What is the role of air filtration in ventilation systems?

Regarding the current Coronavirus situation, we have gathered some frequently asked questions on how air filtration units in ventilation systems can help to create a safe indoor climate and to prevent the spreading of viruses.

The main task of ventilation in buildings is to supply fresh air to closed spaces inside buildings and to exhaust old and used air from closed spaces. In this way, we supply the demanded quantity of fresh air with a sufficient quantity of oxygen needed for breathing. The rest of the supplied air is needed for removing volatile organic compounds (VOCs), CO2 and other emissions from closed spaces.

Air filtration in ventilation systems is a mechanical method of removing solid and liquid particles. There are several levels of air filtration for different sized particles: from larger particles as flies, leaves, medium sized particles like dust or pollen, to very small-sized like water mist, droplets and combustion particles on which micro-organisms and viruses can travel through the air. The latter can be filtered out by HEPA and ULPA air filter systems which retain also very small particles, such as viruses and remove them from the air supply or air recirculation. Air filtration within ventilation systems is crucial for providing clean air. That is why in all surgical rooms inside hospitals and pharmaceutical plants, for example, high efficiency filters are part of the ventilation system as standard for at least 50 years.

Air filtration can remove all undesired particles in the ventilation system which might be harmful for living beings, especially for those who already have respiratory or chronic issues. With the increasing levels of outdoor air pollution, air filtration in buildings is gaining importance. It is expected, that in near future more and more air filtration systems will be used, including recirculation units which will also remove CO2. HEPA and ULPA air filtration systems are state of the art technology for cleaning the air.

Which filters effectively protect against viruses?

The filter efficiency in HVAC systems is defined by the general filter classification according to standard EN 1822:2009. Only filter classes HEPA and ULPA are efficient enough to hold back particles of the size of Covid-19 virus, which are only 1/1000 the width of the average human hair.

Example: Filtration stages in ventilation systems for high risk applications

Air filtration in premises with high requirements regarding air purity is carried out in several stages, starting from filtration of larger dirt particles from the fresh outside air in the first stage to elimination of the finest particles in the final filtration stage, before air is supplied into the room. All components of the HVAC system presented below, as well as air regulation units and Eurovent certified ventilation ducts can be supplied by Lindab and equipped with control elements for optimum system performance.

General recommendations regarding ventilation systems in times of pandemic*

Considering the best available evidence and knowledge to date, some general recommendations on HVAC systems in buildings are given below.

• Secure ventilation of spaces with outdoor air / regular airing with windows (even in mechanically ventilated buildings)
• At nights and weekends, do not switch ventilation off, but keep systems running at lower speed
• Switch air handling units with recirculation to 100% outdoor air
• Do not change heating, cooling and possible humidification setpoints
• Avoid open windows in toilets to assure the right direction of ventilation and flush toilets with closed lid
• It is important to replace central outdoor air and extract air filters according to maintenance schedule, but use common protective measures including respiratory protection

*The above stated short summary of practical measures for building services operation is based on the REHVA guidance document from 3 April 2020, for updates and additional information please visit the REHVA homepage.