Ventilation in school buildings has always been a hot topic – even before Covid came

Since the Sars-Cov-2 virus spread around the world, starting in early 2020, the conditions of public buildings became an important topic on the agenda of policymakers. With more knowledge about the virus, it became clearer that ventilation rate with the provision of fresh air in buildings is one of the crucial factors influencing the infection rate of occupants, as well as indoor air quality in terms of air pollution. However, this knowledge is not new.

In 2004, a study has already revealed that the SARS virus is transmitted via airborne particles in the air, which includes also the SARS-CoV-2 virus responsible for the Covid-19 disease. Of that, indoor CO2 concentrations can be a useful proxy to estimate the infection risk. Apart from Covid-19, it is also known that tuberculosis, a bacterial infection of the respiratory tract, is mainly transmitted via airborne routes. Myatt et al. (2004) concluded that the supply of outdoor air is of crucial importance to reduce the exposure of infectious droplets for occupants.

Additionally, the current Covid-19 pandemic showed that many public buildings, including schools and universities, suffer from insufficient ventilation. 11 percent or 777 schools did not meet the legal criteria for ventilation. As a consequence, the Dutch cabinet provided 360 million euros to invest in technical improvements of ventilation in schools. In Germany, the Commission for Indoor Air Hygiene (Kommission Innenraumlufthygiene) recommends for schools open the windows every 45 minutes. This recommendation is an indication that German schools are not provided with sufficient mechanical ventilation systems.

However, also the knowledge that school buildings are in bad conditions is not newly discovered due to Covid-19. A systematic review from 2017 by Fisk summarized the findings of ventilation conditions in school buildings in Europa and the US. It shows that most school buildings were provided with no mechanical ventilation or insufficient ventilation. The studies included in the review also reveal the harmful effect of insufficient ventilation on humans (see figure below). Some average CO2 concentrations were as high as 0.2% (2000 ppm) for mixed ventilation and natural ventilation (e.g. opening a window). Schools with mechanical ventilation had an average CO2 concentration of around 0.1% (1000 ppm) and lower.

Graph 16

To put this into perspective, the normal CO2 concentration of outside air is at around 0.04% (400 ppm). Studies have shown that CO2 concentrations of 1500 ppm and higher lead to a measurable reduction in the cognition performance of humans [here, here, and here]. The indoor CO2 level is also used as an estimator to indicate the concentration of other harmful substances in the air, so-called Volatile Organic Compounds (VOC) [here and here]. It is assumed that these substances can harm human cognition and health [2016, 2016, and 2020].

Some studies dedicated their research particularly to the effect of bad indoor environmental quality on pupils’ health and academic performance. Their results are striking, showing consistently a negative effect on children’s ability to perform well in school, as well as the chances to develop respiratory disease [for instance: here, here, here, here, and here]. This is especially dangerous for children because they are still in their growth phase, when the respiratory system and nervous system, including the brain, are still maturing. It is well known that fine particles cause inflammations in the respiratory tract, lungs, and the nervous system, including the brain. Preliminary results from a review of studies using MRI imaging show that high levels of air pollution can negatively affect brain development [both here and here].

The review from Fisk did also investigate the impact on the financial cost of increasing the ventilation rate, concluded from several studies that the elimination of mechanical ventilation in school buildings would reduce energy use by 4.4%, gas energy use for heating by 16.4%, and electricity use by 1.3%. Using the energy prices in the US in January 2017 as a reference, this would lead to an annual cost saving for electricity of $0.07 per square meter and $0.45 per square meter for gas usage. Nevertheless, the authors concluded that such small expenditure savings are acceptable, taking the performance and health benefits from installing proper ventilation systems.

To sum it up, a global pandemic needed to emerge first to put the building conditions of schools onto policymakers’ agenda. Nevertheless, due to decades of research, we have a good understanding of how to assess indoor environmental quality, and we see the current need for renovation of school buildings. The next step is now to use this knowledge and invest public funding effectively so that school buildings provide an optimal environment for pupils in terms of their health and cognitive capabilities.