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US Iceman
08-04-2007, 02:25 AM
I happened to find two very interesting articles on controlling vibration in refrigerant piping and thought others might like to read these.

These provide some basic information behind the science and methods to use.

http://www.carlylecompressor.com/Files/Carlyle_Compressor/Local/US-en/newsletters/RSES0406_Prevent_Vibration_lowres.pdf

http://www.carlylecompressor.com/Files/Carlyle_Compressor/Local/US-en/newsletters/RSES0506_Good_Design_lowres.pdf?SMSESSION=NO

Happy reading. This is a topic you don't see very much information on so read carefully.

expat
21-07-2008, 06:33 PM
Hi, US Iceman. I don't know if you're going to catch up with this reply as the thread is a year and a half old. If not I'll make a new thread.

I've been scrounging information from as many threads as I can find that were dealing with the problem of noise control. It is more complicated than I had initially thought!

The problem I am finding most difficult to solve is this tendancy for the compressor to "SHAKE, RATTLE AND ROLL" when it shuts down. What is that and what can I do? People are making agressive and frankly menacing remarks to my customer as the condensing groupe is sending this noise out into the street and waking people up on the third floor above.

I've tried to find answers with searches here, asking fellow technicians, my Uncle with 30 years experience as an engineer with Grundfoss and I don't know where alse to look.

I read the above papers that you posted but I am not qualified to put their equations to good use.

I believe this is a problem (noise)that is going to become more and more significant in our developed countries where tolerance seems to diminish as population density and richess rises.

Any help much appreciated

US Iceman
21-07-2008, 06:41 PM
The problem I am finding most difficult to solve is this tendency for the compressor to "SHAKE, RATTLE AND ROLL" when it shuts down.


This tends to be a different issue than mechanical vibration (whether it is induced by rotating parts or sound).

The first thing that comes to mind is: what is the discharge pressure and system application?

Where I have seen this occur is on systems that are running with high discharge pressure and when the compressor shuts down it sometimes bangs around a lot. These sorts of issues are the most difficult to solve in my estimation because there could be many factors which force this behavior.

chemi-cool
21-07-2008, 07:01 PM
Hi expat,

I had a similar problem with 40 Hp Copeland,

The condenser was way above the compressor and I've lost quite a few discharge flappers,

I installed NRV straight after the compressor and all my problems gone.

chemi-cool
21-07-2008, 07:06 PM
Mr M. iceman,

Your links don't upload, please recheck them.

chemi-cool
21-07-2008, 07:17 PM
Look At this picture Iceman.

You have mentioned vibrations.....

http://www.refrigeration-engineer.com/forums/showthread.php?t=1949

US Iceman
21-07-2008, 07:51 PM
Your links don't upload, please recheck them.


Hi chemi. I just did and they worked OK for me. I'm not sure why you would be having problems with those. Sorry.

I have seen some vibration eliminators that looked just like the pictures you referenced. The braiding broke and let the bellows expand.

GXMPLX
21-07-2008, 07:57 PM
Im new here but so far never seen US_Iceman miss a post and will lead you to solve system noise Ill give you other recomendations ... unless he gives me the can again!

Noise is a wave that bounces off walls (or any surface) and turns around corners.

If the unit is placed above the ground, the third floor could be getting the noise from the unit directly plus any bounces off the walls and floor multiplying its effect.

There are materials that attenuate this noise, the problem is they are also thermal insulators so be careful not to cover anything that needs cooling or ventilation. For example Armacell 3/8" sheets attenuate 30dB.

Like a wave, noise has zones of shadow and with high peaks (constructive interference). If this is happening it is easier to solve than straight noise from the unit, just place sound barriers (materials that absorb noise like a sponge or corrugated carboard) between the unit and the problem area. Be careful not to produce hot air short circuits to the condenser.

Unfortunately there are no formulas to solve this problem, all you can do is use trial and error and I would suggest strongly you get a soundmeter and measure at the problem area. If the people that live there wont allow this, use a pole to place the meter in a line with the window. If the meter has a highly directional microphone you can verify if the noise is bouncing from other unexpected sources like nearby buildings.

US Iceman
21-07-2008, 08:23 PM
...unless he gives me the can again!


Not much danger in that on this sort of problem!:D

These are VERY difficult problems to resolve.

I think the first issue is to try to identify what the driving factor is first. Vibration is too broad of a field to say it is this or that.

And without any accelerometer or displacement or noise data it is all guess work.

As I said earlier, you have two factors (that I know of); mechanical or noise induced.

From the posted question by expat it would appear his situation is one of something other than vibration in general. The shake, rattle, and roll syndrome is usually caused by something that is causing the compressor to operate in abnormal conditions or there is something broken in the compressor like a mounting spring, etc.

expat
21-07-2008, 08:46 PM
This tends to be a different issue than mechanical vibration (whether it is induced by rotating parts or sound).

The first thing that comes to mind is: what is the discharge pressure and system application?


I havn't measured the pressures yet. I was more concerned with the noise leaving the area. But,... after your question I have seen that this compressor does not seem to be suited to low temerature applications. It is an UH (Tecumseh) TAJ4519Z.

In all the catalogues that I have looked this compressor only ever gets references as low as -10c. Yet it is here being used for a walk in freezer.

I wonder what happens here?

Does the compressor mange to come down in temp even though it is trying to do something it was not disigned for. And is all this happening with no ill effect. Or is the excessive noise, indeed the ill effect

I'll add one more thing, when the comp stopped the wobble and nocking sound was enough to make me jump when I was standing beside it! Now that didn't seem right.

Hey, and thanks for the quick responses, you guys are great!

expat
21-07-2008, 08:52 PM
Hey, no fair! Your answering before I've had time to think let alone type! OK, I'll check the spring mountings tommorow morning and report back.

If you're right I'm going to go hide in the corner.

US Iceman
21-07-2008, 09:00 PM
Hey, no fair! Your answering before I've had time to think let alone type!


Well... you asked a question, got a reply and now you're complaining?;)

The springs I mentioned might be of two different types.

1) it might be the internal springs in the compressor housing if this is a hermetic compressor.

or...

2) if the compressor is a semi-hermetic and mounted on springs you might need to see if the springs are too tight. I've seen this happen before. When the compressor shuts off there is a loud smack that occurs when the compressor foot hits the mounting bolt. The compressors are supposed to be able to "float" on the mounting springs, not be clamped down.

GXMPLX
21-07-2008, 09:00 PM
TAJ4519Z is a HBP compressor. Gas re expansion causes the piston to be pressed against the pin during almost all the suction stroke causing the pin hole to wear. Eventually the piston hits the valve plate causing very loud noise ... but it would be present continuously.

If this is so, changing the compressor to the right one could help with noise.

US Iceman
21-07-2008, 09:04 PM
It is possible that there is something broken in the compressor besides the mounting springs also.

I've seen others where the noise was very loud and occured for several seconds upon shut down.

Does this happen once on shutdown (quickly), or occur for several seconds?

expat
21-07-2008, 09:26 PM
This happened on shut down. The sound was a shake, nock of less than a second but neverteless enough to annoy the neighbours. I saw the comp sway by about 2 centimetres (1 inch) to the right.

US Iceman
21-07-2008, 09:33 PM
Does it do the same thing when it starts back up?

And, have you looked at the piping installation to see if the pipes jump and hit something else when this does occur?

This almost sounds (no pun intended) like an installation issue, rather than mechancial fault.

expat
21-07-2008, 09:57 PM
No, I didn't notice the noise when it started up, just when it stopped.

Anyway, I've just varnished up some board to fix around and enclose the comp and condensing unit so that the isophonique insulation sticks well but I'm still intrigued as to why the comp has this (noisy) shake on shut down. I'll be changing the rubber bungs it sits on (whatever they're called in English) so I'll let you know the outcome tomorrow.

The pipe work is simple. No pipes are touhing each other.

Tomorrow I will take pictures.

demain mes amis:)

US Iceman
21-07-2008, 10:01 PM
I'll be changing the rubber bungs it sits on (whatever they're called in English)...


I think the word you are looking for is "grommets".

Best of luck... I'll be looking forward to the pictures.

And audio clip would be helpful too if there is anyway you get one.;)

expat
22-07-2008, 02:28 PM
Update

Firstly I must start by saying that yesterday I made the classic mistake of taking the customer's word for it and believing everything he said. The condensing group was actually serving his positive cold room and not the negative cold room.

This, ironicaly, was difficult to make him believe. Even when I showed him that his evaporating temperature was -15C so how could his freezer get to -19C. So, the comp is the right one for the job.

Changing the grommets (thankyou US) has resolved the problem of the shaking comp.
2345

2346

I hope the attatched files are clear enough to see. You should be able to see that I have put isophonic insulation around the unit and put a lid on it. This has reduced the higher frequency sounds dramatically but the lower droneing unfortunately persists. Tonight we shall see if the neighbours complain.

If all else fails what would anyone think of putting the comp in an isolated box under the shelf that the condensing unit is currently sitting on

expat
22-07-2008, 02:31 PM
Those pictures look c***p.

Could someone perhaps tell me how to do the thing with the miniatures. I'll try and figure it out for myself in the meantime.

US Iceman
22-07-2008, 03:51 PM
The droning as you call it is reasonance. As I can know see the installation the compressor vibration is being transmitted to the structure. If you isolate the compressor/condensing unit mounting with resilient rubber mounts, these will help to absorb some of the vibration to keep it from being transmitted to the structure.

Glad to be of help.;)

US Iceman
22-07-2008, 03:54 PM
I made the classic mistake of taking the customer's word for it and believing everything he said.


:D

Ohhh, don't ever do that! Ask them a lot of questions and nod your head like you understand them. Then use the information to help you sort out the issues.

Some of the information is usually good, while at other times you just toss out what they say.:)

expat
22-07-2008, 09:11 PM
You can't see it but I actually did put the rails of the unit on some strange pink pads that I found at the distributor's. They are 70mm * 70mm * 20mm. They have a kind of rough coating on top and bottum and the sandwich is filled with a high density silicon.

It looks like it would be great under swings and slides. Except the catalogue price is (before tax) 85 euros (135usd) for four at that size.

GXMPLX
22-07-2008, 09:54 PM
... Installing the unit on solid ground would also help.

US Iceman
22-07-2008, 11:00 PM
GXMPLX has a good point also. The mounting structure should be extremely rigid. A flexible mounting structure tends to induce the reasonance. This is actually one of the most difficult aspects to solve. It is similar to placing equipment on a mezzanine.

The floor (mounting location where the compressor is) can flex up and down. The old timers term for this is oil-canning. If you remember those old oil cans that had a flexible bottom you pushed like a diapraghm, that is what these mounts can be like.

Graham
23-07-2008, 04:17 PM
That box looks like it's going to get hot enough to cook a roast.

GXMPLX
23-07-2008, 06:25 PM
That box looks like it's going to get hot enough to cook a roast.

I don't think he'll close the box with more insulation though I do not like the execution.

Placing foam inside the box is good only if things that vibrate are inside the walls of the box but here the whole box will vibrate.

It can work, it will decrease noise level but I think would have been better on the outside of the box not with foam and you can place the foam far enough the air suction and air discharge to absorb/reflect noise bouncing in those directions.

But as I said if he solves the problem with this, OK.

expat
24-07-2008, 02:00 PM
The work I did has reduced certain noises leaving the compartment. Some noises are however pesisting to an unacceptable level.

GXMPLX and US Iceman, you both have good points about putting the unit on a solid foundation which will take the resonance out of the flexible walls of the compartment.

GXMPLX
24-07-2008, 02:51 PM
You could reinforce the box but I think youd have to interfere with air flow.

Installing it on the ground also eliminates one surface the noise is bouncing from.

Unfortunately there are no formulas that let you anticipate the right solution

expat
26-07-2008, 02:00 PM
I think the problem is solved.

I took the board up off the floor that you can see the bucket standing on in the picture. Under the board I was hoping to find a flat hard surface but to my annoyance I found a Turkish toilet. So I placed the unit in such a way that the rear end (no pun intended) had it's mounting rails standing on floor tiles and the front was standing on a piece of 4*2 hard wood (teak I think) that I cemented into the toilet.

The result was very good but the unit was able to move slightly and would cause new rattles and hums each time I tried to adjust. It was too late for me to try and fix the unit down firmly, and I'm not sure what the results would have been anyway. So, I settled for putting two of my silicon pads under the rails that were sitting on the ceramic tiles and leaving the front standing on the piece of hard wood.

This is working but I don't know if it is a permanent repair. I am now more aware of the indecipherables involved in locating the source of a sound or even identifying the the noise which is considered to be the problem one. Consequently, I will be a bit more wary in future of committing myself to trying to resolve this sort of problem.

GXMPLX
26-07-2008, 02:43 PM
I think the problem is solved.

Good Im glad, congratulations!



This is working but I don't know if it is a permanent repair.

Unfortunately youll never know. Noise is a personal and subjective perception if the person in that apartment changes or they install a new division somewhere you could get it back.



I am now more aware of the indecipherables involved in locating the source of a sound or even identifying the the noise which is considered to be the problem one. Consequently, I will be a bit more wary in future of committing myself to trying to resolve this sort of problem.

Great if you find general rules, post them here!

Unfortunately acoustics is a more complicated subject than refrigeration.

You need to have the correct tools too, just ask the architect of the Sydney Opera House the problem it was for him and all the research they had to do to solve acoustics problems (not to mention money spent) and these are guys who really know and think before doing!

The can owner may help with his experience until you get the compressor noise out, I'd suggest you be wary on getting low noise compressors too if the site is crowded.

expat
26-07-2008, 03:33 PM
In view of a hyperthetical sutuation where by I get asked to do this sort of install, what would be a more suitable proposition for a customer?

At a quick glance in the catalogues quiet (36db) condensing units look to be about double the price and up.

You spoke about low noise compressors. Would this be things like a Copeland scroll that was in a air con system that I recently installed.

There were two main noises from the unit: the hum the fan was making and the buzz the comp was making. The movement of air doesn't seem to be worrying anyone for the time being as I noticed such noises in other parts of the alley.

Just say if you're getting bored and I'll stick a sock in it. But the reason I'm asking is because this unit has been there for a number of years and it is only recently that the neighbours have started complaining. My theory is that here in the south peoples tolerance is wittling away for things they used to just put up with as being a part of life. In the twelve years I have been here I have watched attitudes change and intolerance is becoming more and more common place so I expect to see more of these problems cropping up.

People will sue whoever they can pin blame on nowadays and that could be the installer...me!

US Iceman
26-07-2008, 04:51 PM
As GXMPLX noted, refrigeration is a basic art when compared to something like acoustics. notice I said art and not science. Both are based on science, however the art is developed over long years of experience and findings on other past projects. It is sort of a cumulative effort if you will.

As you have yourself seen, being able to isolate the vibration away from the materials through which the mechanical energy is transmitted can be a big first step.

The second issue to to use equipment that offers the lowest noise potential. Some of this may be due to fans. The tip speed of fans can generate a lot of noise also.

Some compressor manufacturers offer a sound insulating blanket also. These look like socks that fit over the compressor. There are also manufacturers who make insulating blankets for sound or thermal purposes.

Part of this issue is with the perceptions of people. Some notice these disturbances, while others disregard them. Unfortunately, as people become more frustrated with things beyond their control they look for things that they may be able to control. This is why I think these issues happen.

GXMPLX
26-07-2008, 04:53 PM
A good way to tackle this problem is always informing the customer in writing and quoting a lower noise unit and a normal one and let him choose.

This takes a lot from your shoulders but the legal aspect depends on local laws and rules.

Yes people tend to get intolerant if you rub them the wrong way as Ive come to learn from these posts too, I seem to do that a lot!

You were right to mention the fan noise it is an important issue, you can lower it with slower fans but probably need larger condensers, and be careful when installing them in windy areas because you normally dont consider wind force but you must with slow fans.

expat
26-07-2008, 08:44 PM
I would like to thank you two experienced men for the time you have allocated me.

Your ideas have led me to a satisfctory solution - but your encouragement has pushed me to try, which was much more important.

Thankyou, and lets keep in touch for these kinds of issues. Who knows we may start to get good at it;)

expat
15-10-2008, 03:37 PM
This comp gave up last week.

Cut it open and found, as UsIceman suggested, a broken mounting spring:p

US Iceman
15-10-2008, 03:49 PM
Thank you for posting a follow-up story for this project. It is helpful for members to see the final results as well as the discussion. This is how everyone learns by sharing.

expat
15-10-2008, 09:09 PM
Well I learnt that's for sure. Anyhow I started another thread on this same comp in the commercial forum. The client claims this to be the third comp change in as many years (possibly an exageration) and I'm trying to find out why.