Air Filtration For Dummies

As simple as it may seem, most people have very little knowledge of how an air filter, home, car, industrial, commercial institutional varieties actually work.  There is an assumption that the filter media itself does all the filtering and the more dense the media the better. While denser media is certainly more effective at removing finer, smaller particles, these types of filter media also have a much higher resistance or pressure drop both initially and when they load up with dust and dirt. Also, the filter media is really just the base for what really does all the filtering of the fine, sub-micron airborne particulate.

Most filters today use a MERV rating to indicate their level or efficiency with the higher number being more dense and more effective at initially removing fine particulate and the lower numbers being more of a general duty filtering capability. However, if a MERV 18 filter is best for fine particulate removal even a MERV 6 or 8 rated filter will eventually reach the same overall efficiency of the MERV 18 filter, and here is the reason.

 Even with “see through” filter medias, the internal areas of the filter fibers will, over time, fill up with larger airborne particles and make the passage ways through the media smaller and smaller eventually capturing even sub-micron dust particles as they are trapped in the now mostly blocked filter media. Unfortunately as the filter loads up the air resistance through the filter increases to the level where is significantly restricts the airflow through the filter and will reduce the performance of the fan and/or air handler.

Therefore, most HVAC filters are relatively open or low on the MERV scale so they will last at least 3 months before needed to be changed. For applications where a MERV 18 filter or true HEPA filter is required, a more powerful blower/motor assembly will be required along with a prefilter to keep the final filters from loading up too quickly.

A good, medium duty, Merv 6 or 7 rated filter is fine for most general duty applications. These give you best filtration performance over the life of the filter.

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Understanding MERV Ratings For Air Filters

Taking the Confusion Out of Air Filter Efficiency or What Do They Really Mean When They Say That?

I will try to keep this simple and short so as not to add to some of the confusion over air filter efficiencies. First, I would like to point out that any company that sells an air filter that states an efficiency rating without basing it on a particle size is providing you with basically useless information. For example: an air filter that has a statement reading “this filter will remove up to 95% of all airborne contaminants in your home or office”, doesn’t really tell you anything. Since most of the respirable particles that actually are harmful are usually less than 2 microns in size, don’t you think it would be important to tell you what size particles they actually remove from the air? So, let’s look at this statement again. “95% of all airborne contaminants” sounds pretty good, doesn’t it? Our HEPA air filters remove 99.97% of all airborne contaminants at 0.3 microns and smaller. At first glance these two air filters look similar in capability. But the first air filter provides no particle size range or efficiency based on particle size.

Recently the American Society of Heating Refrigeration and Air Conditioning Engineers (ASHRAE) and the air filter industry have come up with a standardized rating system, based on the European concept, of a MERV rating for each type of air filter. This numbering system makes it easier to evaluate and compare mechanical air filters and will hopefully eliminate some of the confusion regarding the overall effectiveness of any type of a mechanical air filter on removing airborne particulates, especially those that are less than 2 microns in size.

Bbelow you will see the new MERV ratings. This MERV rating chart has the MERV ratings, 1-16 on the left hand column and then there are five other columns showing the average efficiency in microns, average arrestance and the final resistance as measured in inches of water. Most companies that make air filters are now using this MERV rating, so you will see a MERV number on the air filter and perhaps some rated efficiency.

Comparing Various Air Filters to MERV Ratings

  • Throw-Away Fiberglass Media MERV 1 -MERV 4
  • Pleated Media Air Filters 30% ASHRAE MERV 10 – MERV 11
  • Pleated Media Air Filters 65% ASHRAE MERV 13 *
  • (* 65% ASHRAE is about 20% effective on less than 1 micron particles)
  • Pleated Media Air Filters 95% ASHRAE MERV 14

Some of the man-made synthetic media like that used in the 3M Filtrete air filters may be rated MERV 15. However, they hold very little dust and load up quickly and have a relatively high-pressure drop (static pressure) and can affect the performance of the heating / cooling system.

MERV Ratings Comparison Chart

RESPA Air Filter Efficiency – MERV Rating Chart

Series 9000 Dimensions diagram IMPORTANT NOTES:It is important that you select the RESPA Filter that best fits your application.MERV is an acronym for “Minimum Efficiency Reporting Value”. The MERV rating on an air filter describes its efficiency as a means of reducing the level of 3 to 10 micron-sized particles in air which passes through the filter. Higher “MERV” means higher filter efficiency. The purpose of the MERV standard is to permit an “apples to apples” comparison of the filtering efficiency of various air filters. <Read more about MERV and HEPA filter ratings>HEPA air filters are not MERV rated as they exceed the ASHRAE test protocol 52.2 used in determining the MERV ratings. In fact, HEPA air filters are the ONLY mechanical air filters that are tested and certified to meet a specific efficiency at a specific particle size. All HEPA air filters must meet a minimum efficiency of 99.97% at 0.3 microns. <Read more about MERV and HEPA filter ratings>

Comparison of EU Standards to ASHRAE 52.1, 52.2 (MERV Ratings)
Considerable differences exist between filter ratings in North America and Europe. This article helps the reader to understand the differences between ASHREA and EU standards for Filtration. Additional light is shed on the significant differences in the HEPA filtration standards between the US Government and the European standards. This article will help the reader to appreciate the MERV 16 filtration offered by Sy-Klone International. <Read more about European filter standards and how they compare to MERV ratings>

>> Go to RESPA-SD Product Information
>> Go to RESPA-SDX Product Information

RESPA
Filter Model
European Filter Rating Efficiency Standard 52.5 Minimum
Efficiency Reporting
Value (MERV)
Dust Spot
Efficiency
Arrestance Typical Controlled
Contaminant
Typical Applications and
Limitations
Typical Air Filter/Cleaner Type
HEPA Filter* 

(FEFF004 for RESPA-SD/SDX)Recommended when the very highest level of filtration is needed, or where HEPA filters are required by regulatory requirements.
n/a n/a n/a 0.30 micron particle size:

All Combustion smoke
Radon Progeny
Sea Salt
Carbon Dust
Orthopedic Surgery
Carcinogenic Materials
>99.97% eff. on .30 pm Particles
MERV 16 Filter*

(FEFF005 for RESPA-SD/SDX)Covers all uses that require up to MERV 16 rating. Recommended for uses where airborne contaminants place operator at risk, including contaminants such as Diesel Particulate Matter and Respirable Silica. We highly recommend this filter as it represents the best mix of high efficiency filtration, operator protection and economy.
EU P3** (~16+) n/a n/a .30-1.0 micron Particle Size

All Bacteria
Most Tobacco Smoke
Proplet Nuceli (Sneeze)
General Surgery
Hospital Inpatient Care
Smoking Lounges
Superior Commercial Buildings
Bag Filter – Nonsupported microfine fiberglass or synthetic media, 12-36 in. deep, 6-12 pocketsBox Filter– Rigid Style Cartridge, Filters 6 to 12″ deep may use
lofted or paper media
16 n/a n/a
15 >95% n/a
14 90-95% >98%
13 89-90% >98%
12 70-75% >95% 1.0-3.0 micron Particle Size:

Legionella Humidifier Dust
Lead Dust
Milled Flour
Auto Emissions
Welding Fumes
Superior Residential
Better Commercial Buildings
Hospital Laboratories
Bag Filter – Nonsupported microfine fiberglass or synthetic media, 12-36 in. deep, 6-12 pocketsBox Filter– Rigid Style Cartridge, Filters 6 to 12″ deep may use
lofted or paper media
11 60-65% >95%
EU P2** 10 50-55% >95%
9 40-45% >90%
MERV 8 Filter*

(FEFF003 for RESPA-SD/SDX)Covers all uses that require up to MERV 8 rating. Recommended for non-human respiratory environments, such as electrical compartments.
8 30-35% >90% 3.0-10.0 micron Particle Size:

Mold Spores
Hair Spray
Fabric Protector
Dusting Aids
Cement Dust
Pudding Mix
Commercial Buildings
Better Residential
Industrial Workplace
Paint Booth Inlet
Pleated Filters – Disposable, extended surface area, thick with cotton-polyester blend media, cardboard frameCartridge Filters– Graded density viscous coated cube or pocket filters, synthetic mediaThrowaway– Disposable
synthetic panel filter.
7 25-30% >90%
6 <20% 85-90%
EU P1** 5 <20% 80-85%
4 <20% 75-80% >10.0 micron Particle Size:

Pollen
Dust Mites
Sanding Dust
Spray Paint Dust
Textile Fibers
Carpet Fibers
Minimal Filtration
Residential
Window A/C Units
Throwaway – Disposable
fiberglass or synthetic panel filter.Washable– Aluminum MeshElectrostatic – Self charging
woven panel filter.
3 <20% 70-75%
2 <20% 65-70%
1 <20% <65%

This is an important chart to keep for future reference in determining the best filter style and type for your specific application. Understand that the higher the MERV rating the greater the resistance or static pressure will be across the filter media. For most HVAC furnace filter applications a MERV 8 and lower since these filters will allow for lower resistance with good filtration of larger particles.  Using the 3M type filtrete filter not recommended for most general duty residential heating/cooling systems. These filters load up very quickly and will actually reduce the HVAC fan performance requiring longer cycles to both heat and cool your home.

Pure Air Systems has been manufacturing commercial grade HEPA and Carbon based air filtration systems since 1985. These units are designed to be used either attached to existing ducted HVAC systems or as stand-alone units. The ability to use a true HEPA filter system ( which would have a MERV rating of 18 if they rated them) in a residential application makes these unit unique in the filter market.

For more information on the complete line of HEPA and Carbon based air filtration systems please go to our website at: www.pureairsystems.com or follow us on Twitter @pureairsystems and like us on Facebook. Of course you can always call us on our toll-free number at: 800-869-8025.

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Carpe Diem

The first time I actually paid attention to this Latin phrase was when I saw the 1989 movie Dead Poets Society, staring Robin Williams. The term Carpe Diem means “Seize The Day.”  The movie was about boys coming of age in a prep school and their teacher was providing new ideas and ways to think differently about themselves and the world around them. Some of us look at the world through rose colored glasses while many of us look at the world in wonder.

It is in my nature to question everything. While it is easier to sit back and accept what we hear and read, questioning takes energy but also tasks the informer to explain their position. We seldom question information from sources we believe to be credible or from associates who seem to know more about certain issues than we do. We certainly don’ t want to be cynical all the time and yet we get trapped into accepting something based solely on a small amount of information.

Information on product performance is especially susceptible to this problem. Well-known companies with well establish product lines can come out with a new product or service and we immediately accept their “hyped” performance claims simply because of our product loyalty. We will purchase their product and deem it unacceptable only after we have determined over continued use that it just doesn’t meet the performance claims.

Pure Air Systems has been manufacturing commercial grade HEPA air filtration systems since 1985. The acceptance of true HEPA filters for best choice of removing respirable sized airborne contaminants has slowly progressed over the years. For years ASHRAE standards for pleated media filters ranging in efficiencies of 30% to 95% in particle reduction efficiencies were touted as best choice for airborne particle reduction. However, unlike the HEPA filters which actually have an efficiency rating based upon particle size, the ASHRAE standards were based on particle weight not on particle size reduction efficiency.

Over the years a new “MERV” rating system for filter efficiency came into use to even the playing field. These new MERV ratings established a particle size removal rating for each MERV grade of filter based upon the effectiveness of removing a percentage of particles at 0.3 microns in size. Which, by the way, is the particle size standard for HEPA fitlers. They have to have a minimum efficiency of 99.97% reduction of all particles 0.3 microns in size or lager to be considered a true HEPA filter.

Once the new MERV standards were adopted by the filter manufacturers it opened the eyes of the people and companies that use air filters. Like Robin Williams who stood on the desk in his classroom because he wanted to look at the world from a different point of view, the MERV ratings offered buyers a more objective way to evaluate air filters.

You can view the entire line of HEPA and Carbon based air filtration systems manufactured by Pure Air Systems on our website at: www.pureairsystems.com. Or contact us by phone at: 800-869-8025.

 

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Filter Cake Is Not A Dessert

Filter cake is a term that is not used much anymore in the air filtration industry but it is a very important part of the mechanical method by which air filters capture smaller particles. Removing airborne particles by the use of air filters has been around for over 70 years. The filter medias have changed but the method of removing particle has not.

Whether you use a simple fiberglass furnace filter, a polyester dual layer ring panel filter or a HEPA filter the filter cake is essential in the overall efficiency of the filter. When any mechanical filter ( non-mechanical would be electronic or ozone or electrostatic air purifiers) is used it is normally placed in a return air duct or return air grill and always on the dirty side of the air moving fan device.

Media air filters have different efficiencies and are normally rated using the MERV rating system. In essence the higher the MERV rating ( a rating of 11 or 12 is very good while a MERV of 4 or 5 is low) the better the initial effectiveness of the filter. The operative word here is “initial.” When a new filter is placed in a dirty air stream the tiny spaces between the filter fibers are all open. Initially some of the smaller dust particles will pass through the spaces until these small spaces fill up. As the filter media “loads up” or gets dirtier a cake like layer of dust forms on the air incoming side of the filter. This is normally called the filter cake. This filter cake performs a significant role in the overall dust collection efficiency of the filter.

Since many of the smaller, less than 10 micron particles are tiny enough to pass through many filter medias, the filter cake that forms on the outside layer of the filter itself has enough different dust size particles mashed together to form, in essence, a primary filter bed that actually will capture many of the smaller, tiny airborne particles. The filter cake, or layer of dust, is the primary filter while the filter media, in essence, becomes the secondary filtration media.

As the filter cake builds up so does the pressure drop or resistance of air through the filter. At some point the filter loads up so much that the air flow through the air handling device is actually reduced. This is usually the point at which the filter has to be changed out. Interestingly, the higher rated MERV filters will normally be changed out more often than a lower rated filter because the more efficient filter captures more smaller particles and loads up faster.

Pure Air Systems has been manufacturing HEPA and Carbon based air filtration systems since 1985. All of the HEPA filters used in the PAS fan powered air filtration systems utilize a polyester ring panel filter ahead of the HEPA to remove all the larger particles and reduce the heavy dust loading so that the HEPA filter only sees the fine, sub-micron particulate. For more information on our complete product line please go to our website at: www.pureairsystems. com

 

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The Truth About Air Filter Efficiency

It is always interesting to see how companies that manufacture air filters, especially those for the residential market, use images of dust mites, dirt, dander and other graphic photos to illustrate the significance of using their filter if they really want to rid their home of these nasty airborne creatures.

Usually these companies compare the efficiency of their filter against the standard air filter that you use in your heating/cooling system and show how theirs is much more effective in removing these harmful airborne allergens.

For the most part, all of the air filters available from the retail stores are made from similar filter media and have similar efficiencies. Some are pleated, some aren’t, some are washable and reusable and many are not. Almost all of them have a cardboard frame and come is a wide variety of sizes.  And, their prices vary from less than $1.00 each up to $10.oo or more per filter.

When shopping for these filters you will notice that many or most of them now come with a MERV rating label to indicate their overall efficiency.  These MERV ratings (which are an extension of the old ASHRAE ratings) indicate their filtration efficiency in relationship to how well they remove various sizes of airborne particulate.

In truth, what you really want is a filter that removes as much of the less than 5 micron in size particulate but doesn’t have a high resistance so it won’t affect the performance of your HVAC unit. Typically a MERV 7 or 8 rated filter offers the best combination of particulate removal (small particles) with minimal adverse affect on your heating/cooling air flow.

While it may seem that using a filter with a higher MERV rating than 8 would be better, the truth is that as a filter starts to get dirty and gets a layer of dust on the filter surface, the efficiency of the filter actually gets better as the filter loads up.  And, as the filter gets dirtier the pressure drop or resistance across the filter goes up as well.

Therefore, if you start out with a MERV 9 or higher rated filter you will have  a slightly higher efficiency at first but also a higher initial pressure drop as well. And as the filter loads up the pressure drop will increase rapidly and the air flow across the air handler or HVAC system will drop quickly.  This is why using a MERV 9, 10, 11 or higher rated filter usually requires you to change the filter often, usually once a month verses once every three months for a MERV 8 or lower rated filter. And, these higher rated filters are more expensive.

Pure Air Systems offers a line of MERV 8 rated BioPanel dual-layer polyester ring panel filters that are less expensive than the higher rated media filters, fit more tightly in the filter frame, have zero leakage around the filter and have a much higher dust holding capacity with a lower pressure drop or resistance over the the life of the filter.  These commercial grade filters are not available in the retail market but can be purchased directly from the Pure Air Systems website.

For more information on filter efficiency and the BioPanel filters available from PAS go to our website at: www.pureairsystems.com.

 

 

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