How Effective are Air Purifiers with HEPA Filters?

What is an Air Purifier with Filters?

An air purifier with filters is a device designed to eliminate air pollution (domestic or professional). The HEPA filter is usually the main component, but it requires a pre-filter to prevent it from becoming clogged and obstructed too quickly.

Air purifier manufacturers tend to add various filters with different technologies to give an impression of innovation and efficiency and attract customers...

Therefore, an air purifier typically has several filters through which the air flow passes successively. The most frequent filtration stages are:

• The pre-filter stops dust particles larger than ten or even one hundred microns.
• The HEPA filter, which stands for High-Efficiency Particulate Air, theoretically filters at least 99.95% of fine particles.
• The active charcoal filter captures gaseous pollutants such as volatile organic compounds (VOCs) and bad odors.
• The Ultraviolet-C lamps reduce airborne pathogens such as bacteria, mold, and fungi concentrations.
• The electrostatic filter effectively eliminates suspended pollen, dust, and smoke, regardless of size.
• The ionizer accelerates the elimination of all particulate pollutants.

How do HEPA Air Purifier Manufacturers Communicate Filtration Efficiency?

The term "HEPA" is often presented to consumers as a guarantee of efficiency. Highly regulated, it's awarded to filters that meet stringent filtration criteria defined in the EN 1822 standard.

This standard first measures the MPPS ("most penetrating particulate size", i.e. the particle size for which the filter is least effective) and then ensures a high filtration rate at all points of the filter.

There're two levels of HEPA filtration (H13 and H14), with overall filtration levels of 99.95% and 99.995% respectively. These tests are performed on new filters, which allows for circumvention, as we will explain below.

In practice, this level of filtration captures the entire spectrum of particulate pollutants (non-gaseous) present in the air.

It should be noted that while these tests are very demanding, they don't measure the overall effectiveness of the purifier, either when new or under real-life conditions. Read on to better understand!

Air Purifiers with HEPA Filters: What Factors Limit Their Effectiveness in Real Conditions?

Firstly, there are leaks between the filter and its housing, as well as leaks between the housing and the air purifier itself. In practice, the efficiency rate of an air purifier is often lower. Air will find the slightest gap between the filter and the device (to avoid passing through the tightly packed HEPA filter fibers that generate a high "pressure drop" between the filter's inlet and outlet). Therefore, the efficiency of an air purifier greatly depends on how the HEPA filter is integrated. But manufacturers generally only communicate on the filter's efficiency, not the entire device!

Secondly, the air velocity passing through the filter is another factor: filter efficiency is tested under specific velocity conditions. If the filter is used in a device that allows for higher speeds, the filtration rate often decreases. This also happens if the airflow isn't uniform over the surface of the filter. In some areas, air passes quicker, and the filter loses efficiency. The temperature and humidity of the air can also affect the filter's performance.

To increase the efficiency measured during EN 1822 tests, some HEPA filters use an electrostatic treatment (called "electrets") that disappears after a few hours or days of use. [2] The drop in filtration rate over time can be very high. A German study on the CADR of an air purifier in real-world conditions reports a four-fold decrease in the air purifier's efficiency, depending on whether the filter is new or has lost its electrostatic treatment! [3]

And most important, the efficiency of an air purifier with a HEPA filter decreases rapidly over time due to clogging! As the captured particles block the gaps between the HEPA filter fibers, the passage of air is increasingly restricted, and the airflow rate of the device decreases significantly, which means that its efficiency decreases. For example, a study measured the loss of efficiency of an air purifier with a HEPA filter over time. After 1500 hours of operation (equivalent to two months of continuous use), the air purifier's efficiency in removing pollution from the equipped room was reduced by 50%! In other words, it's as if the device had a purified air flow rate (CADR) divided by two after just a few months of use. [3]

Finally, it's important to remember that, contrary to the marketing of brands using HEPA filtration in their air purifiers, the decrease of air pollution in real conditions isn't at the advertised level. Numerous scientific studies have evaluated this actual pollution reduction at a level ranging from about 45% to 85% for devices with new or recent filters. [4] [5] [6]

Other drawbacks of Air Purifiers with HEPA filters

Although the HEPA filter is the main culprit in the maintenance and energy consumption of an air purifier equipped with it, the number of filters associated with it increases these constraints. The more filters, the more noisy, heavy, difficult to maintain, and energy-consuming the air purifier is.

Depending on the type of device and the filters, maintenance is a mild but essential operation. It's closely related to the ambient pollution rate and the quality of the pre-filters. Specialists are clear: If the air purifier isn't regularly maintained, it loses effectiveness and can become a source of air pollution itself!

You can also read: Active charcoal filter, untangling the true from the false

Here are some things to know about maintaining air purifiers with HEPA filters:

• The pre-filter usually needs to be cleaned every 3 to 4 weeks.
• The generally expensive HEPA filter needs to be replaced at least once a year. It's often recommended to change it every 3 to 6 months for the reasons mentioned above.
• Manufacturers recommend wearing a mask and gloves when changing filters and washing hands thoroughly after changing them. Pollutants disperse very easily. It's strongly advised that people who are sensitive to allergens and asthmatics don't handle filters.

Air purifiers with HEPA filters are effective, but it requires demanding and costly maintenance to remain effective over time, maintenance that is often challenging for daily life.

Air purifiers with HEPA filters also require high energy consumption due to the resistance caused by the filters, which require the fan to use more energy to pass air through the filter. An electrical power of 50W is quite common and it can even reach 100W for the most powerful devices. The annual electricity consumption can therefore represent several hundred kWh per year, depending on the usage of the device, as it is desirable to operate it year-round to effectively reduce exposure to air pollutants.

Indeed, HEPA filters have a negative environmental impact from their manufacture. These filters are often made from synthetic materials (plastic or fiberglass) that are rarely recyclable. [5] Some manufacturers offer recyclable or biodegradable HEPA filters using materials such as paper. However, used HEPA filters are considered hazardous waste: they potentially contain toxic materials (fiberglass, in particular, which is most often used in these filters, is classified as carcinogenic).

Other manufacturers offer a range of efficient, user-friendly, and eco-friendly devices. This is particularly the case with TEQOYA's air purifiers ionizers and e-filters. The e-filtration technology improves indoor air quality and eliminates dust mites and other allergens that can cause asthma and other respiratory problems.

• Healthy and eco-friendly air in your living spaces
• Up to 99.9% of ultrafine particles and germs eliminated
• Energy efficient
• Confortably silent
• Long lifespan
• Easy to use!

Enjoy our highly efficient and eco-friendly air purification solutions now.

Sources

[1] Association Asthme et allergies. “Des Faits et chiffres pour comprendre l'allergie”.

[2] Que Choisir. “Purificateurs d'air - Des résultats mitigés”.

[3] Taiwan Association for Aerosol Research. “Testing of an Indoor Air Cleaner for Particulate Pollutants under Realistic Conditions in an Office Room”. AAQR-19-01-OA-0029_

[4] Smart Air Filters. “HEPA Filter Longevity Test: Day 200”.

[5] Sanalife. “What Are HEPA Filters And How Do They Work?”

[6] Science Direct. “Particle removal effectiveness of portable air purifiers in aged-care centers and the impact on the health of older people”.

[7] Wiley Online Library. “Health benefit/burden, PM2.5 removal effectiveness, and power consumption based comparison of common residential air-cleaning technologies in the United States”.

[8] Science Direct. “The effect of air purifiers on the reduction in indoor PM2.5 concentrations and population health improvement”.