Electronic vs Non-Mechanical Filtration

Most people refer to air filtration devices as either air filters or air purifiers. In truth, these two methods are worlds apart in the way they collect or remove airborne contaminants. The term non-mechanical refers to any media type filter;  i.e. fiberglass, polyester, cotton, woven and non-woven, HEPA, etc. Mechanical or Electronic filters would include electronic air cleaners, ion generators, ozone generators, and any filtering device that uses electricity or some type of moving part incorporated into the device.

Before I get any further I do want to state that the term ” air purifier” is a misnomer. Nothing purifies the air. You can purify water or chemical solutions but not the air. However, this term has become a standard part of the filtration market so I will use it.

From a performance point of view, the purpose of any air filter air purifier should be to “remove” the offending airborne particles from the room, house, or area where you live or work. The operative word here is “remove.” The non-mechanical type of filter incorporates a media that has openings in the media itself that make it either more or less dense. The less dense medias like fiberglass filters allow a lot of air to pass through but collect only the larger dust particles and debris. The more dense medias like polyester and some non-wovens like the Filtrete filter from 3M, collect a much higher percentage of the smaller and finer particles.  The less dense media has a lower pressure drop across its surface and has little resistance to air flow. The more dense media is much more restrictive.

Air purifiers, for the most part, use a combination of a positive/negative process to capture airborne particulate. This usually takes the form of a surface or plate that is charged to collect particles that have the opposite electrical charge. It is like running a comb through your hair to build up a static charge and then placing the comb next to small pieces of paper and watch them stick to the comb. Same principle. Unlike media filters that use the collected particulate on their surface ( sometimes referred to as dust cake ) thus collecting more and smaller particles, the electronic air cleaners or purifiers have no depth collection process and once the plates or collection surface gets too dirty or the collected particles loose their charge, the particulate detach and are put back into the air stream.

There are trade-offs in using the two methods. The non-mechanical filters eventually have to be replaced. As they collect more particles the ability to pass air through them is reduced and the pressure drop becomes too high for the fan/motor assembly normally used to pull the air through the filters. The plates or collection surfaces of the electronic devices can be cleaned manually and then put back into service. They also have very little resistance to air flow. The non-mechanical filters, however, are much more effective at removing small, respirable sized particulate.

The type and design of filtration device you choose depends upon the purpose and type of particulate you need to remove. For what it is worth, non-mechanical filters are predominantly used in the following types of applications and markets. Hospital surgery rooms, medical clinics, pharmaceutical manufacturing, clean rooms, isolation rooms, micro chip manufacturing, optics manufacturing, the CDC, medical laboratories and any process or operation that requires the removal of harmful airborne allergens or pathogens.

For more information on the design and operation air filtering devices please go to our website a: www. pureairsystems.com.

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Some Call It A Spear – Some Call It An Arrow

If you were growing up during the 60’s you’ll remember the ad slogan for spearmint gum, ” Some call it a spear – some call it an arrow”, which simply meant no matter which view you take the product is the same or the end result is the same. This phrase is not used much anymore but was popular at that time. It does, however, fit some circumstances where people may know a product or service by one term or name and not recognize that it may be called another name and still provide the same performance.

The the use of two different names or terms for two systems or products that  perform the same function can be applied to carbon or charcoal and air purification and air filtration.

Carbon is a very commonly used product for both the air and water filtration industries. In most cases the carbon or charcoal is heated in an oven to enhance or activate the charcoal so that both its surface area and adsorptive capacities are expanded. Thus the term activated carbon. For the most part, the air filtration industry uses the term “carbon” rather than charcoal as carbon is more often used in marketing the filters or holding devices that contain carbon.

In the area of air filtration or air purification there are many similarities with these terms but there are also some differences. Air filtration is the more commonly used term as this term to designate products that filter out airborne dust, dirt and contaminants has been around since the early 30’s. There are a wide variety of filter medias and filtration systems using these varied medias used in the market today.

In the 1970’s other forms of non-mechanical ( filter media is considered a mechanical method of dust removal) came into the market that used electrically charged plates ( using a positive/negative capture process) or charged the incoming air to create ozone to purify the air. Thus the term air purification was coined.

Electronic air cleaners or air purification devices do trap and collect airborne dust and dirt particles but are limited to the size of the particle they can collect and the amount. Electronic air cleaners have to be cleaned regularly to keep the plate surface clean and allow for the electrical charge process to be effective. And, unlike air filters that have a collection surface that also uses the filter cake for collection of finer particles, the electronic air cleaners become less effective as the plates collect more dirt.

Air purifiers like ozone generators and Ion generators rely on totally different technologies than air filtration systems. Ozone generators produce O3 or Ozone which reacts with odor and gaseous molecules and changes them by giving up one of its oxygen elements to change the gas molecule. They do nothing for removing airborne dust or dirt.

Ion generators basically generate an electrical charge to charge airborne particles so that when they come in contact with any surface they will stick or “plate out.” This means the dust particles will stick to the walls, floors, furniture, etc. until the charge is diminished. Again, these operate differently that air filters.

For more information on the similarities and differences in air filtration and air purification please go to our website at: www.pureairsystems. com.

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