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Introduction <ul><li>Purpose of Course </li></ul><ul><li>Provide an Introduction to Acoustics and a Review of Practical Ap...
Outline of Presentation <ul><li>Basic Acoustical Definitions </li></ul><ul><li>Indoor Criteria </li></ul><ul><li>Mechanica...
Basic Definitions <ul><li>Amplitude (loudness) </li></ul><ul><li>Frequency (pitch) </li></ul><ul><li>Quality (character) <...
 
Perceived Loudness Rules of Thumb <ul><li>1 dB change not perceptible </li></ul><ul><li>3 dB change is perceptible </li></...
Frequency <ul><li>Frequency is Measured in Hz (cps) </li></ul><ul><li>Human Ear is not Equally Sensitive to All Frequencie...
Audible Frequency Range
Quality of Sound <ul><li>Intermittent vs. Steady-State </li></ul><ul><li>Cyclical, Repetitive, Pulsating </li></ul><ul><ul...
Indoor Noise Criterion <ul><li>Noise Criterion Curves (NC) </li></ul><ul><li>Room Criterion Curves (RC) </li></ul><ul><li>...
NC Curves
NC Curves NC 47
RC Curves
RC Curves RC 35 RVa
RC Mark II
RC Mark II
RC Mark II
ASHRAE Recommendations 1991 Applications 1999 Applications
A-Weighting <ul><li>Good Single Number Descriptor </li></ul><ul><li>Correlates Well with Human Perception </li></ul><ul><l...
A-Weighting
Equipment Source Sound Levels <ul><li>Sound Power Levels (dB, re: 10 -12  Watts) </li></ul><ul><ul><li>Total sound energy ...
Sound Power vs. Sound Pressure Total Radiated Heat/Time (BTU/hr)  ~  Sound Power Heat converts to temperature based  Sound...
Mechanical Equipment <ul><li>Air handling systems sound paths </li></ul><ul><ul><li>Ductborne, low frequency duct break-ou...
Air Handling Unit Sound Paths
Air Handling Design Guidelines <ul><li>Space Planning </li></ul><ul><li>Good intake and discharge duct conditions </li></u...
AHU Design Guidelines
Roof-top Air Handling Unit
Noise Mitigation for Roof-top Air Handling Units <ul><li>Space planning </li></ul><ul><li>Thickened slab below units (5’-8...
Roof-top Unit  Mitigation Concepts
Terminal Boxes <ul><li>Fan powered – constant volume or VAV and single duct VAV </li></ul><ul><ul><li>Discharge noise from...
Terminal Box Design Guidelines <ul><li>To Achieve NC 35 </li></ul><ul><ul><li>Box inlet static pressure ≥1.00” wg </li></u...
Terminal Box Selection
Effect of Ceiling Plenum on  Radiated Noise of Terminal Boxes <ul><ul><ul><li>Distance of box to back of ceiling tile – no...
Terminal Box Noise Example Room 109 Room 107 Room 105 Supply & Exhaust Supply Only Exhaust Only Supply - 2.2&quot; w.g. NC...
Chiller/Pump Design Guidelines <ul><li>Chillers </li></ul><ul><ul><li>Thickened structural slab (above and below) </li></u...
Chiller Vibration Isolation
Pump Vibration Isolation
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Acoustical Design Considerations

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Slides used in a May 11, 2010 presentation at the monthly meeting of the Illinois Chapter ASHRAE by David G. Paoli, P.E., senior engineer, Shiner + Associates, Inc.

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  • Guide to Mechanical System Acoustical Design June 6, 2006
  • Guide to Mechanical System Acoustical Design June 6, 2006
  • Guide to Mechanical System Acoustical Design June 6, 2006
  • Guide to Mechanical System Acoustical Design June 6, 2006 Conversational speech - ~60 dBA Typical Office - ~65-70 dBA Design a typical office to 45-50 dBA
  • Guide to Mechanical System Acoustical Design June 6, 2006
  • Guide to Mechanical System Acoustical Design June 6, 2006 Frequency well-correlated to sensation of pitch
  • Guide to Mechanical System Acoustical Design June 6, 2006 Compare Male &amp; Female Voices Piano Lowest A = 28 Hz Middle C = 256 Hz Highest C = 4096 Hz
  • Guide to Mechanical System Acoustical Design June 6, 2006
  • Guide to Mechanical System Acoustical Design June 6, 2006
  • Guide to Mechanical System Acoustical Design June 6, 2006
  • Guide to Mechanical System Acoustical Design June 6, 2006 AHU Sound from duct in ceiling plenum – Unit in MER in adjacent room
  • Guide to Mechanical System Acoustical Design June 6, 2006
  • Guide to Mechanical System Acoustical Design June 6, 2006 Same sound spectra shown on an RC curve. Note that the RC level is lower, because it is the average of the preferred speech frequencies (250 Hz – 2000 Hz) and the descriptor identifies the quality of the sound spectra.
  • Guide to Mechanical System Acoustical Design June 6, 2006 RC Mark II is a tool used for
  • Guide to Mechanical System Acoustical Design June 6, 2006
  • Guide to Mechanical System Acoustical Design June 6, 2006
  • Guide to Mechanical System Acoustical Design June 6, 2006
  • Guide to Mechanical System Acoustical Design June 6, 2006 Correlation with Loudness Speech Interference Annoyance Hearing Loss (High frequency sounds more damaging)
  • Guide to Mechanical System Acoustical Design June 6, 2006 31.5 -39 63 -26 125 -16 250 -9 500 -3 1000 0 2000 +1 4000 +1 8000 -1
  • Guide to Mechanical System Acoustical Design June 6, 2006
  • Guide to Mechanical System Acoustical Design June 6, 2006
  • Guide to Mechanical System Acoustical Design June 6, 2006
  • A – Vibration inducted structure-borne noise B – Supply system ductborne noise C – Supply system low-frequency break-out noise D – Return ductborne noise E – Radiated noise path through the wall Guide to Mechanical System Acoustical Design June 6, 2006
  • Guide to Mechanical System Acoustical Design June 6, 2006
  • Guide to Mechanical System Acoustical Design June 6, 2006
  • Guide to Mechanical System Acoustical Design June 6, 2006
  • Guide to Mechanical System Acoustical Design June 6, 2006
  • Guide to Mechanical System Acoustical Design June 6, 2006
  • Guide to Mechanical System Acoustical Design June 6, 2006
  • Guide to Mechanical System Acoustical Design June 6, 2006
  • Guide to Mechanical System Acoustical Design June 6, 2006
  • Based on studies commissioned by ASHRAE TC 2.6 conducted at the NRC, National Research of Canada Guide to Mechanical System Acoustical Design June 6, 2006
  • Guide to Mechanical System Acoustical Design June 6, 2006
  • Guide to Mechanical System Acoustical Design June 6, 2006
  • Guide to Mechanical System Acoustical Design June 6, 2006
  • Guide to Mechanical System Acoustical Design June 6, 2006
  • Transcript of "Acoustical Design Considerations"

    1. 1. Introduction <ul><li>Purpose of Course </li></ul><ul><li>Provide an Introduction to Acoustics and a Review of Practical Applications of Mechanical System Noise and Vibration Control </li></ul>
    2. 2. Outline of Presentation <ul><li>Basic Acoustical Definitions </li></ul><ul><li>Indoor Criteria </li></ul><ul><li>Mechanical System Design Guidelines </li></ul><ul><ul><li>Air handling systems </li></ul></ul><ul><ul><ul><li>Large Built-up Systems </li></ul></ul></ul><ul><ul><ul><li>Indoor Package Units </li></ul></ul></ul><ul><ul><ul><li>Roof-top Units </li></ul></ul></ul><ul><ul><li>Terminal Boxes </li></ul></ul>
    3. 3. Basic Definitions <ul><li>Amplitude (loudness) </li></ul><ul><li>Frequency (pitch) </li></ul><ul><li>Quality (character) </li></ul>
    4. 5. Perceived Loudness Rules of Thumb <ul><li>1 dB change not perceptible </li></ul><ul><li>3 dB change is perceptible </li></ul><ul><li>5 dB change is clearly noticeable by all </li></ul><ul><li>10 dB increase sounds twice as loud </li></ul><ul><li>Above discussion applies to </li></ul><ul><li>long periods of time </li></ul>
    5. 6. Frequency <ul><li>Frequency is Measured in Hz (cps) </li></ul><ul><li>Human Ear is not Equally Sensitive to All Frequencies </li></ul>
    6. 7. Audible Frequency Range
    7. 8. Quality of Sound <ul><li>Intermittent vs. Steady-State </li></ul><ul><li>Cyclical, Repetitive, Pulsating </li></ul><ul><ul><li>Air compressors, chillers </li></ul></ul><ul><li>Tonal Sources </li></ul><ul><ul><li>Fan blade pass frequency, screw chillers </li></ul></ul>
    8. 9. Indoor Noise Criterion <ul><li>Noise Criterion Curves (NC) </li></ul><ul><li>Room Criterion Curves (RC) </li></ul><ul><li>RC Mark II </li></ul><ul><li>A-weighted Sound Pressure Level (dBA) </li></ul>
    9. 10. NC Curves
    10. 11. NC Curves NC 47
    11. 12. RC Curves
    12. 13. RC Curves RC 35 RVa
    13. 14. RC Mark II
    14. 15. RC Mark II
    15. 16. RC Mark II
    16. 17. ASHRAE Recommendations 1991 Applications 1999 Applications
    17. 18. A-Weighting <ul><li>Good Single Number Descriptor </li></ul><ul><li>Correlates Well with Human Perception </li></ul><ul><li>In Widespread Use Primarily for Outdoor Use </li></ul>
    18. 19. A-Weighting
    19. 20. Equipment Source Sound Levels <ul><li>Sound Power Levels (dB, re: 10 -12 Watts) </li></ul><ul><ul><li>Total sound energy of a source </li></ul></ul><ul><ul><li>Not affected by surrounding environment </li></ul></ul><ul><li>Sound Pressure Levels (dB, re: 20 µPa) </li></ul><ul><ul><li>Level of sound due to a source </li></ul></ul><ul><ul><li>Levels a function of distance & environment which must be documented. </li></ul></ul>
    20. 21. Sound Power vs. Sound Pressure Total Radiated Heat/Time (BTU/hr) ~ Sound Power Heat converts to temperature based Sound power converts to pressure based on distance and heat conductance based on distance and sound of room surfaces. absorption of room surfaces. Room Temperature ~ Sound Pressure Level This is why we specify noise levels in terms of Sound Power.
    21. 22. Mechanical Equipment <ul><li>Air handling systems sound paths </li></ul><ul><ul><li>Ductborne, low frequency duct break-out, casing, vibration </li></ul></ul><ul><li>Terminal box sound paths </li></ul><ul><ul><li>Ductborne, radiated </li></ul></ul><ul><li>Chillers/Pumps sound paths </li></ul><ul><ul><li>Airborne, vibration </li></ul></ul>
    22. 23. Air Handling Unit Sound Paths
    23. 24. Air Handling Design Guidelines <ul><li>Space Planning </li></ul><ul><li>Good intake and discharge duct conditions </li></ul><ul><ul><li>Achieve uniform flow </li></ul></ul><ul><ul><li>Avoid turbulent flow conditions </li></ul></ul><ul><li>Duct attenuators </li></ul><ul><ul><li>Pressure drop not to exceed 0.3” w.g. </li></ul></ul><ul><ul><li>Do not located directly upstream or downstream of duct fittings, will significantly increase rated pressure drop and regenerate noise </li></ul></ul><ul><li>Internal duct lining and vibration isolation </li></ul>
    24. 25. AHU Design Guidelines
    25. 26. Roof-top Air Handling Unit
    26. 27. Noise Mitigation for Roof-top Air Handling Units <ul><li>Space planning </li></ul><ul><li>Thickened slab below units (5’-8’ around perimeter of unit) </li></ul><ul><li>Duct attenuators </li></ul><ul><li>Duct lining </li></ul><ul><li>Double wall duct </li></ul><ul><li>Vibration isolation curbs </li></ul>
    27. 28. Roof-top Unit Mitigation Concepts
    28. 29. Terminal Boxes <ul><li>Fan powered – constant volume or VAV and single duct VAV </li></ul><ul><ul><li>Discharge noise from the fan or damper transmitted through the duct </li></ul></ul><ul><ul><li>Radiated noise from the fan or damper transmitted through the box wall or box opening in the case of fan powered </li></ul></ul>
    29. 30. Terminal Box Design Guidelines <ul><li>To Achieve NC 35 </li></ul><ul><ul><li>Box inlet static pressure ≥1.00” wg </li></ul></ul><ul><ul><li>Box selection </li></ul></ul><ul><ul><li>Radiated noise </li></ul></ul><ul><ul><ul><li>Single Duct VAV – 1700 cfm </li></ul></ul></ul><ul><ul><ul><li>Fan Powered – 1300 cfm </li></ul></ul></ul><ul><ul><li>Ductborne noise </li></ul></ul><ul><ul><ul><li>10 to 15 feet of internal duct lining </li></ul></ul></ul><ul><ul><ul><li>Duct attenuators </li></ul></ul></ul>
    30. 31. Terminal Box Selection
    31. 32. Effect of Ceiling Plenum on Radiated Noise of Terminal Boxes <ul><ul><ul><li>Distance of box to back of ceiling tile – no effect </li></ul></ul></ul><ul><li>Volume of the plenum has a large impact </li></ul><ul><ul><li>Plenum volume depends on: </li></ul></ul><ul><ul><ul><li>Height (from underside of slab to top of ceiling) </li></ul></ul></ul><ul><ul><ul><li>Extent (area of open ceiling plenum) </li></ul></ul></ul>
    32. 33. Terminal Box Noise Example Room 109 Room 107 Room 105 Supply & Exhaust Supply Only Exhaust Only Supply - 2.2&quot; w.g. NC 54 NC 44 NC 55 Exhaust - 3.0&quot; w.g. Supply - 2.2&quot; w.g. NC 42 NC 42 NC 49 Exhaust - 1.5&quot; w.g. Supply - 1.25&quot; w.g. NC 37 NC 37 NC 37 Exhaust - 1.1&quot; w.g.
    33. 34. Chiller/Pump Design Guidelines <ul><li>Chillers </li></ul><ul><ul><li>Thickened structural slab (above and below) </li></ul></ul><ul><ul><li>Floating floor </li></ul></ul><ul><ul><li>Vibration isolation including neoprene flexible connectors </li></ul></ul><ul><li>Pumps </li></ul><ul><ul><li>Concrete inertia bases </li></ul></ul><ul><ul><li>Vibration isolation including neoprene flexible connectors </li></ul></ul>
    34. 35. Chiller Vibration Isolation
    35. 36. Pump Vibration Isolation
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