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ASHRAE Chapter Meeting Acoustics in HVAC Design

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Presentation on theme: "ASHRAE Chapter Meeting Acoustics in HVAC Design"— Presentation transcript:

1 ASHRAE Chapter Meeting Acoustics in HVAC Design
Presented By Cleve Doyen Noise & Vibration Control, Inc Thank you _________ for the intro and for the opportunity to speak with you all here this evening. Begin with brief background on BRD and then jump into the presentation. In business since 1975 providing noise and vibration control products, systems, and installation services… in addition to testing and analysis services…not only for purposes of noise control but also for purposes of machinery diagnostics and prognostics. Also provide services like precision alignment and dynamic balancing of rotating equipment because they reduce vibration. So we are involved in almost anything noise or vibration related. Our contact info is shown on the display and of course I have business cards, so if anybody would like one you’re welcome to see me after the meeting. The slide also shows the major markets we serve, not the least of which is HVAC, which is to be our focus here tonight so with no further delay let’s move on to the next slide and take a look at the topics of discussion for this evening.

2 Characteristics of Sound
Quantity = Loudness (Intensity) Quality = Pitch (Tonal Content) Character (Cyclical Ramping)

3 Power vs. Pressure PWL vs. SPL Cause vs. Effect Watts vs. Temperature

4 “A” Weighting of Decibels
Octave Band Center Frequency, Hz 31.5 63 125 250 500 1000 2000 4000 8000 A-weighting -39 -26 -16 -9 -3 +1 -1 Correction factors that turn dB into dBA

5 Fundamentals of HVAC Acoustical Engineering
ASHRAE - Detroit, MI 1-12HVAC Acoustics Tutorial 5

6 Best Practices Acoustical Design Answer the 4 questions
Use 3 to 5 dBA safety factor Cursory review on every project; in depth review when warranted Assess site ambient noise levels Evaluate airborne and structure-borne transmission System problems require system solutions

7 Just Right Acoustics Where are we now? Baseline data (standard)
Where do we need to be? Acceptance Criteria (NC, RC, dB, dBA, etc…) What needs to be done to achieve compliance? How much will it cost?

8 Acoustical Tutorial for Rooftop Curb Mounted AHU

9 Construction Trends Less mass in building Less space between floors
Drop ceilings Premium for rentable/usable space Value Engineering Heightened sensitivity of owners/occupants ANSI S12.60 CURB MOUNTED RTUs

10 Typical Rooftop Unit System Problems










20 RTU Case History #1 Downstream Fan Attenuation Internal RTU Isolation
Factory Non-Isolation Curb Deck openings over cut by 4” to 6” Ductwork supports tied into wall studs No In-curb acoustical treatment NC-59/50.1 dBA

21 RTU Case History #1

22 RTU Case History #2 Vibration Isolation Curb SA & RA Sound Attenuators
External Duct Lagging Lightweight roof Duct drops sealed No- In-curb acoustical treatment NC 56/55.3 dBA

23 RTU Case History #2

24 RTU Case History #3 Factory Curb Compressor Grommets Solid deck
OA and horizontal discharge NC 47/ 43.8 dBA

25 RTU Case History #3

26 Specification Strategies

27 Minimize Attenuation Needed
Optimize RTU configurations to minimize baseline sound output Select RTU location over utility or other non-critical space Dialogue with architect regarding roof mass

28 Transmission Paths to Address in the Specification
In-Duct Fan Noise Radiated Noise Ductwork Breakout Noise Structure-borne Transmission Outdoor Noise

29 RTU Specification Goal
Predictable performance to meet objective criteria Measurable Performance Accountability Clear Installation Guidelines for the construction team Equipment/System Compatibility

30 RTU Specification Examples

31 RTU Specification Features
Design specification with embedded acoustical performance Single source supply of Acoustical materials Specify procedure for the HVAC contractor to cut and seal deck openings for SA and RA inside the curb Require acoustical material supplier to inspect & certify Embed acoustical specification with RTU equipment Pre-Assembled construction






37 In-Curb System


39 Isolation Curb Kit Assembly

40 Pre-assembled Construction

41 The Results Performance Improvement of 5 to 10 NC/dBA
No uptick in cost points

42 Higher Performance RTU Acoustical Systems are Rarely Needed

43 Higher Performance Applications
Entertainment/Theatre Venues Libraries/Museums K-12/Higher Education

44 High Performance Design Features
Plenumized Curbs Acoustical panel curb bottom with SA/RA openings offset from the unit opening Silencers closer to unit or recessed in the curb Eliminates the elbow/transition/offset duct connection to the unit opening

45 Higher Performance Detail Illustrations





50 Ductwork Design Duct type and sizing need to be consistent with NC target criteria

51 Ductwork Design Duct layout and configuration needs to follow SMACNA and ASHRAE design guidelines

52 Good/Better/Best Acoustical Design Ductwork Configurations

53 Guidelines for Minimizing Regenerated Noise In Elbows

54 Guidelines for Minimizing Regenerated Noise In Takeoffs

55 Guidelines for Minimizing Regenerated Noise in Duct Tees

56 Guidelines for Minimizing Regenerated Noise in Transitions and Offsets

57 Outdoor Noise Treatments

58 Scroll Compressor Sound Blankets

59 Coil Intake Acoustical Louvers

60 Condenser Fan Discharge Stacks

61 Acoustical Barriers and Screens

62 Condenser Section Enclosures


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