Cleanrooms commonly use HEPA filters in air recirculation. These filters are the main causes of filter system energy consumption in this kind of laboratory. However, filtration of the make-up outside air for a cleanroom also consumes some energy. The air flow usually requires filtration with a 20-25 percent efficient prefilter and a 90-95 percent efficient final filter. [NAFA Guide..., 1993]
All classes of cleanrooms do not require the same recirculation rate or degree of air filtration. Down-flow cleanroom classes can be related to the percentage of the ceiling area that contains HEPA filters. According to the NAFA Guide to Air Filtration (1993), several sources suggest the following relationships between cleanroom class and percent of the ceiling that should incorporate HEPA filters:
ClassPercent
(Fed. Std. 209)(Ceiling Area)
100 90
1,00075
10,00060
100,00040
Air cleanliness of less than Class 100 requires the use of ULPA or SULPA filters in the ceiling. The filters should make up at least 90 percent of the ceiling.
