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Why Return fan CFM ≠ Supply fan CFM - Exhaust fan CFM?

When Open Studio auto-sizes my air handling unit (which has a supply and return fan), it selects the same CFM for each, even though i have a coupled Exhaust fan in the zone. For example, if my supply fan was 6000 CFM and i have a 1000 CFM bathroom exhaust fan, the return fan should only be sized for 5000 CFM, but it thinks it should be 6000 CFM. Why is this? In addition, the economizer should not be balancing the intake and exhaust air from the AHU, it should also reflect this +1000 intake air to keep the building neutral. (i.e. 1000 CFM minimum OA while the exhaust is 0 CFM at the AHU mixing box) Does anyone have advice?

Why Return fan CFM ≠ Supply fan CFM - Exhaust fan CFM?

When Open Studio auto-sizes my air handling unit (which has a supply and return fan), it selects the same CFM for each, even though i have a coupled Exhaust fan in the zone. For example, if my supply fan was 6000 CFM and i have a 1000 CFM bathroom exhaust fan, the return fan should only be sized for 5000 CFM, but it thinks it should be 6000 CFM. Why is this? In addition, the economizer should not be balancing the intake and exhaust air from the AHU, it should also reflect this +1000 intake air to keep the building neutral. (i.e. 1000 CFM minimum OA while the exhaust is 0 CFM at the AHU mixing box) Does anyone have advice?