Information about air filters, mechanical, air conditioning, air handling units, ducting, filtration, particles, strainers, impingement, dry media filters, panel filters, dust, hepa, clean room ...

Mechanical Air Filters - Trapping the Air Particles

By: Thomas Yoon

Air filters have modest, yet important roles to play in an air conditioning system. The effects of poor air filtration can be widespread and extensive. Most people do not realize their importance because these effects happen so gradually. Without filters, the cooling coils of Air Handling Units get choked up, and the ducting collect dusts.

Filtration occurs anytime the air carrying suspended matter flows through a strainer of some sort.

All commercial air filters are statistical filters. This means, that they are built to collect a certain particle size, but they cannot collect all particles. They are not 100% perfect strainers.

Two types of filters used in air filtration are mechanical filters and electronic air cleaners. Mechanical filters are divided into two types: Impingement and Dry Media types.

Impingement filters trap particles in tiny zigzag channels that force the air-stream to change directions frequently as it passes through the media. Because of their inertia, the heavier particles colliding with the media stick there. These zigzag channels could be tiny baffles that are stamped or expanded in a material, or could be layers of spun glass fiber, matted together in a random fashion.

Impingement filters are generally high velocity filters. The velocity of the air moving through the filtering media will range from 250 to 650 fpm.

Viscous impingement filters are panel filters with a viscous coating on the media to capture particles. Usually the coating is an odorless mineral oil. Viscous impingement filters are designed to trap fairly large dust particles. For air conditioning systems, these throwaway filters consist of fiberglass, cellulose fiber, or animal hair mat mounted on inexpensive cardboard frames.

Dry Media Filters lack the tacky coating that viscous impingement filters have. Dry media filters remove particles largely by interception and straining.

Interception means to filter out the particles using the natural forces of attraction between molecules. Straining means to remove the particles that are too large to pass through the openings between the fibers.

The media material can be almost any densely packed fiber, ranging from felt or cotton to synthetics and porous paper. These are made into tightly pleated fiber mats.

Dry media filters are made as plain panel, extended surface and automatic roll types. All these plain panel filters are throwaway. Extended surface dry media filters are made pleated, or as bags.

Super interception extended surface filters called HEPA (High Efficiency Particulate Air) filters are used when there is a need for very clean air conditioning environment.

Folks, it's time to clean up!

Until next time…

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