ASHRAE Chapter Meeting HVAC Noise & Vibration …utahashrae.org/wp-content/links/HVAC Noise and...
Transcript of ASHRAE Chapter Meeting HVAC Noise & Vibration …utahashrae.org/wp-content/links/HVAC Noise and...
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Industrial
Military Aviation
HVAC
OEM
Architectural
EnvironmentalMarine
ASHRAE Chapter MeetingASHRAE Chapter Meeting
HVAC Noise & Vibration ControlHVAC Noise & Vibration Control
Best PracticesBest Practices
Presented By
Noise & Vibration Control, Inc.
610-863-6300
www.brd-nonoise.com
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Why Acoustics Matter!Why Acoustics Matter!
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☺ Introduction to Acoustics
☺ Fundamental Design
Questions
☺ Acoustic Materials
TopicsTopics
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Important Acoustic Terminology
• Loudness vs. Pitch
• Tonal Content
• Decibels: Sound Power vs. Sound
Pressure
• Decibel Weighting Networks
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Loudness = Quantity of Sound
Pitch = Quality of Sound
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What Is The Decibel Scale?
The decibel (dB) is a dimensionless unit calculated using the ratio of a
measured value (p) to a reference value (ref). The values of sound
pressure of most interest range from the threshold of hearing at about 20
µPa to a level of extreme danger at about 200 Pa. This range of
variation translates to 7 orders of magnitude with the high level being
10,000,000 times that of the lower threshold. The use of a logarithmic
scale compresses the unit of measure to a manageable range in order to
simplify calculations, computations and quantitative manipulation of data.
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200
170
160
150
140
130
120
110
100
90
80
70
60
50
40
30
20
10
0
108
105
104
103
102
101
100
10-1
10-2
10-3
10-4
10-5
10-6
10-7
10-8
10-9
10-10
10-11
10-12
100,000,000
100,000
10,000
1,000
100
10
1
0.1
0.001
0.0001
0.00001
0.000001
0.0000001
0.00000001
0.000000001
0.0000000001
0.00000000001
0.000000000001
0.0000000000001
Saturn Rocket
Turbojet Engine
Jet Aircraft at Takeoff
Turboprop at Takeoff
Prop Aircraft at Takeoff
Large Pipe Organ
Small Aircraft Engine
Blaring Radio
Automobile at High Speed
Voice, Shouting
Garbage Disposal Unit
Voice Conversation Level
Ventilation Fan
Office Air Diffuser
Small Electric Clock
Voice, Soft Whisper
Rustling Leaves
Human Breath
Threshold of Hearing
Decibel re: 1012 WWatts – ExponentialWattsSource
200
170
160
150
140
130
120
110
100
90
80
70
60
50
40
30
20
10
0
108
105
104
103
102
101
100
10-1
10-2
10-3
10-4
10-5
10-6
10-7
10-8
10-9
10-10
10-11
10-12
100,000,000
100,000
10,000
1,000
100
10
1
0.1
0.001
0.0001
0.00001
0.000001
0.0000001
0.00000001
0.000000001
0.0000000001
0.00000000001
0.000000000001
0.0000000000001
Saturn Rocket
Turbojet Engine
Jet Aircraft at Takeoff
Turboprop at Takeoff
Prop Aircraft at Takeoff
Large Pipe Organ
Small Aircraft Engine
Blaring Radio
Automobile at High Speed
Voice, Shouting
Garbage Disposal Unit
Voice Conversation Level
Ventilation Fan
Office Air Diffuser
Small Electric Clock
Voice, Soft Whisper
Rustling Leaves
Human Breath
Threshold of Hearing
Decibel re: 1012 WWatts – ExponentialWattsSource
Actual Scale versus Decibel Scale
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Sound wavelengths are the linear measurement
of one full cycle of displacement where the motion
of air molecules is first compressed and then
expanded (forming a pressure pulsation). The
wavelength is determined by the ratio of the speed
of sound to the frequency.
Wavelength (ft)
= Speed of Sound (fps) / Frequency (Hz)
The rate at which these pulsations occur is
called the frequency and is described in
cycles per second (1 cycle per second equals
1 Hz). Each cycle is one complete expansion
and compression.
Frequency and Wavelength
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A 1K Hz tone at 60 dB would require a
102 dB tone at 20 Hz to sound as loud to
the human ear.
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Decibel Addition:
10 log (10dB/10 + 10dB/10 + …)
For example, 87 dB + 87 dB
= 10 log (1087/10 + 1087/10)
= 10 log (108.7 + 108.7)
= 10 log (1.00237 x 109)
= 10 (9.00103) = 90 dB
Calculation Tools
Sound Power to Sound Pressure:
dB = Lw – ((20 Log dist in ft) - 2.4)
For example, at 30'
dB = Lw – ((20Log30) - 2.4)
= Lw – ((20*1.477) - 2.4)
= Lw – (29.5 - 2.4) = Lw - 27.1
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A-weighting network is designed to approximate the human hearing response.
Note that curve is similar but opposite the equal loudness contours.
Octave Band Center Frequency, Hz
31.5 63 125 250 500 1000 2000 4000 8000
A-weighting -39 -26 -16 -9 -3 0 +1 +1 -1
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What is the overall dBA level?
Octave Center Unweighted A-weighting A-weighted Overall
Band Frequency Sound factor (dB) Sound Resultant
Pressure (dB) Pressure (dBA) Level
1 63 94 -26 68
2 125 86 -16 70
3 250 85 -9 76
4 500 89 -3 86 91 dBA
5 1,000 89 0 89
6 2,000 77 1 78
7 4,000 75 1 76
8 8,000 76 0 76
86
89
Decibel
Addition
72
86
89
79
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Why is it important to know dB versus dBA?
946170808589898785dBA
94626979859298103111dB
-1
8k
110-3-9-16-26A-scale
Total
dBA4k2k1k50025012563
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What is Sound Pressure?Decibels of sound pressure (Lp) have a universally
accepted reference pressure of 2.0 x 10-5 Pascals (Pa).
Lp = 20 log10 [Root Mean Square (RMS) Sound Pressure]
2.0 x 10-5 Pa (Reference Pressure)
What Is Sound Power?Decibels of sound power (Lw) have a universally accepted
reference value of 10-12 watts (1 picowatt).
Lw = 10 log10 Watts Sound Power
10-12 Watts (Reference Value)
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PWL vs. SPL Power vs. Pressure
Cause vs. Effect
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Extreme Danger
Threshold of Pain
Threshold of Discomfort
Very Loud
Moderate
Faint
Threshold of Hearing
140
130
120
110
100
90
80
70
60
50
40
30
20
10
0
200.0
63.2
20.0
6.3
2.0
0.6
0.2
0.06
0.02
0.006
0.002
0.0006
0.0002
0.00006
0.00002
Military Jet Takeoff @ 100 ft
Artillery Fire @ 10 ft
Passenger Ramp at Airport
Loud Rock Band
Platform of Subway Station
Large Diesel Engine @ 130 ft
Computer Printout Room
Freight Train @ 100 ft
Conversation Speech @ 3 ft
Window Air Conditioner
Quit Residential Area
Whisper @ 6 ft
Buzzing Insect @ 3 ft
Threshold of Good Hearing
Threshold of Youthful Hearing
Subjective Reaction
Sound Pressure Level dB
SoundPressure
Pa
Typical Sound Pressure Levels
Extreme Danger
Threshold of Pain
Threshold of Discomfort
Very Loud
Moderate
Faint
Threshold of Hearing
140
130
120
110
100
90
80
70
60
50
40
30
20
10
0
200.0
63.2
20.0
6.3
2.0
0.6
0.2
0.06
0.02
0.006
0.002
0.0006
0.0002
0.00006
0.00002
Military Jet Takeoff @ 100 ft
Artillery Fire @ 10 ft
Passenger Ramp at Airport
Loud Rock Band
Platform of Subway Station
Large Diesel Engine @ 130 ft
Computer Printout Room
Freight Train @ 100 ft
Conversation Speech @ 3 ft
Window Air Conditioner
Quit Residential Area
Whisper @ 6 ft
Buzzing Insect @ 3 ft
Threshold of Good Hearing
Threshold of Youthful Hearing
Subjective Reaction
Sound Pressure Level dB
SoundPressure
Pa
Typical Sound Pressure Levels
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Sioux Falls, SD Municipal Code defines tone as:
“any sound which can be distinctly heard as a single pitch or set of single pitches…. and shall exist
of the one-third octave band sound pressure level in the band when the tone exceeds the arithmetic
average of the sound levels of the two contiguous one-third octave bands by five dB for frequencies
of 500 Hz and above, eight dB for frequencies between 160-400 Hz, and by 15 dB for frequencies
less than or equal to 125 Hz.”
Tonal Noise
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Recommended NC levels for various room uses
• OSHA, MSHA, etc.
• Company policy
• Bldg criteria for human comfort
• Local ordinance:
generalcode.com
municode.com
noisepollution.org
amlegal.com
Outdoor Objective Criteria
State, City, Township Ordinances
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www.generalcode.com
www.municode.com
www.noisepollution.org
www.amlegal.com
Researching Outdoor Objective
Criteria
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System Problems Require System
Solutions
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System Problems Require System
Solutions
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(Sound Levels 270 ton Air Cooled Chiller)
-37-37-37-37-37-37-37-37-37Loss100’
1008185929497999890Lw
634448555760626153Lp
A8K4K2K1K50025012563Freq (Hz)
1. Where are we now?
2. Where do we need to be?
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13182022171410----Needed
Attenuation
502628334046526167Ordinance
634448555760626153Chiller
A8K4K2K1K50025012563Freq (Hz)
3. How much noise reduction is required?
4. What needs to be done to achieve compliance?
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ABSORBERS BARRIERS COMPOSITES
DAMPING ELECTRONIC FLOW CONTROL
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Covers Discharge StacksSilenced Discharge
Stacks
Wall Treatments Barriers Enclosures
Air-Cooled Chillers
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Covers Soft Enclosures Hard Enclsoures
Covers Acoustic CurbsDischarge Stacks and
Acoustic Screens
Water-Cooled Chillers
Rooftop Units
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A Specification Should Provide
“Just the Right Prescription”
• Accountability
• Cost Control
• Predictable Performance
• Review of subjective and objective noise
criteria
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Common Specification Common Specification
StrategiesStrategies
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Common Spec Strategies on Noise
Sensitive Projects• Specify sound data for lowest rated model as
equipment basis of design
• Specify all available OEM equipment low noise options
• Specify an equipment model that is not tonal
• Specify the same treatment used on the last noise sensitive project
• Retain an acoustical consultant to write the specification
• Specify base equipment and address any
noise problems at start-up
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Sound Pressure Data for property line 80’ away
(No OEM Sound Kit Options)Overall
A-Wtd
63 125 250 500 1000 2000 4000 8000 (dBA)
1 61 58 56 61 54 52 48 46 61
2 66 67 63 63 62 58 51 48 66
3 31 34 43 47 53 55 52 44 60
4 57 63 61 64 61 55 52 44 66
Sound Pressure Levels 5 (dB) @ 80'
Octave Band Center Frequency (Hz) 4 Different Chiller
Manufacturers &
Models (Screw
and Scroll
Designs)
Sound Pressure Data for property line 80’ away
(with factory OEM options)Overall
A-Wtd
63 125 250 500 1000 2000 4000 8000 (dBA)
63 57 57 59 54 48 44 42 60
52 60 61 59 56 54 46 41 62
31 33 43 46 49 51 48 42 56
57 63 61 61 60 55 52 42 64
Sound Pressure Levels 5 (dB) @ 80'
Octave Band Center Frequency (Hz)
4 Different Chiller
Manufacturers & Models
(Screw and Scroll
Designs)
None of the chillers will comply with typical nighttime
noise ordinance values of 50 to 55 dBA.
Common Specification Strategies:
� Specify sound data for lowest rated model as equipment basis of design
� Specify all available OEM equipment low noise options
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Scroll Chiller Sound
Pressure Levels
Z C A 12
16
20
25
32
40
50
63
80
100
125
160
200
250
315
400
500
630
800
1k
1k25
1k6
2k
2k5
3k15
4k
5k
6k3
8k
10k
12k5
16k
20k Hz
30
40
50
60
70
80
90
100dB
Screw Chiller Sound
Pressure Levels
Common Specification Strategies:
� Specify an equipment model that is not tonal
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Best Practices
Acoustic Design
• Answer 4 design questions
1. Where are we now?
2. Where do we need to be?
3. What needs to be done to get there?
4. How much will that cost?
• Use 3-5 dBA safety factor
• Cursory review on every project, in depth review when
warranted
• Assess site ambient noise levels
• Evaluate airborne and structure-borne transmission
• System problems require system solutions
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Best Practices
Specifications
• Job specific combined design/performance specs
preferred over generic performance specs
• Evaluate project specific objective and subjective criteria
– Indoor criteria: NC, RC, NCB, RC Mark II
– Outdoor criteria: Zoning and ordinance criteria
• Place in Division 15/23 with equipment
• Specify single source for system acoustic performance
• Specify turnkey where installation critical
• Require submission for approval as “or
equal” 10 days before bid date
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