What Types of Filters are Used to Purify Air?

Air filters are devices used to remove airborne particles, contaminants, and microorganisms that can be hazardous to health and the environment. In industrial settings, air filters help maintain product quality and protect critical equipment from damage. Cleanroom environments rely heavily on air filters to control contamination. Exhaust and flue gases are filtered and cleaned before being released into the atmosphere.

Air filters are also found in many homes, offices, retail spaces, laboratories, clinics, and hospitals. Air filtration is the most commonly used technology to remove particles from an air stream due to its relative ease and flexibility.

Cloth

and fibrous filters are both used for the control of suspended particles. Cloth filters are made of woven and felt fabrics that collect particles mainly on their surface. They are often used in the form of bags that hang inside a large housing.

Fibrous filters, which are more commonly used in workplace applications, are a nonwoven mat of individual fibers randomly oriented in two dimensions perpendicular to the air flow. Particles are often collected along the depth of a fibrous filter rather than just on its surface. The fiber diameter range for a given filter is usually wide, and these diameters can range from less than 1 μm to several hundred microns. Fibers are made from a variety of materials, including fiberglass and various polymers. Researchers have studied the mechanisms by which fibrous filters collect particles theoretically, experimentally, and using numerical models.

The most predominant mechanisms contributing to particle collection are interception, inertial impact, and diffusion.

HEPA

filters are better at cleaning particles from the air. The 0.3 micron diameter specification is worst-case or most penetrating particle size (MPPS). Particles that are larger or smaller are trapped with even greater efficiency. Using the worst particle size results in the worst-case efficiency rating (i.e., Minimum Efficiency Report Value or MERV).

MERV values report a filter's ability to capture larger particles between 0.3 and 10 microns (µm). EH&S recommends HEPA filters for particles and aerosols.

Carbon

air filters are the most commonly used filters to remove gases. They are designed to filter gases through a bed of activated carbon (also called activated charcoal) and are typically used to combat volatile organic compounds (VOCs) released by common household products. They are also often used to eliminate odors from the air, such as the smell of tobacco smoke.

However, they cannot remove fine particles such as mold, dust, or pollen from the air.

Foam

air filters are made of designed porous foams made of polyurethane, polyether, polyester, or a combination of those materials. The starting price of this type of air filter for HVAC systems is high but should be considered an investment that will last for many years. Understanding the different types of air filters for homes is the first step to getting the best indoor air quality you deserve. In addition, because it does not remove particles—which are a major type of indoor air pollutant—only part of the problem of indoor air pollution would be addressed. Charcoal air filters can be an important part of your home's air purification system but must be used properly. Paper air filters allow the separation of small particles by allowing air to pass through their fine pores. When it comes to air filters for HVAC systems, media filters can provide more benefits than standard filters with high MERV ratings.

Air sterilization is the physical removal of microorganisms from the air using filters with adequate retention efficiency. Engine air filters must be replaced between 15,000 and 30,000 miles depending on vehicle type and driving conditions. Gas turbine air intake filter technology has improved significantly in recent years due to improvements in aerodynamics and fluid dynamics of the air compressor part of gas turbines. This causes the engine of an HVAC unit or air cleaner equipment to work harder to push air out of the filter media resulting in higher energy consumption. Activated carbon air filters are effective in removing gaseous pollutants, fumes, vapors, and odors present in the air. Some people need HVAC system filters that keep the air free of allergens and other contaminants while others just need a basic filter to get the job done.

These filters aren't known for improving air quality as they can't put much effort into it and can only trap some of the dust and allergens.