Airborne debris indoors (C) Daniel Friedman Guide to Types of Indoor Air Filters, Air Cleaners and Air Purifiers

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Air purifiers and cleaners:

This article explains the types of air cleaners or air purifiers used to improve indoor air quality in homes. We include a table of types of air cleaners and the types of particles they handle, comparing their ability to remove materials from the air, their ease of maintenance, and their operating cost.

We also provide a MASTER INDEX to this topic, or you can try the page top or bottom SEARCH BOX as a quick way to find information you need.

Air Cleaner / Purifier Types

This article includes excerpts or adaptations from Best Practices Guide to Residential Construction, by Steven Bliss, courtesy of Wiley & Sons.

Our page top photo shows that even the naked eye can see comparatively large airborne particles indoors. But many indoor contaminants are simply too small to see, or are not particles at all but rather gases or chemicals.

Table 7-2 Particulate Air Cleaner Comparison

Table Comparing Particulate Air Cleaner Types (C) J Wiley, Steven Bliss

[Click to enlarge any image]

Best Practices Guide to Residential Construction explains:

There are three main types of particulate air cleaners on the market: mechanical filters, electrostatic filters, and ion generators. In addition, there are filters with adsorbents, such as activated carbon, that are capable of removing certain gases (see Table 7-2above) Most filters are available as standalone units or as add-ons to the home’s HVAC or ventilation system. Some hybrid systems on the market combine two or more strategies, such as a filter to remove particles plus activated carbon to remove odors and organic gases.

Mechanical Filters. These use a matrix of fiberglass or synthetic fibers and resin to filter particles out of air passing through. Some are coated with an oil or adhesive to help trap particles, and others have a static electrical charge. Some types of mechanical filters can be cleaned, but most need to be replaced when full.

As mechanical filters clog, they become more efficient at trapping particles, but airflow is reduced. They can either work in stand-alone units or be incorporated into the HVAC or ventilation system.

Electronic (Electrostatic) Air Cleaners

Electronic air cleaners (EACs) use a series of electrically charged metal plates or media filters to pull particles out of the air stream. They are either portable units designed to clean the air in one or two rooms or central systems connected to the return ductwork of the HVAC system. EAC systems create little resistance to airflow but require a separate fan, which along with the electrical charging device use about 30 to 50 watts of electricity.

Electronic air cleaners are highly efficient at removing both small and large particles, but require more maintenance than many homeowners would like. To remain effective, the filters must be removed regularly and hosed down in a large sink or tub. Some are designed to fit in a dishwasher.

In charging the particles with high voltage, EACs also produce small amounts of ozone, which can be an eye or respiratory irritant at high levels. Most people are not bothered by the amount produced. If this a concern, however, look for a unit with an activated carbon filter to remove the ozone.

Negative Ion Generators to Clean Indoor Air

These work by releasing electrically charged ions, which attach to dust particles in the air causing them to settle on walls, ceilings, furniture, and draperies. Placed too near a wall, they might leave a smudge of particles. Some units contain an optional collector to trap the charged particles in the unit, functioning similarly to an EAC.

Over time, however, the particles can lose their charge and reenter the air. Like EACs, they produce small amounts of ozone. There is little scientific evidence supporting the effectiveness of these units.

Watch out: Do not rely on ozone generators to correct indoor air quality issues, and beware of ion generators that may be adjusted to produce high levels of indoor ozone.



Turbulent Flow Precipitators to Clean Indoor Air

The turbulent flow precipitator (TFP) is a new proprietary technology from Canadian-based Nutech Energy System. The device, which attaches to the return ductwork of an HVAC or ventilation system, contains a fan and a labyrinthine core made of aluminum plates and synthetic fibers.

Turbulence in the air flings the suspended particles out of the airstream where they are trapped by a primary and secondary core, which need replacement in one and three years, respectively. Nutech claims that TFPs will capture 99% of particles larger than 5 microns, 97% from 2 to 3 microns, and 90% from 0.5 to 0.9 microns. A TFP unit with HEPA filtration is also available.

Gas Removal Filters to Clean Indoor Air

To remove gases, such as formaldehyde, combustion fumes, or volatile organic compounds, from the air requires the use of special adsorption media. These media contain materials, such as activated carbon or aluminum oxide, which trap the gases in tiny pores.

Different chemical adsorbents are effective with different gases, and none is effective with every gas found in the typical home. Relatively small quantities of activated charcoal can be very effective at reducing odors, but how well they filter out the low levels of multiple chemical compounds typically found in household air is unclear.

In general the rate of adsorption of a gas is reduced as more of the target gas is captured in the filter media. Researchers have also found that, in many cases, some of the gas is reemitted from the filter back into the air. Scientific evidence about the real-life usefulness of these filters in homes is very limited.

-- Adapted with permission from Best Practices Guide to Residential Construction.


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