If you are looking to buy an air purifier, chances are you’ve come across the acronym “HEPA.” Most people simply assume (for good reason!) that any air purifier with a HEPA filter is good, and so, that’s, like, the end of the story.
But for a number of reasons, it’s important for anyone interested in the air quality in their homes to have a deeper understanding of HEPA. And unfortunately, most sites that do attempt to answer the question sound something like, “Hi there, here is a lot of technical jargon, but yeah, you won’t come out of this really understanding much else. Anyway, thanks for clicking!”
Anyway. Might be better to have a better explanation, right? Let’s get right into it.
The Story Of HEPA Filtration
The story of HEPA filters is actually not what you might expect! It was first developed by scientists who were taking part in the Manhattan Project. Because they were dealing with radiation, the scientists needed an incredibly effective air filtration system that could deal with even the smallest particles.
The result was an incredible and innovative filter that removed 99.97% of particles that were .3 microns or larger. It is that standard that has been used since, and which eventually became termed HEPA (“High Efficiency Particulate Air”) filtration. In other words, whenever an air purifier is a true HEPA filter, it can meet or beat this standard.
If you’re interested in reading more about the history of HEPA filtration, feel free to check out our article about it!
How Does HEPA Work?
So, to understand HEPA, we really need to understand how air filters generally are created. Since it’s simply a standard of effectiveness, the real question we need to answer is how do such small particles get filtered?
Diffusion: Using the concept of Brownian motion, a principle that explains how small particles move in the air, diffusion is one way that HEPA filters capture really small air particles. Basically, Brownian motion means that small particles will move randomly when they’re struck, and thus aren’t as affected by the way the air around them is moving. Diffusion causes more of these sorts of collisions, which increases the chances of these particles getting stuck in filter material. It is this effect that HEPA filters use to capture the especially tiny particles in the air. The stuff like gas and all that.
Electrostatics: This is pretty fascinating. Electrostatics is basically a process by which small particles are given a charge, and then are captured by having the filter counter-charged. Just in the way magnets work, electrostatics targets tiny particles by using the opposite charge to get them to come closer. This allows for the capture of particles like dust and smoke.
There is one drawback to this approach: air purifiers that use it tend to work less over time. Which is why our air purifiers use an advanced approach called nano-spinning that that allows us to have even more control and thus have the power of electrostatics without the drawback of them not lasting longer. Pretty cool!
Sieve: This is exactly what it sounds like. Using the same principle as the sieve you use in your kitchen, filters use holes to capture larger particles that wouldn’t be captured by the processes above. It’s kind of fascinating, in fact, when you think about it: every particle of every size needs a different way to be captured by filters, and so even the most advanced approaches won’t capture big particles. Something as simple as sieving is the way to go.
Blocking: This is also what it sounds like! The idea is simply to capture particles by getting them to attach to the fibers of a filter. This is also great for stopping bigger particles.
Interia: Unlike small particles, very large particles tend to follow the path of airflow. Air purifiers use the power of their airflow to push the particles directly towards a filter, and so even as the airflow changes, the particles keep going and get stuck.
Okay! That’s a lot of info! But those are the various approaches of HEPA filters (and other air filters) to capture air.
But wait, there’s more!
What Materials Are Used For HEPA Filtration?
Good question! The truth is that there are actual multiple materials that can be used to filter out the particles in the air. Here are the most common ones.
PET/PP: These are two kinds of plastic, most often used to make stuff like plastic food containers and plastic cups.
PTFE Membrane: Otherwise known as teflon, PTFE isn’t usually used for household filters because of how expensive it is.
What Are The Drawbacks Of HEPA Filters?
Despite what you may think, HEPA filters can’t address all issues when it comes to air filtration. This is exactly why aeris uses some other methods to filter in addition to our HEPA approach, which I’ll talk about in a moment. But first the drawbacks.
Most importantly, HEPA filters are not able to filter out gases or odors. In fact, some can even make odors worse by attracting the gross stuff in the air!
That’s why we use some other methods to help filter out the gas and odors in the air around you, not just the stuff listed above:
All three of these materials are highly porous and have a huge surface area. In fact, the surface are of just a few grains of these materials have a combined surface area of several football fields!
Each of these materials captures different kinds of odors and gases and allow us to capture all the stinky stuff in the air as well as dangerous stuff like VOCs (the gases that are let out by aerosols and paint).