There are tons of different kinds of air cleaner purifiers available for purchase. This article will explain the different technologies that the air cleaner purifiers out there use.
Mechanical Filtration — Filter units vary in sophistication and levels of performance. Filters are typically rated and grouped by how efficiently they remove specific sizes of particulates from the air stream passing through them. Filters capture particles as small as 0.1 microns and on up to 100_ microns or more. Group 1 filters are low efficiency. Group 2 filters are medium efficiency. Group 3 are high efficiency and Group 4 includes ultra high efficiency filters. This will make more sense in the following descriptions.
Furnace filters are in Group 1. They are the filter that is typically located in your furnace or air conditioning system. They are there mainly to protect the equipment from excessive dust build up, which can act as an insulator causing heat build up. They capture large particles 10 microns in size and up. Filters like this are often placed ahead of higher efficiency filters and specialized filters, such as activated carbon filters, to protect them and extend their service life. They are usually made of fibers or a foam material.
Some manufacturers have started to offer furnace filters with greater efficiencies for smaller particles around 5 to 10 microns. That would place these in Group 2 as medium efficiency filters. These may help with reduction of large airborne particles such as hair, fibers, and pollen. Some make claims for removal of mold spores.
Bag and panel filters are not common in residential applications, being used mainly in commercial buildings. They are an example of high efficiency filters, but do not include HEPA (we’ll look at that technology next). Group 3 filters reduce at least 99% of 0.3 micron particles. HEPA and ULPA filters fall into Group 4 as very high efficiency filters. HEPA stands for High Efficiency Particulate Arrestor (or more commonly Air). ULPA is Ultra Low Penetration Air.
HEPA filters are required to have an efficiency of at least 99.97% for 0.3 micron particles. And ULPA filters are required to have an efficiency of 99.9999% efficiency on 0.12_ micron particles. HEPA filters were originally developed for laboratory use to filter out very small particles. In the past 10 years or so, HEPA has became popular for residential usage for sufferers of pet allergies since it can filter out very small particles such as these. ULPA filters are typically only used in certain industries such as in clean rooms where particles may be damaging to the process or product being made.
Filtration in general can be effectively applied to the right situation to reduce particles from the air we breathe. However, there are some limitations to this technology.
• The filter can only capture particles that are brought to it. This requires a component such as a fan to force the air through the filter. All filters create some restriction to air flow, which must be considered when sizing the fan. As the filter captures more and more particles, this resistance increased. Too small a fan and not enough air will be moved through the filter. Too large a fan may reduce efficiency by increasing the velocity through the filter. Fans can be noisy too.
• Filters have little or no effect on odors and gases. Dust and other particles trapped in a filter can lend a great amount of surface area to the filter. These particles can adsorb chemicals from the air, which on one hand is a good thing. However, when the conditions change, such as increase in temperature or humidity, those chemicals can
desorb and enter the air. However, if not installed correctly, they can emit odors and gases by a process called desorption.
• Similar to the problem of desorption, filters can also act as a breeding ground for various microbes if the conditions are right. Studies have shown microbes growing in filter systems. Microbes, such as mold, need moisture to grow and a source of food. Most foam and fiber filter materials are not a food source, but the particles collected in them?especially dead skin cells?can be a food source. If the humidity is high enough, sufficient moisture can be present as well. Cleanable foam filters present a good environment for microbial growth if they are not allowed to dry completely when they are washed (?if they are ever washed!). As part of their metabolism (eating and growing), microbes release odors, which can enter the air stream.
Carbon Filters — Another type of mechanical filter is the carbon filter, which may be made from several different types of carbon that may be applied to it in different ways. The carbon may be “impregnated” into the fibers of the filter. The carbon may be crushed into granules that are kept in the filter, similar to a pillow. The key is how much carbon is available to the air stream, the size of the particles, and the type of carbon used.
Carbon filters, once again, if properly installed and maintained can be effective in reducing odors, gases, and VOCs. However, they suffer most of the same problems as described above about filters. Carbon is a food source for microbes, such as bacteria. Some manufacturers recognize this and add an anti-microbial agent to the filter attempting to eliminate microbial growth. The challenge to this method with carbon is to find the right amount of the agent and the right preparation. Otherwise, the carbon “sites” where the odor and gas reduction is supposed to
take place may become taken up by the additive, rather than the contaminant.
Electrostatic Precipitators — ESPs are electromechanical filters. These types of units capture particles, but do not reduce odors and gases, and are partially effective against microbial contaminants. They work by applying a charge to particles before they enter the collection cell or plates, where the charge is the opposite. Recall that opposite charges attract each other, so the charged particle coming into the unit will be attracted to the collection plates. As more and more particles are collected, the efficiency of the unit will decline. So, the plates have to be cleaned on
a regular basis for the unit to perform at its best. Another challenge to this technology is keeping the charging mechanism (a high voltage wire in most systems) clean. If the wire becomes coated with dust and other contaminants, the efficiency of the unit will decline. Cleaning the charging mechanism is often not easy to do.
As with filters, the collection plates become coated with particulates, bacteria and fungi in addition to other particles. The microbes can grow there if moisture is present.
Ionizers or Needlepoint Ionizers — This can be a confusing segment of air treatment units if one doesn’t know what to look for. There is more than one method to form ions in the air. One of them was just discussed above, the patent-pending AirSource Electron Generation technology. Another is the electrostatic precipitators described above. If the unit has a collection cell or plates, it’s an ESP. If it doesn’t have this, and uses needle points, then it’s a needlepoint ionizer. Needlepoint ionizers have a high voltage applied to them. Since, this voltage is not referenced to
ground it only has one place to go out into the air. The air around the device is subject to a concentrated charge. When particles pass nearby they can pick up that charge. The potential problem with this technology is that the particles can become overly negatively charged and if there isn’t a collection plate to capture them, they will start to stick to oppositely charged surfaces, such as walls, ceilings, and furnishings. This has been described as black wall.
The efficiency of needlepoint ionizers start to suffer with use as the needlepoints wear out from the constant electrical discharging (kind of like the spark plugs in a car engine). They either have to be replaced or sharpened periodically.
Ozone Generators — Units in this category produce ozone for the sake of treating the room with this oxidizer. Ozone has some efficacy in reducing simple airborne odors, but doesn?t work as effectively on gases, VOCs, and microbiological contaminants unless it is present in high concentrations. Such high concentrations are not healthy for people and pets to be in. You should make sure that the unit either has been engineered to produce only low amounts of residual ozone or has a proven mechanism to control the amount of ozone in the treated space. The controls on it should be tamper proof as well so that it cannot accidentally set too high of a level.
Depending on how the ozone is generated, the air within the unit can become very aggressive to the materials used in the construction of the unit.
Photohydroionization — The Photohydroionization process is a complicated chemical chain of events that leads to the
production of particular oxidizing ions. Oxidation is the process of adding oxygen to and causing a loss of electrons from a chemical. Advanced oxidation is the addition of a catalyst to drive the reaction at an accelerated pace.
Here’s the simplified version of the Photohydroionization process. The UV lamp provides the energy of the reaction in the form of full-spectrum ultraviolet light. Two wavelengths are of particular interest. One wavelength is in the middle range and is also called germicidal light. This light can make microorganisms unviable (that is, incapable of reproducing). This light strikes the Tri-metallic Catalyst target and starts the advanced oxidation process. Electrons are made available to react with oxygen in the air at the surface of the trimetallic catalyst. That air also contains moisture. Small amounts of residual ozone are produced by the second wavelength of light from the UV lamp. This wavelength is in the far range and is strong enough to split oxygen gas molecules–if you remember from high school science class; oxygen gas is two oxygen atoms joined together. Superoxide ions are also formed at the surface of the catalyst. This is the oxygen gas molecule with an extra electron, which makes it a strong oxidizer.
This should help you to understand the major differences are between air cleaner purifiers you may be looking at so you can make the most informed decision on the purchase of your new air cleaner purifier.
