HUSHCORE® RTU Acoustical Curb Systems Curb Mounted Rooftop Unit (RTU) Problem Definition
Outdoor
Outdoor
Radiated Structure-Borne
Fan Fan
Breakout Breakout
Structure-Borne Regenerated
Radiated
Multi-Path System Problems Require Comprehensive System Solutions BRD HUSHCORE® Solutions have been helping keep Business, Education, Healthcare and Entertainment facilities quiet, inside and outside, since 1975.
2 | From Problem Definition... to Problem Solved RTU Noise Transmission Paths
Fan Noise Some fan types generate higher sound levels than others, but all supply and return air fans will generate sound that travels in duct to diffusers servicing occupied building Fan spaces. Fan noise is often the primary transmission path except when RTUs are located directly above the space they service where the radiated path may dominate. Pay attention to frequency octave band data to address fan blade passage tones.
Radiated Noise Radiated noise is the sound radiating from the unit cabinet through the roof deck inside the RTU curb confines. Radiated noise is most significant in RTUs with DX cooling having Radiated a condensing section with compressors and cooling fans. In-curb acoustical treatments addressing the radiated path should include provisions for sealing around duct drops.
Structure-Borne Noise Any structure that vibrates radiates airborne sound. Structure-borne vibration if not isolated at the unit by the RTU curb can excite building structural components. Roof Structure-Borne steel, metal decking and gypsum board partitions are very efficient transmitters of vibration. Ductwork inside the building must also be isolated from structure.
Duct Breakout Noise Breakout noise is sound passing through the walls of ductwork and silencer casings. It is a function of the component shape and size. Breakout noise is the reason to place Breakout sound attenuators as close to the unit as possible. Breakout noise is usually greatest in the first elbow and 1O’ to 12’ of ductwork directly below the RTU in a downflow Supply Air (SA)/Return Air (RA) configuration.
Regenerated Noise Regenerated noise is noise attributable to obstructions and discontinuities that create turbulence in the otherwise smooth flow of air in duct systems. Probability for turbulence Regenerated and regenerated noise is greatest at the first duct drop elbows. Regenerated noise transmits in duct downstream and also radiates through the breakout path.
Outdoor Noise Outdoor noise is the radiated sound path to nearby community receptor locations. The sound pressure level at a given property line location is a function of the decay rate for Outdoor a given distance and site influence of nearby grade, roof and/or building wall reflecting planes. Outdoor noise is of greatest concern for RTUs with DX cooling that incorporate a condensing unit section containing scroll compressors and condenser cooling fans.
From Problem Definition... to Problem Solved. Learn more at www.hushcore.net or call 610-863-6300
BRD Noise and Vibration Control, Inc. | 3 Multi-Path HUSHCORE® System Solutions
HUSHCORE® Acoustical Vibration Curb Overview
Duct (by others)
Seismic Restrained Isolators
Duct Drop Rails
Air Flow
Supply HUSHCORE® turnkey or A La Carte solutions HUSHCORE® HIC Vibration Isolation Curb are available for Deck™ System greatest design In-Curb Treatment flexibility. HUSH DUCT™ Elbow Attenuator Return
Air Flow
HUSHCORE® RTU Acoustical Curb Systems Selection Guidelines The table below shows various HUSHCORE® System models with the transmission paths they address.
Fan Radiated Structure-Borne Breakout Regenerated HUSHCORE® Acoustical Curb System Fan Radiated Structure-Borne Breakout Regenerated Comments
■■ Standard™ System Excellent strategy for speci- ■■ Plus™ System fying repeatable Entry Level “Best Practices” ■■ Whisper™ “P” System
■■ Standard™ “E” System All these Systems have HDES ■■ Plus™ “E” System HUSH DUCT™ fan attenuation silencers at the roof deck sup- ■■ Whisper™ “E” System ply and return air openings
■■ Whisper™ “V” System These designs require curb ■■ Ultra™ System heights of 36” to 60” to allow for integrated HUSH DUCTS™ ■■ Custom System inside the curb. Service platforms can be integrated into the taller curbs
Please visit our website www.hushcore.net for more information about our A La Carte, Entry Level, High Performance and Custom Design acoustical curbs. CAD details and guide specifications are available for project bid documents and drawings.
4 | From Problem Definition... to Problem Solved Three Levels of HUSHCORE® Technology
HUSHCORE® Entry Level Systems
Direct ducted designs with fan attenuation addressed elsewhere Radiated Structure-Borne
Base™ HUSHCORE® Plus™ System Base™ System System (HIC Curb) (HIC Curb) HVAC Unit
Return Supply Deck™ System
Roof Deck
Air Flow Air Flow
HUSHCORE® High Performance Systems
Plenum curbs with silencers at deck openings Fan Radiated
Base™ HUSHCORE® Whisper™ “E” System Base™ System System (HPC Curb) (HPC Curb) HVAC Unit Structure-Borne Breakout
Return Air Flow Air Flow Supply Deck™ System Regenerated
Roof Deck
HUSH DUCT™ Elbow Silencers
HUSHCORE® Custom Systems
Complete plenum curb integrated designs Fan Radiated
Base™ HUSHCORE® Ultra™ System Base™ System System (HPC Curb) (HPC Curb) HVAC Unit Structure-Borne Breakout
Return Supply
Regenerated
Roof Deck Deck™ System Air Flow Air Flow HUSH DUCT™ Integrated Silencers
BRD Noise and Vibration Control, Inc. | 5 HUSHCORE® Entry Level Systems
Base™ HUSHCORE® Plus™ System Base™ System System (HIC Curb) (HIC Curb) HVAC Unit
Return Supply Deck™ System
Roof Deck
Air Flow Air Flow
Advantages of Using HUSHCORE® Deck™ Systems for In-Curb Acoustical Treatment of RTU Radiated Noise Radiated Structure-Borne HUSHCORE® Deck™ Systems provide designers/specifiers with due diligence and known performance that is not achievable with a traditional gypsum board and batt insulation.
HUSHCORE® Deck™ Systems Proven Solutions Gypsum Board & Batt Insulation Strategy
Performance ■■ Independently tested w/range of attenuation ■■ Unknown
Commissioning ■■ Submittal required per new specification with ■■ No submittals provision for site inspection/verification ■■ No site verification required/specified ■■ 100% confidence provided 50/50 chance it made it in the curb
Weight ■■ Weighs less but performs better due to lab ■■ Weighs more but performs less testing optimization and research
Cost ■■ Provides the best value considering installed ■■ Lower first cost of materials but no cost cost and greatest dBA reductions per dollar advantage considering proper installation spent labor required
Installation ■■ Details specified, including sealing ■■ No specification direction regarding sealing ■■ Flexible materials allow tighter fit and filling (#1 issue for sound control loss) of tight spaces ■■ Rigid materials create challenges for ■■ Commissioning site verification ensures tight spaces and increase the potential consistent quality for resonance ■■ ■■ No special tools required No special tools required
6 | From Problem Definition... to Problem Solved HUSHCORE® Deck™ System In-Curb Research &
Development Performance Optimization Process Radiated
HUSHCORE® R&D efforts have assisted BRD of Airborne Sound Transmission”. During an ASTM Noise and Vibration Control Inc. in optimizing E90 test, a test specimen is mounted between a material selection and construction for maximum room containing an isolated source of noise and performance. Mock-up testing is done in a a receiving room. Sound transmission loss, the NAVLAP certified 3rd party laboratory to the difference between the sound level in the source ASTM E90 test procedure. The picture below room and the receiving room, is measured at is from our latest round of R&D testing. The specific sound frequencies and used to arrive preferred method for determining the STC rating at the STC rating. The higher the STC rating of a product (ASTM E90) is officially called the measured, the quieter it is in the receiving room. “Standard Method for Laboratory Measurement
ASTM E90 – “Standard Test Method for Laboratory Measurement of Airborne Sound Transmission” Results of multiple R&D efforts teach us the following:
1. In-curb performance is often 3. Flexible insulations and mass counter-intuitive and difficult to barriers outperform rigid predict or calculate. materials of comparable mass. 2. More is not always better so filling up 4. In-curb acoustical the RTU curb is an inefficient solution treatments adhere to the law and may yield lower performance. of diminishing return above 8” thick.
The table below summarizes a sampling of the most cost-effective Deck™ System Octave Band Transmission Loss per the ASTM E90 test standard. We are showing full octave performance from 125 Hz to 4000 Hz.
Deck™ Transmission Loss Octave Bands (Hz) System Class A Model STC Fire Rated Cost 125 250 500 1000 2000 4000
DS-32 32 Yes $ 15 20 31 38 50 53
DS-38 38 Yes $ 18 26 41 54 62 70
DS-41 41 No $$ 19 29 43 54 57 68
DS-43 43 Yes $$-$$$ 20 30 49 59 65 72
DS-49 49 Yes $$$ 29 37 50 57 64 71
DS-50 50 No $$ 29 38 53 62 66 73
DS-52 52 Yes $$$ 33 42 50 60 64 71
DS-55 55 No $$$-$$$$ 34 48 56 61 64 68
DS-57 57 Yes $$$$ 34 45 57 62 66 74
Contact BRD at [email protected] to obtain full data results at all 1/3 octave frequencies
BRD Noise and Vibration Control, Inc. | 7 HUSHCORE® High Performance Systems
Base™ HUSHCORE® Whisper™ “E” System Base™ System System (HPC Curb) (HPC Curb) HVAC Unit
Return Air Flow Air Flow Supply Deck™ System
Roof Deck
HUSH DUCT™ Elbow Silencers
Advantages of Using HUSH DUCT™ Multi-Path Elbow Silencers to Increase Attenuation of Fan Noise and Duct Breakout Noise While Controlling Turbulence Fan Breakout Regenerated
HUSH DUCT™ Elbows at Deck Openings Downstream Straight Silencers
Base™ Base™ System System (HIC Curb) (HIC Curb) HVAC Unit HVAC Unit
Supply Supply HUSH SEALANT™ HUSH SEALANT™ Air Flow
Roof Deck Roof Deck Air Flow
HUSH DUCT™ HUSH DUCT™ Attenuator Attenuator
Fan Breakout Regenerated
Acoustical Performance Breakout Performance Aerodynamic Performance
HUSH DUCT™ Can provide greater overall Addresses breakout path at Radiused internal geometry Elbows at Deck and low frequency acoustical duct drop elbows under RTU reduces turbulence and Openings performance per foot of regenerated noise centerline length
Downstream Performance limited by Does not attenuate break- Downstream location does Straight straight duct lengths available. out noise in first duct drop not address self noise Silencers Less Insertion Loss per foot elbows (regenerated) of first elbow
8 | From Problem Definition... to Problem Solved Typical HUSH DUCT™ Construction & Options
Fan Breakout
6 1
5 Specialty HUSH DUCT™ Designs & Options 4 ■■ Transition Silencers
■■ Packless/Fiber-Free Silencers
HUSH DUCT™ 3 ■■ Hospital Grade Silencers Rectangular 2 ■■ Industrial Silencers
■■ Key Tuned Silencers ■■ Silencers with Accessible 1 Exterior casing 24 ga. to 10 ga. for high TL Acoustical Media 2 Acoustically transparent perforated steel ■■ Galvanized, Stainless Steel and retaining screen internals Aluminum Construction 3 Acoustic standoff spacer for media film
4 Media film (Fiberglass Cloth, Mylar, or Tedlar)
5 Acoustical media (Fiberglass or Natural Fiber)
6 Tested to latest revision of ASTM E477
Advantages of Using HUSHCORE® Integrated and Pre-Assembled Vibration Curbs Instead of Traditional Field Assembled Rail Kits. Structure-Borne
Ship & Pick Ship & Assemble
Construction Welded/Fully Assembled Mechanically bolted (Erector Set)
Quality Control Factory Quality Controlled Subject to human assembly error
Factory Curb No factory curb required Requires additional factory curb
Wind/Seismic CAN be designed to meet code wind and CANNOT meet all code wind and seismic seismic loads for all size RTUs loads for all size RTUs
Value Eliminates field assembly labor First cost savings spent on assembly
BRD Noise and Vibration Control, Inc. | 9 HUSHCORE® Solutions for Air Terminal Units in
Rooftop Variable Air Volume (VAV) Systems Fan Radiated
fresh air VAV/FPVAV Problem Definition exhaust air Rooftop VAV Systems provide energy efficient air handling unit variable-speed forced-draft fan cooling and heating using features that allow the variable-speed return air fan unit to vary capacity and airflow. Typical features include control software, variable frequency drives (VFDs), compressors with staged capacity, and multiple space sensors. The result is an HVAC Sys-
air outlet tem with better temperature and humidity control.
variable-volume return air box Where VAV units or fan powered VAV (FPVAV) units can be located in the ceiling plenum above corridors, bathrooms, utility spaces, etc., sound
return air can be buffered from noise sensitive spaces such grille as classrooms, conference rooms, private offices, etc. Where boxes cannot be buffered or where the building design has exposed ceilings, HUSHCORE® Systems can be used to mitigate some or all of the Image courtesy of Slipstream Group, Inc. transmission paths.
VAV Unit Sound Transmission Paths ■■ Cabinet Radiated ■■ Discharge ■■ Primary Air Inlet ■■ Induction Fan Inlet
HUSHCORE® Premium™, Supreme™ or Zenith™ System Solutions can address some or all of these paths.
ATU Unit Manufacturer
6 1 Air Terminal Unit 4 3 2 Primary Air Inlet 4 3 Unit Outlet (Discharge) 4 1 2 Acoustical Manufacturer Air Terminal Unit 4 4 HUSHCORE™ Premium™ System Velcro™ Removable Acoustical Enclosure
5 HUSHCORE™ Inlet/Return HUSH DUCT™ Silencer 4 5 6 HUSHCORE™ Outlet/Discharge HUSH DUCT™ Silencer
10 | From Problem Definition... to Problem Solved Noise Ratings for Variable Air Volume (VAV)
Boxes and Other Air Terminal Units (ATU) Fan Radiated
The AHRI Standard 880 entitled “Performance Rating of Air Terminals” pertains to air control devices used in air distribution systems that provide control of air volume with and without temperature control by means that may or may not include a fan. Standard AHRI-885-2008 outlines transfer functions to convert certified AHRI-880 sound power levels to sound pressure and to a space specific NC level. AHRI-885 facilitates accurate comparisons across ATU manufacturers. Using transfer functions from earlier version AHRI-885-1998 may understate expected sound pressure and NC levels in the built environment.
Determining ATU Sound Levels ■■ Start with Certified Sound Power per AHRI-880-2011 or later revision
■■ NC Ratings are not part of AHRI-880
■■ Use transfer functions in AHRI-885-2008 (not 1998 version) for power to pressure conversion per Appendix E for manufacturer comparisons
■■ Separate transfer functions for radiated and discharge paths AHRI Test Standards ■■ ATU catalog NC ratings are not likely to match actual NC in the built environment
ATU Manufacturer’s Sound Ratings: Responsible Engineering or Dubious Data
Responsible Engineering Dubious Data
Baseline Data Uses certified AHRI-880 baseline data to the Uses AHRI-880 baseline data from an latest revision outdated standard revision
Transfer Functions Project specific correction factors selected AHRI-885 transfer functions selected per building design without knowledge of built environment
Transfer Function Itemizes selected project specific attenua- May not itemize corrections assumed with Documentation tion values/transfer functions/ corrections listed ATU NC data
Other Contributions Considers RTU upstream contribution and Does NOT consider RTU upstream possible impact on Room NC level contribution to overall level
Typical Transfer Functions per AHRI-885
Octave Band (Hz) 125 250 500 1000 2000 4000 Note
Radiated dB 18 19 20 26 31 36 1
Discharge Attenuation dB 29 30 41 51 52 39 2
Notes: 1. Based on Environmental Effect and Ceiling/Space Effect 2. Based on Environmental Effect, 5’ of lined duct, end reflection, 5’ of flex duct, space effect and sound power division
BRD Noise and Vibration Control, Inc. | 11 How To Specify HUSHCORE® Acoustical/Vibration Curb Systems
Key Elements of Effective Acoustical Design Resources Available at www.hushcore.net Specifications in Word, PDF and CAD File Formats ■■ Acoustical/Aerodynamic Performance ■■ CAD Details
■■ Acceptance Criteria in dBA or NC ■■ Word Specifications in 3-part format
■■ Design Prescription to meet above ■■ Drawing Schedule Templates
■■ Performance Accountability ■■ Short Form Notes
■■ Installation Guidelines ■■ Installation Guidelines
■■ RTU/Equipment Compatibility ■■ Product Literature
CAD Detail Example HUSHCORE® Plus™ “E” System Model HIC-DS-41-E
HVAC Unit Specification Tips: 13 1 3 ■■ Embed Word spec with RTU/Equipment spec 12 6 5 2 4 ■■ Use 2 to 3 dB “Safety Factor” when modeling
■■ Require single source responsibility 11 8 7 9
14 10
RTU Unit Manufacturer HVAC Contractor
1 RTU Base 8 Ductwork
2 SA/RA Unit Openings 9 Roof Deck Flashed to within 0.25" of all Duct Drops but not in contact with Duct Wall
10 Submit Letter of Certification from Acoustical Acoustical Manufacturer Supplier following inspection 3 Integral Curb Duct Supports
4 2” Deflection Fully Assembled HUSH CURB™ General Contractor Model HIC-2 11 Building Steel 5 HUSH SEALANT™ Acoustical Caulk at all Duct Drops & Curb Perimeter 12 Built-Up Roof or Concrete
6 HUSHCORE® DS-41 Deck™ System In-Curb 13 Insulation and Cant Strip Acoustical Treatment (rated at STC-41) 14 Curb Slope requirements where applicable 7 HUSH DUCT™ Model HDES Elbow Silencer
12 | From Problem Definition... to Problem Solved Evaluating RTU Equipment Sound Ratings: Sound Power vs. Sound Pressure
Sound Power (Lw) Sound Pressure (Lp) CAUSE EFFECT
dB Decibel referenced to 10-12 Watts Decibel referenced to 2 x 10-5 Pascals
Accurate Reportable and Verifiable Can vary based on modeling or Consistency Testing Standards measurement methodology
Location Data at the acoustic center of the equipment Data for a location in the built environment
Data is independent of environmental Project specific levels in the built Environmental Factor influence environment
Allows comparisons among equipment Complicates equipment comparisons due Equipment Comparisons manufacturers to modeling variability
Data Uses Used to define equipment baseline Used to define space levels
Recommended AHRI Noise Standards How Do AMCA Noise Standards for Rooftop Units Compare to AHRI? Rooftop Units are one of the few pieces of HVAC Although AMCA 300 and AHRI-260 are both equipment to be rated by two separate noise rated in decibels per octave bands, that is where standards published by the Air-Conditioning, the similarities stop. AMCA 300 is a test proce- Heating and Refrigeration Institute (AHRI). Both dure prescribed by the Air Movement and Control standards are expressed as baseline sound power Association for bare fans while AHRI-260 rates the values. AHRI Standard 260 pertains to RTUs and unit performance inclusive of appurtenances such all HVAC Units that have duct connections. The as coils, filters, mix boxes and cabinet influences. condensing section part of many Rooftop Units Comparisons of unit sound levels tested to AMCA is rated per AHRI Standard 370. These standards vs AHRI standards are not valid or reliable. AMCA produce accurate and verifiable data specific to “fan only” data does not consider the impact of the the equipment configuration. RTU cabinet as more turbulent airflow patterns in and out of the fan can produce higher sound levels. When equipment manufacturers offer AMCA data for their unit performance, it is often because they are a custom manufacturer where standardized AHRI testing of the equipment is not practical/ feasible. AHRI data considers supply fan contribu- tion as well as secondary sources such as return/ exhaust fans and compressors.
"When reviewing manufacturer's sound data, obtain certification that the data has been obtained according to one or more of the relevant industry standards."
BRD Noise and Vibration Control, Inc. | 13 Just Right Acoustics™ Acoustical Modeling and Lay-In Service
Information Needed for Multi-Path Analysis
Transmission Path to be Modeled
Fan Radiated Structure-Borne Breakout Regenerated Outdoor Information Needed Fan Radiated Structure-Borne Breakout Regenerated Outdoor
AHRI Baseline Sound Power
NC Target in Receiver Space RTU CFM Fan RPM Ductwork Layouts & Elevations Ductwork Gauges Size of Receiver Space
Distance to the Property Line
Notes: 1. Regenerated noise levels cannot be modeled where duct design deviates from ASHRAE/SMACNA industry guidelines 2. Diffusers should be selected for NC rating 10 points below NC target 3. See recommended ductwork velocity guidelines at https://hushcore.net/duct-work/
Deliverable Example: K-12 Education RTU-2A with Target NC-35
Noise Criteria Curves 100 Path Summation with Attenuation 90 Octave Band (Hz) 63 125 250 500 1000 2000 4000 8000 80
70 Radiated Path 45 38 29 18 11 1 3 0
60 NC-65 NC-60 Breakout Path 52 24 20 13 9 7 5 5 50 NC-55 NC-50 40 NC-45 Supply Path 45 25 23 18 15 9 7 3 NC-40 30 NC-35 NC-30 Return Path 52 34 29 23 16 11 9 5 20 NC-25 NC-20
Octave Band Level (dB Re 0.0002 Microbar) Path Summation 56 40 33 25 20 14 13 10 10 63 125 250 500 1000 2000 4000 8000 Mid-Frequency (Hz)
RTU-2A (Untreated) - NC-65+ NC-35 Design Goal RTU-2A (Treated) - NC-30
14 | From Problem Definition... to Problem Solved HUSH SCREEN™ Versatile Acoustical/Visual
Equipment Screening Options Outdoor
■■ Equipment concealment without roof penetration ■■ Heights up to 108” depending on cabinet height and design wind load ■■ RTU curb mounted support good up to 90 MPH wind load ■■ Acoustical Performance up to STC-35
■■ RTU direct cabinet mounted support good up to ■■ Sliding panel easy access 225 MPH wind load ■■ Pedestal mounting options (Requires roof pene- ■■ Clearances up to 38” from RTU cabinet tration) for equipment clearances greater than 38”
Available in Both Curb Supported (see below) and Unit Supported Designs
HUSHCORE® wind rated curb with bracketry, out Finished HUSH SCREEN™ with single tier modular riggers, twin track rails and vertical columns with sliding access acoustical panels. This system is wind racking braces. This methodology does not require load rated without roof penetrations. approval by the RTU manufacturer.
HUSH COVER™ Compressor Sound Covers
■■ Reduces compressor radiated noise (whine)
■■ Removable Replaceable Construction
■■ HUSH COVER™ HC-500S-1 rated at STC-29
■■ Outdoor UV compatible construction with Silicone Impregnated Fiberglass Cloth exterior jacket
■■ Also available for use with Air Cooled Chillers, valves and other equipment ■■ Tested per ASTM E-1222 "Standard Test Method for Laboratory Measurement of the Insertion Loss of Pipe Lagging Systems"
1/3 Octave Band (Hz) Insertion Loss Acoustical Performance per ASTM E-1222
315 400 500 630 800 1000 1250 1600 2000 2500 3150 4000 5000
4 4 9 15 12 19 22 23 26 28 27 30 30
BRD Noise and Vibration Control, Inc. | 15 Quiet Buildings Help Make Quiet Communities
With HUSHCORE® Systems, quiet RTUs keep neighbors happy and building owners Outdoor ordinance compliant.
Key
1 Unitary™ "TMSB" System acoustical condenser fan discharge stack
2 Standard™ "SL" System HUSH COVERS™ 6 1 for scroll compressors 5 3 Plus™ System vibration curb with Deck™ 1 System DS-52 acoustical package
3 4 Louver™ System condenser air intake 2 HDAL HUSH DUCTS™ 4 5 HUSH SCREEN™ curb/unit supported acoustical screen
6 Rooftop unit with condenser section
1 5
4 1
Louver™ System RTU condenser Unitary™ “TMSB” top view HUSH RTU curb mounted two-tiered sliding intake, HUSH DUCT™ fan discharge DUCTS™ panel HUSH SCREEN™ stack and compressor HUSH COVERS™
From Problem Definition... to Problem Solved. Learn more at www.hushcore.net or call 610-863-6300
112 Fairview Ave., P.O. Box 127 | Wind Gap, PA 18091-0127 16 | From Problem Definition... to Problem Solved p: 610-863-6300 | f: 610-863-4230 | w: hushcore.net