Post on 04-Apr-2018
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Industrial
Military Aviation
HVAC
OEM
Architectural
EnvironmentalMarine
ASHRAE Chapter MeetingASHRAE Chapter Meeting
HVAC Noise & Vibration ControlHVAC Noise & Vibration Control
Specifications & Best PracticesSpecifications & Best Practices
Presented By
Noise & Vibration Control, Inc.610-863-6300
www.brd-nonoise.com
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☺ Brief Intro to Acoustics
☺ Specification Best Practice
☺ Treatment Best Practices
TopicsTopics
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Why Acoustics Matter!Why Acoustics Matter!
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Important Acoustic Terminology
• Loudness vs. Pitch
• Decibels: Sound Power vs. Sound
Pressure
• Decibel Weighting Networks• Tonal Content
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A 1K Hz tone at 60 dB would require a
102 dB tone at 20 Hz to sound as loud tothe human ear.
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Common 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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PWL vs. SPLSound Power vs. Sound Pressure
Cause vs. Effect
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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 dBA5 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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(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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☺ Common SpecificationStrategies
☺ Specifications Types
☺ Specification Best
Practices
Sub TopicsSub Topics
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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 SpecificationCommon SpecificationStrategiesStrategies
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Common Spec Strategies on NoiseSensitive Projects
• Specify sound data for lowest rated model asequipment basis of design
• Specify all available OEM equipment low noiseoptions
• 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 thespecification
• Specify base equipment and address any
noise problems at start-up
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Published Sound Power Data
(No OEM Sound Kit Options)
OverallA-Wtd
63 125 250 500 1000 2000 4000 8000 (dBA)
1 97 94 92 97 90 88 84 82 97
2 102 103 99 99 98 94 87 84 102
3 67 70 79 83 89 91 88 80 95
4 93 99 97 100 97 91 88 80 105
Sound Power Levels (dB)Octave Band Center Frequency (Hz)
4 Different
Manufacturers &
Chiller Models
(Screw and Scroll
Designs)
Published Sound Pressure Data at 30’ Away
(No OEM Sound Kit Options)Overall
A-Wtd
63 125 250 500 1000 2000 4000 8000 (dBA)1 70 67 65 70 63 61 57 55 70
2 75 76 72 72 71 67 60 57 75
3 40 43 52 56 62 64 61 53 68
4 66 72 70 73 70 64 61 53 74
Octave Band Center Frequency (Hz)
Sound Pressure Levels 5 (dB) @ 30'
4 Different Chiller Manufacturers &
Models (Screw and
Scroll Designs)
Common Specification Strategies:
Specify sound data for lowest rated model as equipment basis of design
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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 6052 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 SoundPressure Levels
Z C A 1 2
1 6
2 0
2 5
3 2
4 0
5 0
6 3
8 0
1 0 0
1 2 5
1 6 0
2 0 0
2 5 0
3 1 5
4 0 0
5 0 0
6 3 0
8 0 0
1 k
1 k 2 5
1 k 6
2 k
2 k 5
3 k 1 5
4 k
5 k
6 k 3
8 k
1 0 k
1 2 k 5
1 6 k
2 0 k 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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☺ Performance
☺ Design
☺ Allowance
Specification TypesSpecification Types
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Performance Specifications
• Typical performance descriptors – Sound Power and/or Sound Pressure
– Octave band and/or overall dB and/or dBA levels
– NC or RC levels• Relies on the acoustical credibility of the equipment
manufacturer – May or may not have the capabilities needed
– Commonly will take an exception
• Spec is difficult to enforce – AHRI 370, AHRI 575, AHRI 260, etc...
• Spec is often not based on project target levels atreceiver positions
• Performance spec may or may not address equipmentintegration issues (operating performance, maintenance,etc…)
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Performance Specification Example
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Performance Specification Example
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Contradictory Performance Specification
Sound attenuation solution quiet
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Contradictory Performance Specification
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Design Specifications = “Just Right Prescription”
• Evaluates noise sensitive location(s) to provide
– Predictable Performance
– Accountability
– Cost Control
• Right amount of attenuation
• Accounted for in the budget
• Describes, provides performance, and/or
illustrates (schematic details) the materials andproducts needed
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Design Specification
Schematic Design
Detail
ABC model JJJ
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SchematicDesign Detail
Design
Specification
ABC solution/model
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“Loose” Design Specification
ABC . . . . . . . . . . . . . . .
Result of a “Loose/Generic” spec
What is criteria for approving or rejecting?
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“Better” Design Specification
ABC model and manufactured by ABC company or equivalent.
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“Detailed” Design Specification
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“Best” Design Specification
Attenuation
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“Best” Design Specification Cont’d
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Allowance Specifications
• Equivalent advantages of pre-
purchased equipment – Provides the right material that is
wanted on the project
• Assures needed design will be built• Levels the playing field for bidders
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Allowance Specification
ABC Acoustic Attenuation DEF Company.
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Specification BestSpecification BestPracticesPractices
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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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Take Away
• Location specific performance is “king”
and drives the design spec• Design specs provide “just the right”
knowledge of costs that can get into
the budget• Acoustic treatments/solutions need to
be in the equipment spec to ensurepredictable performance,acceptability, and accountability
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☺ Construction Trends
☺ Specifications
☺ Vibration Isolation☺ Chiller Noise Treatments
☺ Roof Mounted Treatments
☺ Duct Work & Silencers
☺ Rooftop Unit Treatments
Sub TopicsSub Topics
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Construction Trends• Less mass in building
• Less space between floors• Curb mounted equipment
• Drop ceilings
• Premium for rentable/usable space• Value Engineering
• Heightened sensitivity of owners
• ANSI S12.60• LEED
B t P ti
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Best Practices
• Thickened slab above and
below
• Floating floors
• Pneumatic isolation systems
• 6 sided enclosures• Stay away from midpoints of
column spans
• Buffer from noise sensitive
spaces• Source & path acoustic
treatments
Indoor Chillers
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Source Treatments
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Source Treatments
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Critical Design Factors• Broadband Performance
• Tonal Performance
• Aerodynamic Performance
• Operating Efficiency• Operating Costs
“S ft” E l P th T t t
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“Soft” Enclosure Path Treatments
“Hard” Enclosure Path Treatments
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Hard Enclosure Path Treatments
B t P ti
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Best Practices
Outdoor Chillers• Thickened slab for
rooftop
• Evaluate loudness and
tonal content
• Special consideration for
remote evap piping• Evaluate building and
property line noise
• Optimize aerodynamicand acoustic performance
• Source and path acoustic
treatment
C S T t t
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Compressor Source Treatments
Sound Blankets
• Treat all accessible compressor circuit
components• 3 to 4 lb. surface density
• Fit/refit attachment features must be “user
friendly”
• UL 764C Listed
T ti C Ci it
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Treating Compressor Circuits
Result of “generic” spec
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Result of generic spec
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Air Intake Source Treatments
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Condenser Fan Source Treatments
• Acoustical plenums
• Plenum with baffles
• Plenum with silencer bank
• Individual stack silencers
Open Plenums
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Open Plenums
Plenum with Baffles
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Plenum with Baffles
Plenum with Silencer Bank
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Plenum with Silencer Bank
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Not Recommended by OEMs
“Dedicated” Stack Silencers
Path Treatments
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Wall and Fence Liners
Turnkey Acoustical Barrier Walls
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y
20+ dBA Attenuation Systems
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20 dBA Attenuation Systems
Best Practices
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• Integral vibration/seismic
curb
• Lock down internal
isolation
• Add mass inside curbs
• Seal (acoustic) duct
drops
• Dissipate supply breakoutnoise above deck
• Plenum style acoustic
curbs
Rooftop CurbMounted AHU
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Poor “Best Practice”
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Poor Best PracticeThis is a seismic job!
In-Curb Treatment
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Best Practices
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RTU Configurations• Increase plenum liner thickness
• Utilize RTU discharge plenums on the supplyside
• Avoid vane type flow modulation devices. VFD
controllers are preferred• Slower fan speeds = lower noise levels
• Evaluate fan wheel types. Backward inclined (BI)
and aerofoil (AF) wheels are preferred over forward curved models (FC)
Integrated Sound Attenuators
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External
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External
Acoustic Duct
Lagging
7 - 9 dB reduction in first 3
octave bands
Rooftop Unit Condenser Section
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Treatments
Best Practices
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Roof Mounted Equipment onDunnage Steel
• Restrained isolators if spring• UV compatible shear mounts
• 3” to 4” thickened slab 8’ to 10’ around unit
perimeter
• Locate over utility space
• Keep away from skylights and operablewindows
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Cooling Towers• Similar to Chiller strategies
• Restrained spring isolators• Condenser fan discharge
treatment
• Path treatments
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Best Practices
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Vibration Isolation• Follow ASHRAE guidelines for static deflection
• Review actual deflections• Isolate pipes and ducts at riser and wall
penetrations
• Avoid suspended piping in mechanical roomsbelow noise sensitive space
• Avoid cantilevered loads
• Proper adjustment of isolator lockdowns
and snubbers
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Acoustical Sealant
in ½” Gap Acoustical Batt Mineral Fiber
Packing
Pipe and Duct Penetrations
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Best Practices
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• Concrete inertia bases
• Support elbows on base
• Open springs
• Seismic snubbers for
base• Molded neoprene flexes
• Vibration isolationhangers for 50’ or entiremechanical room
• Acoustic treatment rarelyneeded
Pumps
Best Practices
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• Avoid high pressure
drop models
• Evaluate self
generated noise
• Apply ∆p correction
factors
• Stay 3 equivalent ductdiameters away from
fittings
AHU Duct Silencers
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Guidelines for Sound Trap PlacementNear Fans and Duct Fittings
Best Practices
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Avoiding Respirable Fibers
• Fiber free reactive duct silencers
(packless)
• Media wrap of packed silencers
with spacers• Closed cell thermal insulation
• Open cell melamine foams
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Best Practices
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Duct Design
• Follow ASHRAE guidelines
• Follow SMACNA guidelines• Control ductwork aspect ratios
• Increase gauge and stiffening near units
• Double wall duct
• Duct shape
• Target velocities consistent with targetNC goals
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Turbulence = Regenerated Noise
Regenerated Noise at Fittings
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Recommended maximum airflow
velocities for various installations
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Duct
Shapes
Best Practices
R Diff
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• Select diffusers for 6 to 8NC points below roomtarget NC
• Long radius 90° flexes todiffusers add 1 to 3 NCpoints
• “Kinked” flexes add 7 to 9
NC points• Balancing dampers
should be located threeequivalent duct diameters
away from diffusers andfittings
• Open plenum returngrilles may require linedelbow
Room Diffusers
Best Practices
VAV B
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VAV Boxes
• Lined discharge 10’ to 15’
• First take-off minimum 3’ from discharge
• Single duct VAV 1500 – 1700 CFM
• Fan powered VAV 1100 – 1200 CFM• External wraps for casing radiated noise
Recommended VAV Detail
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Removable Wraps Reduce
R di t d N i
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Radiated Noise
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