Is a filter necessary in an induction unit?
No. The secondary air is drawn from the room and induced into the induction unit. A considerable amount of return air goes back to the primary air AHU where, after mixing with the outdoor air introduced to meet the building code ventilation requirements, it is filtered and cooled or heated. It is the same as an all-air system in that the supply air from the outlet entrains room air as it leaves the outlet, to circulate in the space and satisfy the air distribution criteria. The vast majority of early induction installations are with units located beneath windows, in a decorative enclosure, with a low level return air path to the unit. With the carpets of that time and foot traffic, coils were fitted with lint screens to catch carpet fluff and other dust. To this end, the lint screen was successful. The perception developed that all units should have lint screens. With in-ceiling units, this is not necessary. A review of European makers’ catalogues shows that they do not offer lint scre
