INTRODUCTION SLIDE

REAL-WORLD HVAC ACOUSTICSA presentation by Steffan Kollevoll of BRD Noise and Vibration Control, Inc.

Acoustics 101Terminology SoundNoiseAmbient NoiseFlanking TransmissionAirborne noiseStructure borne noiseTransmission LossInsertion LossReverberated NoiseSound PowerSound PressureSound Transmission Class (STC)Noise Reduction Coefficient (NRC)Near FieldFar FieldSound Power vs. Sound PressureCritical to understanding manufacturer supplied sound dataAHRI Specification ImpactScheduling sound power vs. sound pressure

A-Weighting of Decibels

Correction factors that turn dB into dBA

Sound Decay (Near vs. Far)Near Field Noise

Decay rate of the sound 4 dB per doubling of distance{Insert decay rate of sound equation}5-30 4 dB decay rateFar Field Noise

Decay rate of the sound 6 dB per doubling of distance{Insert decay rate of sound equation}30 or greater 6 dB decay rate

Indoor Chiller Applications

Design questions to considerWhere are we now? Baseline data AHRI 575Where do we need to be? Acceptance Criteria (NC/dBA)Dealing with subjective criteria Dont want to hear anythingWhat needs to be done to achieve compliance?How much will it cost?

Transmission PathwaysVibration energy transferred from unit to building structure(s).

Airborne radiated noise from equipment components.

Mechanical shaft considerations.

Wall and Ceiling penetrations.

Source vs. Path TreatmentsSource Treatment AttenuationEntry LevelTypical reductions range from 5-7 dBAAirborne and structure borne transmission pathway addressed at the equipmentTestingPath Treatment AttenuationDirect Path vs. Indirect PathA bit more cost effective, can get expensive for full enclosuresTypical reductions range from 8-20 dBATestingSource vs. Path Treatments (Examples)SourceDirect PathIndirect Path

Developing the specification Schedule vs. written specificationDetails to support written specification Clarity for the contractor/equipment biddersIdeally embedded in the specification with the equipment (Div 23)Performance accountabilityNC/dBA requirementsMay require dialogue with acoustic consultant (path analysis)Product performance test dataFactory or Off the Shelf Acoustic PackagesEvaluate for basis and other biddersApproved biddersOther Consideration Developing the budgetInstallationRemedial applicationsMay be limited in attenuation strategiesLimited funds available at the end of the projectBuilding Occupants

Outdoor Chiller / Condensing Unit Applications

Questions to considerWhere are we now? Baseline data AHRI 370, AHRI 270Inside the buildingResidential property linesWhere do we need to be? Acceptance Criteria (NC/dBA)Dealing with subjective criteria We dont want any compliantsRisk Management approachWhat needs to be done to achieve compliance?How much will it cost?

Transmission Pathways

Vibration energy transferred from unit.Grade vs. Rooftop Airborne radiated noise Air intakes, compressor/circuit, condenser fansWindow, wall and roof construction.Concern for noise in building unit(s) serviceNeighboring Property LinesAmbient Noise Ordinances/Codes

Source vs. Path TreatmentsSource Treatment AttenuationEntry LevelTypical reductions range from 2-10 dBAAirborne and structure borne transmission pathway addressed at the equipmentTestingPath Treatment AttenuationDirect Path vs. Indirect PathA bit more cost effective, can get expensive for full enclosuresTypical reductions range from 10-25 dBATesting

Source vs. Path Treatments (examples) Source

Source vs. Path Treatments (examples) Path Indirect

Source vs. Path Treatments (examples) Path Direct

Developing the Specification Boiler plate specification vs. Custom developed specificationSchedule vs. written specificationDetails to support written specification Clarity for the contractor/equipment biddersIdeally embedded in the specification with the equipment (Div 23)Performance accountabilityNC/dBA requirementsMay require dialogue with acoustic consultant (path analysis)Product performance test dataFactory or Off the Shelf Acoustic PackagesEvaluate for BOD and other biddersApproved bidders

Other ConsiderationsValue Engineering

Serviceability and Airflow Considerations

Unit placementCost benefit analysis

Installation

Curb Mounted Rooftop Equipment Application

Transmission Pathways

In-Duct Fan NoiseRadiated NoiseDuctwork Breakout NoiseStructure-borne TransmissionOutdoor NoiseAddressing Transmission (Solutions) In-Duct Fan NoiseDuct Liner and SilencersPlacementNoise reduction required to obtain NC level desiredRadiated NoiseIn-curb acoustic treatmentOld approach vs. newer technologies/productsDuctwork Breakout NoiseAcoustical laggingAcoustic panel discharge plenumsStructure-borne TransmissionExternal vs. unit supplied (internal) vibration isolationOld approach vs. Newer technologiesPenetrations in the roof curbNoise leaks around duct drops and pipe chases

Developing the Specification Needs to address multiple noise transmission pathways

Performance AccountabilitySpecified NC valuesProduct test dataScheduled performance embedded with the equipment.

Aerodynamic performance

Pitfalls of a loose specification

Inspection/Commissioning

Case Histories

Indoor CHILLER Application Hampstead Hill AcademyChiller installed in mechanical room with concrete walls and ceilingMechanical shaft for refrigerant piping connects mechanical room with classrooms on the next 4 levels

Screw chiller installed without vibration isolation for the connected piping or treatment to address airborne radiated noise entering mechanical shaft

Boiler plate specification with entry level sound attenuation may have prevented the problem

NC 45-40 in core learning classroomsBuilding owner highly energized and aggravated at current state of classroom noiseNo money left in the budget for a remedial fix, finger pointing

Outdoor ChILLER Application Cabana Hilton Days INN hotel converted to Cabana Hilton HotelNew chillers adding during renovation225 ton air cooled screw chillers

Bare chillers placed on roof of the building, no attenuation provided on chillers

High rise apartments in downtown Miami FL overlooking Cabana Hiltons roof

Legal action taken by tenantsBuilding owner fined $10K a day for being out of compliance with governing noise ordinance for city of MiamiRooftop Application-Norrisville ESPackaged rooftop air-conditioning units installed for in a school building renovationAll units provided with external vibration isolation and silencers in the ductworkProblems with (1) out of (8) rooftop units; unit directly over the stage area in gymnasiumSpace was split between gym, teachers office and music classroomNC 56Inside of the curb left untreatedLight Gauge sheet metal roof construction, Light Gauge sheet metal curb bottomOvercut duct drop openingsTonal noise from the supply and return fans flanking the curb floor and roof deck around duct drop penetrationsBreak-in/Break-out noiseLight Gauge ductwork

Conclusion / RecapSound Power vs Sound Pressure/Terminology Review

Acoustic Design Review4 questions

Assessment and Problem Definition ReviewTransmission pathwaysProject Specific

Subjective vs Objective Criteria Review

Specification Review