ASHRAE Chapter Meeting HVAC Noise & Vibration Control Specifications & Best Practices

Transcription

1 ASHRAE Chapter Meeting HVAC Noise & Vibration Control Specifications & Best Practices Industrial Presented By OEM Architectural Noise & Vibration Control, Inc HVAC Marine Environmental Military Aviation 1

2 Topics Brief Intro to Acoustics Specification Best Practice Treatment Best Practices 2

3 3 Why Acoustics Matter!

4 Important Acoustic Terminology Loudness vs. Pitch Decibels: Sound Power vs. Sound Pressure Decibel Weighting Networks Tonal Content 4

5 A 1K Hz tone at 60 db would require a 102 db tone at 20 Hz to sound as loud to the human ear. 5

6 Tonal Noise Common Municipal Code defines tone as: any sound which can be distinctly heard as a single pitch or set of single pitches. and shall exist of the one-third octave band sound pressure level in the band when the tone exceeds the arithmetic average of the sound levels of the two contiguous one-third octave bands by five db for frequencies of 500 Hz and above, eight db for frequencies between Hz, and by 15 db for frequencies less than or equal to 125 Hz. 6

7 PWL vs. SPL Sound Power vs. Sound Pressure Cause vs. Effect 7

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9 What is the overall dba level? Octave Center Unweighted A-weighting A-weighted Decibel Overall Band Frequency Sound factor (db) Sound Addition Resultant Pressure (db) Pressure (dba) Level dba 5 1, , , ,

10 1. Where are we now? Freq (Hz) K 2K 4K 8K A Lw Loss Lp (Sound Levels 270 ton Air Cooled Chiller) 2. Where do we need to be? 10

11 3. How much noise reduction is required? Freq (Hz) K 2K 4K 8K A Chiller Ordinance Needed Attenuation What needs to be done to achieve compliance? 11

12 Sub Topics Common Specification Strategies Specifications Types Specification Best Practices 12

13 A Specification Should Provide Just the Right Prescription Accountability Cost Control Predictable Performance Review of subjective and objective noise criteria 13

14 Common Specification Strategies 14

15 Common Spec Strategies on Noise Sensitive Projects Specify sound data for lowest rated model as equipment basis of design Specify all available OEM equipment low noise options Specify an equipment model that is not tonal Specify the same treatment used on the last noise sensitive project Retain an acoustical consultant to write the specification Specify base equipment and address any noise problems at start-up 15

16 Common Specification Strategies: Specify sound data for lowest rated model as equipment basis of design 4 Different Manufacturers & Chiller Models (Screw and Scroll Designs) Published Sound Power Data (No OEM Sound Kit Options) Sound Power Levels (db) Octave Band Center Frequency (Hz) Overall A-Wtd (dba) Published Sound Pressure Data at 30 Away (No OEM Sound Kit Options) 4 Different Chiller Manufacturers & Models (Screw and Scroll Designs) Sound Pressure Levels 5 30' Octave Band Center Frequency (Hz) Overall A-Wtd (dba)

17 Common Specification Strategies: Specify sound data for lowest rated model as equipment basis of design Specify all available OEM equipment low noise options Sound Pressure Data for property line 80 away 4 Different Chiller Manufacturers & Models (Screw and Scroll Designs) (No OEM Sound Kit Options) Sound Pressure Levels 5 80' Octave Band Center Frequency (Hz) Overall A-Wtd (dba) Sound Pressure Data for property line 80 away (with factory OEM options) 4 Different Chiller Manufacturers & Models (Screw and Scroll Designs) Sound Pressure Levels 5 80' Octave Band Center Frequency (Hz) Overall A-Wtd (dba) None of the chillers will comply with typical nighttime noise ordinance values of 50 to 55 dba.

18 18 Screw Chiller Sound Pressure Levels Scroll Chiller Sound Pressure Levels Hz Z C A k 1k25 1k6 2k 2k5 3k15 4k 5k 6k3 8k 10k 12k5 16k 20k 100 db Common Specification Strategies: Specify an equipment model that is not tonal

19 Specification Types Performance Design Allowance 19

20 Performance Specifications Typical performance descriptors Sound Power and/or Sound Pressure Octave band and/or overall db and/or dba levels NC or RC levels Relies on the acoustical credibility of the equipment manufacturer May or may not have the capabilities needed Commonly will take an exception Spec is difficult to enforce AHRI 370, AHRI 575, AHRI 260, etc... Spec is often not based on project target levels at receiver positions Performance spec may or may not address equipment integration issues (operating performance, maintenance, etc ) 20

21 21 Performance Specification Example

22 22 Performance Specification Example

23 Contradictory Performance Specification Sound attenuation solution quiet 23

24 24 Contradictory Performance Specification

25 Design Specifications = Just Right Prescription Evaluates noise sensitive location(s) to provide Predictable Performance Accountability Cost Control Right amount of attenuation Accounted for in the budget Describes, provides performance, and/or illustrates (schematic details) the materials and products needed 25

26 Design Specification Schematic Design Detail ABC model JJJ 26

27 Schematic Design Detail ABC solution/model Design Specification 27

28 Loose Design Specification ABC Result of a Loose/Generic spec What is criteria for approving or rejecting? 28

29 Better Design Specification ABC model and manufactured by ABC company or equivalent. 29

30 30 Detailed Design Specification

31 Best Design Specification Attenuation 31

32 32 Best Design Specification Cont d

33 Allowance Specifications Equivalent advantages of prepurchased equipment Provides the right material that is wanted on the project Assures needed design will be built Levels the playing field for bidders 33

34 Allowance Specification ABC Acoustic Attenuation DEF Company. 34

35 Specification Best Practices 35

36 Best Practices Acoustic Design Answer 4 design questions 1. Where are we now? 2. Where do we need to be? 3. What needs to be done to get there? 4. How much will that cost? Use 3-5 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 36

37 Best Practices Specifications Job specific combined design/performance specs preferred over generic performance specs Evaluate project specific objective and subjective criteria Indoor criteria: NC, RC, NCB, RC Mark II Outdoor criteria: Zoning and ordinance criteria Place in Division 15/23 with equipment Specify single source for system acoustic performance Specify turnkey where installation critical Require submission for approval as or equal 10 days before bid date 37

38 Take Away Location specific performance is king and drives the design spec Design specs provide just the right knowledge of costs that can get into the budget Acoustic treatments/solutions need to be in the equipment spec to ensure predictable performance, acceptability, and accountability 38

39 39 Sub Topics Construction Trends Specifications Vibration Isolation Chiller Noise Treatments Roof Mounted Treatments Duct Work & Silencers Rooftop Unit Treatments

40 Construction Trends Less mass in building Less space between floors Curb mounted equipment Drop ceilings Premium for rentable/usable space Value Engineering Heightened sensitivity of owners ANSI S12.60 LEED 40

41 Best Practices Indoor Chillers Thickened slab above and below Floating floors Pneumatic isolation systems 6 sided enclosures Stay away from midpoints of column spans Buffer from noise sensitive spaces Source & path acoustic treatments 41

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43 43 Source Treatments

44 Critical Design Factors Broadband Performance Tonal Performance Aerodynamic Performance Operating Efficiency Operating Costs 44

45 45 Soft Enclosure Path Treatments

46 46 Hard Enclosure Path Treatments

47 Thickened slab for rooftop Evaluate loudness and tonal content Special consideration for remote evap piping Evaluate building and property line noise Optimize aerodynamic and acoustic performance Source and path acoustic treatment Best Practices Outdoor Chillers 47

48 Compressor Source Treatments Sound Blankets Treat all accessible compressor circuit components 3 to 4 lb. surface density Fit/refit attachment features must be user friendly UL 764C Listed 48

49 49 Treating Compressor Circuits

50 50 Result of generic spec

51 51 Air Intake Source Treatments

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53 Condenser Fan Source Treatments Acoustical plenums Plenum with baffles Plenum with silencer bank Individual stack silencers 53

54 54 Open Plenums

55 55 Plenum with Baffles

56 56 Plenum with Silencer Bank

57 Not Recommended by OEMs Dedicated Stack Silencers 57

58 Path Treatments Wall and Fence Liners 58

59 59 Turnkey Acoustical Barrier Walls

60 dba Attenuation Systems

61 61 Rooftop Curb Mounted AHU Integral vibration/seismic curb Lock down internal isolation Add mass inside curbs Seal (acoustic) duct drops Dissipate supply breakout noise above deck Plenum style acoustic curbs Best Practices

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63 63 Poor Best Practice This is a seismic job!

64 64 In-Curb Treatment

65 Best Practices RTU Configurations Increase plenum liner thickness Utilize RTU discharge plenums on the supply side Avoid vane type flow modulation devices. VFD controllers are preferred Slower fan speeds = lower noise levels Evaluate fan wheel types. Backward inclined (BI) and aerofoil (AF) wheels are preferred over forward curved models (FC) 65

66 66 Integrated Sound Attenuators

67 External Acoustic Duct Lagging 7-9 db reduction in first 3 octave bands 67

68 Rooftop Unit Condenser Section Treatments 68

69 Best Practices Roof Mounted Equipment on Dunnage Steel Restrained isolators if spring UV compatible shear mounts 3 to 4 thickened slab 8 to 10 around unit perimeter Locate over utility space Keep away from skylights and operable windows 69

70 Cooling Towers Similar to Chiller strategies Restrained spring isolators Condenser fan discharge treatment Path treatments 70

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72 Best Practices Vibration Isolation Follow ASHRAE guidelines for static deflection Review actual deflections Isolate pipes and ducts at riser and wall penetrations Avoid suspended piping in mechanical rooms below noise sensitive space Avoid cantilevered loads Proper adjustment of isolator lockdowns and snubbers 72

73 Pipe and Duct Penetrations Acoustical Sealant in ½ Gap Acoustical Batt Mineral Fiber Packing 73

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80 Best Practices Pumps Concrete inertia bases Support elbows on base Open springs Seismic snubbers for base Molded neoprene flexes Vibration isolation hangers for 50 or entire mechanical room Acoustic treatment rarely needed 80

81 Best Practices AHU Duct Silencers Avoid high pressure drop models Evaluate self generated noise Apply p correction factors Stay 3 equivalent duct diameters away from fittings 81

82 Guidelines for Sound Trap Placement Near Fans and Duct Fittings 82

83 Best Practices Avoiding Respirable Fibers Fiber free reactive duct silencers (packless) Media wrap of packed silencers with spacers Closed cell thermal insulation Open cell melamine foams 83

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85 Best Practices Duct Design Follow ASHRAE guidelines Follow SMACNA guidelines Control ductwork aspect ratios Increase gauge and stiffening near units Double wall duct Duct shape Target velocities consistent with target NC goals 85

86 86 Turbulence = Regenerated Noise

87 Regenerated Noise at Fittings Recommended maximum airflow velocities for various installations 87

88 Duct Shapes 88

89 Best Practices 89 Room Diffusers Select diffusers for 6 to 8 NC points below room target NC Long radius 90 flexes to diffusers add 1 to 3 NC points Kinked flexes add 7 to 9 NC points Balancing dampers should be located three equivalent duct diameters away from diffusers and fittings Open plenum return grilles may require lined elbow

90 Best Practices VAV Boxes Lined discharge 10 to 15 First take-off minimum 3 from discharge Single duct VAV CFM Fan powered VAV CFM External wraps for casing radiated noise 90

91 91 Recommended VAV Detail

92 Removable Wraps Reduce Radiated Noise 92

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