Front A Practical Guide To Noise And Vibration Control For HVAC Systems
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- figures
- Introduction
- Chapter 1
- Chapter 2
- Chapter 3
- Chapter 4
- Chapter 5
- Chapter 7
- Chapter 8
- Appendix A
- Appendix B
- Appendix C
- tables
- Chapter 1
- Chapter 2
- Chapter 3
- Chapter 5
- Chapter 7
- Appendix A
- Appendix B
- Appendix C
- A Typical Approach
- A Better Approach
- Summary of This Guide
- Main.pdf
- System Type Determination
- Preliminary Equipment Selection
- Mechanical Room Sizing
- Figure 1-1 Guideline for duct chase, shaft, and enclosure sizing.
- Space Planning
- Figure 1-3 Guidelines for the preliminary selection of mechanical room walls.
- Slab Selection
- Mechanical Equipment Rooms and Outdoor Equipment Areas
- Central Plants
- Figure 1-7 Downward noise control using an auxiliary ceiling.
- Figure 1-10 Electrical conduit routing into a mechanical room.
- Air-Handling Unit Rooms
- Figure 1-11 Pipe lagging for noise control includes a compressible spacer layer and a heavy barrier layer.
- Figure 1-12 Examples of rumbly and quieter parallel fan installations.
- Built-Up Air-Handling Systems
- Figure 1-13 Guidelines for a basement built-up fan system.
- Figure 1-14 Typical duct silencer arrangement at vane-axial fan.
- Equipment Room Walls and Slabs
- Wall Selection
- Figure 1-15 Reflected and refracted equipment sound at a building perimeter. Do not locate noisy equipment near a roof perimeter where this can happen.
- Wall Penetrations
- Duct Chases · Shafts · Enclosures · Laggings
- Location
- Figure 1-18 Duct and pipe penetrations through walls.
- Sizing
- Construction
- Figure 1-19 Plan view of return air shaft with supply duct takeoffs obstructing return airflow.
- Figure 1-20 Acoustical comparison of several duct chase, shaft, and enclosure constructions.
- Figure 1-21 Two typical duct laggings.
- Figure 1-22 Noise control duct enclosure.
- Figure 1-2 Acoustical comparison of various building core area layouts.
- Figure 1-4 Sample mechanical penthouse equipment layout.
- Table 1-1. Maximum Mid-Span Deflections for Above-Grade Structures that Support Vibration-Isolated HVAC Equipment
- Table 1-2. Selection Guidelines for Slabs Separating Mechanical Equipment Rooms from Noise-Sensitive Occupied Spaces
- Figure 1-5 Labyrinth air path used for sound attenuation at an equipment room ventilation opening.
- Figure 1-6 Upward noise control for mechanical rooms.
- Figure 1-8 Section views through two types of floating floor assemblies.
- Figure 1-9 Sound transmission at perimeter mechanical rooms.
- Figure 1-16 Structural support of rooftop equipment for vibration control.
- Figure 1-17 Guidelines for mechanical room wall selection.
- Fans
- Centrifugal Fans
- Figure 2-1 Inlet and discharge octave band LW values for a 925 mm plenum fan.
- Inline Fans
- Mixed Flow Fans
- Figure 2-2 Sound power level comparison for three types of centrifugal fans.
- Plenum Fans
- Figure 2-9 Inlet side of a direct- drive plenum fan.
- Power Roof Ventilators
- Panel Fans
- Figure 2-11 Power roof ventilators (mushroom fans) mounted on intake duct silencers and roof curbs.
- Ceiling Exhaust and Cabinet Fans
- Figure 2-12 Mushroom type exhaust fan on vibration-isolated roof curb.
- Air-Handling Units (AHU) and Fan-coil Units (FCU)
- Air-Handling Units (Draw-Through and Blow-Through)
- Air-Handling Units Using Plenum Fans
- Figure 2-19 Minimum clearance at AHU and cabinet fan inlet.
- Fan-coil Units
- Terminal Units (CAV, VAV, and Fan-powered VAV Boxes)
- Figure 2-22 Guidelines for VAV unit installation.
- Figure 2-23 Laboratory air valve and its “noise flow” directions.
- Laboratory Air Valves
- Grilles, Registers, and Diffusers (Air Devices)
- Duct System Components
- In-Duct Attenuation
- Figure 2-24 Good inlet duct connection to a supply air ceiling diffuser. With a straight flex duct path, the diffuser will produce the manufacturer’s cataloged noise levels.
- Figure 2-26 The effect of installing a damper behind a grille.
- Breakout Transmission Loss (BTL)
- Figure 2-27 Attenuation for lined and unlined sheet metal ductwork.
- Self-Noise
- Figure 2-28 Breakout transmission loss for three types of sheet metal ductwork.
- Duct and Plenum Linings
- Figure 2-33 In-duct attenuation for various duct liner thicknesses.
- Fiberglass Ductboard
- Elbows and Takeoffs
- Flexible Ducts
- Duct Silencers, Plenums, and Acoustical Louvers
- Duct Silencers (Also Called Sound Traps, Duct Attenuators, Mufflers)
- Acoustical Plenums
- Acoustical Louvers
- Figure 2-50 Basis for fan selection in a VAV system.
- Special Variable-Air-Volume (VAV) System Concerns
- Fans and AHUs
- Control System
- Raised floor air distribution
- Figure 2-3 Guidelines for centrifugal fan installations.
- Figure 2-4 Inline fan airflow patterns.
- Figure 2-5 Cutaway view into a mixed flow fan.
- Figure 2-6 Inline fan sound power level comparison.
- Figure 2-7 Guidelines for ducted axial flow fan installations.
- Figure 2-8 Guidelines for unducted axial flow fan installations.
- Figure 2-13 Inlet octave band LW comparison for three propeller fans.
- Figure 2-14 Propeller fan with a 12-socket aluminum hub and plastic blades. This fan can be selected for use with 2, 3, 4, 6, 8, 9, or 12 blades of any custom length or blade twist to optimize airflow and acoustical performance.
- Figure 2-15 Ultra-low-noise propeller fan with backswept airfoil blades. Versions of this fan are available with 2, 3, or 4 blades of adjustable blade twist and diameters up to 12.3 m for very large capacities.
- Figure 2-16 Lined hood for propeller fan noise control.
- Figure 2-17 Vibration isolation suspension for propeller fans.
- Figure 2-18 Noisy and quiet installations of ceiling-mounted exhaust fans.
- Figure 2-20 Plenum AHU with supply ducts attached to the top of discharge plenum.
- Figure 2-21 Cutaway sketch of a plenum fan air-handling unit.
- Table 2-1. Suggested Maximum Airflow Velocities for Various Ductwork Installations
- Table 2-2. Suggested Maximum Airflow Velocities in Elbows for Rectangular Ductwork
- Figure 2-29 Guidelines for minimizing regenerated noise in elbows.
- Figure 2-30 Guidelines for minimizing regenerated noise in takeoffs.
- Figure 2-34 The speaking tube (cross-talk) problem.
- Figure 2-31 Guidelines for minimizing regernated noise in transitions and offsets.
- Figure 2-32 Guidelines for minimizing regenerated noise in duct tees.
- Figure 2-35 Attenuation of rectangular elbows with and without turning vanes (lined and unlined).
- Figure 2-36 Attenuation of rectangular and radius elbows (lined and unlined).
- Figure 2-37 Flexible duct with spunbond nylon inner liner.
- Table 2-3. Acoustical Characteristics of the Various Types of Ductwork
- Figure 2-40 Cutaway view of a reactive (“packless,” “no-fill,” or “no-media”) duct silencer.
- Figure 2-41 Cutaway view of an elbow duct silencer.
- Figure 2-46 General guidelines for sound-attenuating plenum design.
- Figure 2-47 Acoustical louver cutaway.
- Figure 2-48 Sound transmission loss of acoustical and weatherproof louvers.
- Figure 2-49 Acoustical louver in a parking garage ventilation shaft.
- Figure 2-38 Cutaway view into a dissipative duct silencer.
- Figure 2-39 Cutaway view of a duct silencer with film-lined baffles.
- Figure 2-44 Guidelines for duct silencer placement near fans and duct fittings.
- Figure 2-42 In-duct attenuation of duct silencers and lined ductwork.
- Figure 2-43 Comparative insertion loss of dissipative, film-lined, and reactive duct silencers.
- Figure 2-45 Duct silencer placement near a mechanical room wall.
- Figure 2-51 Nested inlet vanes obstruct airflow.
- Figure 2-52 Variable-frequency drive.
- Chillers
- Figure 3-1 Water-cooled screw chiller with several noise and vibration control treatments.
- Figure 3-2 ARI-370 LW values for a 875 kW air-cooled chiller with and without factory noise reduction options.
- Cooling Towers · Evaporative Coolers· Air-Cooled Condensing Units
- Figure 3-3 ATC-128 octave band LP values at 15 m from the air inlet side of three types of 2800 kW cooling towers.
- Figure 3-4 ATC-128 octave band LP values for cooling towers of the same fabrication series but with fans of different diameters.
- Figure 3-7 ATC-128 octave band LP values for cooling towers with “standard” and wide-chord fan blades.
- Figure 3-12 Low-noise control sequence for a two-cell cooling tower.
- Boilers
- Figure 3-13 Pump impeller sizing guideline for minimizing the strength of the blade passage frequency tone.
- Pumps
- Figure 3-14 Proper installation of an end-suction pump.
- Piping Systems
- Figure 3-15 Proper installation of an inline pump.
- Table 3-1. Maximum Recommended Waterflow Rates
- Figure 3-5 View of “standard” cooling tower induced-draft fan.
- Figure 3-6 View of an induced-draft fan with wide-chord blades. This fan type can be as much as 12 dBA quieter than a “standard” fan of the same diameter.
- Figure 3-8 Cooling tower basin with free-falling condenser water.
- Figure 3-9 Honeycomb water basin silencers installed several centimeters above the water surface to reduce the velocity of the falling water before it hits the basin.
- Figure 3-10 Outdoor noise control barrier installation.
- Figure 3-11 Close-up view of a sample of a sound-absorbing, outdoor noise barrier panel. The perforated front layer faces the noise source. Noise penetrates through the perforations and is absorbed by the fibrous fill material. The solid back layer c...
- Figure 3-16 Vibration isolation for piping riser. The use of neoprene pads under the steel load-distributing plates indicates that the nearby occupancy was not very noise-sensitive. For more critical cases, steel spring isolators would be used.
- Figure 3-17 Duct and pipe penetrations through walls.
- Figure 3-18 Sealing pipe penetrations for sound isolation.
- Rooftop Package Units (Air-Conditioning and Air-Handling Versions)
- Water-source Heat Pumps
- Wall-mounted Package Units
- Small Commercial and Residential Split Systems (under 35 kW)
- Figure 4-7 Small condensing unit noise control.
- Standby, Emergency, and Distributed Energy Generator Sets
- Figure 4-11 Outdoor condensing unit typically used with ductless split systems; it can also be used with ducted fan coil units.
- Figure 4-12 Remote radiator for engine-generator sets can be quiet with an oversized, variable-speed cooling fan.
- Figure 4-1 Very noisy rooftop unit installation.
- Figure 4-2 Moderately noisy rooftop unit intallation.
- Figure 4-3 Moderately quiet rooftop unit installation.
- Figure 4-4 Quietest rooftop unit installation.
- Figure 4-5 Guidelines for suspended heat pump units.
- Figure 4-6 Guidelines for floor-mounted heat pumps.
- Figure 4-8 Guidelines for fan coil unit installations.
- Figure 4-9 Guidelines for vibration isolation of split systems.
- Figure 4-10 Indoor fan coil section of a ductless split system. This type of equipment with a variable-speed tangential fan can be very quiet.
- Isolator Types
- Type 1—Ribbed or Waffled Neoprene Pad or Compressed Fiberglass Pad
- Figure 5-1 Elastomeric pads. The elastomeric bushing inserted in the metal load-distributing plate prevents metal-to-metal contact between the plate and its thru-bolt.
- Type 2—Neoprene-in-Shear or Compressed Fiberglass Floor Mount
- Figure 5-2 Elastomeric or compressed fiberglass isolation mounts are used where a static deflection less than 10 mm is needed.
- Type 3—Steel Spring Floor Mounts and Hangers
- Figure 5-5 Spring hanger installation with proper spring compression and hanger rod centered through hole at bottom of hanger box.
- Type 4—Restrained Spring Isolator
- Base Types
- Other Isolator Types
- Figure 5-6 Two types of spring floor mounts with seismic/wind-loading standby restraints. The mount on the left is for low loads and static deflections under 25 mm. The mount on the right is for larger loads and static deflections greater than 25 mm.
- Figure 5-9 Thrust restraint at mid-height of fan inlet panel prevents contact between the panel and the equipment housing framework. An identical restraint is installed on the opposite side of the fan.
- Figure 5-12 Floor mount spring isolator under a height-saving bracket with a separate seismic restraint.
- Special Concerns with Seismic and Wind-Loading Restraints
- Figure 5-13 Pump mounted on combination isolator/restraint under height- saving bracket. This type of isolator is not recommended because it is prone to short-circuiting.
- The Importance of the Supporting Structure
- Table 5-1. Vibration Isolation Selection Guide
- Figure 5-3 Seismically rated elastomeric mounts. The mount on the left (75 mm tall) has a nominal load rating of about 40 kg. The mount on the right (165 mm tall) has a nominal load rating of as much as 700 kg.
- Figure 5-4 Two types of spring floor mounts. The mount on the left is for low loads and static deflections of less than 25 mm. The mount on the right is for larger loads and static deflections greater than 25 mm.
- Figure 5-7 Pneumatic isolators (“air bags”) supporting a rooftop air-cooled chiller. Thin metal tubing connects 700 kPa compressed air to each isolator.
- Figure 5-8 Cast-metal floor mount is prone to “short-circuiting” and should never be used. Instead, use a floor mount like that shown in Figure 5-6.
- Figure 5-10 Flanged and threaded flexible pipe (pump) connectors.
- Figure 5-11 Braided metal pump connector is not an effective vibration isolator.
- SAMPLE SPECIFICATIONS
- Fans
- Air-Handling Units and Fancoil Units
- Chillers
- Duct Silencers
- Vibration Isolators
- Duct and Plenum Liners
- Terminal Units
- EXAMPLES OF HOW “NOT” TO SPECIFY
- VALUE ENGINEERING (COST-CUTTING)
- SUBMITTALS and SHOP DRAWING REVIEWS
- Fans, Air-Handling Units (AHU), and Fancoil Units (FCU)
- Table 7-1. Common Value Engineering Proposals and Their Potential Acoustical Impacts
- Table 7-2. Procedure for Converting from A-Weighted LW Values to Unweighted LW Values
- Terminal Units and Lab Air Valves
- Air Devices
- Water-Source Heat Pumps
- Cooling Towers and Evaporative Coolers
- Water-Cooled Chillers
- Air-Cooled Chillers
- SHOP DRAWINGS
- Figure 7-1 Overhead plan views of AHU rooms showing the effects of a duct offset.
- SITE INSPECTIONS
- Figure 7-2 Properly installed dual-duct variable air volume unit. The unit is installed high in the plenum cavity and the two inlet ducts are straight for several duct diameters upstream of the unit. Airflow is from right to left.
- Figure 7-3 Check of large duct elbow verifying screw attachment of turning vanes.
- Figure 7-4 Conduit debris short-circuiting isolator effectiveness. The small piece of flexible conduit forms a rigid contact path between the equipment frame and the slab, allowing equipment vibration to bypass the spring. Also note that the spring i...
- Figure 7-9 Taut outdoor “flexible” conduit forms a vibration “short-circuit” at cooling tower. The grillage under the cooling tower is resting on spring isolators, but the short conduit between the disconnect and the roof penetration transmit...
- Figure 7-10 Pipe risers without vibration isolation. The pipe clamps transmit pipe vibration to the slab.
- Figure 7-5 Overloaded spring hanger.
- Figure 7-6 Overloaded free-standing floor mount. The overloading allowed the gussets welded to the side of the equipment frame to rest on top of the isolator baseplate. The lower right corner of the gusset was burned off to eliminate the gusset/basep...
- Figure 7-7 Short-circuited floor mount isolator whose shipping shims have not been removed.
- Figure 7-8 Faulty spring hanger installation with hanger rod touching the hanger box. This allows pipe vibration to bypass the spring and enter the building structure above.
- GENERAL APPROACH
- Figure 8-1 Frequency ranges of the most likely sources of common acoustical complaints.
- SPECIFIC COMPLAINTS
- Buzz
- Click—Intermittent
- Drumming: “It sounds like a drum roll or a machine gun”
- Hiss
- Hum
- Roar: “It's as noisy as when I'm driving on the freeway”
- Rumble: “I can see the walls shaking and can almost hear/feel the air vibrating around me”
- Figure 8-2 Example of poor fan discharge duct design. The mitered elbow with turning vanes and steep transition downstream of the fan outlet cause fan instability and accompanying noise and rumble. A better installation would have used a horizontal d...
- Figure 8-3 Fan installation with poor discharge duct system aerodynamics. The close-coupled discharge damper and reverse-direction elbow create extremely high turbulence that creates rotating fan stall, performance reduction, and rumble.
- Squeal
- Surge: “The roar or hum comes and goes about once every second or so”
- Tap
- Throb
- Whine
- Whistle
- Figure 8-4 Restrained spring isolator with a “short circuit” between its baseplate and equipment mounting plate. This type of isolator has become obsolete and is not recommended for any type of HVAC equipment.
- SITE INSPECTION PHOTOGRAPHS
- Figure 8-5 View into the fan section of a rooftop unit; the tight cabinet clearance and airflow obstructions at the fan inlet cause excessive turbulence, pressure drop, and noise.
- Figure 8-6 Excellent rooftop package unit installation; the unit is resting on spring isolators and an elevated frame, thereby avoiding contact with the roof.
- Figure 8-7 Improperly installed fan-powered variable-air-volume unit. The unit is resting on the ceiling grid. This allows unit vibration to transmit directly into the partition below. The partition then acts as a sounding board, radiating noise into...
- Figure 8-8 Proper installation of an indoor self-contained packaged HVAC unit. Note the dual radius supply duct split on top of the unit; the return air sound traps to the left of the supply duct, the black plenum liner on the mechanical room wall, a...
- Figure 8-9 Closely spaced circular duct fittings produce turbulence and noise. This duct run does not follow the guideline recommending 3 duct diameters between adjacent fittings. It has five fittings within 8 m.
- Figure 8-10 Closely spaced rectangular duct fittings produce turbulence and noise. A better offset around the pipes could have been made with a duct section on a 45° slope between the vertical and horizontal sections.
- Figure 8-11 Improper duct transition at fan inlet. The high-velocity airflow in the short, abrupt transition between the fan outlet and the vertical duct causes turbulence and rumble.
- Figure 8-12 Vane-axial fan intakes too close to wall. Airflow through the restricted area between the fans and the wall causes turbulence, surging, and rumble.
- Figure 8-13 Duct split using radius elbows. This design is preferred because it produces less pressure drop and noise than a bullhead tee.
- Figure 8-14 Faulty installation of a large equipment isolator with stanchion restraints. The spring top plate is touching the near stanchion and the equipment mounting plate is resting on the stanchions. Both conditions allow equipment vibrations to ...
- Figure 8-15 Proper installation of a large equipment isolator with stanchion restraints. Note that the springs are centered between the stanchions and are properly compressed and that the equipment mounting plate is floating about 6 mm above the stan...
- Figure 8-16 Braided metal pump connectors do not provide significant vibration isolation.
- Figure 8-17 Neoprene pump connectors provide better isolation of pump vibration from attached piping.
- Figure 8-18 Incomplete vibration isolation at cooling tower. Even though the tower is isolated, the condenser water pipe supports are mounted rigidly to the roof. This allows some tower vibration to enter the roof structure.
- Figure 8-19 Taut “flexible” conduit forms a vibration short-circuit at vane-axial fan. Spring isolators under the vane-axial fan perform as expected, but the tight conduit arc transmits fan vibration into the disconnect, which is rigidly supporte...
- Figure 8-20 Correctly installed flexible conduit between electrical disconnect and motor. The flexible installation reduces fan and motor vibration in the floor slab.
- Figure 8-21 View of pipe penetration from below roof. The pipe on the right is contacting the left edge of its penetration. This installation allowed pipe vibration to excite the roof slab, which radiated the energy as noise.
- Figure 8-22 Non-isolated pipe penetration. Rigid contact allows pipe vibration to enter the wall, which radiates the energy as noise.
- Figure 8-23 Improperly placed neoprene hanger. The drywall assembly forms a vibration transmission bridge across the isolator. This type of interference can be identified and corrected in pre-construction coordination meetings.
- AIRBORNE and STRUCTUREBORNE SOUND
- Figure A-1 Airborne and structure-borne sound transmission.
- BASIC TERMINOLOGY
- Figure A-2 Airborne and structure-borne sound transmission from equipment.
- Decibel
- Figure A-3 Chart for adding decibel values.
- Frequency
- Figure A-4 Everyday sound sources—their frequencies and wavelengths.
- Octave Bands
- Sound Pressure Level
- Figure A-6 Sound pressure levels of some everyday activities.
- Table A-2. Subjective Impressions of Sound Level Differences
- Sound Power Level
- CHARACTERISTICS OF HVAC NOISE
- Figure A-5 Frequencies at which various types of HVAC equipment generally control their sound spectra.
- Table A-1. Octave Band Center Frequencies and Their Frequency Ranges
- A-WEIGHTED SOUND LEVEL (dBA)
- Figure B-1 Frequency weighting curves. Effects of linear, A-weighting, and C- weighting filters.
- C-WEIGHTED SOUND LEVEL (dBC)
- LOUDNESS LEVEL (SONES)
- ROOM CRITERIA (RC) and RC Mark II
- NOISE CRITERIA (NC) AND BALANCED NOISE CRITERIA (NCB)
- Which Rating Method is Best?
- ACCEPTABILITY CRITERIA
- Indoor Sound Criteria
- Table B-1. Recommended Indoor Sound Criteria
- Outdoor Sound Criteria
- Speech Communication in a Noisy Environment
- Table B-2. Industrial Noise Levels Requiring Employer Action
- Table B-3. Sample Municipal Code Limits
- Figure B-7 Quality of speech communication in background noise.
- Figure B-2 Blank RC chart.
- Figure B-3 Blank RC mark II chart.
- Figure B-4 Blank NC chart.
- Figure B-5 Octave band spectrum rated at NC-45.
- Figure B-6 Blank NCB chart.
- Instrumentation
- Measurement Plan
- Figure C-1 Sound level meter with a foam windscreen protecting its microphone.
- Figure C-2 Sound measurement plan.
- Vibration Measurements
- Table C-1. Adjustment Values for Determining Equipment Sound Levels in the Presence of Constant Background Noise
- Figure C-3 Blank sound measurement data sheet.
- Figure C-4 Completed sound measurement data sheet.
- DEFINITIONS
- ABBREVIATIONS
- BOOKS
- INDUSTRY MANUALS, HANDBOOKS, AND BULLETINS
- INDUSTRY PERIODICALS
- JOURNALS