acoustical presentation to the rocky mountain ashrae chapter

1. Acoustical Presentation to theRocky Mountain ASHRAE Chapter April 16, 2010

3. Acoustics - A Brief Overview 1. Sound Isolation 2. Noise Control 3. Vibration Control 4. Interior Acoustics Sound Isolation: Partition construction, glazing, doors, Vibration Control: MRI, Sensitive Lab Sound Isolation: Partition construction, glazing, doors, Vibration Control: MRI, Sensitive Lab

4. Acoustics 101 Frequency is the rate of repetition of a periodic event. Most sound sources, except pure tones, contain energy ever a wide range of frequencies. For measurement and analysis of sound, the frequency range is divided into sections labeled as octave bands

5. Acoustics 101 Decibel (dB): Measure on logarithmic scale of the magnitude of sound pressure, sound power, or sound intensity level with respect to a standard reference value. L = 20 log (Prms/Pref) Pref = 20µPa Human Hearing Threshold of Audibility: 0 dB Threshold of Pain: 120 dB Ear cannot differentiate less than 1 dB of change Due to log scale, dB does not add algebraically 2 – 35 watt light bulbs are not twice as bright as one2 – 35 watt light bulbs are not twice as bright as one

6. Acoustics 101

7. Definitions of Terms: Sound Power vs Sound Pressure Noise data is typically sound power but occasionally sound pressure. Sound pressure will include a distance (7 meters)Noise data is typically sound power but occasionally sound pressure. Sound pressure will include a distance (7 meters)

8. Definitions of Terms: dBA A-Weighted Sound Levels (dBA) dBA does not completely represent human perception of noise. dBA is used primarily in environmental noise studies and LEED for Schools Requirements. A single number representing a sound level of a noise containing a wide range of frequencies in a manner representative of the ear’s response. Does not represent human perception of noise: Example humming of refrigerator humming or neighbor vacuuming. Both have same dBA rating but are heard differently. People’s individual sensitivity to sound varies with frequency content, duration, or psychological factors. A single number representing a sound level of a noise containing a wide range of frequencies in a manner representative of the ear’s response. Does not represent human perception of noise: Example humming of refrigerator humming or neighbor vacuuming. Both have same dBA rating but are heard differently. People’s individual sensitivity to sound varies with frequency content, duration, or psychological factors.

9. Definitions of Terms: NC Noise Criteria Level (NC) Industry Standard Does not address frequencies below 63 Hz Does not provide sound quality assessment. It is the maximum background sound level due to the normal operation of building equipment serving the room(s), typically the air distribution system. Does not assess the system based on sound quality: NC defined by highest number.It is the maximum background sound level due to the normal operation of building equipment serving the room(s), typically the air distribution system. Does not assess the system based on sound quality: NC defined by highest number.

10. Definitions of Terms: RC Room Criteria (RC) Probable industry standard for future Addressed frequencies below 16 and 31.5 Hz Provides sound quality assessment. N, R, H, RV Sound levels in shaded area A indicate a high probability that noise-induced vibration in lightweight wall and ceiling construction will be clearly feelable and audible. Levels shaded in area B indicate moderately feelable vibrations. N identifies a "neutral" or balanced spectrum. R indicates "rumbly." H represents "hissy." RV denotes "perceptible vibration Sound levels in shaded area A indicate a high probability that noise-induced vibration in lightweight wall and ceiling construction will be clearly feelable and audible. Levels shaded in area B indicate moderately feelable vibrations. N identifies a "neutral" or balanced spectrum. R indicates "rumbly." H represents "hissy." RV denotes "perceptible vibration

11. Comparison of dBA, NC, RC

12. Perception of Sound Decrease of 3 dB represents a halving of sound energy but is a just noticeable difference. Decrease of 10 dB represents a halving of perceived sound levels Decrease of 20 dB represents ¼ of the perceived sound levels

13. Frequency Ranges of Mechanical Noise

14. Design Criteria for Typical Spaces

15. Mechanical Noise Control : Areas of Interest Equipment Selections Type of Fans, Variable vs Constant, Diffusers/Grilles Noise Data for Equipment Selections AHU’s, RTU’s, VAV Boxes, Cooling Towers, Fan Coil Units, etc… Ductwork layouts Overhead Ducted, Displacement, Under Floor Distribution Ducted vs. Plenum Return Airflow Velocities Plumbing noise Vibration Isolation

16. Sound Transmission Paths

17. Sound Transmission Paths

18. Sound Transmission Paths

19. Sound Transmission Paths

20. Sound Transmission Paths

21. Sound Transmission Paths Path E Controlled with architectural measuresPath E Controlled with architectural measures

22. Typical Ductborne Mitigation Methods Internal Ductliner Attenuates Mid to High Frequencies Distance of ductwork from mechanical equipment Sound Attenuators Most effective at attenuating Mid to High Frequencies Increases Static Pressure Drop Lined Plenum Most effective method for attenuating low frequencies Can be incorporated into AHU and RTU Casing Length of ductwork from mechanical equipment. Location of noise critical spaces: Architectural item.Length of ductwork from mechanical equipment. Location of noise critical spaces: Architectural item.

23. Typical Ductborne Mitigation Methods Double Wall Ductwork Utilized when internally lined ductwork is not allowed. Hospitals, Laboratories Diffuser/Grille Selection Diffusers/grilles should be selected 5 NC points below room criteria. Flex duct connection Airflow velocity Ductwork Airflow velocity Number of elbows and junctions Ductwork: Aspect Ratio - Oil CanningDuctwork: Aspect Ratio - Oil Canning

24. Terminal Units

25. Good Design Practices Fan Discharge Configurations Inlet Configuration Poor discharge and inlet conditions not only result in poor fan efficiency but greatly increased noise levels (10 dB or more) There should be at least two duct diameters straight run Inlet guide vanes alone can increase noise by up to 10 dB Elbows within two diameters should have guide vanesPoor discharge and inlet conditions not only result in poor fan efficiency but greatly increased noise levels (10 dB or more) There should be at least two duct diameters straight run Inlet guide vanes alone can increase noise by up to 10 dB Elbows within two diameters should have guide vanes

26. Typical Duct Breakout Mitigation Methods Lagging or Wrapping Attenuates Mid to High Frequencies Utilized primarily for plumbing noise Ductwork Enclosures Most effective at attenuating low frequencies Primarily used for RTU’s Utilized as an extension of Mechanical Room Cast iron piping vs. ptexCast iron piping vs. ptex

27. Typical Structure-borne Noise and Vibration Mitigation Methods Concrete Inertia Bases Pumps/Large Fans Spring Isolators Pumps Rotating Equipment Above Grade Chillers/Cooling Towers Neoprene Pads On Grade Chillers/Cooling Towers More Structure-borne Noise and Vibration Mitigation Methods but architectural items Curbs although expensive provides: Vibration isolation for unit (panel resonances) and stiffness to light weight roof deck construction Can include sound barrier materials to offset roof decks with no concrete. Flex Connections: Double bellows are really good for plumbing because they help reduce water noise: Braided hoses do not provide a high level of isolation unless incorporated in 2 direction to allow 3 degrees of freedom. More Structure-borne Noise and Vibration Mitigation Methods but architectural items Curbs although expensive provides: Vibration isolation for unit (panel resonances) and stiffness to light weight roof deck construction Can include sound barrier materials to offset roof decks with no concrete. Flex Connections: Double bellows are really good for plumbing because they help reduce water noise: Braided hoses do not provide a high level of isolation unless incorporated in 2 direction to allow 3 degrees of freedom.

28. Typical Structure-borne Noise and Vibration Mitigation Methods Rooftop Isolation Curb RTU’s Spring/Neoprene Hangers Ductwork/Piping 30 foot critical distance Flex Connections Double Bellows

29. Mechanical Design affecting Sound Isolation Crosstalk between Spaces Length of ductwork Junctions and Elbows Internal Ductliner Plenum Return Z or U Shaped Internally Line Transfer Ducts

30. Mechanical Design affecting Sound Isolation Penetrations Full Height Partitions More Structure-borne Noise and Vibration Mitigation Methods but architectural itemsMore Structure-borne Noise and Vibration Mitigation Methods but architectural items

31. Mechanical Design affecting Environmental Noise Control Most states, counties, cities, and towns have property line noise ordinances. Typical Day/Night level of 55/50 dBA Typical Equipment Culprits Emergency Generators Radiator, Exhaust, Intake Cooling Towers Fans Rooftop Units Alignment of Compressor/Condenser Section

32. Mechanical Design affecting Environmental Noise Control Mitigation Measures Equipment Locations Adjacent Properties Barrier Walls/Screens Materials Height Louvers Type

33. LEED for Schools Acoustics is now a mandatory LEED credit for Schools Prerequisite 3 Background Noise Requirements: Max BNL of 45 dBA OR Achieve an RC (N) Mark II level of 37 EQ Credit 9: Enhanced Acoustical Performance Background Noise Requirements Max BNL of 40 dBA (1 point) or 35 dBA (2 points) 2: Achieve an RC (N) Mark II level of 32 (1 point) or 27 (2 points) • Children are ineffective listeners for speech in noise • Children do not effectively listen and understand speech in reverberation • Children are especially susceptible to ear infections (weeks, months) • 20% of school population have permanent hearing loss • 2.5 million (1990) school-aged children had limited English proficiency • Noisy classrooms causes teacher vocal stress and fatigue• Children are ineffective listeners for speech in noise • Children do not effectively listen and understand speech in reverberation • Children are especially susceptible to ear infections (weeks, months) • 20% of school population have permanent hearing loss • 2.5 million (1990) school-aged children had limited English proficiency • Noisy classrooms causes teacher vocal stress and fatigue

34. Thanks for Attending Any Questions???? Additional Resources ASHRAE Application Handbook Chapter 47 Architectural Acoustics: David Egan

35. Case Studies Ritz Carlton Denver Boardroom and Conference Areas NC 45+ due to breakout noise (125 Hz) NC 35 Criteria Remedial Measures: Incorporated ductwork enclosure around high pressure running over spaces. NC 34 after implementation of remedial measures

36. Case Studies UCDHSC Research 1 Facility Vibration Issues in NMR and Crystallography Growth Chambers Acoustical testing: Issues at 32 Hz Short circuited spring isolators in AHU fans: Still bolted down for shipping

37. Case Studies