hvac noise control · 2019. 3. 22. · generator noise control solutions are like puzzles consider...

HVAC Noise ControlAdding Value and Reducing Project Risk Through Noise Control

(1 PDH / CEU)

Garrett Hartwellghartwell@vibro-acoustics.com

Game Plan Acoustics 101 Silencer Demo Common Noise Problems System Effect & System Design Breakout Noise Application Specific Solutions

Roof Top Units Generators Air Cooled Chillers

What is Noise?

Sound Pressure Level (SPL)

What we can measure and hear Measured in pascals/decibels

at some distance Threshold of hearing: 0 dB Threshold of pain: 140 dB

Sound Power Level (PWL)

Sound

50 80 100 160 200 315 400 630 800 1250 1600 2500 3150 5000 6300 10000

HVAC Noise (sound quality)

16 31.5 63 125 250 500 1,000 2,000 4,000 8,000

RUMBLE ROAR WHISTLE HISSTHROB

Fan InstabilityTurbulent Airflow

Fan & Pump Noise

VAV Unit Noise

Chillers

Diffuser Noise

Hz

Poor vibration isolation Frequency ranges of likely sources of sound-related complaints (ASHRAE handbook)

Formula

(c) = speed of sound through air = 1,128 ft/sec(λ) = c/f where (f) is frequency

(λ) Wavelength at…63 Hz 17.90 ft

125 Hz 9.03 ft

250 Hz 4.51 ft

500 Hz 2.26 ft

1000 Hz 1.13 ft

2000 Hz 0.56 ft

4000 Hz 0.28 ft

8000 Hz 0.14 ft

What is Dynamic Insertion Loss> Difference in sound pressure levels at a given point before and after the installation of noise

reduction equipment while under flow. Measured in dB.> It is essentially a measure of the amount of noise that the silencer or other equipment is

removing.

63 125 250 500 1000 2000 4000 8000"Typical" IL Required 4 8 11 12 11 9 6 410' of 30x24 duct w/1" lining 2 2 5 13 27 21 17 1510' of 30x24 duct w/2" lining 3 3 9 24 34 21 17 15RMB-MLV-F9x36 - 0.19"wg@1000fpm 3 5 12 24 35 28 19 13RMB-MLV-F1x36 - 0.19"wg@1000fpm 4 9 14 15 18 16 14 12

0

5

10

15

20

25

30

35

40

Insertion Loss Data Table, dB, per Octave Band, Hz

Lined duct reduces PDhowever it performs poorly in the critical lowoctave bands (63 Hz, 125 Hz & 250 Hz)

These 3 octave bands are where most AHU fan problems occur

Duct-Liner: Fiberglass

Wrong silencerCorrect silencer

CORRECT IL

Optimal Silencer

NC - Requirement

Where To Apply Noise Control In A Building

> Most occupied spaces have free ducted supply and free plenum returns

> Openings are required between spaces to make sure that air moves freely between spaces

CROSS-TALK SILENCERS VS. AIR TRANSFER DUCTWORK

Reference ASHRAE for some basic guidelines?

Our 50 years of experience allows us to design within ASHRAE guidelines on your project

We have identified 14 common noise path problems when applying NC to HVAC systems

Common problem #1 - Installed Pressure DropIdeal laboratory (Catalog) selection vs actual operating conditions

ASHRAE (Chapter 48 – Sound & Vibration Control): Do not locate the silencer in close proximity (3 to 5 duct diameters) to any fan, elbow, plenum, fitting, or other flow disturbing device

(ASTM E-477)*: Leave at least 5 diameters of straight duct on the silencer inlet and 10 diameters on the silencer outlet

*This is the test method used to obtain catalog data… what does the installed pressure drop look like if you don’t have that much straight duct available?

System Effects

• Increase silencer pressure drop

• Increase in airflow generated noise

CFD Analysis

Straight silencer next to elbow

Duct Silencer

Scheduling System Effects

Catalog

BREAK OUT

2nd common problem with this approach

•A Technical Analysis is always needed to determine where break-out will occur and how much break-out will happen

•The location of the silencer in the system is more important than the silencer itself

•HTL (High Transmission Loss) casing is needed. What thickness?

Break-Out

•Noise Risk Assessment

•Product selection, fit the silencer to the duct layout, not the other way around.

•Breakout Calculation and System Effect Pressure Drop (CFD Analysis)

•Silencer Spec and Schedule

Noise Risk Assessment

Product Selection• Without compromising your building design

• In the actual space, not only in ideal test conditions

• And add value (Space, IAQ, Energy, and Total Cost)

Silencer Spec and Schedule

Rooftop Units

Most common HVAC solution in the industry…

Inexpensive…

Why?

Most common noise control problem with Roof Top Units• Lighter weight building construction

• Packaged equipment (AHUs), located closer to the occupied space

• Higher sound power levels of equipment (higher RPM, AC, etc)

Break-Out

Rooftop Units – High Sound Power Levels

– Minimal budget for noise control– Lighter weight construction (RTU)– Tight footprints – Smaller fans spinning at high RPMs

Rooftop Units – Design Practice

– Ideally, where do you locate an RTU? Over the occupied space

Rooftop Units – Design Practice

Why?

1. Energy efficient design – less pressure drop & thermal losses2. Lower building cost – Less material and installation labor 3. Space saving design – Ceiling space4. Time saving design – Do not have to design duct runs

However, high sound power levels + locations directly over the occupied space = Noise Problems & Client complaints

Less Ductwork

Rooftop Noise, Vibration, & Seismic/wind problems

Integrated Noise Control Curb

RTU Integrated System Solution

GENERATORSCummins 2.5 MW Units

GENERATOR NOISE CONCERNS

Noise transmission through air intake opening

Noise transmission through engine exhaust

Noise build-up due to reverberation inside room

Noise transmission through building walls and roof

Noise transmission through air discharge/exhaust opening

Noise transmission through the floor of the room

Noise break in/out from the air intake duct

Noise break in/out from the air discharge/exhaust duct

Intake Silencer Banks

Transitional Silencers

Generator noise control solutions are like puzzlesConsider all noise paths.

Intake Silencer/LouversTo reduce noise transmission

Targets problem 1

HTL (High Transmission Loss)

Targets problems 7 8

Discharge Silencers/LouversTo absorb noise transmission

Targets problem 5

Floating FloorsTo reduce noise transmission

Targets problem 6

Absorption PanelTo absorb noise and reduce noise reverberation

Targets problem 3

Acoustic PanelsTo reduce noise transmission

Targets problem 4

GENERATOR NOISE CONTROL SOLUTIONS

Transitional silencers: attenuate sound and keep to a space restraint

GENERATOR NOISE CONTROL SOLUTIONSMISAPPLIED SILENCERS - TRANSITIONS

Air Flow

Dead Zone

Dead Zone

Transition is too abrupt between exhaust and plenum/silencer

Abrupt transition will not allow air to expand fully

Dead zones may cause eddies, backflow, and increased PD

Air Flow

Dead Zone

GENERATOR NOISE CONTROL SOLUTIONSTRANSITIONAL SILENCERS

Air Cooled Chiller Noise Control

• Environmental Noise concerns for Residential and Commercial (dBA Levels)• Equipment has multiple cooling fans on top (multiple noise sources)• Compressors can be problematic and require the unit to be enclosed• Units produce broadband noise (compressors and cooling fans)

“Noisy” Air Cooled Chiller Components• Compressors – Most produce tonal noise• Reciprocating – Noise has a “drumming” quality caused by pistons – decreased

capacity does not affect SPL level – No longer used• Scroll – Have weak tonal noise – one of the best for reducing noise• Screw (Helical / Rotary) – Strong tones in 250 Hz to 2000 Hz bands – resonances

can be present – This type has most complains and requires most attention to address

Noise Control Solutions for Air Cooled Chillers

• Circular Discharge silencer application• Center bullet of silencer matches fan hub diameter for “static regain”

condition

Noise Control Solutions for Air Cooled Chillers

• Noise Control solution with acoustical screen wall and Discharge Silencers

Noise Control Solutions for Air Cooled Chillers

• Noise Control solution with integrated components (Zero PD Enclosure)

Noise Control Solutions for Air Cooled Chillers

• Noise Control solution with integrated components (Intake / Discharge Silencers)

Thank you!Garrett Hartwell

ghartwell@vibro-acoustics.comVibro-Acoustics

The application of the product is more important than the product itself