Boiler harmonics/piping fix

EricSch1337 · April 2

I have an rbi boiler that’s been installed for roughly 5 years. Apparently it’s been having harmonics issues since the beginning. I added pictures of the existing piping where they tried to do closely spaced tees with a building loop. After speaking with tech support they suggested changing the pump speeds and that should help. It didn’t. I have a feeling my common piping or building loop is way to small and clearly doesn’t run through the entire building. I have a 10 degree delta T at the boiler and I think that’s part of the problem. The harmonics only happen when the boiler temp gets up to 170 degrees and stops when the boiler/boiler pump turn off. It seems like a flow issue. I want to redo the piping with the drawing I added. The first zone is my largest “sanctuary” and my other 2 zones are just small classrooms with 3/4 fin tube. With my suggested piping should my largest zone be first and last back to evenly distribute heat? Has anyone seen harmonics like this? If so is there a quick fix with the existing piping or should we just rip it out and start over? We did

remove piping and flush heat exchanger, no signs of annealing at this time and the copper fin tube wasn’t plugged up internally or externally. Tech support is saying the ups26 should be the right size pump for this size boiler, so it brings me back to the lack of common piping. Any advice is appreciated

EricSch1337 · April 2

Jamie Hall · April 2

I'm not quite sure what you mean by "harmonics". That's a term I would usually use for an acoustic problem…

Your diagram shows three zone pumps, as well as the primary pump. Is that correct? If so, does the problem occur regardless of which zone pump or pumps are operating?

I also note a big compression tank overhead. That is not shown on your diagram; how does it connect to the rest of the system?

And last, to get back to the harmonics problem — I see a lot of somewhat poorly supported, though elegantly assembled, piping. That can cause vibration or harmonic problems.

More information, I think.

EricSch1337 · April 2

Yea for some reason it isn’t letting me upload the video. You can hear it through the building like a ghostly wail. The old compression tank has been abandonded and it’s using that bladder style tank. The drawing is how I would like to change the existing piping if needed. Yes it’s a 3 pump system, one for each zone, one for the boiler and one for the secondary “building loop”. Yes it happens when any zone calls and when they’re all calling, and only stops when the boiler turns off. If the pumps are still running for the heating demands and the boiler isn’t the house is gone. I can email you the video if you don’t mind.

jesmed1 · April 2

You can do some simple experiments to see if the noise is related to flow velocity. You said you already turned the boiler circulator to low speed, but that could still be over-pumped. Try throttling the flow through the boiler loop by partially closing one of the ball valves near the boiler supply or return. Ball valves aren't the best choice for flow control, but this is just an experiment. If that eliminates the noise, we might reasonably conclude the noise was from the boiler loop water velocity being too high.

You also have a manual bypass valve. Does the valve position make any difference?

Jamie Hall · April 2

I'm still confused. You say "three pump system" and then you reference four pumps: one for each zone (3), one for the boiler (in the boiler?) and one for the secondary "building loop".

From the above, however, may I suppose that you only hear the noise when the boiler (internal) pump is running, but always hear it when that one pump is running? Is there any way you can run that one pump without the boiler firing? And are there any valves on that particular circuit?

And how does that pump relate to the secondary "building loop" pump.?

Intplm. · April 2

From what I can see from the picture you have many pipes that are either not supported or supported metal to metal or concrete to hanger etc. This can cause the noise that you are describing. The hydro-sorb type -b-line strut hangers seem to have that rubber cushion on some hangers but not all of them. This can make the whine, hum or harmonic problem you describe.

Go to the boiler while it is running and place your hand on different pipes. Push and pull on them a bit to see if or how the music changes.

This boiler is piped into a corner and will take some doing to add and reinforce your current supports as many pipes are in the way.

I would add and fix current supports to soften and even eliminate the noise before repiping everything.

Here are some pictures of different types of what can be called hydro-sorb supports.

EricSch1337 · April 2

Yes there are 5 pumps total. One for the boiler a grundfos ups26 multi speed one for the primary loop also a ups26 multi speed (we’ve tested it every speed combination) then each of the 3 zones has a taco pump installed. The noise only happens when the boiler water is heated up at 170-180, we’ve tried moving and resupporting pipes but the noise still occurs at higher temperatures only. When the boiler turns off and all of the other pumps run the noise is gone and it is as silent as it’s supposed to be. While the boiler is heating up the water from 60-170 the acoustics aren’t happening, it almost seems like the water is flashing and not being pumped properly at certain temperatures. The balance valve has been in every position trying to alleviate the noise but it doesn’t seem to matter where it’s located the noise still happens. I’m wondering if that secondary loop/building loop doesn’t have enough runway of pipe and is causing my delta T to only be a 10 degree split. And since the boiler is getting basically the same the return temp as supply temp that it’s flashing off through the boiler pump?

jesmed1 · April 2

Do you have enough radiation to heat the building with 165 degree water? If so, you could just turn the high limit down on the aquastat. But obviously that's more of a temporary band-aid than a fix.

If you think the pump is cavitating at higher temps, you could raise the system pressure, but obviously you don't want to get to close to the relief valve opening pressure, so you may not have much room for an increase.

160-degree water will boil at 5 psia, so in theory a low-pressure condition could cause problems, but 5 psia is negative 10 psi gauge pressure, and if your system pressure is, say 15 psi gauge (30 psia), you'd need a 25 psi reduction on the suction side of the pump to get down to 5 psia, which seems unlikely. But it may be worth experimenting with the pressure to see if adding a few psi helps.

109A_5 · April 2

Videos have to be hosted elsewhere and the link posted here.

Jamie Hall · April 2

One minor caution in all this troubleshooting — keep in mind that with metal piping, a noise created in one part of the system will travel all over the house. It can take real patience — and if it's a motor or pump, turning it on and off — to track down the source.

HomerJSmith · April 2

I haven't posted lately because I felt insulted. My nature is to be helpful & hopeful rather than hurtful. Kinda like Ed. But, I felt compelled to address this post.

Eric, I have, in any installation, rules that I always try to follow. The supply piping into any pump, 10 to 12 pipe diameters of straight pipe and 5 pipe diameters of straight pipe on the output of the pump before any directional change in flow. Common Manifold piping should be generously sized. ( I don't know whether yours is 1" or 1 1/4". You have 3 zones of 3/4" pipe at 4 GPM for 12 GPM when all zones are operating. The Common Manifold piping should be sized for that.) The Extank should be on the imput to the pump(s). Yours appears to be. I always pump into the highest pressure loss in a circuit. The Air Eliminator should be on the hottest water from the boiler. Yours is kinda iffy. There are more rules, but let me say that I like an install to be as aesthetically pleasing and symmetrical and minimal as possible. Yours, Eric, is not. Let's address the Delta T.

The Delta T is not sacrosanct, but it does indicate how a system is functioning. A 10 deg Delta T can lead to short cycling of the boiler and a 50 deg Delta T can indicated an undersized boiler, excessively long heat emitters, an excessively high heat exchange rate to the environment, etc. This is my thinking on your sys as to the Delta T. (The reason for a bypass valve is to prevent or minimize boiler condensation. All boilers condense at some point in the heating cycle. The idea is to prevent sustained condensation which is destructive to the flue and boiler heat exchanger.) The boiler bypass valve between the input and the output of the boiler is a ball valve. It appears to me to be 1" piping and valve. This means that the valve would have to be 97% closed to provide any real regulation. Aside that, a ball valve is a poor choice for bypass valve. You would have been better off with a 1/2" pipe and 1/2" ball valve as it would have given you better regulation. I prefer a Caleffi boiler bypass valve and I have used with great success a Taco I- Series modulating valve with sensor set at 135 degs.

Mixing the hot water from the boiler output to the boiler input will lower the Delta T. What is helping lower the Delta T, also, I think that the Grundfos pump in the common manifold piping. I DO NOT think that that pump is necessary and I would remove it as your diagram shows. I have used your diagram many times and would only change the location of the pump. Per my rules, I would pump into the boiler not away. I do not know the BTU rating of your boiler, but for every 10,000 BTUs you need 1 GPM thru the boiler. So, size the boiler pump on the flow you need to over come the pressure loss of the boiler circuit, which I would think is pretty minimal. Look at the Grundfos UPS26-99FC 3 speed flow chart and select the GPM you need at the pressure loss and select the proper speed or maybe a different pump. One last thing before I close this comment.

As the boiler reaches 170 deg when the harmonics start, close the bypass valve and see if that makes a difference and measure the Delta T. Also, I would put balancing valves on the output zone piping to the Common Manifold and set them to about 4GPM. This would balance out your 3 circuits so that the greatest flow wouldn't be going thru the shortest circuit. I like Caleffi Quick Setter balancing valves.

https://www.supplyhouse.com/Caleffi-132552A-3-4-NPT-QuickSetter-Balancing-Valve-w-Flow-Meter

EBEBRATT-Ed · April 2

I would find out what is causing the noise before repiping. I would hate to have it repiped and not solve the problem.

It may need repiping but the noise problem needs to be found first.

HomerJSmith · April 2

I have use a mechanic's stethoscope you can get at Harbor Freight or any auto parts store and checked the sys. It is helpful in pinpointing noisy components. Or, Amazon's

allsun Auto ultrasonic Car Noise Finder Diagnostic Listening Device Stethoscope 100Hz-10kHz Black. Or,

Chassis Ear Automotive Engine Noise Finder Tool, 6 Channel Chassis Ears Sound Detector Identify the Troubling Engine Noises (Over-Ear Headphones)

Noise is not necessarily a harmonic. Harmonic has a specific definition.

EricSch1337 · 12:30AM

@HomerJSmith I agree with everything you’re saying, not my install but has since become my problem. I like the simplicity of as well and that drawing I sketched up is how I would like to pipe to keep it as minimal as possible. Even with the bypass completely closed this is still an issue. Do you think it would be better to just lengthen the runway of pipes in this application or just try to do the straight common piping without the closely spaced tees? When I disconnect the wiring from the pump on the common piping the heat doesn’t travel through the common piping causing the boiler to over heat and not work at all so I’m not sure removing that pump in this current set up will help. The main thing I’m not understanding is why the loud harmonics are only happening at high temperatures and not all the time.

Boiler harmonics/piping fix

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