What Are HEPA Filters And How Do They Work?
HEPA Filtration Technology & Effectiveness
Air filtration and ventilation systems keep our indoor air clean. Not only is this necessary for the safety and comfort of residential spaces, like apartments and homes, but clean air is a governmental requirement for commercial spaces.
HEPA filters are just one of the technologies that can be used to clean air as it passes through a ventilation system and into the spaces we work.
There are several different types of air filters, and each performs a specific function. Here’s everything you need to know about HEPA air filters and why you should consider getting one to improve your indoor air quality.
What is a HEPA Filter?
The HEPA filter is a fibrosis air filter that stands for high-efficiency particulate air filter, which refers to a standard for air filtering efficiency.
Basic HEPA filters are typically built using borosilicate glass fibers, plastic fibers (also known as polypropylene), or fiberglass (and if this is the case, then these fibers can get into the air and be harmful to your health) bound together with up to 5% acrylic binder (the compound that binds latex paint to a house).
There are other types of particulate filters, each of which collects aerosols (but they may do so by mechanical or electrostatic methods):
- Mechanical: This removes dust by capturing it on the filter media.
- Electrostatically Charged Filter Media (passive and active): This increases the efficiency of trapping particles by positively/negatively charged particle attraction of fibers.
- Electronic Air Cleaners (two-stage): An external power source imposes charges on particles.
Other particulate filters include fibrosis, low-efficiency, mechanical, and polarized. Each of these filter types is graded by filter efficiency based on the MERV rating system. So, for example, low-efficiency filters are MERV 12, and HEPA filters are MERV 17. Therefore, organizations can buy higher efficiency (higher MERV ratings) or numerous filters with a range of MERV ratings to optimize their air quality.
The HEPA Standard
When you buy HEPA filters, you aren’t purchasing the HEPA brand, but you are buying a type of filter that can effectively clean air according to HEPA standards.
HEPA is an official government and industrial (non-consumer) standard defined by the US Department of Energy (DOE), but there are also European standards (if you see a filter with a rating that looks like H13 or U16, the European standard is being used).
The DOE’s definition of HEPA was developed in the 1940s during the Manhattan Project because they needed filters that could screen radioactive particles. It’s important to note that the standard does not define how the filter must be made or what it is to be made out of, but it indicates that it can trap certain particle diameters and types.
Unfortunately, any filter using the HEPA name does not have to go through any certification through the DOE. Government contractors must adhere to strict standards when installing HEPA filters in ventilation systems or nuclear facilities. In those cases, they would have to prove that they achieved DOE’s HEPA standard. However, this approval does not apply to commercial products like air purifiers.
Particles HEPA Filters Remove
The standards that HEPA falls under requires that any filter which is approved to be HEPA must remove 99.95% to 99.97% of particles in the air that passes through it. This refers to a certain diameter of particles, specifically (for HEPA) ones equal to 0.3 µm (which refers to a micrometer or micron, one-millionth of a meter).
Common particles that a HEPA filter captures include:
- Submicron liquid aerosol
This type of filter is extremely common and usually found in smaller and portable air filters.
HEPA filters cannot capture gaseous pollutants like chemicals, fumes, gases, and odors, nor do they affect odors or volatile organic compounds (VOCs). If an air purifier says it can remove VOCs and gaseous pollutants, it may be more than just a HEPA filter. They may be a hybrid filter with a carbon or activated carbon filter.
When it comes to improving air quality, air filtration systems balance the airflow, air pressure, and air filtration to clean as much air as possible. Most air purifier systems look at cleaning a quantity of air measured in cubic feet per minute (CFM; or Q). They also usually promote a Clean Air Delivery Rate (CADR), or the rate that air flows through the filter.
How Do HEPA Filters Work?
There are different types of HEPA filters, but True HEPAs filter by mechanical air filter method. Air is forced through a fine mesh, which can trap particles of 0.3 µm in size.
What does a HEPA filter do? HEPA filters are made by randomly arranging the polypropylene or fiberglass fibers (between 0.5 and 2.0 µm). While sometimes the fibers are arranged in a tangle, the fibers can pass air through and trap some of the particles. The important part is that the fibers create narrow pathways for the air to pass through. Larger particles are trapped because they can’t keep up with the constant movement and maneuver through the fibers. But some smaller particles have very little inertia and can pass through with the air and along with the twists and turns of the fiber mesh.
Critical factors of HEPA filtration are the fiber diameter, filter thickness, and face velocity. The filters capture particles through diffusion, interception, and impaction.
- Diffusion: Diffusion is the intermingling of substances by the natural movement of their particles. At lower airflow, particles below 0.3 µm are captured due to the collision of gas molecules with small particles (0.1 µm).
- Interception: Interception occurs when a dust particle follows the air but still comes in contact with the fiber as it passes. This is dependent on the fiber and is enhanced when the size of the fiber is closest to the size of the particle. Most mid-sized particles are captured by interception.
- Impaction: Larger particles can’t avoid fibers while they curve through the air, so they must embed on a fiber directly.
Types of HEPA Filters
There are different types of HEPA filters. Ones labeled True HEPA should conform to the DOE standards for HEPA filtration.
- True HEPA: A consumer air filter labeled as True HEPA should conform as close as possible to DOE’s HEPA air filter standard. At its highest efficiency, it should remove 99.97 percent of all particles that are 0.3 microns in size. Only the label True HEPA (and sometimes Absolute HEPA) has any real meaning because it is the only one to claim to adhere to a standard (although there is no verification for this).
- Absolute HEPA: Sometimes means the same thing as True HEPA, but it claims a higher filtration power (up to 99.999 percent at 0.3 microns).
- UltraHEPA: Some brands used UltraHEPA, claiming that their product is “100x more effective than HEPA air filters,” able to remove particles down to 0.003 microns in size. This is technically impossible and may be misleading marketing.
- HEPASilent: HEPASilent is a trademarked proprietary filter that combines electrostatic charge and a mechanical filter. The charge in this filter supposedly makes particles more likely to stick to the filter fibers.
- Permanent HEPA: Permanent filters are marketed as meeting the HEPA rating but can also be washed and reused rather than replaced. It is not recommended that you wash HEPA filters because the washing process can reduce effectiveness over time.
- HEPA Type: Calling a filter a HEPA Type filter does not mean anything. It does not conform to any standard.
- HEPA Like: Similar to HEPA type, HEPA like cannot be assumed to conform to the actual HEPA standard.
The Importance of HEPA Filters for Indoor Air Quality
HEPA filters are great at cleaning particulates from the air and should be used as one air purifier method. Look for True HEPA filters or air purifier systems that can provide some data on the effectiveness of their HEPA filter at removing 0.3 µm.
Sanalife’s air purifier systems, for example, uses five stages to clean the air:
- Stage one: Negative Ionization and Pre-Filter, which attracts air particulates and then clumps them together for easier capture during the filtration process.
- Stage two: Activated Carbon, which acts as a pre-filter for HEPA and can adsorb harmful gases & VOCs.
- Stage three: True HEPA Filtration, capturing over 99.97% of particles as small as 0.1 microns in size.
- Stage four: Photocatalytic UV-C (PCO Technology), which removes airborne viral particles, airborne microorganisms, airborne bacteria, mildew, and mold spores.
- Stage Five: Absolute Air and Surface Protection, which continuously neutralizes harmful contaminants in the air and surfaces. This final stage neutralizes surface and airborne bacteria, mildew, mold spores, and surface and airborne viral particles like RNA and DNA flu viruses
Whether you are looking to improve your indoor air quality to meet health standards or to reopen following the COVID pandemic, it’s essential to get an air purifier with a HEPA filter in it. See today how an air purifier system with Sanalife can improve your air quality and keep your building occupants safe and healthy.
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