ASHRAE Chapter Meeting HVAC Noise & Vibration Control ...

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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 to

the 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. SPL Sound 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 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

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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 Specification

Strategies

☺ 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 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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Published Sound Power Data

(No OEM Sound Kit Options)

Overall

A-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 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


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 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


� 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 at receiver positions

• Performance spec may or may not address equipment integration 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 and

products needed

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Design Specification

Schematic Design

Detail

ABC model JJJ

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Schematic

Design 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 Best Specification Best

PracticesPractices

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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 ensure predictable 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

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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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Critical Design Factors

• Broadband Performance

• Tonal Performance

• Aerodynamic Performance

• Operating Efficiency

• Operating Costs

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“Soft” Enclosure Path Treatments

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“Hard” Enclosure Path Treatments

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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 aerodynamic

and acoustic performance

• Source and path acoustic

treatment

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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

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Treating Compressor Circuits

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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

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Open Plenums

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Plenum with Baffles

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Plenum with Silencer Bank

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Not Recommended by OEMs

“Dedicated” Stack Silencers

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Path Treatments

Wall and Fence Liners

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Turnkey Acoustical Barrier Walls

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20+ dBA Attenuation Systems

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Best Practices

• Integral vibration/seismic

curb

• Lock down internal

isolation

• Add mass inside curbs

• Seal (acoustic) duct

drops

• Dissipate supply breakout

noise above deck

• Plenum style acoustic

curbs

Rooftop Curb

Mounted AHU

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Poor “Best Practice”This is a seismic job!

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In-Curb Treatment

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Best Practices

RTU Configurations

• Increase plenum liner thickness

• Utilize RTU discharge plenums on the supply

side

• 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)

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Integrated Sound Attenuators

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External

Acoustic Duct

Lagging

7 - 9 dB reduction in first 3

octave bands

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Rooftop Unit Condenser Section

Treatments

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Best Practices

Roof Mounted Equipment on

Dunnage 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 operable

windows

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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

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 rooms

below 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

• Concrete inertia bases

• Support elbows on base

• Open springs

• Seismic snubbers for base

• Molded neoprene flexes

• Vibration isolation hangers for 50’ or entire mechanical room

• Acoustic treatment rarely needed

Pumps

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• Avoid high pressure

drop models

• Evaluate self

generated noise

• Apply ∆p correction

factors

• Stay 3 equivalent duct

diameters away from

fittings

Best Practices

AHU Duct Silencers

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Guidelines for Sound Trap Placement

Near Fans and Duct Fittings

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Best Practices

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

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 target NC goals

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Turbulence = Regenerated Noise

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Regenerated Noise at Fittings

Recommended maximum airflow

velocities for various installations

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Duct

Shapes

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Best Practices

• Select diffusers for 6 to 8 NC points below room target NC

• Long radius 90° flexes to diffusers add 1 to 3 NC points

• “Kinked” flexes add 7 to 9 NC points

• Balancing dampers should be located three equivalent duct diameters away from diffusers and fittings

• Open plenum return grilles may require lined elbow

Room Diffusers

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Best Practices

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

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Recommended VAV Detail

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Removable Wraps Reduce

Radiated Noise

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