ASHRAE 90.1-2007 section G3.1.2.8 states that if return and relief fans are in the proposed, they must be "modeled" (i.e., they must be accounted for) in the baseline. However, G3.1.2.9 very clearly states that "System fan electrical power [the combined total for each System] for supply, return, exhaust, and relief (excluding power to fan-powered VAV boxes) shall be calculated using the following formulas..." And the term CFMs ("s" subscript is for "supply") is defined as the "the baseline system maximum design supply fan airflow rate in cfm" for both the Sys 1-2 formula and the TABLE G3.1.2.9 formulas used for Sys 3-8. Therefore, because a fan component in ApacheHVAC is essentially an airflow meter that determines fan energy consumption associated with a particular flow rate according to corresponding curves for total static pressure and efficiency, it makes sense that for the Baseline system (and the Baseline ONLY... not the Proposed) the energy consumption for all non-FP-box fans on a baseline system is most accurately accounted for by applying the appropriate combination of static pressure and efficiency values to just the Supply Fan. Doing this will provide exactly the baseline fan power required in the baseline system, per 90.1 PRM, at any particular system supply airflow rate. And, because the entire allotted baseline fan energy is thus determined according to the Supply fan flow rate (just as it is in the PRM formulas), the Baseline system should most definitely NOT have additional fan power modeled for exhaust and relief fans.
