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ASHRAE Chapter Meeting Acoustics in HVAC Design Presented By Cleve Doyen Noise & Vibration Control, Inc. 610-863-6300

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Presentation on theme: "ASHRAE Chapter Meeting Acoustics in HVAC Design Presented By Cleve Doyen Noise & Vibration Control, Inc. 610-863-6300"— Presentation transcript:

1 ASHRAE Chapter Meeting Acoustics in HVAC Design Presented By Cleve Doyen Noise & Vibration Control, Inc

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

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

4 4 Correction factors that turn dB into dBA “A” Weighting of Decibels Octave Band Center Frequency, Hz A-weighting

5 5 Fundamentals of HVAC Acoustical Engineering

6 6 Best Practices 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 Acoustical Design

7 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 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 10 Typical Rooftop Unit System Problems

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20 RTU Case History #1 20 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 21

22 RTU Case History #2 22 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 23

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

25 RTU Case History #3 25

26 Specification Strategies 26

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 27

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

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

30 RTU Specification Examples 30

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 31

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37 In-Curb System 37

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39 Isolation Curb Kit Assembly 39

40 Pre-assembled Construction 40

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

42 Higher Performance RTU Acoustical Systems are Rarely Needed 42

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

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 44

45 Higher Performance Detail Illustrations 45


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

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

52 Good/Better/Best Acoustical Design Ductwork Configurations 52

53 53 Guidelines for Minimizing Regenerated Noise In Elbows

54 54 Guidelines for Minimizing Regenerated Noise In Takeoffs

55 55 Guidelines for Minimizing Regenerated Noise in Duct Tees

56 56 Guidelines for Minimizing Regenerated Noise in Transitions and Offsets

57 Outdoor Noise Treatments 57

58 Scroll Compressor Sound Blankets 58

59 Coil Intake Acoustical Louvers 59

60 Condenser Fan Discharge Stacks 60

61 Acoustical Barriers and Screens 61

62 Condenser Section Enclosures 62

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