Goofy4TheWorld

Can anyone tell me why this is, or if it's just a GIANT typo in Generac's spec sheets seen here.

Comparing all 3 generators' (16/20/22) specs for full load natural gas consumption, the 20kW uses less gas than the 16kW. The 16-20-22 consumption is listed as 218-204-228. This only applies to natural gas, propane follows a logical pattern of higher wattage equals higher consumption.

What is going on here?

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Geoff Z
I asked that question some time ago. I was told by tech it is correct. However I didn’t come away with a real good explanation. The numbers you have listed are 1/2 load. Full load numbers are in keeping where 16kw shows more consumption than 20kw. 
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RJRENTON
Gentlemen, 
My opinion deals with the heating value of the gas or propane fuel.  Natural gas has a NOMINAL heating value of 1000 BTU / cubic foot at 0.6 gravity at the intended use pressure,  The heating value of the natural gas can vary from 920 BTUs - 1020 BTUs) and in this case,  3" WC - 4" WC (inches water column pressure).  Propane (C3H8) has a heating value of approximately 2.5x greater than natural gas (methane or CH4) or 2500 BTU / cu.ft.   But because the natural gas' heating value can change from well head to well head and area,  its performance when combusted varies.  The same thing applies to propane because propane is a derrivitive of crude oil cracking its beating value varies as well.  The only method of determining the fuel's heating value is by a gas calorimiter and measuring the BTU content.  The other variable is the delivery pressure.  Higher pressures will result in more BTUs delivered per unit volume (standard cubic foot) due to the super compressibility factor.  The HP delivered by the engine being fueled is a nomimal number, based on an AVERAGE heating value of the fuel consumed.  There are other trace components of the gases (butane and its isomers, propylene, etc.) that may influence the heating values, depending on their percentages.  And sometimes, gas suppliers add a little nitrogen to the mix to help maintain the volume of the delivered product during periods of high demand.  This is added when the methyl mercapton (the oderant) is introduced into the mix.     But....this is my opinion.
Bob Renton 
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Cobranut
Bob, Shouldn't the fuel consumption specs be quoted using fuel standardized to consistent test values, to enable direct comparison between models, and even between different manufacturers? 
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78buckshot
We have several HVACR techs on this site and I think most would agree that the "standard" for these fuels are as RJRENTON stated. When setting up heating equipment the pressure and orifice size can be changed to meet manufacturers specs for BTU input. In most of the installation specs that I have seen 1000 BTU/cu.ft. for natural and 2550 BTU/cu.ft. for propane are considered as standard. If the exact BTU content is needed you can contact the supplier for more info. I think the generator world uses the same info. Elevation will have an impact on combustion and the machine can be fine-tuned to meet specs, natural gas flow rates can be checked by 'clocking' the gas meter to read cu.ft./hour. I have not seen or used a flow meter on LP but the factory specs for heating equipment already have the BTU content figured in the input charts, we adjust orifice size and manifold pressure for the local elevation.
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Brian Baughman

Can anyone tell me why this is, or if it's just a GIANT typo in Generac's spec sheets seen here.

Comparing all 3 generators' (16/20/22) specs for full load natural gas consumption, the 20kW uses less gas than the 16kW. The 16-20-22 consumption is listed as 218-204-228. This only applies to natural gas, propane follows a logical pattern of higher wattage equals higher consumption.

What is going on here?



Those are the values at 1/2 load, not full load.  The generator fuel consumption is based on many different factors, not just the generator kW rating.  The efficiency of the alternator at loaded levels does play a role in fuel consumption.  Even though those 3 generators use the same engine, they each have a different alternator.
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restosud
The nexus and evolution controlled generators also have different fuel consumption even with equivalent kw ratings.
Perhaps generac uses different testing facilities that have different sources of gas???
one would think a “standard fuel “ would be used.
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BillM
I asked Generac the question directly.  They stated the numbers are correct, it's a different engine design.  I was spec'ed out a 17kW, but wanted to go one up and ended up going two up, to the 22kW because it's quieter.  Did you catch that difference?  It's quieter than the lower watt units and when I bought mine 3 years ago, the 22kW had an aluminum shell where the others were steel.  Now, in hindsight, the aluminum front panel latches is a poor design on mine.  Those tabs get bent.
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Goofy4TheWorld
BillM wrote:
...I was spec'ed out a 17kW, but wanted to go one up and ended up going two up, to the 22kW because it's quieter.  Did you catch that difference?  It's quieter than the lower watt units and when I bought mine 3 years ago, the 22kW had an aluminum shell where the others were steel...


The specs I see show the dB for the 16/20/22 to be 66/66/67, meaning the 22kW is slightly louder...?
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BillM
@Goofy4TheWorld I stand corrected.  You are indeed correct.  The 22 is indeed 1dB louder.  Somewhat related but really doesn't matter, it's listed as quieter in low speed exercise mode by 2 dB.  
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