Heat Rejection from Kohler Air Compressors - confusing literature

[BronYrAur]

I am trying to understand some literature on Kohler Air compressors. I tried calling them, but got no where fast. Please take a quick look at the attachment from the specs on a 60kW, 60Hz unit.

My task is to ventilate the unit, but I don't fully understand the information. There is a "Cooling" section that discusses the radiator (which will be mounted directly to the unit). In that section, it lists "heat rejected to cooling water" as 3120 BTU/ min.

The next section on "Operation Requirements" lists "heat rejected to ambient air" as 1760 BTU/min for the engine and 440 BTU/min for the Alternator. What are these values? Are they in ADDITION to the radiator heat rejection? In other words, if I remove all the radiator heat, do I still need to remove this heat?

This same section of "Operation Requirements" shows that 6,000 scfm are required for "Radiator-cooled cooling air". What is this? Is it the CFM of the radiator fan? Or is it the additional CFM recommended for general room ventilation?

Thanks for your input.

 

[BronYrAur]

Sorry, brain freeze. I meant generator, not air compressor.

 

[IRstuff]

Don't see your model number, but other Kohler brochures, like:

http://kohlerpower.com/onlinecatalog/pdf/g5206.pdf

seem to suggest that those heat loads are additive, which kind of makes sense to me. While the radiator would ostensibly carry the brunt of the cooling load, the generator is not insulated, so the entire external surface area of the generator and alternator housings would be expected to dump some amount of heat into the air.

That said, your specific brochure seems to show a much poorer efficiency than the one I ran across. Nonetheless, the values are roughly consistent.

An alternate approach is to look at the fuel consumption, i.e., 22.4 m^3/hr and convert that to the equivalent amount of energy. I expect that it will show consistency with the diesel generator with about 146 kW energy consumption rate, which, subtracting out the generated power, leaves roughly 86 kW of heat to be removed. My particular example only specifies about 64 kW of total heat rejection, but that's close enough, I think, since there's nothing about radiated heat rejection.

TTFN

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[BronYrAur]

That's what I'm thinking, but I'm still not sure about the 6,000 SCFM. I plan to duct the radiator to the outdoors, but I don't think the 6000 SCFM is referring to the radiator air flow.

Based on the "heat rejected to ambient air" loads of 1760 and 440 BTU/min, that's a total of 132,000 BTUH. If you do the math with 6,000 cfm, it works out to be approx a 20 deg F delta-T, which is probably typical for overall generator room ventilation.

 

[Wareagl487]

BronYrAur (Mechanical)
29 Dec 11 8:12
That's what I'm thinking, but I'm still not sure about the 6,000 SCFM. I plan to duct the radiator to the outdoors, but I don't think the 6000 SCFM is referring to the radiator air flow.

Based on the "heat rejected to ambient air" loads of 1760 and 440 BTU/min, that's a total of 132,000 BTUH. If you do the math with 6,000 cfm, it works out to be approx a 20 deg F delta-T, which is probably typical for overall generator room ventilation.

Looks correct to me - just so happens the air flow numbers work out essentially the same (6,000 cfm) for both the radiator and heat rejection to the room. Have an intake louver @ 12,000 cfm with a fan @ 6,000 cfm and call it a day.

Andy W.

 

[KLH]

The 6000 cfm is the radiator fan's flow rate. I usually size the discharge louver for 1000 to 1200 fpm. The radiator fan can handle 0.5 inches external s.p., not including the radiator.

Don't forget the intake louver or fan. Size for 6000 cfm (make-up air for the radiator) plus 185 cfm (combustion air).

The make-up air enters the generator room at outdoor ambient temperature, absorbs the heat given off by the generator and alternator, increasing to 20 deg. F above outdoor ambient (like Wareagle487 mentions) and is exhausted through the discharge louver.

Your generator is designed to operate in 122 deg. F ambient. So unless your summer temperatures are above 102 deg. F, this will work fine.

 

[BronYrAur]

This unit is to have a sound enclosure as well, so I won't have much static left over for ductwork. It's too bad that they don't provide external static data.

A quick thought on the delta-T. I am still thinking that the reported "Cooling" load of 3120 BTU/min must be added to the "heat rejected to ambient air" loads of 1760 and 440 BTU/min. Correct?

The air will sweep across the unit and pick up a 20 degrees there and then pass through the radiator coil and pick up another 30 degrees. I am calculating a total load of 319,200 BTUH, which will give a total approx rise of 50 deg.

Agree?

 

[KLH]

The 3120 BTU/min is heat rejected to the cooling water which is then rejected to the exhaust air stream through the radiator. The room never "sees" this heat....you do not have to add it to the other heat rejected to ambient.