ASHRAE Generator Noise Presentation

1 Generator Noise Control - An OverviewIntroductionlTypes of GeneratorslGenerator Noise SourceslNoise Reduction TechniqueslCase StudyReturn to are two categories of generators: diesel andspark ignited. Spark ignited types include propane andnatural gas right hand graph on the next page shows the soundpower level difference between the two types ofstandard, unhoused generators. Y-axis is sound powerlevel, x-axis is sound pressure level. As can be seen inthe graph, the sound power level for natural gas andpropane are the power level is similar to horsepower it relates tothe total energy produced by the Generator . Independentof distance or left hand graph illustrates the variation of soundlevel with fuel type. This time the values are SoundPressure Levels, dBA. Sound Pressure Level varies withdistance and location from the reference, the SPL of a quiet residentialneighborhood is 45 dBA during daytime hours, 35 dBA atnight.

2 100 feet from a busy freeway is 70 dBA. Normalconversation at 3 feet is 60 TC Noise Control - An OverviewTypes of GeneratorsoDieseloPropaneoNatural GasComparison of Generator Noise with Fuel Band Center Frequency, Power Level, dB re 1 picowatt125 kW Diesel125 kW Natural Gas 125 kW PropaneSound Pressure Level by engine Type, 7 kW Diesel125 kW Natural Gas 125 kW PropaneFuel TypeSound Pressure Level, dB re 20 microPascalsASHRAE TC of GeneratorsComparison of diesel Generator Noise with Size020406080100120140160631252505001000 200040008000 Octave Band Center Frequency, Power Level, dB re 1 picoWatt125 kW Diesel500 kW Diesel1 MW Diesel2 MW DieselSound Pressure Level by engine Size, 7 kW Diesel500 kW Diesel1 MW Diesel2 MW DieselSizeSound Pressure Level, dB re 20 microPascalsAs expected, Noise levels increase with size of of the additional low frequency Noise associated with the 2 MWgenerator is due to the Noise from the radiator fan.

3 As will be shown in alater slideASHRAE TC Noise Control - An OverviewGenerator Noise SourcesoGenerator EngineBlock and AirIntakeThis is the dominantsource of Noise out theair intake openings intorooms containing TC Noise Control - An OverviewPrimary Noise SourcesoRadiator FanRadiator fan Noise combineswith the engine block to be thedominant sources of noiseradiating out of the discharge airopening in rooms we will see in the next slides,with larger engines the noisefrom the radiator fan candominate at least some portionsof the frequency spectrumproduced by the TC Noise Control - An OverviewPrimary Noise SourcesoExhaustoTurbo ChargerASHRAE TC Noise Control - An OverviewPrimary Noise SourcesoLoad Bank 95 dBA @ 10 feetoVibrationnEnginenConnections to ductwork, exhaust pipe,electricalIn our experience load banks are often portable, brought in for occasional are very noisy. Many Noise ordinances will allow portable equipment toexceed a code limit.

4 If the load bank is not portable, or if the Noise ordinancedoes not allow an exemption, it would need to be placed inside the is not normally a significant Noise source, unless the Generator islocated on an upper floor or roof. Spring vibration isolators are normally used toreduce the vibration to the supporting structure. Larger engines can damage thesupporting structure if vibration isolation is not TC Noise Control - An OverviewPrimary Noise Sources2 MW diesel Generator Sources 0204060801001201401606312525050010002000 40008000 Octave Band Center Frequency, Power Level, dB re 1 picoWattEngine Block + RadiatorEngine Block, no RadiatorExhaust Noise , no Muffler2 MW diesel Generator Block + RadiatorEngine Block, no RadiatorExhaust Noise , no MufflerSourceSound Pressure Level, dB re 20 microPascalsThe significance of radiator fan Noise is apparent in this slide,which shows engine sound levels with and without radiatorpresent.

5 No exhaust Noise is present unless TC Noise Control - An OverviewNoise Reduction TechniquesoGenerator RoomsnRoom EnclosureoRoofoWallsoDoorsoInternal LiningnIntake Air andDischarge AiroDuct SilencersoAcoustic LouversoExterior ScreensASHRAE TC Noise Control - An OverviewNoise Reduction TechniquesoExhaust NoisenResistive MufflersnActive Noise ControloStructure Borne Noise & VibrationnSpring Isolators on Generators larger than floor joint is present, weight of concretebeneath Generator should be not less than twicethe Generator pipe connectors, duct connectors,electrical connection at TC mufflers are available in at least three grades grade silencers reduce exhaust Noise by 12-18 grade silencers reduce exhaust Noise by grade silencers reduce exhaust Noise by 25-35 Noise cancellation silencers used to be available as amanufactured product, but are not currently available. Theywere effective in reducing the low frequency tones associatedwith the cylinder TC Noise Control - An OverviewCase Studieso1000 kW Generator , housed inequipment roomoDirect RadiatoroClosest Receiver Property 50 feetASHRAE TC Noise Control - An OverviewCase Studyo1000 kW diesel GeneratoroIn Generator room in lowest level of buildingo50 feet to closest propertyThis shows plan view of generatorinside an enclosed room.

6 This isthe most typical silencers are shown on intakeand discharge openings to room, ascreen is on the outside of theintake opening, and a muffler on theexhaust pipe. Acoustical louversare used sometimes instead of TC Noise Control - An OverviewCase StudyoNoise out of intake air opening to roomnUnhoused Generator SPL at 50 feet, free field =89 dBAnIf Generator is in a room, internal 4 thick liningon two adjacent walls of room, with large inletlouvers close to the side of the Generator asshown in previous slide, SPL at 50 feet = 88 dBAnIf low pressure loss silencers are added to inlet(static pressure drop = at -1000 fpm), SPLat 50 feet = 73 solid screen of sufficient size and mass isincluded outside of intake louvers, SPL at 50feet = 65 TC the inlet louvers were substantially removed fromthe side of the Generator , more reduction would beachieved by placing the Generator in a room withacoustical absorption most cases, the size of the room is limited due tocost, and the outside air inlet louvers are very close tothe engine TC Noise Control - An OverviewCase StudyoNoise out of discharge air openingnSimilar to intake of opening might be slightly less,but radiator fan is closer to Noise levels would be theroughly the same as the intake 89 dBAwithout room, 86 dBA with room, 73 dBAwith silencers, 65 dBA with additionalsolid TC Noise Control - An OverviewCase StudyoExhaust NoisenIn free field, at 50 feet, exhaust with no muffleris 84 dBA, in direction of exhaust up, roughly 5 dBA attenuation, =79 dBA at 50 Industrial Silencer.

7 15 dBA attenuation, 64dBA at 50 Residential silencer instead, 22 dBAattenuation on average, 57 dBA at 50 Critical grade silencer instead, 30 dBAaverage attenuation, 49 dBA at 50 TC Noise Control - An OverviewCase StudyoCombine Noise levels from = 65 dBAoDischarge without screen = 73 dBAoExhaust Noise = 57 dBA withresidential grade silenceroCombined level = 74 dBAoWith screen on discharge, combinedlevel is 68 TC Noise Control - An Overview Return to Case Studyo68 dBA is higher than most ordinance limits forresidential with these significant Noise control measures,required distance between Generator room and closestresidential property would need to be approximately200 feet to reduce Noise levels to 55 dBA would be compatible with most noiseordinances at residential 20 dBA Noise reduction in the room designcan be achieved with longer duct silencers andmultiple exhaust mufflers, but space requirements remote Generator radiators can further reducenoise levels from Generator TC