Indoor climate in Danish primary and lower secondary schools still poor

20:e sep. 2022

The latest mass experiment investigating the indoor climate in schools shows that the situation is just as bad as it was during the 2009 investigation. This was no surprise to Realdania’s project manager, who believes, however, that the municipalities are in a better position today, with more concrete tools.

Ceilings with Troldtekt acoustic panels in school buildings
Ceilings with Troldtekt acoustic panels in school buildings

In 53 per cent of classrooms, high CO2 concentrations were measured that exceed the Danish Working Environment Authority’s recommended limit. In 18 per cent of classes, concentrations were twice as high as the recommended level.

The results come from the nationwide Mass Experiment 2021 investigation of indoor climate and well-being, in which 709 classes from 234 Danish schools participated in late 2021. The experiment is organised by the Astra national science centre, in collaboration with the Department of Environment and Resource Technology at DTU. The experiment is funded by the Realdania philanthropic association, as part of its work with indoor climate in schools.

It is disheartening that the results are largely the same as in previous mass experiments in 2009 and 2014, even though a number of initiatives have been implemented to give students a better indoor climate. A few more classes now have ventilation systems, compared to last time, yet over half of the classes still have excessive CO2 concentrations.

Indoor climate in Danish primary and lower secondary schools still poor

Lack of knowledge and tools

Although schools have been renovated across municipalities in recent years, these changes have not been reflected in the mass experiment results.

“The results from Mass Experiment 2021 do not surprise me. Things do look better for the schools with ventilation. But improving indoor climate in schools is a long, hard process that involves all links in the decision-making chain – the individual class, the school management and the municipal administration, and also a local and national political focus. And this takes a long time,” says Anne Gade Iversen, project manager at Realdania.

“The results from the mass experiments in 2009 and 2014 also received attention, but we did not have the same tools to improve the indoor climate back then, targeted at municipalities, that we have now. We are therefore in a stronger position today, and we also see examples of municipalities that have found solutions and serve as an inspiration to others,” she adds.

Indoor climate in Danish primary and lower secondary schools still poor

Healthy indoor climate improves well-being

During the mass experiment, students collected data in their classrooms over two days, one week apart. On the first day they did what they normally do during recess, and the following week they aired out and went outdoors during recess. The students also completed an anonymous well-being survey and tested their concentration on both days.

When students left the classroom and aired out thoroughly during recess, the proportion of classes with excessive CO2 levels dropped from 53 to 36 per cent. Students experienced fewer indoor climate symptoms such as eye irritation, headaches and fatigue, and had better concentration and interest in schoolwork following a thorough airing out and more time outdoors. The concentration test showed 6 per cent fewer mistakes following airing and an outdoor recess. 

The form of ventilation also had a major impact on air quality. Classes with a ventilation system with both supply air and exhaust had better air quality than classes that could only open windows to air out.

Indoor climate in Danish primary and lower secondary schools still poor

Action plan as the necessary first step

Realdania’s ‘school indoor climate’ project, has now been run twice since 2016, where municipalities have been helped to formulate strategic indoor climate plans. Anne Gade Iversen feels that both the level of attention and knowledge have risen.

“We focus on the strategic indoor climate plans, by bringing clarity and creating an action plan. It costs money, and indoor climate is not necessarily at the top of the agenda right now, so it is important to have a long-term action plan and the right initiatives in the municipalities, so they start with the schools with the biggest problems,” says Anne Gade Iversen.

“Schools buildings are built differently, so the solutions are also different. Changes in behaviour may be enough in one school, while others might need a new ventilation system.

Indoor climate in Danish primary and lower secondary schools still poor

Troldtekt contributes to a healthy indoor climate

Indoor climate is about more than just the CO2 levels in the classroom. Acoustics are also of great importance to student learning and well-being, if noise reverberates around the room. Acoustics were also studied in Mass Experiment 2021, where students measured the reverberation time in their classroom.

Reverberation time measures how long sound takes to ‘die out’ in a room, and should ideally be measured in an empty room. This was not possible in the experiment, as the students acted as ‘sound absorbers’, and the measured reverberation time may therefore be a little understated.

The reverberation time must be less than 0.6 seconds in a classroom, as a legal requirement. Although the measurements were subject to some uncertainty, they showed that this limit was met in most classrooms.

Indoor climate in Danish primary and lower secondary schools still poor

Facts: Realdania and indoor climate

  • Realdania’s ‘school indoor climate’ project targets municipalities, professionals, knowledge institutions, schools and pedagogical staff.
  • In Mass Experiment 2021, 709 classes from 234 Danish primary and secondary schools participated by measuring the indoor climate in their classroom. All data was collected and analysed.
  • The project has four strands: The strategic work of the municipalities in indoor climate plans, investigating the indoor climate effect of new physical approaches to learning in class, creating an overview of operating and financing models municipalities use to finance renovations, and keeping indoor climate on the agenda in schools and municipalities and among professionals.