Air Filters: An important step in Air treatment is filtration. Filters can be made from several materials, including paper products and metallic meshes. Filters can come in different MERV ratings, according to the size of particle that cannot pass through. Location of filters vary, but there is almost always one before the main components of the AHU, so as to not introduce contaminants into the sensitive heating/cooling/handling components. There are often filters placed again before the supply ducts to further cleanse the air of contaminants before they reach the occupants.
