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Copyright © Carrier Corp. 2005

Technical Development Program

APPLICATIONS

Acoustics andVibration

PRESENTED BY:

Shivam VadanSigler

COMMERCIAL HVAC DIVISION


Objectives• Explain the role of acoustics in HVAC design and equipment selection

• Define fundamental terminology associated with acoustics

• Add and subtract decibel levels

• Explain the subjective effects of changes in sound levels.

• Describe NC and RC Curves

• Understanding the source, path and receiver model to evaluate sound

• Overview of which rating procedures should be applied for differentequipment types and applications

• Describe vibration and what methods are used to control it

Section 1 – Introduction


SECTION 1

Introduction

ACOUSTICS AND VIBRATION


TotalEnvironmental

Quality

AirQuality

Acoustics(Noise) Lighting Interior

Design

AirContaminants

TemperatureHumidity

Air Motion

GasesParticulates

Total Environmental Quality


ThermalProperties


Acoustic QualityIdeal Sound is Balanced, Smooth and Steady

Not Too Quiet Doesn’t Destroy Acoustic Privacy

Not Too Loud Avoid Hearing DamageDoesn’t Interfere with Speech

Not AnnoyingNo Rumble, No Hiss

No Identifiable Machinery SoundsNo Time Modulation

Not To Be Felt No Sensible Wall Vibration



SECTION 2

Acoustics Fundamentals



Sound Waves

Section 2 – Acoustic Fundamentals


Frequency (Hz)

16 31.5 63 125 250 500 1000 2000 4000

Fan InstabilityTurbulent Air Flow

Diffuser Noise

74 37 19 9.4 4.7 2.4 1.2 .60 .30 .15

RUMBLE ROAR WHISTLE HISSTHROB

Centrifugal Chillers

Fan and Pump Noise

VAV Unit Noise

Frequencies and Wavelengths

Wavelength(ft)


Low-Frequency Mid-Frequency High- Frequency

Various Types of Mechanical Equipment


Sound Pressure vs. Sound Power

Watts Sound Power(Watts)

Illumination(Lumens)

Sound Pressure(Pascal's)


LW Lp


2

1210Lp )pascal(10levelReference(pascal)levelSoundlog10dB ú

û

ùêë

é= -

Sound Pressurewatts)(10levelReference

(watts)levelSoundlog10dB 1210Lw -=

Sound Power

• Primary unit of sound measurement• Measures both sound pressure and sound power

What is a Decibel?



Sound Pressure

Threshold of Hearing0

20

40

60

90

120

Buzzing Insect

Window AC

Speech

Chiller

Air Plane andThreshold of Pain

Soun

dPr

essu

re(d

BA)



Typical SoundPressure Levels

SoundPressure

Pa

SoundPressureLevel dB

SubjectiveReaction

Military Jet Takeoff @ 100 ftArtillery Fire @ 10 ftPassenger Ramp at AirportLoud Rock BandPlatform of Subway StationLarge Diesel Engine @ 130 ftComputer Printout RoomFreight Train @ 100 ftConversation Speech @ 3 ftWindow Air ConditionerQuit Residential AreaWhisper @ 6 ftBuzzing Insect @ 3 ftThreshold of Good HearingThreshold of Youthful Hearing

200.063.220.06.32.00.60.20.060.020.0060.0020.00060.00020.000060.00002

140130120110100

9080706050403020100

Extreme Danger

Threshold of PainThreshold of Discomfort

Very Loud

Moderate

FaintThreshold of Hearing


Typical Sound Pressure Levels


Source Watts Watts – Exponential Decibel re: 1012 WSaturn RocketTurbojet EngineJet Aircraft at TakeoffTurboprop at TakeoffProp Aircraft at TakeoffLarge Pipe OrganSmall Aircraft EngineBlaring RadioAutomobile at High SpeedVoice, ShoutingGarbage Disposal UnitVoice Conversation LevelVentilation FanOffice Air DiffuserSmall Electric ClockVoice, Soft WhisperRustling LeavesHuman BreathThreshold of Hearing

100,000,000100,00010,0001,0001001010.10.0010.00010.000010.0000010.00000010.000000010.0000000010.00000000010.000000000010.0000000000010.0000000000001

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

2001701601501401301201101009080706050403020100


Typical Sound Power Levels (Power Output)


Combining Sound Sources

78dB

Pump

AHU

75dB

90dB


+

+

+

90dB

Water-Cooled Chiller


90.0 dB+ 3.0 dB

Difference in decibels betweentwo values being added (dB)

0

0.5

1

1.5

2

2.5

3

0 2 4 6 8 10

88.0 dB+ 1.7 dB

89.7 dB

1

Cor

rect

ion

tobe

adde

dto

high

erva

lue

(dB)

Decibel Addition ExampleTo add first three decibel values:

85 dB 88 dB and 90 dB1. Find the difference between

the two lowest values: 3dB2. From the chart:

Add 1.7 dB to the next higher value3. Repeat for the second, the sum and

the next value (difference is 0.3 dB)

93.0 dB



Decibel Addition Example


Total noise measuredby sound meter = 95.0 dB

Sound level with machineturned off(Background Sound) = 91.0 dB

Difference = 4.0 dB

From Chart: Subtract 2.2 dB

Machine Noise = 92.8 dB

Difference between Total Soundand Background Sound (dB)

= Total Noise

Machine Noise+ Background Noise


0

0.5

1

1.5

2

2.5

3

3 4 5 6 7 108 9

Decibel Subtraction Example


Decibel Subtraction Example

•


Difference in dB dB+• 0 to 1 3• 2 to 4 2• 5 to 9 1• 10 or more 0

Example:• 3 sound sources at 45 dB• 45 dB + 45 dB = 45 + 3 = 48 dB• 48 dB + 45 dB = 48 + 2 = 50 dB

Simplified Method to Add Multiple SourcesTo add multiple sound sources use the table



Free Field With No Reflecting Surfaces

When you double the distance between the noise sourceand the receiver (in a free field), a sound pressurereduction of 6 dB may be expected.

Where: Lp1 = Sound Pressure at distance d1

Lp2 = Sound Pressure at distance d2

Lp3 = Sound Pressure at distance d3

Noise Point Source

d2 = 2d1d1

Lp1 Lp3 = Lp2 – 6 dBLp2 = Lp1 – 6 dB

d3 = 2d2


Point Source


Point Sources

Receiver

Point source



For High Frequencies (Above 125 Hz Octave)1 dB Not Noticeable3 dB Just Noticeable5 dB Noticeable

10 dB Doubling / Halving20 dB Much Louder / Quieter

For Low Frequencies(<125 Hz Octave ... Rumble Region)3 dB Noticeable5 dB Doubling / Halving

10 dB Much Louder / Quieter

CHANGES IN SOUND PRESSURE LEVEL


Response to Sound Level Changes


Octave Bands

Sound is a combination of manyfrequencies and intensitiesFor analysis we use octave bandand 1/3 octave band



Octave Band Lower Center Upper0123456789

22.44590180355710

1,4002,8005,60011,200

31.563125250500

1,0002,0004,0008,00016,000

4590180355710

1,4002,8005,60011,20022,400


Octave Bands of Frequency (Hz)


Direct Air Path

Reflected FromCeiling

Transmitted ViaStructure

PathNoise Source Receiver


Sound is produced when there are dynamic changes in the air pressurewithin the frequency range of hearing

Source - Path - Receiver Concept


• Identify and quantify all sound sources

• Identify all possible sound paths

• Identify all attenuating elements alongsound path

Performing an Acoustic Analysis

Section 5 – Performing an Acoustical Analysis


Performing an Acoustic Analysis

Section 5 – Performing an Acoustical Analysis

• If noise level is too high, either addadditional attenuation, select quieterunits or relocate the equipment

• Pay particular attention to areas adjacentto mechanical equipment rooms

• Don't forget the return side of the system


Airborne SoundRadiated by

Vibrating StructureDirect

AirborneSound

Structure-Borne Sound(Vibration Induced by Machinery)


Airborne and Structure-Borne Sound Transmission


Transmission of Sound

Source-Path-Reciever• Size and construction of source surfaces• Sound wave frequency and amplitude• Reflecting surfaces• Ducts in the path• Barriers• Room characteristics



Noise Reduction/Insertion LossdB = 80 dB = 70

NR = 10dB

IL = 10dB

dB = 80 dB = 70

NoiseReduction

InsertionLoss



End Reflection

End Reflection



Roomto

Room

Transmission Paths


Atmospheric

Duct

Structure-Borne

Flanking


Discharge / Reflected

Radiated Sound

Return Air

ReflectedReflected

TransmittedTransmitted



Reverberation Time



Space Effect

Absorbed

Absorbed

Reflected

Reflected

carpet tile


Distance to receiverDistance to receiver


Break-out

Sound Transmitted by the Ductwork


Break-in

Turbulence generatesTurbulence generatessound waves


HVAC Sources of Noise

Motors

Aerodynamically –Generated Sound

Compressors

Pumps

Fans

Combustion


VAV Terminals

Inverters


When Sound Becomes Noise• Loud

• Unexpected

• Uncontrolled

• Contains pure tones

• Happens at the wrong time

• Unwanted or distracting information

• Unpleasant or reminiscent of unpleasant conditions

It often has many of these characteristics



SECTION 3

Acoustic Ratings and Methods



Measuring Sound

Section 3 – Acoustic Ratings and Methods

FILTERS


Methods of Rating Sound• Loudness

– phons, sone and bel (used for smaller fans)

• Weighted spectrum– A-weighted, B-weighted, C-weighted, Lin

(common for outdoor sound)• Noise Criteria (NC)

– room sound levels• Room Criteria (RC)

– room sound levels• Frequency Spectrum

– manufacturers data• Noise Reduction Coefficient (NRC)

– sound attenuating materials• Sound Transmission Class (STC)

– attenuation of a room



A, B, and C-Weighted Networks

20,00020Frequency, Hz

Rel

ativ

eR

espo

nse,

dB

Linear

-50

-40

-30

-20

-10

0

10

50 100 200 500 1,000 2,000 5,000 10,000


Copyright © Carrier Corp. 2005Section 3 – Acoustic Ratings and Methods

Noise Criteria (NC) Curves


NC Curve Example Problem

Determine:The room NC rating by plotting the sound pressure data

Given:The following measured sound pressure data:

Sound Level, dB

Octave Band, Hz 63 125 250 500 1K 2K 4K 8K

56 60 49 43 35 33 31 34

Measured Sound Data



NC Curve Example

NC rating given isNC-45 since this isthe highest pointtangent to an NCcurve



NC Curve Example 2

Both noisespectrums

would be ratedNC-35.

However, theywould subjectivelybe very different!

Typical fan noisefrom adjacent

mechanical room(low-frequency)

Typical grillenoise at adistance of 10 ft(high-frequency)



Region A:High probability that noise inducedvibration levels in light wall andceiling structures will be noticeable.Rattling of lightweight light fixtures,doors and windows should beanticipated.

Region B:Moderate probability that noise-induced vibration will be noticeablein lightweight light fixtures, doorsand windows.

Threshold ofAudibility


Room Criteria (RC) Curves


Noise Reduction Coefficient (NRC)Sound Energy Absorbed250 Hz 3 dB500 Hz 8 dB

1000 Hz 15 dB2000 Hz 25 dB

Fiberglass Panel



STC Class

DescriptionEstimated

STCRating

Wall Assembly

3-5/8” metal studs, 5/8” gyp (2 layers total),No insulation 38 to 40

3-5/8” metal studs, 5/8” gyp (2 layers total),Batt insulation 43 to 44

Staggered studs, 5/8” gyp (2 layers total),Batt insulation 46

2 x 4 studs, 5/8” gyp (2 layers total),Batt insulation 34 to 39

2 x 4 studs, 5/8” gyp (2 layers total), ResilientChannel, Batt insulation 45 to 52



Sound Fields in Testing

Lp

DistanceDirect Field Reverberant Field

Far FieldNearField

Ambient Noise



Anechoic Test ChamberMicrophones



Use of Mock-up TestSample room designed per

architects specifications


Room to be evaluatedfor sound


OSHA Sound Requirements


OSHA Compliance Strategy SummaryMeasure Noise

Exposure

50% PEL

100% PEL

115 dBA

Determine Feasibility ofEngineering Controls orAdministrative Controls

Determine cost ofHearing Conservation

Program

AreEngineering/Administrative

Controls Feasible

No Action

HearingConservation

Program

InstallEngineering

Controls and/orAdministrative

Controls

>

<

>

<

<

>

YES NO

Permissible NoiseExposures (OSHA)

Duration per Day(Hours)

Sound Level dBA(Slow Response)

86432

1 ½1½

¼ or less

90929597100102105110115

Note that OSHA permits a 5 dBincrease in permissible levels for areduction of 2:1 in exposure time(often referred to as the 5 dBexchange rate).


SECTION 4

Dinner Break

Determining Acoustic Design Requirements



Acceptable Design CriteriaOccupancy Recommended

NC or RC RangePrivate Residence 25-30Hotels/MotelsPrivate, Meeting & Banquet Rooms 25-30OfficesPrivateExecutive, Conference RoomOpen AreasComputer Rooms, Public Circulation

25-3030-3535-4040-45

HospitalsPrivate RoomsWardsOperating Rooms, Corridors, Public Areas

25-3030-3535-40

Churches/SchoolsLecture/ClassroomsOpen-Plan Classrooms

25-3030-35

Libraries & Courtrooms 35-40Movie Theatres 30-35Restaurants 40-45Concert Halls/Recording Studios 15-20TV Studios 20-25

Section 4 – Determining AcousticDesign Requirements


Steps in Selecting Outdoor Goals

1. Select a unit location thatgives the greatest distanceto the property line

2. Locate the unit to avoidareas with multiplereflection/paths

3. Select a unit with soundpower levels which willachieve the soundrequirement• Low sound options• Compressor blankets

4. Consider barriers to blocksound

Determine local code requirement for outdoor soundBest location for the unit



Typical Municipal Code Noise Limits

Note: Sound levels listed are maximum values as measured at the property line.

Maximum Sound Level (dBA)Type of District 7am to 7pm 7pm to 7am

Single Family Residential

Multi-Family Residential

Commercial

Industrial

50

55

60

70

45

50

55

70

Section 6 – Acoustic Guidelines for EquipmentSelection and Application


4. Consider sound masking andsound attenuation

5. Establish sound power requirements forthe fans, air terminals, diffusers, grilles,and all other mechanical sound sources

Steps in Selecting Indoor Goals1. Specifying too low a goal

will result in complaints2. Specifying too high a goal

will result in unnecessary cost3. Consider the Source-Path-Receiver

in establishing goals

Establish appropriate and practical acoustic goals

RC 35N



3. Use the lowest static requirements possibleHigher Static = Higher Sound• Balance System• Use realistic fan static estimate in

unit selection• Select fan to operate near peak efficiency

1. Use accurate sound power datatested or certified by ARI or AMCA

2. Locate air terminals, diffusers andgrilles to avoid noise sensitiveareas and consider discharge andradiated sound

Minimizing Noise in the Conditioned Space



5. Select Duct fittings for sound generation6. Consult ASHRAE, ARI, SMACNA, and

AMCA Guides

4. Design ductwork for sound• Consider Break out sound

in selecting duct locations• Flex duct and fiberglass

ductboard allow morebreakout sound

• Keep flex duct runs short

Minimizing Noise in the Conditioned Space



SECTION 5

Acoustic Guidelines forEquipment Selection and Application



Equipment Selection and Design Guidelines

• Identify some of the more common acoustic problemswith installing various types of equipment

• You should consult manufacturer’s specific applicationliterature in addition to using these guidelines

• Types of equipment discussed:– Rooftop Units– VAV and Fan-Powered Mixing Boxes– Central Station Air Handling Units– Outdoor Equipment– Ductwork– Grilles, Registers and Diffusers



Rooftop Unit Sound RecommendationsTypical Sound Data 63 125 250 500 1k 2k 4k 8k

Supply 91.1 91.2 89.4 83.8 76.8 70.4 62.6 52.7Return 83.1 73.2 70.4 63.8 59.8 59.4 49.6 36.7

Outdoor 100 97 95 93 92 88 87 88Watch for Rumble

RA

Condenser Fan

Compressors

Gas HeatExchangers

Supply Fan

VFD

SA

14”RoofCurb



Rooftop Unit Guidelines1. Use isolation curb on noise sensitive applications2. Insulate duct on supply and return

(except if supply is to near critical space)3. Allow at least 10 feet to the first diffuser4. Provide Plenum Space5. Stiffening Ductwork

10 ft Insulated before first diffuser

Mount unit to steel supports

Insulate with acoustic insulation andlag with gypsum board to reduce breakout

Plenum Space

IsolationCurb

Use Return Elbow


Stiffening Ductwork


Stiffening Rectangular Ductwork


•2 to 10 lb/ft2 barium-loaded wrap

•One or more layers of drywallscrewed directly to the duct

•Sometimes used with 2 or 4-inch 3lb/ft3 fiber board


Rooftop Unit Guidelines• Size units for load using diversity

– Oversized results in surge– Undersized results in high fan speed

• Use VFD rather than inlet guide vanes• Be careful of sound generated by VFD

AIRFLOW (1000 cfm)

EXT

ER

NA

Lin

.wg Select

nearpeak

RP

SC

Full flow

To avoid rumbleDO NOT operate

in this region15

%M

axim

umcf

m



1. Allow 1 to 1½ fan diameters2. Use Spring Isolators3. Provide flex connections

4. Fittings should have 15° or less angle5. Use long radius elbow with turning vanes6. Follow SMACNA

recommendations

Central Station Air Handler Guidelines



1. Use a VFD on VAV units2. Allow 3 duct diameters

before a duct fitting3. Consider double wall AHU

4. Blow through units offer best attenuation5. Seal all gaps between room walls

and ductwork

Central Station Air Handler Guidelines

VFD



Air Handler Sound Ratings

RA

RA

Outdoor Air

SA

Vibration can cause structure transition sound

SupplyAir

Sound

Casing RadiatedSound

Return AirSound



Fan Selection Guidelines

Airflow (1000 cfm)Tota

lSta

ticP

ress

ure

(in.w

g)

Airflow (cfm)

Tota

lSta

ticP

ress

ure

(in.w

g)

1. Select as efficient a fan as possible2. Operate to the right of the

Static Efficiency (SE) curve3. On VAV consider minimum part load4. Do not overestimate total static



D * cfm/1000

Sound Traps

Sound TrapD

Min Distance

15° or Less

Direct connection is permitted


SoundTrap

30° Max

SoundTrap

Centrifugal Fan

Axial Fan


Sound Traps



1. Use masonry walls with 1 to 4 in.fiberglass insulation on walls

2. Resilient sleeves on allpenetration and seal all gaps

3. Provide sound traps

Indoor Unit Recommendations

4. Use doors of at least 5 lb/ft3 with doorseals and hinges out

5. AHU room should have a area of10 to 15 ft2/1000 cfm

SoundTrap



Noise Control in Ductwork

• Should only be necessary if noise and vibration cannot becontrolled at the source

• Use ASHRAE/SMACNA design guidelines

• Internal duct lining provides excellent attenuation ofhigh-frequency noise but little for low-frequency noise (<125 Hz)

• Low-frequency duct rumble must be attenuated by the stiffnessto the duct system itself

• When common ductwork connects adjoining areas, consider asound trap to reduce “crosstalk”, if acoustical privacy is a concern

• Air velocities should be as low as possible (1750 fpm maximumfor rectangular, 3500 fpm maximum for round ductwork),to control noise generation in ducts, due to airflow



Ductwork Guidelines

Fiberglass liningfor high frequency

Gypsum board laggingfor low frequency

Flex duct allows some breakout

Design to SMACA Guidelines

For RC 35 keepduct velocityless than 1750 fpm

Insulated elbowson return grillesprevent “cross talk”

Velocity



• Establish the NC or RC ratings for all noise-sensitiveareas in the building (consult ASHRAE)

• Select supply and return air device to have amanufacturer’s NC or RC rating at least 5 dB less thanthe desired NC or RC rating

• Supply ductwork serving an air device should be straightfor at least 3 equivalent duct diameters upstream of thedevice's duct collar

• A balancing damper attached to the device’sduct collar can generate between 5 to 40 dBof additional noise

Noise Control for Grilles, Registers and Diffusers

42



SECTION 6

Identifying Acoustic Problemsand Recommended Solutions



Direct Path Control for Chiller• Direct path control• Mechanical room of nursing home• Composite acoustical

curtain enclosure

Untreated Liquid Chiller

Sliding Panel Curtain Enclosure Piping Cutouts

Section 7 – Identifying Acoustic Problemsand Recommended Solutions

(Pho

tos

cour

tesy

ofBR

DN

oise

and

Vibr

atio

nC

ontro

l,In

c.)


• Source control

• Mechanical room ofelementary school

• 22 dBA reduction of noisesource levels

• Modular solid/perforatedmetal panel enclosure

• Vibration isolation ofenclosure or machine

Enclosure WithoutRemovable Panels

Full Enclosure

Source Control for Chiller


(Pho

tos

cour

tesy

ofBR

DN

oise

and

Vibr

atio

nC

ontro

l,In

c.)


Structure Borne Sound Control

Pneumatic Isolation System

WITH SPRING ISOLATORS WITH PNEUMATIC ISOLATORS


• Source control (structure-borne)

• Mechanical room withcommon wall to auditorium

• Pneumatic isolators toreplace conventional springs

• Curtain enclosure also used

(Pho

toco

urte

syof

BRD

Noi

sean

dVi

brat

ion

Con

trol,

Inc.

)


Air-Cooled Chiller Direct Path Control

Acoustic Barrier Wallwith Acoustic Louvers

• Direct path control• Hospital in urban area• 18 dBA insertion loss• Modular solid/perforated metal

panel barrier wall

Barrier Wall During Erection


(Photos courtesy of BRD Noise and Vibration Control, Inc.)


Parallel Baffle System

Silencer Bank SystemSilencer Stack System

Unitary Panel System

Condenser Fan Noise Control Options


(Pho

tos

cour

tesy

ofBR

DN

oise

and

Vibr

atio

nC

ontro

l,In

c.)


• Duct silencers provideexcellent mid to high-frequency sound control

• Round ductwork controlslow-frequency sound

• SMACNA design guidelineshelp minimize air turbulenceand regenerated noise

• Locate first 20 feet ofsupply ductwork abovenon-sensitive spaces

In-Duct Silencing

Circular DuctSilencers

RectangularDuct Silencers


(Photos courtesy of BRD Noise and Vibration Control, Inc.)


Seismic Protection

SSE (Safe Shutdown Earthquake)– Unit survives

SnubberSpecial seismic mountsHard mount is best

Section 8 – Vibration


Vibration Isolators

Section 8 – Vibration


SECTION 8

Summary



Summary

• The industry trend is towards Total Environmental Quality,of which acoustics is an integral part

• Acoustics is an important part of the design process

• Acoustic quality must be designed into the job since it isdifficult and very expensive to achieve once the installationis complete

• Acoustic problems are SYSTEM problems, not justEQUIPMENT problems

S-4Section 10 – Summary


Technical Development Program

Thank YouThis completes the presentation.

TDP-901 Acoustics and Vibration

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