App G says that if the proposed building has return fans, the baseline
building is to be modeled with them as well, sized either at the minimum
required to ensure ventilation, or 90% of the supply volume, whichever
is greater. And the fan power calculations show that the KW allowance
is for all supply, return, exhaust and relief fans combined.

How do you generally pro-rate the fan power between supply and return
fans in the baseline model? Ultimately it probably doesn't make too
much difference, but is there an actual ruling that tells you how to do
this?

Thanks,

James Hansen, PE, LEED AP