1. FG Wilson Acoustics Session Wednesday 18th April – Stream 4 – 11:30 – 12:40

2. Acoustics in Generator Applications Section A:
Acoustics in Generator Applications Section A: 11:30 – 12:00 Section B: 12:10 – 12:40

3. Section A: Acoustics Agenda Generator Noise - Background
Vibration Isolation
Engine firing sequence effects
Packaged Generator – advantages / disadvantages
Generators over residential units
Section B:
Noise and vibration issues associated with pipework and cabling
Common Issues noise and vibration control
A good specification document
Summary of the testing methods available and how useful they are.
Interesting case studies

4. Mechanical Considerations
ENERGY
25-35%
Engine Radiation
(~3%)
Exhaust
39%
20-30%
Electricity
Radiator
Alt In-efficiency
(~5%)
# Noise < 1% of Energy Balance #

5. Generator Noise
FAN NOISE
ENGINE NOISE

6. Sound Power Sound Power (SWL) Does not vary with distance
The average amount of sound energy being transferred by a sound source to the surrounding environment over a given period. (Unit: Watt)
Does not vary with distance
Is a characteristic
of the vibrating
object

7. Sound Pressure Sound Pressure (SPL) Varies with distance
The perceived noise level at a given point from the sound source.
(Unit: Pascal)
Varies with distance

8. 30dB 195dB Range of Sound - dB 0.000000001 Watt - whispering voice
40,000,000 Watts
- Concorde at Take-Off
30dB
195dB

9. Generator – Open Set Noise Data
Typical Spectra – Single Octave and A-Weighted

10. Spectra
Sound Waves
Noise Data is made up of waves of many different frequencies

11. Typical Generator Noise Spectra
1/3 Octave Analysis
(Typical V-12 Cylinder)
Single Octave Analysis

12. Accuracy of Sound Measurement
Measurement of noise:
Hemi-Anechoic Chamber
Free Field Environment
Reverberant Effect
Absorptive Effect
Accurate noise levels offer cost effective and compact acoustic solutions

13. Make-up of Spectra Open sets as either 6 or 8 Position Array
1/3 Octave Analysis
(Typical V-12 Cylinder)
Usually analysed as A-Weighted

14. Achieving Noise Requirement
To achieve the required noise level we must Attenuate this sound source
~ 116dB
52dBA

15. Difficult / Transmits / Flanking Risk
Acoustic Treatment
We require the implementation of different methods and techniques in the reduction of various frequencies
Restrictive / Troublesome
Difficult / Transmits / Flanking Risk
Standard Methods

16. Treatment Attenuation Reducing the amount of noise
emanating from a noise source.
2 Basic Methods
Sound Absorption
Vibration Isolation.

17. Treatment Nothing Distance Solid barrier Absorptive attenuation
Reactive attenuation

18. Treatment Distance Location of noise source
Location of noise sensitive area

19. Treatment
Solid barrier
The barrier effect

20. Treatment Thin sheet metal- Poor Sheet metal with lining- Better
Absorptive attenuation
Wall Construction
Thin sheet metal- Poor
Sheet metal with lining- Better
Concrete- Better Still
Composite wall- Good
Cavity Wall - Excellent

21. Treatment Absorptive attenuation Splitters Acoustic Louvres Gap Width
Attenuation properties based on
Gap Width
Element Width
Length
Acoustic Louvres
Single bank
Double bank
Chevron

22. Treatment Reactive attenuation Ducts / Silencers
Used for handling and directing
inlet and outlet air.
Attenuation based on
Bends
Constrictions
Enlargements
Duct length

23. Vibration
Vibration Isolation
Minimising the amount of vibrational energy transmitted to building or enclosure structure.
Degree of Isolation required often quoted as a percentage (% Isolation).
Sometimes quoted as deflection in mm
meaningless unless AVM type is specified.

24. Vibration Types of AVM Rubber Standard (75%) Spring
Higher isolation (95%)
Spring & Damper
Bespoke isolation (99%)
Captive
Anti-shear design

25. Floating floor Purpose To reduce the transmission of airborne noise
Reduce low frequency noise / vibration
Prevent flanking noise

26. Methods Employed Treatment Reactive attenuation Solid barrier
Absorptive
attenuation
Absorptive
attenuation
Vibration
isolation

27. Generator Attenuation
Acoustic louvres
Distance
Solid barrier – walls
Prevent vibration
Absorption

28. Exhaust Noise
“RAW” Exhaust Noise is measured at a distance of 1m and 90o to the flow
Temperatures tend to be in excess of oC.

29. Typical Exhaust Silencer
Absorptive / Reactive Silencer

30. Exhaust Silencer Performance
Actual Measured Performance of a “35dB” Silencer

31. Exhaust Silencer Consideration
Flow Noise:
No matter what insertion loss may be provided by the silencer system, there can be risk of noise being generated by the passage of high velocity exhaust gas through a small orifice
Dependant on:
Temperature
Flow Rate
Diameter

32. Exhaust Silencer Consideration
Addition of Silencers into Exhaust System will increase temperature & pressure
Higher temperature gas will increase volumetric flow termination point

33. Break 10 Mins Section B: 12:10 – 12:40

34. Common Acoustics Issues in Generator Applications Section B:

35. Engine Firing Order
Diesel & Gas Engines will generally be 4 Stroke Cycle
Generally:
V-Form
In-Line
The Order dictates the “Dominant” frequency

36. Packaged Generators Standard Generator Acoustic Packages
Standard Acoustic Canopies
Smaller Gensets / CHP units
Sized per family of power nodes
~ 80-85dBA (75% or 100% Load?)
Standard Acoustic Containers
Structural
Typically 65dBA, 75dBA or 1m
Bespoke Acoustic Enclosures
Can be Drop-over or Containers
Containers can have acoustic floors
From 1m upwards
Can be used as “Box in Box” for lower requirements

37. Vibration Transmission
Pipework & Cabling etc.
Reduce the transmission of vibration
Direct vibration
Vibration due to airborne noise
Methods
Use of flexible hangers and spring isolators
Flexible couplings to avoid transmission of vibration
Power cabling connection to bus duct etc.

38. Common Issues Example:
Generator canopies designed and tested for EC Noise Directive 2001
Tested to ISO3744 at 75% Load for LWA
Corrected to 1m & 7m for published data
Published 1m & 7m data assumed to be full load
Un-welcome surprise during site full load (High Frequency & Low Frequency)

39. Common Issues
Common issues that we generally find will be due to two distinct points:
Poor installation
AVM’s “bottom out”
Springs & Hangers too tight
Incomplete insulation / Gaps
Poor product selection for application
Exhaust selections
Fans

40. Good Specification Best Specifications:
Those that specify intent and quality
AVM’s
Test Methods
Method to install
That don’t “Over specify”
Sometime combinations of equipment may not be optimum when combined
Manufacturers data can be “sales orientated”

41. Test Methods Equipment Tests Product Test Data FAT testing Source data
Attenuation data
Silencers
Attenuators
AVM’s
FAT testing
Engines / Gensets
Radiators

42. Test Methods Site Testing Product and Installation Test
1m Testing
Receptor testing
Background
BS4142
24hr / 48 hr
Analysis of Peak, Max, Min LAeq etc.

43. Case Studies Exhaust Noise
Initial issues from local resident complaints
High levels at specific distances / directions

44. Case Studies Exhaust Noise Highly reverberant field
Directing noise into enclosed area
Tonal effect

45. Case Studies Exhaust Noise
After treating the reverberant field we then have a clear disturbing frequencies at receptors and directional.
Analysis of flue termination levels show low performance of exhaust silencer selection

46. Issues Case Studies Selected on levels that are 75% load
Canopy Noise
Above Planning Consent
Receptor Tonal Issues
Weather dependant
Issues
Selected on levels that are 75% load
Operating at 100%
Base tanks empty
Exhaust Silencer performance

47. Case Studies Issues Selected on levels that are 75% load
Operating at 100% is 12dB higher overall
Base tanks empty
Exciting at 40Hz with panel exciting at 100Hz
Exhaust Silencer performance
Only effective above 250Hz

48. Case Studies Measures of control Acoustic Barriers Absorptive lining
Mass added to walls of base sections
Base below canopy sealed
Silencer addition and redirection

49. Case Issues Door vibration
Low frequency noise transmitting through building structure and being perceived as “unwanted noise and vibration” at other floor levels
Typical breakout at door heads
Vibration of large span glass panels

50. Floating Floors Purpose To reduce the transmission of airborne noise
Reduce low frequency noise / vibration
Prevent flanking noise

51. Treat Airborne Noise Box in Box
To achieve very low noise levels – Typically Below 1m
To reduce the transmission of airborne noise to the building structure
Reduce the transmission of Low Frequency Vibration
To achieve low NR levels in neighbouring or lower levels

52. Thank you for your time

53. Back-up Slides For Information

54. Common Noise Requirements
NR Curves
Developed by ISO
each octave must be met
Do NOT equate to an overall SPL
Used to determine the acceptable indoor environment for hearing preservation, speech communication and annoyance

55. Common Noise Requirements
LAeq,T
The equivalent continuous A-Weighted sound pressure level measured over time T

56. Background Noise Background Noise Levels are typically
in the region of:
City day time dBA
City night time - 48dBA
Rural Land day time - 49dBA
Rural Land night time - 41dBA
These are typical levels which would
be measured over a 5 minute period.
For True Background Noise Survey, the measurement should be LA90,24hr

57. Noise effects Noise in an enclosed space
Noise within any Enclosure (Box) is dependant on the characteristics of both the Noise Source and the Box.
This is due to:
Noise being Generated.
Noise being Reflected.
Noise being Absorbed.

58. Acoustic Intensity
Noise radiates equally in all directions from source
Acoustic intensity = i
i = amount of energy passing through unit area per unit time
We perceive the noise intensity depending on how far we are from the source

59. Noise effects Directivity Factor
Each plane causes a doubling of the amount of energy being radiated.
Directivity factor 1
(free-field)
Directivity factor 2
+3 dB
Directivity factor 4
+6dB
Directivity factor 8
+9dB

60. Main contributing factors are:
Noise effects
Reverberation
This is the combined effect of Reflection & Absorbtion on the initial Sound Source.
Main contributing factors are:
The size of the room.
The size of the Sound Source.
The characteristics of the surfaces within the room.

61. Noise effects
Reverberation is the collection of reflected sounds from the surfaces in an enclosure.

62. Common Noise Requirements
X y metres
NR & NC Curves
LAeq,T
Background Noise Levels

63. What’s New