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The "noise industry" is generally woefully ignorant of diagnostic techniques and modern noise control methods. Consequently, thousands of people are needlessly exposed to stressful noise over prolonged periods, resulting in unnecessary deaths from stress (BMJ/WHO reports). Very large sums of money are also wasted on inappropriate mitigation - there is a diagnostic process that must be followed to evaluate any noise nuisance problem. The presentation includes case studies illustrating how so much money has been wasted on poor diagnoses and inappropriate noise control measures - plus examples of how it should be done using best practice...
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Industrial Noise and Vibration Centre: www.invc.co.uk
The Environmental Noise The Environmental Noise Industry is Not Fit for Industry is Not Fit for
Purpose…Purpose…
Peter Wilson MSc. MIOAPeter Wilson MSc. MIOA
Noise Control Best Practice
noise
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In Summary
The “Noise Industry”• Generally displays a woeful ignorance of both diagnostic
techniques and modern noise control methods
The Victims• Thousands of people are therefore needlessly exposed to
stressful noise from industrial / commercial premises over prolonged periods
• Many unnecessary deaths consequently (BMJ and WHO reports)
• Companies waste a fortune on inappropriate mitigation
The Best Practice to Avoid the Problems• The diagnostic procedure that must be followed to
evaluate any potential noise nuisance problem• Case studies illustrating poor practice in attempted
mitigation (and failed mitigation) of common noise problems• Examples of best practice
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Noise Kills…
WHO Report: 2011• Europe: c3% of deaths from heart attacks is attributable to
long term exposure to (mainly nighttime) environmental noise
• 2% of the population suffer from severe sleep disturbance• 15% suffer from serious annoyance• UK noise complaints increased by x5 over the last 20 years• Learning abilities of children badly affected
BMJ Report: 2013• Environmental noise increases the risk of stroke and
coronary heart disease due to raised blood pressure and hypertension
• Near Heathrow, 24% increased hospital admissions due to stroke; 21% increase due to coronary heart disease; 14% increase for cardiovascular disease cf low noise areas
All dB(A) based – but many noise issues are low frequency,so these figures seriously underestimate the problem…
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BS 4142 – technically…
BS 4142 is almost ubiquitous, largely because it exists…However, it is often (badly) applied to situations where it is not suitable.
• BS 4142 is supposed to assess the likelihood of complaints from people inside a building by measuring dB(A) outside
• inside rooms, the T.L. of windows shapes the spectrum, reducing mid and high frequency components - almost un-'A' weighting the sound
• does not work well for noise containing low frequencies • 5dB(A) correction for noise with tones• tonal noise at 5dB(A) below non-tonal noise should be
equally disturbing• should not be used where background noise levels are very
low (<30dB(A))
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Environmental Noise Control is ....
…not just about the overall level…
• Effective noise control must be based on an accurate diagnosis that relates noise features to subjective impact, not just on assumptions about overall dB(A).
• Although dB(A) may also be an additional planning / specification requirement, this is often a completely separate issue.
• Noise control is an engineering problem that should be solved by engineering means at source wherever practical.
• All the options must be considered, not just the high cost conventional palliatives of barriers, enclosures and silencers.http://www.invc.co.uk/noise/noise-control/environmental-noise-control/
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o.ukAttitude, Attitude, Attitude - Placebo Silencers
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Best Practice Elements
• Attitude
• Diagnosis - understand the cause of the subjective problem
based on detailed diagnosis, objective evaluation linking noise features to complaints – temporal and tonal components
link problem noise features to specific mechanical / aerodynamic plant elements.
• Assess the Noise Control Options based on current best practice. The majority of noise
control recommendations that we see are either not fit for purpose or are far more costly than necessary.
• Recommend / Implement Best Practice Noise Control Option
typically reduces noise control costs by 50% - 110%! reduces the time required to solve problems (often from
years to weeks)
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Diagnosis, Diagnosis, Diagnosis…
You’re just guessing…The approach taken to mitigate noise problems is often based on guesswork.There should be no guesswork involved.
•Temporal DiagnosisEvents, intermittency, turn plant on and off, variation over time…
•Frequency ContentBroadband: octavesTones: narrow band frequency analysis
Note: 1/3 octaves are largely a waste of time. This is the 21st century - FFT is available free on smartphones…
•Audio RecordingsAny SLM can be used to produce calibrated audio files that can then be analysed by ear and by softwarePlay back modified audio to the complainant
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Source Identification and Ranking
Identification Techniques
• run each source separately - measure in far field at reference points
• measure each source close in and predict noise levels (sound power and propagation)
• use narrow band frequency analysis - compare far field and close in signatures
Rank the Sources• …by the subjective impact, NOT just dB(A)
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Cooling Towers
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Rank Multiple Sources Cooling Towers
Ranked sources
• large cooling tower
• small cooling tower
• main pumps (5)
• lift pumps (13)
Ranked local sources for dominant contributor:
Large cooling tower
• tower air outlets (3)
• tower air inlets (3)
• fan motors
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Rank Multiple Sources Cooling Towers
Ranked sourcestower air outlets (3)tower air inlets (3)main pumps (5)lift pumps (13)
Conventional:3 sets of silencers (outlets) + noise barrier at boundary at c £30,000; 56dB(A)
Detailed DiagnosisModify outlets and inlets, silence main pump cooling fans, local screening for lift pumps at c £5000; <50dB(A)
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Cooling Tower: Untreated / Treated
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Cooling Tower Pumps: Untreated / Treated
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Battery Stack Diagnosis
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Battery Factory Stacks
Diagnostic measurements• synchronise recording time and engineer's watch• define shut-down and start-up sequence for stacks• engineer notes time of each operation• record whole period• analyse recording - use timings to identify sources
Solution• purpose designed silencer inserts dropped into 4 of
the 5 stacks• 12 - 15 dB(A) reduction in stack noise
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Press Shop Noise Complaints
•£12k wasted on factory end wall treatment, £65k additional roof improvements planned (no guarantee) and £40k+ legal fees spent…
•3 presses required treatment - c£12k solved problem.
http://www.invc.co.uk/noise/noise-control/environmental-noise-control/#casestudies
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Air Handling / Chiller Units
The ProblemSeveral chillers and 2 large AHUs installed at the rear of a high tech facility were causing serious environmental noise complaints (more than 10dB(A) above background with tonal content). £100k spent on ineffective noise control - one chiller fitted with silencers, simple noise barrier erected (which also caused air-flow problems) - but with no effect on complaints….
The SolutionThe primary requirement was to carry out an accurate diagnosis that would allow the sources to be ranked in terms of their contribution to the environmental noise and then to rank the noise sources within each of the significant contributors.
http://www.invc.co.uk/noise/noise-control/environmental-noise-control/#casestudies
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AHU Diagnosis and Noise Control
Diagnosis• 2 existing acoustic louvres on each unit for extract and
supply air. Detailed noise measurements were carried out inside each plenum and outside each louvre over the operating range of the unit.
- top louvre (extract) 4dB(A) noisier- poor design due to potential for air recirculation
Noise Control• turn top louvre round (also improve performance)• line plenums with acoustic absorbent• fit baffle to extract fan outlet to reduce noise transmission
down into supply plenum and out through louvre• plenum lining and baffle reduced noise by 5.5dB(A)• total noise reduction just over 10dB(A)
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Air Handling Unit: Re-directed Extract
Extract
Supply
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Diagnosis Outside Plenums
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AHU Modifications
complainants
before
after
extract
supply
84dB(A)
80dB(A) filter
louvres
absorbent
baffle78dB(A)
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Chiller Silencers and Barrier
Intake and exhaust silencers fitted by supplier. Exhaust silencers have some benefit, intakes none as the chiller is open at the far end. The barriers have only a small effect for similar reasons.
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Dry Chiller: Impellor Change
noisy impellor
quiet impellor
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Panel Vibration Reduction
damped
undamped
Total 8dB(A) noise reduction under chiller (damping + absorbent)
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Source Ranking and Target Level
Overall target at complainant: 40dB(A): (35dB(A) + 35dB(A) + 35dB(A))Eliminate tonal components
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Chiller Plant Noise Reduction
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bedroomwindow open/shut
grinder 5m
cooling towers 1 / 2 at 2m
Cooling Tower Tonal Source ID
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Cooling Towers: Detail
Only 71.3Hz blade pass of fans in tower 1 matches bedroom spectrum - grinder and tower 2 are eliminated as sources
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Remote Control of Noise
video sound photos
email -internet
Specialised analysis
BPM
BAT
Costs
database
experience
@@
http://www.invc.co.uk/noise/noise-control/remote-control-of-noise/
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Remote Control of Noise
Roof-top fans
£50k wasted on acoustic lagging – no effectAerodynamic modifications135Hz reduced by 17dB270Hz reduced by 22dB
http://www.invc.co.uk/noise/noise-control/remote-control-of-noise/
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Noise Complaints from Industrial Premises
Source: National Physical Laboratory
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Fan Noise Control Options
Techniques by priority and cost effectiveness….
•Control at sourceengineering modificationsefficiency – lowest fan noise coincides with maximum efficiencyvibration isolation and vibration damping
Only if the above are not practical should you consider…
•Silencing
•Enclosures
•Lagging
•Barriers
•Building modifications
Conventionally, these high cost techniques have been the only measures that are considered….
http://www.invc.co.uk/noise/noise-control/fan-noise-reduction/
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Innovative Noise Control Technology
These are some of the innovations we use as part of current best practice in environmental noise control.
• Quiet Fan technology (QFt)
typically 10% - 20% of the cost, no effect on fan efficiency
• Chiller / HVAC noise control
<20% of the cost, free cooling unaffected, higher efficiency
• Fan / combustion stacks
retro-fit, low cost, fast
• Burner / combustion noise
source control technology – typically <5% of the cost
• Acoustic Camouflage
psychological electronic silencing
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London: Office A/C Plant…
• Chillers on top of high-rise office block caused noise complaints in an adjacent street
• Noise consultancy carried out BS 4142 assessment and recommended replacing one of the chillers
• Chiller replaced at cost of £100k, several dB(A) quieter at 1m• Complaints unabated as the noise nuisance was caused by
low frequency tonal noise from a different chiller…
http://www.invc.co.uk/noise/noise-control/fan-noise-reduction/#chiller
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Diageo Chiller
Cooling tower noise experts report conclusion:-• “A “pure tone” is extremely difficult to eradicate as it
requires changes to the mass being excited and as indicated is a direct result of the noise power at a primary frequency being amplified and combined with other harmonics across the frequency band.
• There is no quick fix or simple change that can cure such phenomena. In order to cut the generated noise level from this cooling tower we believe the only solution is to correct the fault at source with a fan change out but while doing so install a low sound fan i.e. wide cord, sophisticated profile, larger diameter and run at slower speed.”
• £30,500 plus downtime of several days.
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Diageo Chiller
Diagnosis•£30k recommendation made with no frequency analysis…•Analysis of video soundtrack via email – 10 minutes•670Hz tone is gear-mesh frequency of motor pinion•Recommended replace gear•Whole gearbox replaced <£3,000, downtime c one day
Video soundtrack analysis
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Dryer Fan
The recommendation from the first noise specialist was the following:• Replace impeller or whole fan if practicable to prevent tone
being generated. A cost estimate for a replacement fan and discharge silencer was obtained at approximately £100k and would require an extended shutdown to install and modify the existing duct-work to suit.
• Fit attenuators to fan if necessary to reduce noise levels at stack by 5 - 10 dB. The proposal was to add a top conical section to the stack to increase the exit velocity. This was not pursued as it had high installation cost as the stack could not self-support the new section.
http://www.invc.co.uk/noise/noise-control/fan-noise-reduction/
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Dryer Fan
Diagnosis•£100k recommendation made with no frequency analysis…•An internet search by the Precipitates Plant Manager led company to approach us about our Quiet Fan technology…•The noise control measures reduced the tone by 20dB, cost <£7k and paid for themselves in around 9 months as they reduce power consumption…
Noise analysishttp://www.invc.co.uk/noise/noise-control/fan-noise-reduction/
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Corrugation Plant
• Abatement notice - £150k quoted for building modification - with no guarantee of success. EHO suggested our 2nd opinion…
• Diagnosed corrugator roller tones and defined BPM.
• Reduced tonal content at source by 12dB – and eliminated PPE requirement – for cost of £25k…
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Restaurant Fans and Chiller
Kitchen extract exhaust system and chiller on roof65dB(A) outside bathroom window; 33dB(A) in bedroomConsultant recommendation: move chiller + build noise barrier; expensive silencer in duct
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Restaurant Fans and Chiller
Naked chiller Proposed silencer (£400)
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Restaurant Fans and Chiller
Bedroom and room below chiller
Chiller tone at 48.5Hz + harmonics – previous recommendations would not have worked….
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Chiller Fans
Low frequency noise complaints (48.5Hz)Money wasted on recommended noise barrier…
Emailed this video. Analysed soundtrack to reveal tonal content…
http://www.invc.co.uk/noise/noise-control/fan-noise-reduction/#chiller
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Chiller Fans
Aerodynamic modifications reduced 48.5Hz tone by 13dB and other tones by up to 20dB plus improved efficiency… 8 fans, < £4k
http://www.invc.co.uk/noise/noise-control/fan-noise-reduction/#chiller
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Schiller Biomass Power Station Fan
• 50MW station (largest in USA) noise problem: 2 storey ID fan.
• Conventional silencer had a very big impact on efficiency
• QFt fitted in only 12 hours!• 10dB reduction in noise• Fan power consumption
reduced• No site visit…“…the 3m wide ID combustion
fan could be heard across the river… after installation (only 12 hours)…10dB drop in noise, which is huge…recorded a reduction in ID fan power after QFt had been installed.” – Jim Granger, Senior Engineer
http://www.invc.co.uk/noise/noise-control/fan-noise-reduction/
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Scrap Can Extract and Chopper Fans
modified fan
ProblemOccupational + environmental tonal noise
Conventional•silencers, lagging and
enclosures•capital cost > c£35000 +
maintenance costs
BPM Engineering•internal fan modification
reduced tones by 23dB and overall noise by 22dB(A)
•cost c £3000 - no maintenance costs (lasts the lifetime of the fans despite passage of cans)
http://www.invc.co.uk/noise/noise-control/fan-noise-reduction/
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Thermal Oxidiser Fans
New plant – supplier suggested earth berm, enclosures etc
CMB asked for a 2nd opinion
BPM – Quiet fan technology, remove “beating”, damper type and location changed, small secondary silencers: 15dB(A) reduction >£100k saved and more efficient….
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Axial Vent Fans
8 off axial vent fans with 8m long silencers several stories up
112Hz blade pass problem tone reduced by 20dB by fitting invertors to change speed slightly to avoid resonant condition.
http://www.invc.co.uk/noise/noise-control/fan-noise-reduction/#chiller
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Chiller Farm
£300k quoted to reduce fan noise - several stories up – loss of free cooling
Innovative geometries + control systems + control at source15dB(A) reduction, no loss of efficiency, c £40k…
http://www.invc.co.uk/noise/noise-control/fan-noise-reduction/#chiller
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o.ukYoghurt-Based Noise Control - Boiler Burner
16dB tonal noise reduction
http://www.invc.co.uk/noise/noise-control/environmental-noise-control/
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Cement Works Stack Noise Control
•Plant update to improve efficiency had a disastrous effect on stack noise, causing complaints over a wide area.
•Planned conventional silencing would have been very costly and would have caused unacceptable down-time.
•We designed tuned inserts that were installed over a weekend.
•Noise reduced by 19dB with no effect on system efficiency and at a small fraction of the cost.
http://www.invc.co.uk/noise/noise-control/environmental-noise-control/
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Remote Control of Noise
BP Refinery: $1.25m conventional silencers: $0.25m via engineering – no impact on efficiency, no site visit
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In Summary
The “Noise Industry”• Generally displays a woeful ignorance of both diagnostic
techniques and modern noise control methods
The Victims• Thousands of people are therefore needlessly exposed to
stressful noise from industrial / commercial premises over prolonged periods
• Many unnecessary deaths consequently (BMJ and WHO reports)
• Companies waste a fortune on inappropriate mitigation
The Best Practice to Avoid the Problems• The diagnostic procedure that must be followed to
evaluate any potential noise nuisance problem• Case studies illustrating poor practice in attempted
mitigation (and failed mitigation) of common noise problems• Examples of best practice
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Industrial Noise and Vibration Centre: www.invc.co.uk
Questions?Questions?
Peter Wilson MSc. MIOAPeter Wilson MSc. MIOA
Contact us for further informationContact us for further [email protected] +441753 [email protected] +441753 698800
Noise Control Best Practice
noise
