Silencers. Attenuators. Enclosures. Lagging. Conventional fan noise control techniques that can compromise the efficiency of fans or make silencing costly. This presentation provides a guide to best practice in fan noise control, including alternative technologies that can even provide stealth and efficiency, reducing energy consumption and carbon footprint. Remote analysis techniques allow us to apply our fan silencing technology anywhere in the world from the UK.

1. Noise Control Best Practice
noise
www.invc.co.uk
Fan Noise Control
Best Practicable Means (BPM)
Industrial Noise and Vibration Centre
http://www.invc.co.uk/noise/noise-control/fan-noise-reduction/

2. Industrial Noise and Vibration Centre
• Award winning noise control technology for fans
 £800k capital and £250k / p.a. running cost savings for Corus
• Best Practicable Means (BPM)
• Best Available Technology (BAT, BATNEEC)
 In many cases, (including centrifugal fans, chiller / HVAC plant, large
stacks, burners / combustion) BPM / BAT often cannot be claimed
without reference to our technology….
• BPM / BAT Evaluation
 Often used as the arbiter of what constitutes BPM / BAT – including
court cases
www.invc.co.uk
• Buy Quiet Policy
 De-facto UK standard noise purchasing policy
• Presentations and Training
 Noise training providers for English, Scottish, Irish Environment
Agencies and local authorities

3. www.invc.co.uk
Noise Complaints from Industrial Premises
Source: National Physical Laboratory

4. Environmental Fan 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 on 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.
www.invc.co.uk
• Noise control should not be implemented at the expense of fan system
efficiency. Conventional silencing will often have a significant detrimental
effect on fan performance, increasing power consumption (running costs)
and the carbon footprint.
• All the options must be considered, not just the conventional high cost
conventional palliatives of barriers, enclosures and silencers. These
techniques should only be used where it can be proved that there is no
engineering alternative.

5. BS4142 Fails at Low Frequencies.....
BS 4142 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
 Inside rooms, the T.L. of windows shapes the spectrum, reducing mid
and high frequency components - almost un-'A' weighting the sound.
www.invc.co.uk
 BS 4142 is supposed to assess the likelihood of complaints from
people in the building.
 It should not be used where background noise levels are very low
(<30dB(A))

6. Noise Control Best Practice
noise
www.invc.co.uk
Fan Noise Control
Diagnosis
Industrial Noise and Vibration Centre
http://www.invc.co.uk/noise/noise-control/fan-noise-reduction/

7. Cooling Tower Source ID
cooling towers 1 / 2 at 2m
www.invc.co.uk
grinder 5m
bedroom
window
open/shut

8. www.invc.co.uk
Cooling Towers: Detail
Only 71.3Hz blade pass of fans in tower 1 matches bedroom
spectrum - grinder and tower 2 are eliminated as sources

9. Restaurant Fans and Chiller
www.invc.co.uk
Bedroom and room
below chiller
Chiller tone at 48.5Hz +
harmonics – previous
recommendations would not have
worked, must isolate from roof

10. Noise Control Best Practice
noise
www.invc.co.uk
Noise Control Techniques
Industrial Noise and Vibration Centre: www.invc.co.uk

11. Fan Noise Control Options
Techniques by priority and cost effectiveness….
•Control at source
engineering modifications
efficiency – lowest fan noise coincides with maximum efficiency
vibration isolation and vibration damping
Only if the above are not practical should you consider…
•Silencing
•Enclosures
www.invc.co.uk
•Lagging
•Barriers
•Building modifications
Conventionally, these
high cost techniques
have been the only
measures that are
considered….

12. Innovative Noise Control Technology
These are some of the innovations we use as part of current best practice
in environmental noise control.
• Award winning 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
www.invc.co.uk
• Burner / combustion noise
 Unique source control technology – typically <5% of the cost
• Acoustic Camouflage
 Psychological electronic silencing

13. www.invc.co.uk
Placebo Silencers + Acoustic Camouflage

14. Centrifugal Fan Installation
high pressure
NOISY
www.invc.co.uk
QUIET
low pressure

15. www.invc.co.uk
Fan: Outlet dampers

16. Axial Fan Installations
www.invc.co.uk
NOISY
QUIETER

17. Axial Fan Installations
>2-3 duct diameters
www.invc.co.uk
NOISY
QUIETER

18. Efficiency: Fan Speed v Noise
• Variable speed drives
• Two speed motors (day and night)
• Proportional control systems
noise reduction dB
10%
20%
30%
40%
50%
www.invc.co.uk
speed reduction
2
5
8
11
15

19. Splitter Silencer
www.invc.co.uk
Mineral
Wool
Perforated
Steel

20. www.invc.co.uk
Cooling Tower Silencer
Little attenuation due to material build-up

21. Fan Outlet Silencer Cowl
steel / plywood
www.invc.co.uk
acoustic absorbent
A simple, cheap absorbent lined cowl can give a 10 - 20dB(A) noise
reduction in fan inlet /outlet noise

22. Noise Control Best Practice
noise
www.invc.co.uk
Reactive and Other Silencing
Industrial Noise and Vibration Centre: www.invc.co.uk

23. Drying Oven
Problem
95dB(A) from gas burners at low firing
82Hz "boom" dominant
www.invc.co.uk
Enclosure
large oven - 8m x 4m x 3m @ c
£30,000 with serious hygiene and
maintenance problems
INVC BPM
organ pipe resonance excited due to
weak mixture at low firing
standard weld fume extract motor
controlled valves fitted to each inlet
21dB off boom; 8dB(A) overall
reduction; £100 each for 12 burners

24. Extract Fan System Duct Resonances
www.invc.co.uk
30dB tonal noise
reduction
Improved efficiency

25. www.invc.co.uk
Damped Dry Chiller
Total 8dB(A) noise reduction
under chiller (damping +
absorbent)

26. www.invc.co.uk
Fan: Steel and Elastomeric Spring Isolators

27. Axial Vent Fans
www.invc.co.uk
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.

28. www.invc.co.uk
Yoghurt-Based Noise Control - Boiler Burner
16dB tonal noise reduction

29. Noise Control Best Practice
noise
www.invc.co.uk
Quiet Fan technology
Industrial Noise and Vibration Centre: www.invc.co.uk

30. OG Centrifugal Fans: Corus
12dB noise reduction
>£1 million cost saving
>£800k capital +
c£250k p.a. on power
www.invc.co.uk
“INVC’s modifications have brought about a huge reduction in fan noise,
“INVC’s modifications have brought about a huge reduction in fan noise,
improving the environmental conditions across a wide area around the
improving the environmental conditions across a wide area around the
Plant. They’ve also saved us a large amount of money by negating the
Plant. They’ve also saved us a large amount of money by negating the
requirement for major capital expenditure, so it’s been a remarkably
requirement for major capital expenditure, so it’s been a remarkably
successful project.” – Grahame Wallace, Corus.
successful project.” – Grahame Wallace, Corus.
…for the most significant development in noise control technology

31. OG Centrifugal Fans: Corus
www.invc.co.uk
Conventional solutions not suitable:
varying fan speed
x3 4 megawatt fans (c3.5m high) - loss in
efficiency due to silencers unacceptable
Source Control
173Hz tone reduced by 12dB
saving of 0.6 - 1.2 megawatts power
consumption (carbon footprint)
>£250,000 capital cost saving plus 5
figure savings on annual running costs

32. www.invc.co.uk
Fan Silencing – without silencers

33. Fan Noise Control Options
Techniques by priority and cost effectiveness….
•Control at source
engineering modifications
efficiency – lowest fan noise coincides with maximum efficiency
vibration isolation and vibration damping
Only if the above are not practical should you consider…
•Silencing
•Enclosures
www.invc.co.uk
•Lagging
•Barriers
•Building modifications
Conventionally, these
high cost techniques
have been the only
measures that are
considered….

34. Remote Control of Noise
video
sound
photos
@
@
www.invc.co.uk
BPM
BAT
Costs
Specialised analysis
database
experience
email
-internet

35. Remote Control of Noise
www.invc.co.uk
Romanian power station
Roof-top fans
Laundry fan
Garage A/C plant
Ship unloading
Punch press

36. www.invc.co.uk
Remote Control of Noise
BP Refinery: $1.25m conventional silencers: $0.25m via
engineering – no impact on efficiency, no site visit

37. Noise Control Best Practice
www.invc.co.uk
noise
Fan Noise Control
Best Practicable Means (BPM)
Industrial Noise and Vibration Centre: www.invc.co.uk