Definitions


Media Filter - Media Air Filters are made from paper or fibre "fabric" stretched across a plastic or metal frame.  Usually the media is arranged in pleats - a zigzag pattern that increases surface area devoted to collecting particles.

Although they appear solid to the naked eye, media filters are actually quite porous when viewed under a magnifying glass. The fibres criss-cross to form an overlapping pattern, with plenty of tiny spaces for air (and small particles) to pass right through.

Media filters clean the air in three ways: by straining, by impaction (interception), and by diffusion.

Larger particles are strained out of the air, similar to the way "particles" of cooked pasta are strained when poured into a colander. The pasta (particles) are too large to fit through the holes in the colander; the water (air) passes through easily.

Smaller particles are able to pass through the same microscopic holes that allow air through. During their quick journey through the filter fibres, however, these small particles are jostled by random collisions with air molecules, which causes diffusion. This diffusion causes many particles that would otherwise pass through the filter to collide with and stick to the fibres in the process of impaction.

Portable air Cleaner
- Portable Room Air Cleaners are used when central air cleaning isn't possible or practical. People in condominiums, apartments, and individual offices can use a portable room air cleaner, such as the Honeywell® HEPA filter Portable Room Air Cleaner, or Five Seasons Portable Room Electronic Air Cleaner to remove indoor air pollutants.

When properly sized for the room area, these portable air cleaners are just as efficient at removing indoor air pollutants as central air cleaning.

Many allergy sufferers have found that supplementing their central air cleaning with a portable room air cleaner in the bedroom gives them even cleaner air to breathe as they sleep and helps their symptoms significantly.

Charged Media - Charged Media Air Filters also rely on straining, impaction, and static electricity to collect particles. Charged media filters use an external, direct current (dc) voltage source to generate the electrostatic field. Charged media filters are made of fibre glass or cellulose fibres, which can pick up an electrostatic field when a high dc voltage is supplied.

Unfortunately, charged media filters share the same weakness as self-charging filters. The strength of the electrostatic field is insufficient to polarize most particles and the media is too thin for effective straining and impaction.

Electronic Air Cleaner (EAC) - Electronic Air Cleaners operate from a principle everyone learns early in life - that opposites attract.

In scientific jargon, electronic air cleaners are "two-stage electrostatic precipitators". In the first stage, dust particles enter the charging section of the electronic air cleaner and pass between high-voltage ionizing wires. Charged to 8000 volts, these ionizing wires rip electrons from any particle in the vicinity. Particles leave this section carrying an intense positive or negative charge.

In the second stage, these charged particles enter the collection section and encounter a series of collector plates. Positively and negatively charged collector plates shove the particles toward oppositely-charged collector plates, while those same plate exert a nearly irresistible tug on the particles. The dirty air particles strike the charged plates, where hey stick like glue to electrostatic attraction until they are washed away.

Only the very smallest particles can get through, pulled along by a fast-moving airstream before they have a chance to be collected. At maximum airflow rates, Honeywell® electronic air cleaners are approximately 70% efficient, and can be up to 95% efficient at lower airflow rates.

Not all electronic air cleaners are equally efficient, however. Differences in power supply design, ionization voltage, and collector plate spacing all affect efficiency. Taking all of these factors into consideration, Honeywell® builds the most efficient home electronic air cleaners in the industry.

Electrostatic Filter - Self-Charging Media Air Filter (Electrostatic) rely on straining, impaction, and static electricity to clean the air. The media consists of plastic fibres that are excellent electrical insulators, such as polystyrene and polypropylene.

One of the properties of polystyrene is its ability to create static electricity as air moves quickly through the filter. This is why "packing peanuts" cling to anything in their path. Moving air leaves random charges, and the effect is similar to the electrostatic charge that builds up on your body as you shuffle across the carpet in winter, then discharges when you touch a doorknob.

In theory, this electrostatic field polarized dirty air particles, causing more of them to stick to the medium. In practice, self-charging media filters are only marginally better performers than throw-away fibre glass filters of the same density. The strength of the electrostatic field is insufficient to polarize most particles, and the polystyrene media is too thin for effective straining and impaction. Moist air also reduces the static charge.

HEPA Filter - High Efficiency Particulate Air, or HEPA, filters use deeply-folded media to trap particles.  With efficiency ratings of close to 100%, true HEPA filters are the top performers in the air cleaner circle and are used in settings where perfectly clean air is the highest priority.

It takes a powerful fan or blower to move air through a HEPA filter, which rules out their use in typical central system, forced-air applications. But they are perfectly suited for portable air cleaning in conjunction with a powerful fan.

Applications where central system HEPA filters are found include hospital burn-patient rooms and clan-room manufacturing areas.

Some manufacturers offer "HEPA-like" or "HEPA-type" filters. These filters are actually extended-surface media filters and have efficiency ratings of only 10% to 35%.



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