Generac Generator Enclosure to reduce sound

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Designer101

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Location
California
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Solar and ESS Designer
AHJ didnt approve the Generator with higher than 55db.
we already installed solar before and client wants to add Generator to the system.
i found some enclosure online but thy could not provide us the enough documentation to convince AHJ How its going to reduce sound to 55 DB and lower.
they are asking about all the use of dampers and materials and experimentation data to show as proof.
If any body has dealt with Generator enclosure before Please help.
 
retirede said:
I’d start by contacting Generac.
Installing an acoustical enclosure you select on your own could cause all kinds of warranty issues.
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Ya they said they will void any warranty, thanks for the advise I called and asked Generac. Now have to find low rpm generator probably that will have less Kw output and less sound.
 
Designer101 said:
55 Db is the max generator Sound they allowed, They just saw the specs and said it cant be higher than 55 db. The installation is for residential home ,
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How loud something appears to be is exponentially proportional to how close to the source the loudness is measured. If you take a reading on a dB meter an inch from the generator and then do it again at the property line you will get very different numbers.
 
ggunn said:
How loud something appears to be is exponentially proportional to how close to the source the loudness is measured. If you take a reading on a dB meter an inch from the generator and then do it again at the property line you will get very different numbers.
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Exactly! I can’t even hear it at my house!
 
Designer101 said:
55 Db is the max generator Sound they allowed, They just saw the specs and said it cant be higher than 55 db. The installation is for residential home ,
Click to expand...
Designer101 said:
Ya they said they will void any warranty, thanks for the advise I called and asked Generac. Now have to find low rpm generator probably that will have less Kw output and less sound.
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Probably will have to go liquid cooled, 1800 rpm. I think they start at 20-24 KW.
 
Is the AHJ not approving the generator based on the cutsheet of the gen set or is it already installed and the sound level was measured at the property line? Depending on the town, the noise ordinance sound level limits can vary by the time of day and day of the week. I believe the industry standard for generator sound data is based on measuring it at 23 ft. away. It will likely be a challenge to find a gen set that will have a rating of 55DB. If the AHJ has approved units before then you should ask him to provide you with units that they have previously approved. Worst case you may have to hire an acoustical engineer and provide them with the DB data over the different sound frequencies for them to calculate the sound level at the property line.
 
cyriousn said:
Is the AHJ not approving the generator based on the cutsheet of the gen set or is it already installed and the sound level was measured at the property line? Depending on the town, the noise ordinance sound level limits can vary by the time of day and day of the week. I believe the industry standard for generator sound data is based on measuring it at 23 ft. away. It will likely be a challenge to find a gen set that will have a rating of 55DB. If the AHJ has approved units before then you should ask him to provide you with units that they have previously approved. Worst case you may have to hire an acoustical engineer and provide them with the DB data over the different sound frequencies for them to calculate the sound level at the property line.
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Another thing: 55dB isn't very loud, and other ambient noise unrelated to the genny could add to the noise level at the property line.
 
Onan did have a real quiet 20 kw air cooled, looked kinda like a mushroom. Then they went to an aluminum enclosure, so now they are just as loud as Generac. Probably the same enclosure manufacturer as Generac.
 
ggunn said:
How loud something appears to be is exponentially proportional to how close to the source the loudness is measured.
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Not exponential, just a power law. If it were exponential (like the weak nuclear force), nobody would be able to hear anything (or else we'd all go deaf when we get near any sound source)..

Cheers, Wayne
 
wwhitney said:
Not exponential, just a power law.
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Whoops, the sound energy falls as a power law with distance. But how loud something is perceived is logarithmic in sound energy. So sound perception falls logarithmically with distance, not exponentially.

Cheers, Wayne
 
In general, the sound level drops 6dB every time the distance is doubled. So technically at 46 ft. the gen unit sound level should be reduced by 6dB.
 
Along the lines of Hillbilly's posts, the quietest generator I have installed was a diesel Onan with sound enclosure but it was a 250KW, I don't know what they offer in a their smaller versions. You could literally stand next to it under full load and have a conversation at just slightly elevated speaking levels.

Roger
 
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