Minnich Member Posts: 2,758
    When the noise correlates to the modulating burner, my first thought is further tuning is needed via combustion analysis and adjusting the throttle.

    As far as glycol, I use the premixed Rhomar RTU45 - more of an exact science.
    Steve Minnich
    Minnich Hydronic Consulting & Design, LLC
    [email protected]
  • Zman
    Zman Member Posts: 7,331
    @JMA Are you still out there?
    You have a pretty unique system with that many boilers on snowmelt. I have never seen a snow melt system that needs that kind of turn down.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein