Air filtration and purification: what is it, what systems are available and what will they cost?

If you are concerned with the indoor air quality in your home, you may be considering installing air filtration or purification. This technology is in greater demand today due to a growing awareness of the danger of exposure to indoor microorganism pollutants, which cause diseases, allergies, and long-term illnesses. Research has shown that transmission of infection through the air poses a far bigger threat than surface transmission. Contaminated droplets are sprayed out during a coughing fit and a fine mist of virus-bearing aerosols is emitted when someone speaks or breathes.As we emerge from the recent pandemic, with all of the necessary responses at its peak, homeowners are facing the need to look at sustainable solutions for the future. Cleanliness, including indoor air quality, is a paramount concern to ensure the wellness of a space's occupants.When you search the internet, you will find a multiplicity of information relating to air purification, with claims and counterclaims from many different manufacturers, and begin to wonder who is right. At Calibre, we have an experienced design team who can guide you in your choice to give you the best selections for your home.

What is the difference between air filtration and air purification?

Air filtration and purification technologies for indoor air quality can be divided into passive and proactive systems. Air filtration is a passive purification technology that effectively traps a large proportion of particles, such as dust, soot, and pollen. Purification includes proactive technologies that treat the space within the ventilated zone, providing effective elimination of bacteria, viruses, and mould. They are often installed together, as they serve different functions and complement each other.There is a whole range of technologies and manufacturers with different claims. Some are available as standalone systems, while others are available to install within mechanical ventilation systems. The thing to understand is that all of these technologies work in different ways and are better in some situations than others. We will look at a few of the available options, how effective they are, and how they can be installed.

Air filtration systems, how they work, and what types there are

Fibre air filtration can be described as the first line of defence against airborne contaminants. Climate control and mechanical ventilation systems contain filters, which can range from standard filters that would filter sand, hair, and coarse particles to specialized High-Efficiency Particulate Air (HEPA) filters, which can trap particulate matter as small as 0.3 microns. However, while filters may be effective at trapping a large proportion of particles, they do not remove odours, chemicals, or gases, they do not treat contaminates on internal surfaces, and require air to pass through a filter to clean it.Fibre activated carbon and electrostatic precipitators are both filtration types suitable for being installed in air conditioning or mechanical ventilation systems. The correct filtration method is essential to ensure the indoor air is protected from dust, soot, and pollen from outside, while capturing smaller particles such as bacteria and finer dust, and gases such as VOCs from inside. As always, there is a balance between the best filter that is available and the most appropriate for the application.

What is the best filter for removing different airborne contaminants?

Fibre filters are most commonly used for removing particles and have performance classifications based on the size and efficiency at which they can remove that particle size. For example, an ePM1 85% can filter a particle of 1 micron (µm) at 85% effectiveness. The PM 1 size is deemed to be the smallest and most dangerous and able to pass through the cell membrane of the alveoli, enter the bloodstream and reach major organs including the brain, and consideration should be given to the static pressure to ensure fan capacity is adequate to overcome the pressure drop created.Activated carbon filters use small pieces of carbon, typically in granular or powdered block form, that have been treated to be extremely porous and are very effective at capturing chemical emissions including Volatile Organic Compounds (VOCs), smog, ozone, tobacco smoke, and fumes from cooking. However, they are ineffective at removing microorganisms and fine particles. For this reason, they are typically installed before a fibre filter to provide additional protection and indoor air quality.Electrostatic Precipitator filtration uses a high voltage electric charge to remove solid particles or liquid droplets from the air. Whilst they are commonly used in industrial settings, they are also available for residential use, and have the advantage of drastically reducing fan power energy, as unlike standard fibre filters, they have a very low-pressure drop. Electrostatic Precipitators are extremely effective at removing solid particles or liquid droplets. In addition, the high voltage charge will neutralize a high level of bacteria and viruses within the air stream.

Air purification systems, how they work, and how effective they are

Ultraviolet light has been used for a long time to purify water, surfaces, and air, and has been proven to be a reliable and safe method. Ultraviolet light has a shorter wavelength than visible light and a much higher energy level. When this energy is absorbed by a microorganism such as bacteria, viruses, and mould, it damages the DNA of the cell, triggering a self-destruct mechanism which renders it harmless. Whilst there is no doubt about ultraviolet light’s ability to deactivate microbes, its effectiveness at purifying the air depends on several factors. Firstly, the pollutants must travel to the ultraviolet light source and come in direct contact with it. They must be exposed to the correct dosage, which is dependent on the level of UV being emitted, and how long the pollutant is exposed to the rays. As bacteria and mould are resistant to UV radiation, they require a high dosage of UV light, which is often much more than the few seconds when air passes through a device. For this reason, UV light technology is not as suitable for ducted indoor air quality as other systems.Bipolar Ionization is an air purification technology that can be used in ducted ventilation systems to generate positively and negatively charged ions. These ions magnetically attract small airborne particles such as pollen and dust, until the newly-formed particle is too heavy to remain in the air or is large enough to be removed by a filter. Some manufacturers claim removal of viruses and disinfection of surfaces within a treated area, however, as the charged ions exist for a relatively short time before returning to their natural state, this technology is not as effective in systems that have a high airflow with long travel distances. Bipolar Ionization is an emerging technology and manufacturers must be able to back up their claims with data to demonstrate their effectiveness.Hydro ionization is a technology that neutralizes bacteria, viruses, mould spores, noxious gases and vapours, and odours that are found in the air and on surfaces inside buildings. They do this by producing an oxidizer from the oxygen (O₂) and water humidity (H₂O) in the air. These hydrogen peroxides are safe and effective for the elimination of harmful organisms, either by destroying them, or rendering them harmless by damaging their cell structure. They have a long-lasting effect and proactivity treats every space within the ventilated zone. Hydro ionization technology produces hydrogen oxide which is widely used as a medical antiseptic and cleanser in homes and hospitals. Whilst it has been demonstrated as being safe, it is a relatively new technology, like an air purifier, and just like the bipolar ionization systems, it is essential that manufacturers can back up their claims with verified data as to their effectiveness.

What pollutants should I be concerned about?

The main external pollutants of concern are particulates of 10 and 2.5 micrometres and Nitrogen Oxide. Before considering what system to choose, you will need to consider the external air quality. You may obtain this information from the local authority website or you may consider employing a specialist air monitoring company to provide live data before a decision. Near busy road networks, you are likely to find unacceptably high levels of particulate matter from brakes and tyres, and nitrogen oxides (NO) from diesel engines. You should remember that it is primarily the weather that dictates what will happen once it is released into the air. During wet or windy conditions, pollution concentrations remain low, and will either be blown away or removed from the air by rain. During still, hot weather, pollution can build up to harmful amounts, leading to what is known as pollution episodes.Internal pollutants include pathogens, Volatile Organic Compounds, and carbon dioxide. In addition, radon gas may be a concern, but this is most common in areas of underground granite. Excessive humidity may also give rise to mould and dust mites. This should be controlled by maintaining a relative humidity of between 40 – 60%.

What is the best system to maintain indoor air quality?

The best system will depend on what you are trying to remove from the air and whether it is to be installed into an air conditioning system or mechanical ventilation system. In most cases, this will involve a combination of passive filtration and active purification.

Type of SystemHow it worksTypes of PollutantFibre Filter ePM10FiltersParticles 0.3 microns to 10 micron- Larger particles caused by crushing and grindingFibre Filter ePM2.5FiltersParticles 0.3 microns to 2.5 microns - Smaller particles produced by combustion enginesFibre Filter ePM1FiltersParticles 0.3 microns to 1 micron - Fine dust, mould, bacteria, and pollenActivated carbon filtersFiltersVolatile organic compounds, odours, nitrogen oxides, and other gaseous productsElectrostatic PrecipitatorFilters and NeutralisesParticles down to 1 micron - Fine dust, mould, bacteria, and pollenUltraviolet lightNeutralisesBacteria, viruses, and mouldBipolar IonizationAssist filtering and neutralisingSmall particles, some virusesHydro ionizationNeutralisesBacteria, viruses, mould spores, noxious gases and vapours, and odours

As you can see, it is not necessarily a straightforward selection, and if there are a range of pollutants of concern, a careful selection of passive filtration and active purification will be required.A good combination to deal with external pollutants such as particulates and nitrogen oxide would be to install an activated carbon and fine fibre filter to the supply air. Alternatively, a coarser pre-filter to trap larger particles, followed by an Electrostatic Precipitator and activated carbon would filter in the same way.UV light air purifiers are generally combined with a fine filter in a forced-air system such as air conditioning. The UV lamp is usually placed downstream of any filter.Bipolar Ionization and Hydro ionization are always used in combination with filtration and may be installed in ducted mechanical ventilation or air conditioning systems.