Harmonics

Dan Law

We do factory start up and service for Raypak (low mass copper finned) boilers.
I've
seen (heard) the harmonics you describe. Raypak publishes a recommended
Delta F for the boilers - I'd first check to see what your manufactuer wants for temp
rise.

9 times out of ten the harmonics can be corrected by proper flow AND the
addition of a by pass at the boiler from supply to return. The resonance is a
combination of the frequency of the flame (yes, flame has a frequency) coming
into "harmony" with the frequency generated by the flow of water through the heat
exchanger. Flow frequency changes with temperature, thus the harmonic point
occurs at a specific set of circumstances of temp, flame propagation, and flow.
This explains why you can alter the noise by reducing the gas
pressure - you change the flame frequency. Of course this is no answer, because
you need to fire the boiler at recommended manifold pressure.

The by pass arrangement allows you to keep the gas pressure where you need it,
and instead alter the flow frequency. You end up adjusting the delta F in the
process. I don't think that the engineers specifically worked out that the proper
delta F would result in a lack of harmonics, but in fact you do eliminate it when
the flow, delta F, and gas pressure are all in spec. Give it a try. It's the right thing
to have anyway, and it will only cost you a valve and a bit of piping.

I recommend circuit setters rather than ball valves, in that you get the added
advantage of actually being able to check GPM in the process.

Good Luck

[Deleted User]

Harmonics

I ran into something I have not seen in my 25 yrs of doing hydronic heating and would love to see what the opinion of others is. The system I am talking about is built P/S with 2 100,000 btu RBI copper fin boilers. The boiler that provides second stage heat at 150 degrees starts to sing, like loud. There is a harmonic noise and vibration. I have my ideas around this but dont want to mess around trying things. I know turning down the gas pressure stoped the noise but this is not the ansure since this system has been in now for 7 yr with no problems. Please I welcome all ideas and look forward to your responce

Mark A. Custis

Mike:

What sings? The burners? The gas valve itself? Water in the chest?

Mark

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[Deleted User]

Harmonics

the vibration is coming from the tube bundle and when i reduice the gas pressure ie, the flame , the noise goes away. I feel this could be due to possable build up in the tube itself and this is not good due to minerals come only from new water and this is no good.

tim from Reed Wright

harmonics

Sounds like flow problems through the heat exchanger, either wear on impellar of pump or some sort of build up inside or outside of heat exchanger. I had the same problem before several times, sounds like a ghost??

[Deleted User]

Flow

This is what I was thinking . There is a flow switch to protect the boiler from low or no flow . The pump I did check of course and the delta T was about 12 degrees. The boiler I am refering to is also the second stage boiler so I dont know why the primanry boiler would not be doing this as well. The noise also only starts at 150 degrees up to the 175 set point

Mark A. Custis

I think you are on to the solution:

What if there are deposits in the #2 boiler tubes, caused by settling and not by new water. Can you run the #2 pump a few days without the burners? Move the burner control to 2nd stage call for heat, and see if you can "clean up" the tubes.

Mark

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Ben_3

Noise

Your right Mike it is probably flow related. Copper boilers a very touchy on this. I used to see this problem a lot especially on antifreeze mix systems for snowmelt. The boiler will howl like a banshee becuase of the slower flow, Especially when it was cold, Anti-freeze mix becomes very sluggish. Mant copper boilers need to be delimed on a regular basis to keep the flow strong. With a 12 degree delta tee it sounds like your not picking up the heat. When you reduce the gas prss you also reduce the load for the water to pick up which is probably why your noise stops. For heating I step them up for 25-30 degree drop and for DHW/storage tank setups your delta tee might even be @ 40 depending on set up and mfg

D lux_2

cst gas line ?

I have heard a copper fin noise w/ cst to small

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jeff_25

noise

if the noise sounds like the power steering on your truck with the wheel cranked the problem is in the heat exchanger if you watch the boiler gage it problem does not start intill boiler water gets hot yu can watch presure jump and temp bounce it could be scale and or air in the boiler I have an apt. building with a copper boiler one of the problems is load we have replaced burner then heatexchanger then new boiler they changed the exchanger little bit good luck jeff

Troy_3

Copper fin noise

Sometimes just increasing the pressure will settle them down.

Alan(CaliforniaRadiant)Forbes

Have heard this

on Lochinvar and Laars as well; the noise begins just as they approach setpoint, but I don't know the fix for it.

Joan Mishou at Laars....are you out there?



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ScottMP

I had this problem years ago

I contacted Teledyne-Laars and they sent me some "turbulators ". Small twisted lenghts of stainless steel that I was to install in the heat exchangers. Took the boiler down and seperated the tubes formt he manifold.

Sound went away, but I have never heard of anyone else doing this ?

Scott " it hums cause it dos'nt know the words " Milne

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Joannie

I'm here now

You guys that mentioned water flow are probably right. A whining / moaning / howling sound from a copper heat exchanger usually means that you are starting to get some steam in the heat exchanger. The fact that you only hear it when the unit is heating up is further evidence of this.

If severe, this will show itself as banging and knocking, and you'll be able to see the pressure gauge bouncing. If there is just a small amount of steam, you can picture the small steam bubbles sort of "rubbing" the inside of the copper tubes.

First thing to check is the pumping and the piping. When there is a problem with only one boiler in a two boiler system, make sure the piping is balanced.

If there is glycol in the system, make sure you don't have more than is recommended by RBI. Glycol mixtures do not give up their heat as easily as just water, so you need to compensate for that, usually by pumping it faster through the boiler. In some cases, the glycol can break down, and deposit sludge (of sorts) on the inside surface of the tube, which can lead to noise. In the case of a glycol mixture, make sure that the glycol has been maintained, and make sure that you are using properly inhibited HVAC glycol. Anti-foamant agents are recommended by most manufacturers, also.

Since the unit that is not run as often is the one with the noise, you will want to check inside the heat exchanger for any deposits. The boiler that works more often may also have more of a chance to clean its tubes with the action of the water. If the water in the system is a bit yucky (technical term), the stuff in the water may have settled on the walls of the tubes.

When a unit is 7 years old, like this one, what may have happened is that you had questionable water flow going through the unit for 7 years, and now the copper tubes have started to anneal (soften, from the excess heat), so the copper cannot remove the heat as well as it used to be able to. The outside of the heat exchanger should be checked for annealing.

As an aside, someone here mentioned a Laars boiler that we suggested turbulators for. This was a Mighty Max boiler. The Mighty Max throws alot of heat at a compact heat exchanger, and we found that if we put turbulators (flat sheet metal bands, that were twisted, and are the length of the tubes) inside the tubes on the bottom row of the heat exchanger, we broke up the "laminar" flow inside the tubes, and the turbulance sort of broke up any steam that occurred on the inside surface of the copper. Don't use turbulators, unless the manufacturer has designed and manufactured them for that particular unit.

These are pretty general things to check when you hear a noise such as this from a copper boiler. Copper boilers are easy to pipe and pump correctly, but they will tell you if they are getting too hot. Make sure you talk with RBI to get specifics on the unit that you have, however, since all copper boilers are not the same.

hot_rod

If it is HX noise

there are a number of hydronic system cleaners on the market that may help. If deposits on the tube are the issue, generally add the cleaners and circulate for a few days and flush. Add good quality water and hydronic system conditioners.

If it is a glycol check percentages. As Joanie mentioned some copper tube boiler manufactures limit the mix to 35%. There are conditioners that can be added to glycol and left in the system to "take away the moaning"

How old is this boiler?

hot rod

"Expert in Silent Warmth" ™

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[Deleted User]

Water temp only part of the equation...

You stated that you were seeing a 12 degree delta T. In my minds eye, the water is going through too fast. However, delta T being low with a known high flow rate indicates lime scale accumulation, retarding the flow of heat from the flue gasses to the water. Two ways to check for sure.

First, try choking the flow until you acheive a 20 to 25 degree delta T and see what happens to the noise.

Second, if at all possible, check the pump for delta P and using the pump makers performance curve verify flow in GPM across the coil.

Lastly, look at the combustion efficiency of the appliance. If the HX is limed up, you should see an excess flue gas temeprature with all the other parameters being correct.

If so, you need to delime the HX.

If the system is a closed loop, you need to start looking for the leak in the system and fix it.

If the system is open loop, you may want to look into softening the water.

If the system is glyconized, do what everyone else tells you to do.

Lets us know how you make out.

ME

Alley

Fixing Harmonic in water heater

My new water heater harmoniced. It was aloud humming noise after running hot water. The plumber said to take it up with the manufacturer. The manufacture said it was probably lyme or mineral build up in water. This was B.S.

To fix this usually there is air trapped in tank. When the tank is off bleed air from the pressure relief valve for about 15 seconds. In addition to this, increase the water temperature. Periodically, I still need to bleed air from take via pressure relieve valve.



Another problem I encountered with this new  A.O. Smith water heater  was temp. surges during showers. Again, the installation plumber said to call the manufacturer. When installing the plumber placed heater on a aluminum catch pan. The information guild told me new heaters draft air from bottom of tank. I realized the air flow is being blocked by pan. I drilled 3/8 th holes around pan lip every 6 inches to increase air flow.This resolved the temp surge problem. This plumber is a horses a-----! I could have sued and won, however; this would take much time. Also, never buy  an A.O. Smith heater.