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Indoor Air Quality (IAQ) and especially IAQ in schools has been receiving increasing attention in recent years. Of course, that has been partly happening because of the Coronavirus and the need to find ways to minimize the spread of the virus in indoor environments.

Read more here on how to prevent the spread of Coronavirus with mechanical ventilation


But even before the spread of the Coronavirus, several European studies on the respiratory health of children (*, **) had shown that, in most European schools, the values of PM10, or pollutants, as well as viruses and bacteria, are significantly higher than the threshold of concentration of particulate matter considered acceptable for outdoor environments (*), highlighting how the air inside schools is much more polluted than the outside.


The table shows the average levels of particulate matter concentration detected over one day in classrooms in different European countries. The red line at 50 μg·m -3 is the maximum daily value allowed in the EU for outdoor environments.

The European countries indicated in the table report average concentrations of particulate matter within schools significantly higher than the maximum daily value allowed in the EU for outdoor environments.


Children spend large amounts of time at school, which can significantly contribute to their exposure to air pollutants. And besides that, because they are still developing their defence mechanism, they inhale a higher volume of air per bodyweight than adults, which makes children even more impacted by the exposure to indoor air pollutants.

Indoor air quality at school


Indoor air quality in schools often depends on the level of ventilation the building can offer, which is, most often than not, poor. In fact, schools frequently present elevated indoor CO2 levels. Not to mention great quantities of other pollutants such as bacteria, moulds, VOCs and PM. The concentration of these pollutants is a major issue, which can often result a “sick building syndrome”, meaning occupants respiratory and/or allergic symptoms, and diseases linked to the time spent in the building.

High levels of indoor pollutants in schools are usually caused by poor building construction and maintenance, poor cleaning and, most importantly, poor ventilation. In fact, the only ventilation usually provided in schools is natural ventilation, by opening windows, which is not usually enough.

In fact, if a school principal were to assess the indoor air quality level of any school relying on natural ventilation only, he (or she) might very well find that natural ventilation is not even nearly adequate to provide the indoor air quality standards required to create a healthy environment for the occupants.

Analyzing IAQ levels at school


A simple analysis of the concentration of pollutants in a school in the city center of a European capital would show important variations of CO2 concentration, to the point that CO2 concentration levels would be higher than the advised threshold and particulate matter concentration would be easily higher than the threshold identified by the WHO (World Health Organization) guidelines.

According to simulations and analysis conducted using the Daikin IEQ sensor (more information here), given the context described above, we would have the differences described in the graphics below, where graph a) describes how the CO2 concentration might change in a school only using natural ventilation, where windows in classrooms are opened for 15 minutes every hour;


while graph b) describes how the CO2 concentration might change in a school using decentralized mechanical ventilation, most specifically a Daikin Modular L unit.



What is shown in the above-mentioned simulation is essentially that natural ventilation is simply not enough to guarantee healthy indoor air quality levels and can only provide acceptable levels in those moments when rooms are emptied.


Mechanical ventilation, instead, can offer greater control over CO2 and pollutants concentrations, maintaining their concentration at a very low level, with no spike whatsoever depending on occupancy.



Ventilation is fundamental to make schools healthier environments for children and adolescents.

Exposure to air pollutants, viruses and bacteria increases exponentially in indoor environments, where impurities can be 2 to 5 times more concentrated than in outdoor environments. Schools, as demonstrated, are not immune to this trend.


There is no doubt that mechanical ventilation systems can provide premises with higher air quality levels than natural ventilation only, strongly improving the environment for the occupants of the buildings where mechanical ventilation is provided.


A well-designed mechanical ventilation system, able to guarantee the correct exchange of air in indoor environments, can be very important to reduce pollutants and CO2 levels, but also to minimized the spread of viruses, improving the health of those who spend most of the day in school environments.


The introduction of clean air and the simultaneous extraction of exhaust air helps to purify the indoor air, thus reducing the possibility of infection among the occupants of a building.


Mechanical ventilation also allows all this without generating heat loss in the building, which happens opening windows, for example.


Mechanical ventilation systems, in fact, are able to recover heat from the exhausted air thanks to the heat exchangers. These allow heat transmission from exhaust air leaving the building to clean air introduced into the building, without any contamination between the two air flows; thus allowing – besides air exchange – better energy efficiency and lower CO2 emissions of the building.



* RESEARCH: School Environment and Respiratory Health of Children; HESE: Health Effects of School Environment.

** Indoor Air Pollution in Schools (



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