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ACT Technical Meeting, 9 March 2016
Acoustics for HVAC EngineersPresented By
Jerremy Lofts
Contents
Basics of Acoustics Environmental Noise in the ACT
Internal Noise RequirementsVibration Control Basics
Important Acoustic Design Principles
Noise and sound levels – InterchangeableNoise typically “unwanted sound”
We will look at: Internal and external noise sourcesBarriers & EnclosuresNoise reduction through building elementsAcoustic absorption and reverberation
Noise Level Descriptors
Decibel – dBA measure of sound energy – Logarithmic
A Weighted Decibel – dB (A) or dBAWhat we hear
130 dBA Jet engine, top fuel dragster
120 dBA Hammer Drills, grinders, jackhammers etc.
110 dBA Rock band or night club
100 dBA Child screaming, dog barking
90 dBA MP3 player through earphones
80 dBA 4 stroke lawn mower
70 dBA Light vehicle traffic
60 dBA Typical speech level is about 65 dBA
50 dBA Occupied office, Quiet conversation
40 dBA Unoccupied office
20 dBA to 30 dBA Quiet bedroom
Spectral Content of NoiseBoth are 86 dBA
0.0
10.0
20.0
30.0
40.0
50.0
60.0
70.0
80.0
90.0
No
ise
Le
vel (
dB
)
0.0
10.0
20.0
30.0
40.0
50.0
60.0
70.0
80.0
90.0
No
ise
Le
vel (
dB
A)
1/3 Octave Band Centre Frequency (Hz)
Statistical Noise LevelsN
ois
e L
evel
Time
Lp L10 Leq L90
Sound Power and Sound Pressure
Sound Power – Raw sound energy emitted
Sound Pressure – Noise level at a given distance
Reverberant Field, Near Field and Far Field
Effect of Objects
Effect of Atmosphere
Measurement Methods and Standards
Environmental Noise in the ACT
Environmental Noise in ACT
Environment Protection Act 1997
Environment Protection Regulation 2005 includes Schedule of Noise Zones and Noise Standards
Environment Protection Policy – Jan 2010
Outdoor Concert Noise Environment Protection Policy 2001
Motor Sports Noise Environment Protection Policy 2002
It is the responsibility of the person/entity making the noise to ensure Noise Standards are achieved, regardless of “who was there first”
ACT Noise Standards Summary Seven noise zones – defined by land zones under the Territory Plan Each zone has a day standard and a night standard
Day7am to 10pm Monday to Sat8am to 10pm Sunday and public hols
Night10pm to 7am Monday to Sat10pm to 8am Sunday and public holidays
Zone based - not use/occupancy based Relatively Consistent – set standards, not based upon background noise Allowance for zone boundaries – averaging Standards Boundary compliance location (Typically, but can change) LA10 based – most manufacturer data is LAeq based Covers mechanical or electronically amplified noise sources Does not cover noise from people or crowds
ACT Noise Standards Summary
Table
Typical Noise Sources
Transport / mobile sources - road, rail, aircraft
Fixed / Mechanical sources – chillers, dry coolers, condensers, cooling towers, fans, pumps, generators
Natural Sources – Birds and insects, wind, rain, hail, thunder
Other sources – people and crowds, maintenance and construction, roadworks
Environmental Noise Example
Example – Encroachment of Noise Sensitive Receivers
Night Noise Standard V’s Distance
30
35
40
45
50
55
60
65
70
75
0 5 10 15 20 25 30 35 40 45 50 55 60
No
ise
Le
vel (
dB
A)
Distance from Source (Metres)
Point Source - Nominal Distance Noise Reduction
70 dBA Reference Level Zone A Zone B Zone C Zone D / Zone G Zone E
Solution 1
Barrier
Approximately 10dB reduction (Frequency dependent)
Advantages
Relatively Inexpensive
Simple design and construction
Disadvantages
Shadowing and loss of light and vision
Often not enough noise reduction
Note: All solutions assume we cannot make a new fan selection
Solution 2 Attenuators and/or Ductwork
Can be designed to achieve required reduction (within limits –generally determined by length and pressure drop)
Advantages
Moderate noise attenuation achievable
Disadvantages
Can be expensive
Fans need to be capable of running with attenuators
Noise from underneath may still be a problem
Solution 3 Enclosure
Can be designed to achieve required reduction (within limits –generally determined by space constraints)
Advantages High noise attenuation achievable
Disadvantages Can be very expensive Restricts air flow to equipment – can lead to increase in
running costs – especially if supplementary fans necessary Manufacturer limitations regarding airflow and warranties Shadowing and loss of light and vision
ExampleEnclosure
Problem 2 - Loss of Barrier Effect
Solutions
– Essentially the same
– Attenuator
– Enclosure or increased barrier height
Acoustic Barriers and Absorbers Acoustic barriers are continuous, solid panels that block
sound Eg. Concrete, Plasterboard, timber, Wavebar
Acoustic absorbers are blankets/batts that absorb sound Eg. polyester, glasswool or Rockwool insulation
Rigid, lightweight panels (eg. polystyrene) are poor barriers and poor absorbers
A combination of a barrier and an absorber works extremely well when designing enclosures and barriers
Acoustic Attenuators
Common Types:
Splitter Attenuator
Circular podded/non-podded
Cross-Talk
Internally Lined Ductwork – Thickness important
Acoustic Barriers (Walls)Heavy v’s Lightweight Construction
0
10
20
30
40
50
60
70
80
50 63 80
100
125
160
200
250
315
400
500
630
800
1000
1250
1600
2000
2500
3150
4000
5000
Sou
nd
Tra
nsm
issi
on
Lo
ss (
dB
)
1/3 Octave Band Centre Frequency (Hz)
Rw 54 Concrete Rw 54 Stud Wall
Acoustic EnclosuresWall Integrity
10
15
20
25
30
35
40
45
50
55
60
50 63 80 100 125 160 200 250 315 400 500 630 800 1000 1250 1600 2000 2500 3150 4000 5000 Rw
Tran
smis
sio
n L
oss
(d
B)
Frequency (Hz)
Insulated wall Wall with 3mm gap along wall head
Acoustic Enclosures – Internal Linings
Problems with Solutions
Barriers may not be able to be built high enough
There may not be enough room to implement a solution
Ideal solution may be extremely expensive
Either solution may restrict air flow
Equipment may not be capable of operating under such conditions
Recirculation of air probable with barriers
May void manufacturer warranty
Internal Noise Levels
Australian Standards
AS/NZS 2107:2000 is the primary acoustic design standard for all buildings
Sets recommended satisfactory and maximum internal noise levels and reverberation times
Used to assess steady state or semi steady-state building services noise
Used to assess road traffic noise
Not used to assess noise from building occupants
Not used to assess intermittent or irregular noise
Background Noise levels• Goal – Low, even noise levels – Noise Rating (NR)
10
20
30
40
50
60
70
80
90
100
110
31.5 62.5 125 250 500 1000 2000 4000 8000
Sou
nd
Lev
el (
dB
)
Frequency (Hz)
NR 20
NR 30
NR 40
NR 50
NR 60
NR 70
NR 80
Good Mechanical Design
Vibration Control
Vibration Isolation Efficiency
Source: Embelton
Vibration Deflection Guide
Source: Embelton
Important Principles
Correct mount selection – type and rating
Provide full isolation of all components
Machine
Pipework
Cable reticulation (cable trays etc.)
Ductwork
Install and adjust correctly during commissioning
JERREMY LOFTSPrincipal Acoustic Consultante: [email protected]
t: 02 6240 2964 or 0438 017 087 f: 02 6280 9951
a: Unit 1, 5 Bodalla Pl, Fyshwick ACT 2609
