On a large old central AHU (30000 cfm), the maintenance wants to increase the airflow. I think that the chill water coil should have been designed for a specific airflow and we can not just increase the fan cfm. Please comment.
Thanks
A big issue to watch would be the velocity over the coil (as AbbyNormal alludes to). If the air over the coil velocity increases significantly over 500fpm you'll start blowing water off the coil and into the ductwork... not usually a good thing.
If the air flow face velocity is les then 500 fpm then you can increase it. With draw-through systems, limit cooling-coil average face velocity at design conditions to 500 fpm.
Because of the difficulty in predicting variations in localized coil velocities, avoid blow-through designs when possible. When a blow-through design is necessary, limit cooling-coil face velocity at design conditions to less than 500 fpm to avoid carryover from certain sections of the coil.