Reducing the transmission risk with AirMaster

The current evidence on the spread of COVID-19 shows that recirculation of indoor air is one of the main methods of transmission, enabling transfer of virus from person to person. To combat this, the guidance from REHVA is that all air indoors must be fresh, clean air from outside.

As our children return to school, parents, teachers and children must be increasingly conscious of the risk of transmission. In schools, BB101 (guidelines on ventilation, thermal comfort and indoor air quality in schools, 2018) sets out the types of ventilation systems that can be used. This was published pre-COVID-19.

Of the acceptable ventilation systems defined in BB101, hybrid and natural ventilation systems will be required to mix room air with fresh air, to raise the temperature before supplying it into the classrooms, avoiding draught but recirculating the soiled air in the room. This air could contain the SARS-CoV-19 virus.


As an example of the damage recirculating air to control temperature can do, Germany’s Gütersloh meat factory had over 2,000 cases of COVID-19 amongst their employees resulting in 21 deaths. Why? According to the BBC, their ventilation system recirculated untreated cold air to maintain a low room temperature. Many schools built in recent years are now finding themselves in a similar situation, although they are recirculating air to avoid draughts as opposed to keeping temperatures low. 

What is the solution? Mechanical ventilation with heat recovery (MVHR). MVHR systems bring fresh air from outside, passing it through a filter to arrest pollutants, followed by a heat exchanger, increasing the supply air temperature before pushing it into the room. At the same time, the stale air in the room is extracted, filtered and exhausted to outside. The result is fresh air supplied at close to room temperature, with minimal energy consumption.


To further minimise transmission, an increase in the number of air changes per hour is recommended. With a natural ventilation system in the winter, this figure may be very low. For mechanical ventilation with heat recovery, air changes can be consistent throughout the year, typically being in the range of 5-6 air changes per hour.

SAV Systems have been supplying AirMaster Smart Mechanical Ventilation (SMVs) to school since 2012. All classrooms with this equipment should be COVID-ready, without the need to retrofit or modify the equipment, having a set of filters and heat exchanger from inception.


Whilst normally supplied with CO2 sensors to enable demand control based on room occupancy, the current guidance suggests that a fixed air change rate would be more appropriate. On any existing and future AirMaster installation, this change can easily be made via the control panel.

The recommendations for COVID-19 do not just extend to schools. We have been contacted by several organisations who wish to bring their employees back to work. Their existing ventilation systems simply cannot achieve the required air changes to create a safe workplace. By making use of a decentralized mechanical ventilation solution, rooms can be treated individually reduce the transmission-risk of COVID-19 for all. Furthermore, AirMasters do not require connection to existing systems, making them simple to retrofit.


By design, AirMasters operate with a slight negative pressure in the room. As such, air will not be pushed out of rooms through spaces under doors, for example, preventing room-to-room transmission by air.

The filters in an AirMaster must be changed annually to ensure consistent operation. The current guidance on COVID-19 recommends assuming the normal maintenance pattern, so the frequency of filter change should not be changed.

Where Airlinq Online is present, AirMaster installations can be managed online so filter changes can be anticipated and organized in advance, limiting equipment downtime.


Whichever ventilation systems we use, we must make sure that recirculation is minimised whilst maximising the fresh air indoors by increasing the air change rate. Buildings equipped with MVHR will already be a step ahead, but as we look to the future, mechanical ventilation may need to become to the default choice to keep ourselves healthy.

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