Air purifier

A Sharp FU-888SV Plasmacluster air purifier.

The same air purifier, cover removed.

File:Stand Alone.JPG

A Genano 310

An air purifier is a device which removes contaminants from the air. Air purifiers for residential use are commonly marketed as being particularly beneficial to allergy sufferers and asthmatics, and at reducing or eliminating second-hand tobacco smoke.Commercial grade air purifiers are manufactured as both a small stand-alone unit, and as larger units that can be affixed to an air handler unit (AHU) or to an HVAC unit found in the medical, industrial, and commercial industries.

Use of purifiers

Dust, pollen, pet dander, mold spores, and 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. Exposure to various components such as VOCs increases the likelihood of experiencing symptoms of sick building syndrome. Additionally, with the advancement in technology, air purifiers are becoming increasingly capable of capturing a greater number of bacterial, virus, and DNA particulates. Air purifiers are used to reduce the concentration of these airborne contaminants and though very useful for people who suffer from allergies and asthma, technological and scientific studies are finding that poor air quality is more a contributing factor of some forms of cancer, respiratory illnesses, COPD, and other pulmonary infections and illnesses. They also reduce the need for frequent room and area cleaning. Air purifiers use a small amount of electrical energy, causing a small amount of 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 become very ineffective for particles smaller than 0.01 micrometer. HEPA purifiers which filter all the air going into 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. HEPA filters do not generate ozone or other harmful byproducts.

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 that of 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 using 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 because of 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 and consequently increasing energy costs.

• Activated carbon is a highly porous material that can adsorb volatile chemicals on a molecular basis, but does not remove larger particles. It is important to note that the adsorption process when using activated carbon must reach equilibrium thus it may be difficult to completely remove contaminants. Activated carbon is merely a process of changing contaminants from a gaseous phase to a solid phase, when aggravated or disturbed contaminants can be regenerated in indoor air sources. Activated carbon can be used at room temperature and has a long history of commercial use. It is normally used in conjunction with other filter technology, especially with HEPA. Other materials can also absorb chemicals, but at higher cost.

• Photocatalytic Oxidation (PCO) is an emerging technology in the HVAC industry that has great potential for application toward improvement of indoor air quality. In addition to the prospect of IAQ benefits, it has the added potential for limiting the introduction of unconditioned air to the building space, thereby presenting an opportunity to achieve energy savings over classical prescriptive designs. As of February 2007 there was disputable concern raised by Lawrence Berkeley National Laboratory that PCO may increase the amount of formaldehyde in real indoor environments. As with other advanced technologies, sound engineering principles and practices should be employed by the HVAC designer to ensure proper application of the technology. Photocatalytic oxidation systems are able to completely oxidize and degrade organic contaminants. For example, Volatile Organic Compounds found low concentrations within a few hundred ppmv or less are the most likely to be completely oxidized.(PCO) uses short-wave ultraviolet light (UVC), commonly used for sterilization, to kill 99.9% of 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. Photocatalytic Oxidation systems often have high commercial costs.

• Air Ionizer purifiers use charged electrical surfaces or needles to generate electrically charged air or gas ions. These Ions attach to airborne particles which are then electrostatically attracted to a charged collector plate. This mechanism produces trace amounts of ozone and other oxidants as by-products. Most ionizers produce less than 0.05 ppm of ozone, an industrial safety standard. There are two major subdivisions: the fanless ionizer and fan-based ionizer. Fanless ionizers are noiseless and use little power, but are less efficient at air purification. Fan-based ionizers clean and distribute air much faster. Permanently mounted home and industrial ionizer purifiers are called electrostatic precipitators

• Liquid Ioniser purifiers use a capillary to feed liquid into an ionisation field that creates electrically charged liquid ions. Liquid ions only retain a small enough charge so that they are able to float on the wind whilst still effectively purifying the air. Liquid ions attach themselves to airborne particles in a similar way to air ionizer purifiers. However as liquid is charged rather than air/gas they absorb the pollutants in the air. In the process of creating Liquid ions there are no by-products produced such as ozone or oxidants.

Liquid ions can be seen by the naked eye under the correct lighting conditions unlike plasma which cannot.

• Ozone generators produce ozone, and are sometimes sold as whole house air cleaners. Unlike ionizers, ozone generators are designed to produce significant amounts of ozone, a strong oxidant gas which can oxidize many other chemicals. The only safe use of ozone generators is in unoccupied rooms, utilising "shock treatment" commercial ozone generators that produce over 3000 mg of ozone per hour. Restoration contractors use these types of ozone generators to remove smoke odors after fire damage, musty smells after flooding, mold (including toxic molds), and the stench caused by decaying flesh which cannot be removed by bleach or anything else except for ozone. However, it is not healthy to breathe ozone gas, and one should use extreme caution when buying a room air purifier that also produces ozone.

Consumer concerns

When selecting air purifiers, consumers are influenced by several factors besides cleaning ability. These include possible hazardous gaseous by-products, noise level, frequency of filter replacement, electrical consumption, and visual appeal. Ozone production is typical for air ionizing purifiers and has received much attention recently. Although high concentration of ozone is dangerous, most air ionizers produce low amounts of ozone (<0.05 ppm). The noise level of a purifier can be obtained easily through a customer service department and is usually reported in decibels (dB). The noise levels for most purifiers are low compared to many other home appliances and are not expected to cause hearing loss. However, purifiers are expected to operate over long periods of time. Therefore, even a moderate level of noise can be disturbing to some people. Frequency of filter replacement and electrical consumption are the major operation costs for any purifier. There are many different types of filters; some can be cleaned by water, by hand or by vacuum cleaner, while others need to be replaced every few months or years. Some purifiers are certified as ENERGY STAR and are energy efficient.

HEPA technology is often used in portable air purifiers as it removes common airborne allergens. The US Department of Energy has rigid requirements manufacturers must pass to meet HEPA requirements. The HEPA specification requires removal of at least 99.97% of 0.3 micrometres airborne pollutants. Products that claim to be "HEPA-type", "HEPA-like", or "99% HEPA" do not satisfy these requirements and may have been tested in independent laboratories.

Other factors that buyers consider when purchasing an air purifier are: the area coverage; the Air Changes Per Hour, which indicates how frequently the air purifier can exchange all the air in a given room; the Clean Air Delivery Rate, which determines how well air has been purified; energy usage; and the cost of the replacement filters.

Air ionizers and ozone

As with all health-related appliances, there is some controversy surrounding the claims of certain companies, specifically involving ionic air purifiers. Particularly, some ionic air purifiers generate ozone, an energetic allotrope of three oxygen atoms, and in the presence of humidity, small amounts of NOx (laughing gas). Ironically, people who have asthma and allergy are most prone to the adverse effects of high levels of ozone. For example, increasing ozone concentrations to unsafe levels can increase the risk of asthma attacks. Due to the below average performance and potential health risks, Consumer Reports have advised against using ozone producing air purifiers. Ozone Generators used for shock treatments (unoccupied rooms) which are needed by smoke, mold, and odor remediation contractors as well as crime scene cleanup companies to oxidize and permanently remove smoke, mold, and odor damage are however considered a valuable and effective tool when used correctly for commerical and industrial purposes. However, there is a growing body of evidence that these machines can produce undesirable by-products as evidenced by an Environmental Protection Agency report that can be found at http://www.epa.gov/iaq/pubs/ozonegen.html

In September, 2007, the California Air Resources Board announced a ban of in-home ozone producing air purifiers. This law, which will take effect in 2009, will require testing and certification of all types of air purifiers to verify that they don't generate too much ozone. This ban does not affect shock treatment ozone generators however for commercial and industrial use. Studies indicate that some ionic air purifiers produce ozone at 3.3 to 4.3 mg. Ozone generators used for shock treatments on the other hand produce over 3000 mg/h, the amount of ozone needed to create a "shock treatment" over a 6 hour period in a 100-200 sq ft room. The ozone generators which are subject to this ban use cermic Mica plates that produce 300-400 mg/h of ozone and are intended to be used indoors in occupied rooms.

See also

• Air filter
• Air ioniser
• Electrostatic precipitator
• Ozone generator
• HEPA

References

• R.L. Corsi, J.A. Siegal, M.S. Waring. (2008). “Ultrafine particle removal and generation by portable air cleaners”. Atmospheric Environment: [1]

External links

• AHAM Association of Home Appliance Manufacturers
• CADR.org Information on Clean Air Delivery Rate by AHAM
• DOE HEPA Filter Standards HEPA filter specifications for DOE contractors
• EPA report on the effectiveness of ozone generators
• EPA report on indoor air quality
• DOE HEPA Filter Standards HEPA filter specifications for DOE contractors