Explained: the different types of air filtration technology
The two main standards relating to air filtration are the ‘international technical standards’ and the ‘Minimum Efficiency Reporting Value (MERV)’. The international technical standards were developed by the International Organisation for Standardisation (ISO) and the MERV was developed by the ‘American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE)’.
In 2016, two new ISO standards were released: ISO 16890:2016 for particle filter testing and ISO 10121:2013 for molecular gas filters. Added to this is the updated Eurovent energy-rating scheme which now offers an A+ energy rating for top-performing low-energy air filters. It is designed to improve selection of effective air filters by an improved descriptive classification. This is based on ability to remove PM1, PM2.5 and PM10. There is a fourth classification, which is known as PM coarse, which is for filters that are less than 50% efficient at the PM10 particle size.
The MERV rating, is a measurement used to rate the effectiveness of air filters. The scale takes the worst-case performance of a filter exposed to contaminants of different sizes (0.3-10 microns). A score is given between 1 and 16. Higher MERV values correspond to a higher percentage of particles captured by the filter, with a MERV 16 filter capturing more than 95% of particles over the full range.
HEPA Air Filtration
High-efficiency particulate air (HEPA) filters form a mesh that traps particles, when air flows through the filter. Made from an assembly of fibres that are randomly laid perpendicular to the airflow, the fibres range in size from less than 1 micron to greater than 50 microns in diameter. Fibres are made from cotton, fibre glass, polyester, polypropylene, or numerous other materials. The way in which these fibres filter particles are four-fold:
Impaction: when a particle traveling in the air stream, collides with a fibre due to particle inertia resulting in deviation from the air stream causing it to embed in that fibre. Increased fibre density and increased velocity of air flow will increase the chances of this happening.
Interception: occurs when a large particle, because of its size, collides with a fibre in the filter that the air stream is passing through, like being caught in a net.
Diffusion: when the smallest particles (especially <0.1 micron) collide with gas molecules this results in these molecules being slowed down, increasing the probability the particle is then stopped by either impaction or interception.
Electrostatic attraction: the fourth mechanism, plays a very minor role in mechanical filtration. After fibre contact is made, smaller particles are retained on the fibres by a weak electrostatic force. This effect can be improved using electrostatically enhanced fibres, which actually attract the particles.
HEPA filters can eliminate larger dust, hair, PM2.5, PM10 and pollen particles from the air.
Tesla announced in 2016 that it would be installing HEPA air filtration in its vehicles.
All Aqua Perfecta air filtration models use HEPA13 air filtration. See shop for cleaner air.
HEGA Air Filtration
High-Efficiency Gas Absorption filters (HEGA) work by employing two mechanisms – physical adsorption and chemisorption. Activated carbon filters are frequently used for this function. HEGA filters remove gaseous pollutant, such as odours, gases and volatile organic compounds (VOCs). The PerfectAir Sense has active carbon filtration.
UVGI Air Filtration
Ultraviolet Germicidal Irradiation (UVGI) air filtration uses specific wavelengths of ultraviolet (UV) light, which are effective at killing microorganisms.
UV-C light is generated by passing an electrical charge through a low-pressure gas chamber.
UVGI can kill Coronavirus, as well as other airborne pathogens. Dr. Edward A. Nardell, a professor of global health and social medicine at Harvard Medical School said: “We’ve done the studies. We know it works.” The PerfectAir Sense employs UVGI technology, for enhanced air pollution eradication.
Ionic Air Filtration
Ionic air filters use a device that emits ions that come into contact with airborne and surface-borne contaminants.
Generally speaking, once these ions come into contact with the contaminant, they either cause direct damage to the cells of the contaminant or cause small airborne particles to clump together, making them too heavy to float or too large to pass through the filter. Within this category of filtration there are various different types:
Electrostatic ionisers work by electrically charging particles in the air stream using corona wires or by generating ions (e.g. pin ionisers), and collecting them on oppositely charged collection plates/precipitators.
The fraction of particles removed by the filter is called the “removal efficiency.” For portable, self-contained electronic filters, the rate of particle removal from air is termed the Clean Air Delivery Rate (CADR = Airflow Rate x Removal Efficiency).
Bipolar ionisation emits a blend of both positively and negatively charged ions that attract oppositely-charged contaminants. It results in the deactivation of single-celled organisms such as fungi, viruses and bacteria, whether they’re in the air or resting on surfaces.
Basic Photocatalytic Oxidation (PCO) is an extension of UV technology, and works by shining a UV light on a catalyst (usually Titanium Dioxide) that is coated onto a substrate material. This releases electrons which react with water (H20) in the air, breaking them up into hydroxyl radicals (OH·), which are highly reactive, short-lived, uncharged forms of hydroxide ions (OH−). These small, agile hydroxyl radicals then attack bigger organic (carbon-based) pollutant molecules, breaking apart their chemical bonds and turning them into harmless substances such as carbon dioxide and water. However, these radicals don’t last long enough to travel very far, limiting the effectiveness of basic PCO compared to more advanced forms. The major drawback to this technology is that it may produce ozone which itself is a contaminant/pollutant.
Advanced Photocatalytic Oxidation (APCO): while standard PCO only produces short-lived hydroxyl radicals, advanced PCO technology uses a more complex catalyst formula to create a much more effective mixture of additional ions. These ions actively hunt contaminants and damage their DNA to stop them from growing, eventually killing them off. Advanced PCO is also known to be especially effective at controlling odours.
The most advanced form of this technology is Advanced Hydrated PCO (AHPCO). AHPCO releases the longest lasting ions in the greatest number which also seek out contaminants breaking them down at a very high rate. This works as the hydrating agent accelerates and maximises the production of ionised hydroperoxides that more effectively clean the air. The catalyst of AHPCO consists of nano-sized particles that are bonded to the walls of the device’s surface, which increases the reactive surface area and the rate of reaction. Our PerfectAir Ultima and PerfectAir Shield use AHPCO technology.