Indoor air quality and maximum comfort temperature criteria in schools may need to be reviewed in light of a growing body of evidence which highlights the importance of indoor air quality and temperature on pupils’ academic performance.
School buildings are complex facilities to design. A typical school can have an occupancy density of up to four times that of a typical office building, which means that heat gains from occupants and levels of carbon dioxide can be significant.
50 years ago, fresh air would have been introduced into a typical classroom by opening a window. This relatively uncontrolled approach to ventilation is not always effective, particularly when windows are located on a single elevation, which restricts the ability of air to move through a room. As a result, air temperatures in classrooms were often high and, in crowded classrooms in particular, the concentration of CO2 in the air increased significantly.
More recently, the Building Schools for the Future (BSF) initiative called for classroom ventilation rates to comply with the demands of Building Bulletin 101: Ventilation of School Buildings. The bulletin includes the requirement that pupils have a sufficient quantity of fresh air all year round and that schools do not get too hot in the summer.
This requirement is not always met. A 2006 study by BRE for the Department of Education looked at eight naturally-ventilated BSF schools and found that, of these schools, half regularly did not open their windows in the winter because the untreated outside air was too cold.
In 2011, the Priority Schools Building Programme (PSPB) heralded a new era in school design by making draught-free ventilation mandatory in an attempt to improve air quality and pupil comfort. Under the new rules, designers are now required to pre-mix the incoming cold air with enough warm air to mitigate any cold draughts.
The PSPB also set out to prevent overheating in classrooms in summertime by introducing the concept of operative temperature – a function of air temperature, humidity, air speed and the temperatures of the surfaces to which the occupants are exposed.
The PSPB also introduced the concept of a variable maximum internal temperature, termed the running mean temperature, which is based on allowing the maximum internal temperature in a space to vary, depending on the maximum outside air temperature over the last seven days. This recognises that during a period of warmer weather, most people will adapt to the recent conditions and tolerate a higher temperature.
One way a scheme can meet the summertime temperature criteria is for the classroom ventilation system to incorporate crossflow ventilation using ducted stacks with “wind-catcher” type devices. With these devices installed, the ventilation system will typically work in one of three modes:
- In the morning, manually opened windows will provide ventilation by operating in conjunction with the wind-catcher to exploit free cooling from outside air.
- Once external air temperatures rise above internal air temperatures, classroom windows should then be closed and the system switched to minimum ventilation mode based on the CO2 levels in the room.
- At night, opening windows for ventilation allows cooler night air to remove the absorbed heat from interior surfaces ready for the next day.
The threat of overheating in high occupancy spaces, such as classrooms, is set to increase as the climate continues to warm. This should be of concern to all those involved with the design and specification of schools, following the publication of a report by The Bartlett Institute for Environmental Design and Engineering, part of the Faculty of the Built Environment at University College, London, in 2014. This reviewed the evidence from various studies from around the globe which highlighted the impact temperature appears to have an impact on academic performance.
The Effects of Thermal Conditions and Indoor Air Quality on Health, Comfort and Cognitive Performance of Students says that: “Schools should not allow temperatures to drift above the recommended range of 20 to 22°C in the winter and 22 to 24°C in the summer.” The report says: “There is evidence that lower temperatures in the range between 25 to 20°C improved student performance by 2% to 4% for every 1°C reduction.”
Effects on academic performance
Of more concern is the evidence which suggests that current guidelines, which allow classroom temperatures in the range 25°C to 32°C, may be having “an impact on cognitive performance and comfort of the students”.
In addition to temperature, the document also highlights the importance of limiting average indoor CO2 concentrations in all teaching and learning spaces to an average of 1000ppm (a minimum fresh air supply rate of 8l/s per person) during a teaching day, which is a lower concentration than current guidelines.
Overall the report found “indicative evidence” that CO2 levels in classrooms lower than those recommended in current guidelines could improve academic performance, health and comfort of occupants. High CO2 concentrations are also indicative of a higher risk of transmission for airborne diseases and increased risk of respiratory disease.
The research project is ongoing. Professor Dejan Mumovic, one of the report’s authors, will be revealing the results of the latest research at this year’s CIBSE Building Performance Conference. To hear Dejan’s presentation or to book a place at the conference, which takes place 17 to18th November 2016 at London’s QEII Conference Centre, go to www.performanceinbuildings.co.uk.