If this is a radiator cooled machine and the radiator fan is attached to the engine where air is pulled into the room across the alternator and out the radiator then size the inlet to the room 1/3 larger than the radiator square meter size and you are finished.

If you still want to get scientific, you must also consider the engine air consumption if the intake air via the air filters is in the same room. The engine consumes air and 'pumps' it out as exhaust !

Alternator heat is kW x efficiency so if you have a 100 kVA machine at 0.8 PF this is 80 kW x estimated 96% eff = 3.2 kW entering the room and the balance goes to the grid.

Any large generator manufacturer (Cummins, Cat, MAN, etc) has free programs to calculate all this.

thanks for your points. In fact I had worked on this subject some years ago and forgotten the issue. Engine air consumption was also considered at the time.

I'm from the shipbuliding side. While designing the ventilation system for the Engine Rooms on ships we consider Heat loss due to radiation from alternator as 6% of the alternator rating. Exact figure can be taken from the alternator supplier.

Regards.

Anant.

Anant is more accurate with 6% than I was. I just looked at some generator efficiencies and they vary greatly with load. A 2 MW machine has 6-8% losses depending on load (92% - 94% eff) but in any case, get an eff curve from the alt maker and then you have a real number.

Cheers