Air Handling Units Air Filters

Like most heating/cooling systems, Air Handling Units require air filters to keep the blower/motor clean and to keep dust and dirt off the heating and cooling coils. Some of the older systems use roll filters, which is a very minimum duty air filter media that moves on a roll and maintains a clean air filter area continuously. Roll media filters are MERV 3 or less. In most air handlers today, a MERV 6 or 30% ASHRAE filter is used. These provide good air filtration to protect heating and cooling systems equipment without adding much in static pressure or pressure drop. Like all air moving devices, Air Handling Units are affected by static pressure as well. The ductwork (both supply and return) as well as the air filter, cooling and heating coils and any dampering system will all affect the static pressure or pressure drop and thus affect the amount of horsepower required by the blower/motor to move the required amount of air through the system.

ALL heating/cooling systems is designed with the minimally effective air filters. The air filter that comes with the HVAC system is GENERALLY designed to keep the coils/blower/motor assembly clean. It is not designed for any thing else. THEREFORE... when you add any other type of in-line air filter to the HVAC system, you MUST know the total system static pressure as to make sure the airflow is not affected by adding an air filter that is too restrictive. If, as we mentioned in the above paragraph, you add an air filter that increases the total system static to .6" or .7" you can reduce the airflow by 100 CFM to 200 CFM with a clean air filter. This additional static load increases as the air filter loads up, and decreases the airflow even further and decreases the overall efficiency of the HVAC system

Some Air Handling Units Air Filter Manufacturers

AAF