Factory Utilities
Air changes and dust dilution are different questions. Size for whichever is larger, then check the other has not quietly failed.
— CFM
The larger of the ventilation and dilution requirements
Dilution ventilation is the weakest control in the hierarchy — it lowers average concentration and does nothing for a worker standing beside a source. Occupational cotton dust exposure is regulated and is assessed by personal sampling against the applicable limit, not by a shed-average calculation.
Weaving Shed Dust Extraction Airflow Calculator — free, with the formula and a worked example, at Textile School.