HVAC Noise and Vibration Control

7/29/2019 HVAC Noise and Vibration Control

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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!



4

Important Acoustic Terminology

• Loudness vs. Pitch

• Decibels: Sound Power vs. Sound

Pressure

• Decibel Weighting Networks• Tonal Content



5

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


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


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.


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


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



34

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



62

Poor “Best Practice”



63

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



66

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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