Air Purifiers

An air purifier is a device which removes contaminants from air. Whilst marketed as being of particularly beneficit to allergy sufferers and asthmatics and to reduce second-hand tobacco smoke. more...

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Use of purifiers

Dust, pollen, pet dander, mold spores, dust mite feces can act as allergens, triggering allergies in sensitive people. Smoke particles and volatile organic compounds (VOCs) can pose a risk to health. Air purifiers are used to reduce the concentration of these airborne contaminants and are especially useful for people who suffer from allergies and asthma. They also reduce the need for frequent household cleaning. Air purifiers use a small amount of electrical energy, causing some expense and environmental effect.

Purifying techniques

Several different processes of varying effectiveness can be used to purify air. Different processes may remove different contaminants, so there is advantage in using more than one process in a purifier.

Filter-based purification traps airborne particles by size exclusion. Air is forced through a filter and particles are physically captured by the filter.;

HEPA filters can, by definition, remove at least 99.97% of 0.3 micrometer particles, and are usually more effective for particles which are larger or slightly smaller. They are effective down to 0.01 micrometers in many cases, but becomes very ineffective for particles smaller than 0.01 micrometer. HEPA purifiers which filter all the air going into, say a clean room, must be arranged so that no air bypasses the HEPA filter. In dusty environments, a HEPA filter may follow an easily-cleaned conventional filter (prefilter) which removes coarser impurities so that the HEPA filter does not need to be changed or cleaned frequently.

Filter for HVAC at MERV 13 or above can remove airborne particles of 0.3 micrometers or larger. A medium efficiency MERV 13 has a capture rate of 75% for particles between 0.3 to 1.0 micrometers. Although the capture rate of a MERV filter is lower than a HEPA filter, a central air system can move significantly more air in the same period of time. Using a high grade MERV filter can be more effective than a high-powered HEPA machine at a fraction of the initial capital expenditure. Unfortunately, most furnace filters are slid in place without an airtight seal, which allows air to pass around the filters. This problem is worse for the higher efficiency MERV filters due to the increase in air resistance. Higher efficiency MERV filters are usually denser and increase air resistance in the central system, requiring a greater air pressure drop, consequently increases energy costs.

Activated carbon is a highly porous material that can absorb volatile chemicals on a molecular basis, but does not remove larger particles. It is normally used in conjunction with other filter technology, especially with HEPA. Air cleaners that do not feature at least 15 lb (7 kg) of carbon can not efficiently remove VOCs, chemicals, and strong odors from the air. Other materials also can absorb chemicals, but at higher cost.; Photocatalytic oxidation (PCO) uses short-wave ultraviolet light (UVC), commonly used for sterilization, to kill 99.9% of bacteria and viruses. Independent research confirms its effectiveness against molds, bacteria, and viruses. UVC in-duct units can be mounted to an existing forced-air HVAC system. PCO is not a filtering technology, as it does not trap or remove particles. It is sometimes coupled with other filtering technologies for air purification. UV sterilization bulbs must be replaced about once a year; manufacturers may require periodic replacement as a condition of warranty.; Electrostatic precipitators are HVAC air cleaners which remove particles from air effectively if used properly.;

Read more at Wikipedia.org