I am modeling a residential building under LEED 2009. With reference to
ASHRAE 90.1-2007, Exception 'a' in section G3.1.1 which states that we
should use additional system types for nonpredominant conditions if they
apply to more than 20,000 SF of conditioned space - I am confused which
system type I should use for my corridors and other non-residential
conditioned spaces, which are about 21,000 SF total, spread across 20
floors. Do I use System 7, because my non-residential spaces are located
on more than 5 floors, or use System 3 or 5 because the area is less
than 25,000 SF?

Thanks,

Ritwik Kakati