As noted by the NAFA Guide to Air Filtration (1993), there are two types of air filters: mechanical air filters and electronic air cleaners.
·Mechanical air filters remove dust by capturing it on the filter media, the material that makes up the filter element. This capture involves two different considerations. The first is the probability that a dust particle will collide with one of the "fibers" which make up the filter media. (The word "fibers" is used in the broadest sense to cover any component of filter media). The second is the probability that the particle, once contacting the filter fiber, will continue to adhere to it.
·Electronic air cleaners are devices that, while the dust-laden air is passing through them, impose a charge on dust particles and then set up an electrostatic field to attract the charged particles to oppositely-charged collectors. These collectors are usually parallel plates between which the air passes. They can also be filter media actively electrostatically charged by a continuous external power source.
Various types of media are available. Synthetic media provide high performance in wet or moist conditions and deliver improved overall performance when compared to glass fiber media. Heat sealed, synthetic bag filters are preferred to stitched, fiberglass bag filters. Synthetic media reduces fiber shedding, provides longer life, and lowers resistance to airflow. Additionally, synthetic media filters are available with antimicrobial treatment. Antimicrobial treatments reduce colonization and proliferation of microbes on air filters; an important issue when considering mold production in the filter bank. [Robinson, 1999]
Robinson (1999) notes that, "Electrostatically-charged media also provide very high performance. This charge enables the filter to have very high initial efficiencies with a low resistance to airflow. This media is electrostatically charged at the factory and then made into either a bag type or box type filter." Robinson (1999) also points out that, "…new carbon composite media…can provide a significant performance increase over carbon trays or bulk carbon in HVAC applications." [Robinson, 1999]
Filtration application—chicken house case study
Filtration arrangement—case study
