I'm not really too much in commercial duct design. I most of the time work in refrigeration racks, so forgive my ignorance. Here is the case: as part of the remodeling of a commercial fruit salad preparation / packing area, one of my clients wants to set up an air conditioning system provided with state of the art filtration and air flow. He wishes to install pre-filters, HEPA filters and laminar flow diffusers. All of these combined with the existing 5-ton commercial AHU, 3/4 HP blower motor. When I add up all the expected static pressure drops, I come out with a total external static pressure drop far greater than the unit's allowance, taken from the catalog. What can be done in this case? Some fellow tech recommended an in-line tube-axial belt driven booster fan, located downstream from the AHU, upstream from the pre-filters and HEPA filter racks. Is this the only option or someone knows about any other ? Thank You.