Singing Snowmelt

JMA

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?

DZoro

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?

kcopp

What boiler? Any possibility of a HX that would allow you to not have to run glycol through the boilers?

HomerJSmith

I assume all the boilers had a combustion analysis done on them.

Mark Eatherton

Sounds like whales in heat?

ME

Henry

Sounds like steam is being made or no combustion test. Who designed the system including the loops, boilers, piping and pump selection?

hot_rod

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?

Tinman

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.

Zman

@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.