Acoustical Presentation to the Rocky Mountain ASHRAE Chapter

Acoustical Presentation to the Rocky Mountain ASHRAE Chapter April 16, 2010

Discussion Topics Ø Ø Ø Ø Ø Acoustics Overview Frequency Ranges of Mechanical Noise Design Criteria for Typical Spaces Mechanical Noise Control : Areas of Interest Sound Transmission Paths Typical Ductborne Mitigation Methods Typical Duct Breakout Mitigation Methods Typical Structure-borne Noise and Vibration Mitigation Methods Mechanical Design affecting Sound Isolation LEED for Schools

Acoustics - A Brief Overview 1. Ø 2. Ø 3. Ø 4. Ø 2 Sound Isolation Noise Control Vibration Control Interior Acoustics 3 1 4

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

Acoustics 101 Ø Ø Decibel (d. B): Measure on logarithmic scale of the magnitude of sound pressure, sound power, or sound intensity level with respect to a standard reference value. Ø L = 20 log (Prms/Pref) Pref = 20µPa Human Hearing Threshold of Audibility: 0 d. B Ø Threshold of Pain: 120 d. B Ø Ear cannot differentiate less than 1 d. B of change Ø Ø Due to log scale, d. B does not add algebraically 1 Vacuum = 90 d. B 2 Vacuums ≠ 180 d. B 2 Vacuums = 93 d. B

Acoustics 101

Definitions of Terms: Sound Power vs Sound Pressure

Definitions of Terms: d. BA Ø A-Weighted Sound Levels (d. BA) Ø d. BA does not completely represent human perception of noise. Ø d. BA is used primarily in environmental noise studies and LEED for Schools Requirements.

Definitions of Terms: NC Ø Noise Criteria Level (NC) Ø Industry Standard Ø Does not address frequencies below 63 Hz Ø Does not provide sound quality assessment.

Definitions of Terms: RC Ø Room Criteria (RC) Ø Probable industry standard for future Ø Addressed frequencies below 16 and 31. 5 Hz Ø Provides sound quality assessment. Ø N, R, H, RV Excerpted from Chapter 7, “Sound and Vibration, ” of the 1993 ASHRAE Fundamentals Handbook

Comparison of d. BA, NC, RC NC 36 39 d. BA RC 18 (R) 39 d. BA

Perception of Sound Ø Decrease of 3 d. B represents a halving of sound energy but is a just noticeable difference. Ø Decrease of 10 d. B represents a halving of perceived sound levels Ø Decrease of 20 d. B represents ¼ of the perceived sound levels Picture from Bell Telephone Laboratories

Frequency Ranges of Mechanical Noise Frequency (Hz) Perceptible Sound Possible Reason for Mechanical Noise 0. 8 to 31. 5 Throb Turbulent Airflow and Fan Instability 31. 5 to 125 Hz Rumble Turbulent Airflow and Poor Vibration Isolation 125 to 500 Hz Roar Fan Noise, Turbulent Airflow, VAV Boxes 125 to 1000 Hz Hum & Buzz Poor Vibration Isolation, Fan Powered VAV Boxes 500 to 2000 Hz Whine and Whirr Pumps and Chillers 1000 to 8000 Hz Hiss and Whistle Grilles, Diffusers, Water Valves

Design Criteria for Typical Spaces Space NC Level RC (N) Level 15 15 20 to 25 Tele/Videoconferencing; Distance Learning Classrooms 25 to 30 Conference Rooms; Classrooms 30 to 35 25 to 30 Private Offices; Residences 35 30 to 35 Lobbies, Corridors, Computer Classrooms; Retail 40 35 to 45 Laboratories; Toilets 45 40 to 50 Kitchens, Laundry Rooms, Computer Equipment Rooms 50 45 to 55 Recording Studios; Concert Halls Studios Auditorium; Sanctuary

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

Sound Transmission Paths Excerpted from Chapter 7, “Sound and Vibration, ” of the 2003 ASHRAE Fundamentals Handbook

Sound Transmission Paths Excerpted from Chapter 7, “Sound and Vibration, ” of the 2003 ASHRAE Fundamentals Handbook

Sound Transmission Paths Excerpted from Chapter 7, “Sound and Vibration, ” of the 2003 ASHRAE Fundamentals Handbook

Sound Transmission Paths Excerpted from Chapter 7, “Sound and Vibration, ” of the 2003 ASHRAE Fundamentals Handbook

Sound Transmission Paths Excerpted from Chapter 7, “Sound and Vibration, ” of the 2003 ASHRAE Fundamentals Handbook

Sound Transmission Paths Excerpted from Chapter 7, “Sound and Vibration, ” of the 2003 ASHRAE Fundamentals Handbook

Typical Ductborne Mitigation Methods Ø Internal Ductliner Attenuates Mid to High Frequencies Ø Distance of ductwork from mechanical equipment Ø Ø Sound Attenuators Ø Most effective at attenuating Mid to High Frequencies Ø Increases Static Pressure Drop Lined Plenum Ø Most effective method for attenuating low frequencies Ø Can be incorporated into AHU and RTU Casing Ø

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

Terminal Units CONSTANT OR VARIABLE AIR VOLUME Ø Integral Sound Attenuators Ø Manufacturer NC Ratings FAN-POWERED, SERIES FLOW, VAV

Good Design Practices Ø Ø Fan Discharge Configurations Inlet Configuration Excerpted from Chapter 7, “Sound and Vibration, ” of the 2003 ASHRAE Fundamentals Handbook

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

Typical Structure-borne Noise and Vibration Mitigation Methods Ø Concrete Inertia Bases Ø Pumps/Large Fans Ø Spring Isolators Ø Pumps Ø Rotating Equipment Ø Above Grade Chillers/Cooling Towers Ø Neoprene Pads Ø On Grade Chillers/Cooling Towers

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

Mechanical Design affecting Sound Isolation Ø Crosstalk between Spaces Ø Length of ductwork Ø Junctions and Elbows Ø Internal Ductliner Ø Plenum Return Ø Z or U Shaped Internally Line Transfer Ducts Excerpted from No Noise Classroom Acoustics Publication

Mechanical Design affecting Sound Isolation Ø Penetrations Full Height Partitions

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

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

LEED for Schools Ø Acoustics is now a mandatory LEED credit for Schools Ø Prerequisite 3 Background Noise Requirements: Ø Max BNL of 45 d. BA OR Ø Achieve an RC (N) Mark II level of 37 Ø EQ Credit 9: Enhanced Acoustical Performance Background Noise Requirements Ø Max BNL of 40 d. BA (1 point) or 35 d. BA (2 points) Ø 2: Achieve an RC (N) Mark II level of 32 (1 point) or 27 (2 points)

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

Case Studies n 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

Case Studies n 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

Case Studies