Download ASHRAE - HVAC Noise and Vibration Control...
Description
ASHRAE Chapter Meeting HVAC Noise & Vibration Control Specifications & Best Practices Industrial
OEM
Presented By
Noise & Vibration Control, Inc. 610-863-6300 www.brd-nonoise.com Architectural
Marine 1
HVAC
Environmental
Military
Aviation
Topics ☺ Brief Intro to Acoustics ☺ Specification Best Practice ☺ Treatment Best Practices
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Why Acoustics Matter!
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Important Acoustic Terminology • Loudness vs. Pitch • Decibels: Sound Power vs. Sound Pressure • Decibel Weighting Networks • Tonal Content
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A 1K Hz tone at 60 dB would require a 102 dB tone at 20 Hz to sound as loud to the human ear.
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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.”
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PWL vs. SPL
Sound Power vs. Sound Pressure Cause vs. Effect
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8
What is the overall dBA level? Octave Center Band Frequency 1 2 3 4 5 6 7 8
3. How much noise reduction is required? Freq (Hz)
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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
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--
10
14
17
22
20
18
13
4. What needs to be done to achieve compliance?
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Sub Topics ☺ Common Specification Strategies ☺ Specifications Types ☺ Specification Best Practices
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A Specification Should Provide “Just the Right Prescription” • • • •
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Accountability Cost Control Predictable Performance Review of subjective and objective noise criteria
Common Specification Strategies
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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
Published Sound Power Data (No OEM Sound Kit Options) 4 Different Manufacturers & Chiller Models (Screw and Scroll Designs)
1 2 3 4
63 97 102 67 93
Sound Power Levels (dB) Octave Band Center Frequency (Hz) 125 250 500 1000 2000 4000 94 92 97 90 88 84 103 99 99 98 94 87 70 79 83 89 91 88 99 97 100 97 91 88
8000 82 84 80 80
Overall A-Wtd (dBA) 97 102 95 105
Published Sound Pressure Data at 30’ Away (No OEM Sound Kit Options) 4 Different Chiller Manufacturers & Models (Screw and Scroll Designs)
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 (No OEM Sound Kit Options) 4 Different Chiller Manufacturers & 1 Models (Screw 2 and Scroll 3 Designs) 4
Relies on the acoustical credibility of the equipment manufacturer – –
•
•
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May or may not have the capabilities needed Commonly will take an exception
Spec is difficult to enforce –
•
Sound Power and/or Sound Pressure Octave band and/or overall dB and/or dBA levels NC or RC levels
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…)
Performance Specification Example
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Performance Specification Example
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Contradictory Performance Specification
Sound attenuation solution
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quiet
Contradictory Performance Specification
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Design Specifications = “Just Right Prescription” •
Evaluates noise sensitive location(s) to provide – – –
Predictable Performance Accountability Cost Control • •
•
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Right amount of attenuation Accounted for in the budget
Describes, provides performance, and/or illustrates (schematic details) the materials and products needed
Design Specification Schematic Design Detail
ABC model JJJ
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Schematic Design Detail
ABC solution/model
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Design Specification
“Loose” Design Specification
ABC . . . . . . . . . . . . . . .
Result of a “Loose/Generic” spec What is criteria for approving or rejecting?
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“Better” Design Specification
ABC model and manufactured by ABC company or equivalent.
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“Detailed” Design Specification
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“Best” Design Specification
Attenuation
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“Best” Design Specification Cont’d
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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
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Allowance Specification
ABC Acoustic Attenuation
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DEF Company.
Specification Best Practices
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Best Practices Acoustic Design •
Answer 4 design questions 1. 2. 3. 4.
• • • • • 36
Where are we now? Where do we need to be? What needs to be done to get there? 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
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
• • • •
37
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
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
Sub Topics ☺ Construction Trends ☺ Specifications ☺ Vibration Isolation ☺ Chiller Noise Treatments ☺ Roof Mounted Treatments ☺ Duct Work & Silencers ☺ Rooftop Unit Treatments
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Construction Trends • • • • • • • • • 40
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
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
Best Practices Outdoor Chillers • 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 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
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Treating Compressor Circuits
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Result of “generic” spec
50
Air Intake Source Treatments
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52
Condenser Fan Source Treatments • • • •
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Acoustical plenums Plenum with baffles Plenum with silencer bank Individual stack silencers
Open Plenums
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Plenum with Baffles
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Plenum with Silencer Bank
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Not Recommended by OEMs
“Dedicated” Stack Silencers 57
Path Treatments Wall and Fence Liners
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Turnkey Acoustical Barrier Walls
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20+ dBA Attenuation Systems
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Best Practices 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 61
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Poor “Best Practice” This is a seismic job!
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In-Curb Treatment
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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
Integrated Sound Attenuators
66
External Acoustic Duct Lagging
7 - 9 dB reduction in first 3 octave bands 67
Rooftop Unit Condenser Section Treatments
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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
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71
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
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Acoustical Batt Mineral Fiber Packing
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75
76
77
78
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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
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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
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Best Practices Duct Design • • • • • • •
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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
Turbulence = Regenerated Noise
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Regenerated Noise at Fittings Recommended maximum airflow velocities for various installations
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Duct Shapes
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Best Practices Room Diffusers
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• 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 • • • • •
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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
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