Air Filter Devices

Mechanical Air Filters can be portable units as well as used in central filtration systems. This type of filter has a resistance to air flow that increases with time. As it captures more and more particulate it becomes more efficient due to the clogging factor. On the negative side, they also become less and less energy efficient as it takes more power to force a sufficient amount of air through them.

There are different designs of mechanical filters. A Flat-panel for example, places all the filter media on the same plane. A typical furnace filter is only efficient at removing the particles larger than one micron. This efficiency can be increased by adding layers of fibrous material but of course that increases the resistance to air flow velocity.

Electronically charged mechanical filters, or electrets, have no effect on airflow resistance but can also become mechanically blocked. The deposited material obstructs the electrostatic effect and reduces the collection efficiency.

Electronic Filters are generally marketed as electronic air cleaners and previously referred to as electrostatic precipitators. The simplest form is the negative ion generator which charges particles suspended in the air which then become attracted to and deposited on surfaces within the room. This of course causes soiling problems.

The modern Two Stage Electrostatic Precipitator is still used in central filtration systems (HVAC) as well as in portable units with fans. They collect particulate as it passes between two parallel electrically charged plates.

Advantages: affects sub micron range, low energy costs, constant airflow, reusable plates
Disadvantages: Air must pass through device, efficiency falls off, frequent cleaning, high initial cost, can cause soiling on walls, furniture, etc

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