Hi everyone,
I have to model system fan power in VAV with PFP boxes in accordance with Table G3.1.2.9 ASHRAE 90.1 2007.
I calculate the system fan power with value of supply air (value calculated by software). Is this the sum of the supply fan, the return fan and the exaust fan powers? If I calculate the supply fan power in this manner, the return fan power as indicated in G3.1.2.8 (with 90% of the supply fan air quantity) and the exhaust fan power based on the exhaust air, when I fill these values in Table 1.4, the allowed fan power is just nearly half of the sum.
I have also considered the Pressure Drop Adjustments.
I have doubts about the fan calculations, because I use the same formula for three calculations.

Could you help me?
Thanks a lot.