ASHRAE Chapter Meeting HVAC Noise & Vibration Control Specifications & Best Practices Industrial Presented By OEM Architectural Noise & Vibration Control, Inc. 610-863-6300 www.brd-nonoise.com HVAC Marine Environmental Military Aviation 1
Topics Brief Intro to Acoustics Specification Best Practice Treatment Best Practices 2
3 Why Acoustics Matter!
Important Acoustic Terminology Loudness vs. Pitch Decibels: Sound Power vs. Sound Pressure Decibel Weighting Networks Tonal Content 4
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
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 160-400 Hz, and by 15 db for frequencies less than or equal to 125 Hz. 6
PWL vs. SPL Sound Power vs. Sound Pressure Cause vs. Effect 7
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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 1 63 94-26 68 72 2 125 86-16 70 86 3 250 85-9 76 86 4 500 89-3 86 91 dba 5 1,000 89 0 89 6 2,000 77 1 78 89 7 4,000 75 1 76 8 8,000 76 0 76 79 89 9
1. Where are we now? Freq (Hz) 63 125 250 500 1K 2K 4K 8K A Lw 90 98 99 97 94 92 85 81 100 Loss 100-37 -37-37 -37-37 -37-37 -37-37 Lp 53 61 62 60 57 55 48 44 63 (Sound Levels 270 ton Air Cooled Chiller) 2. Where do we need to be? 10
3. How much noise reduction is required? Freq (Hz) 63 125 250 500 1K 2K 4K 8K A Chiller 53 61 62 60 57 55 48 44 63 Ordinance 67 61 52 46 40 33 28 26 50 Needed Attenuation -- -- 10 14 17 22 20 18 13 4. What needs to be done to achieve compliance? 11
Sub Topics Common Specification Strategies Specifications Types Specification Best Practices 12
A Specification Should Provide Just the Right Prescription Accountability Cost Control Predictable Performance Review of subjective and objective noise criteria 13
Common Specification Strategies 14
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
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 63 125 250 500 1000 2000 4000 8000 (dba) 1 97 94 92 97 90 88 84 82 97 2 102 103 99 99 98 94 87 84 102 3 67 70 79 83 89 91 88 80 95 4 93 99 97 100 97 91 88 80 105 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 (db) @ 30' Octave Band Center Frequency (Hz) Overall A-Wtd 63 125 250 500 1000 2000 4000 8000 (dba) 1 70 67 65 70 63 61 57 55 70 2 75 76 72 72 71 67 60 57 75 3 40 43 52 56 62 64 61 53 68 4 66 72 70 73 70 64 61 53 74 16
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 (db) @ 80' Octave Band Center Frequency (Hz) Overall A-Wtd 63 125 250 500 1000 2000 4000 8000 (dba) 1 61 58 56 61 54 52 48 46 61 2 66 67 63 63 62 58 51 48 66 3 31 34 43 47 53 55 52 44 60 4 57 63 61 64 61 55 52 44 66 17 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 (db) @ 80' Octave Band Center Frequency (Hz) Overall A-Wtd 63 125 250 500 1000 2000 4000 8000 (dba) 63 57 57 59 54 48 44 42 60 52 60 61 59 56 54 46 41 62 31 33 43 46 49 51 48 42 56 57 63 61 61 60 55 52 42 64 None of the chillers will comply with typical nighttime noise ordinance values of 50 to 55 dba.
18 Screw Chiller Sound Pressure Levels Scroll Chiller Sound Pressure Levels Hz Z C A 12 16 20 25 32 40 50 63 80 100 125 160 200 250 315 400 500 630 800 1k 1k25 1k6 2k 2k5 3k15 4k 5k 6k3 8k 10k 12k5 16k 20k 100 db 90 80 70 60 50 40 30 Common Specification Strategies: Specify an equipment model that is not tonal
Specification Types Performance Design Allowance 19
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 Performance Specification Example
22 Performance Specification Example
Contradictory Performance Specification Sound attenuation solution quiet 23
24 Contradictory Performance Specification
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
Design Specification Schematic Design Detail ABC model JJJ 26
Schematic Design Detail ABC solution/model Design Specification 27
Loose Design Specification ABC............... Result of a Loose/Generic spec What is criteria for approving or rejecting? 28
Better Design Specification ABC model and manufactured by ABC company or equivalent. 29
30 Detailed Design Specification
Best Design Specification Attenuation 31
32 Best Design Specification Cont d
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
Allowance Specification ABC Acoustic Attenuation DEF Company. 34
Specification Best Practices 35
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
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
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 Sub Topics Construction Trends Specifications Vibration Isolation Chiller Noise Treatments Roof Mounted Treatments Duct Work & Silencers Rooftop Unit Treatments
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
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 Source Treatments
Critical Design Factors Broadband Performance Tonal Performance Aerodynamic Performance Operating Efficiency Operating Costs 44
45 Soft Enclosure Path Treatments
46 Hard Enclosure Path Treatments
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
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 Treating Compressor Circuits
50 Result of generic spec
51 Air Intake Source Treatments
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Condenser Fan Source Treatments Acoustical plenums Plenum with baffles Plenum with silencer bank Individual stack silencers 53
54 Open Plenums
55 Plenum with Baffles
56 Plenum with Silencer Bank
Not Recommended by OEMs Dedicated Stack Silencers 57
Path Treatments Wall and Fence Liners 58
59 Turnkey Acoustical Barrier Walls
60 20+ dba Attenuation Systems
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 Poor Best Practice This is a seismic job!
64 In-Curb Treatment
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 Integrated Sound Attenuators
External Acoustic Duct Lagging 7-9 db reduction in first 3 octave bands 67
Rooftop Unit Condenser Section Treatments 68
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
Cooling Towers Similar to Chiller strategies Restrained spring isolators Condenser fan discharge treatment Path treatments 70
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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
Pipe and Duct Penetrations Acoustical Sealant in ½ Gap Acoustical Batt Mineral Fiber Packing 73
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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
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
Guidelines for Sound Trap Placement Near Fans and Duct Fittings 82
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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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 Turbulence = Regenerated Noise
Regenerated Noise at Fittings Recommended maximum airflow velocities for various installations 87
Duct Shapes 88
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
Best Practices VAV Boxes Lined discharge 10 to 15 First take-off minimum 3 from discharge Single duct VAV 1500 1700 CFM Fan powered VAV 1100 1200 CFM External wraps for casing radiated noise 90
91 Recommended VAV Detail
Removable Wraps Reduce Radiated Noise 92
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