HEPA is a type of pleated mechanical air filter that is renowned for its efficiency in removing particles from the air. The CADR (Clean Air Delivery Rate) measures the volume of filtered air supplied by an air purifier per unit of time, with three different scores for smoke, pollen and dust, representing different particle sizes. The MERV (Minimum Efficiency Reporting Value) classification of an air filter describes its effectiveness in reducing the level of particles ranging from 0.3 to 10 microns in the air passing through the filter. Therefore, when a cabin air quality system uses a prefilter, such as the RESPA-CF2, it can extend the lifespan of the air conditioning system and reduce downtime, since fewer contaminants reach the filter. If a filter were 100% efficient, none of the particles in a given size range would escape the filter and the air that had passed through it would not contain any particles.
HEPA air filters are tested with DOP (Dioctyl Phthalate), mineral oil and other materials that generate monodisperse particles, which are all of them. In the case of bipolar ionization, positive and negative ions surround the air particles, destroying germs and pathogens present, and the added mass helps air particles to fall to the ground and become trapped in the building's air filter. This means that if an air filter removes particles down to 0.3-10 microns, it is also at least as effective at removing larger particles. On the other hand, in HEPA purifiers, a fan extracts particles suspended in the air through a dense, felt-like filter that has billions of small holes of different sizes. The purpose of the MERV standard is to allow a comparison between apples of the filtering efficiency of various air filters.
It is important to note that your purifier should contain both a good quality Hepa filter and a decent activated carbon filter. If you were to use the HEPA test on a 95% ASHRAE air filter, it would have an efficiency of around 50% on particles the size of 0.3 microns once they have been charged with dust. In fact, HEPA air filters are the ONLY mechanical air filters that have been tested and certified to achieve specific efficiency with a specific particle size. Air purifiers with filters pass air through a filter, where polluting particles or gases are trapped, and return clean air to the room. The only thing that will do this effectively is an activated carbon filter placed directly behind the Hepa filter.
