Question about Operating Decibels

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Mark
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We've installed a number of Generac whole house generators on homes we've built for our customers, some air cooled but mostly larger liquid cooled units. My question is about the operating decibels as we get asked this quite a bit by our clients considering having a whole house generator. I've been pleased with the QuietSource Series and especially the 48kW 5.4L V-8, however this unit was recently discontinued and replaced by a 48kW 4.5L 4 cylinder engine. Last week we installed a QT Series 80kW which also has the 5.4L V-8 but operates at 3600RPM vs the 48kW which operates at 1800 RPM. The 80Kw unit is considerably louder, surprisingly so. I've got another project that may require something larger than the 80kW, maybe 130 or 150kW. Can you give us some insight on which liquid cooled units operate the quietest? The 80kW operating in quiet exercise mode which I believe is 1800RPM is very low decibels, I'm quite pleased about that in comparison to when it is operating at load. Also I wish they had not discontinued the 5.4L 48kW unit, that was a good strong engine and I'm not sure about the new version 4.5L engine. Any thoughts on this would be helpful too, thank you.
78buckshot
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When noise is a big concern the 1800 RPM units are the winner. With the big kw units you are dealing with the location of the generator is probably the bigger factor. 4.5 litre 4 cylinder?, what brand engine?
Mark
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I believe the new 4.5L engine being offered in the 48kW units are made by Generac.
78buckshot
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I have not seen the specs on the newest units, 4.5 litre comes up as a diesel Iveco engine. Can you drop down to a 70kw which uses the 6.8 litre Ford running at 1800 RPM. Generac sources all of the liquid cooled engines from other manufacturers - nat. gas, Lp, diesel. I would be very specific when ordering the generator that you want the four pole 1800 RPM unit closest to the size needed.
Chris
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The 4.5L is designed and built by Generac (according to them) and is basically half of their popular 9.0L engine used in their Industrial platforms.

As Buckshot said, 1800 RPM units are where it's at.

The 100kW and 130kW operate the engine at a lower RPM though (2300 and 3000) and then use a gearbox to turn the alternator at the desired RPM.
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Mark
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Thank you for your insight, I did notice in the comparison detail that the 100kW and the 130 kW do operate below the 3600RPM level, I just wasn't sure how much of a difference that would make. According to the spec's published by Generac, the 70kW sound emissions (dB at 23ft.) is 64 in exercise and 72 at normal load. The 80kW is 65 & 74, 100kW 68 & 72, 130kW 69 & 75 and the 150kW is 66 & 79. I just wasn't sure of the impact of that amount of difference. We are currently figuring what we will need to supply a home with whole house backup that has 800 amp switch gear.

All of these units are very good at what they do, we just try to inform our end users as to what to expect so they are not disappointed after the installation. We did do one installation with a 400kW Industrial Unit and it was surprising quiet, as a matter of fact, a lot quieter than the 80kW.

(On a side note - I currently have the 48kW 5.4L Generac with a load shedding transfer switch at my own house and have been quite pleased with the operation and the sound emission - stated to be 63 in exercise and 68 under load in the specification literature.)
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