Presently, most AHUs have a secondary filter which can be possibly an Digital air filter or bag filter which has a filtration grade of all around F9 or MERV13. This kind of filtration grade not only shields the AHUs but will also offers cleaner air for the men and women. https://chiller-hire00987.blogdal.com/32630394/a-simple-key-for-air-handling-unit-ahu-hire-unveiled