This graph from the SINPHONIE study conducted in 114 schools in 23 European countries4, gives a clear indication of the times at which windows are opened during the day. No evidence of the use of night ventilation was reported.
Even when the outdoor air temperature is slightly higher than indoors, the elevated air speed due to increased airflow will increase cooling of the body.
Natural ventilation for cooling can be done in two ways – day ventilation and night ventilation:
- Ventilation during the day removes excess heat from inside the building by creating high levels of movement in the air.
- Night ventilation (also referred to as night cooling) will cool down a building’s thermal mass (walls, floor, furniture, etc.) at night using cool outdoor air. The following day, less cooling energy is needed within the building as the thermal mass has already been cooled.
Orientation of the classroom and shading control also play an important part in creating consistent thermal comfort. Large windows and skylights can be oriented to allow maximum sunlight to penetrate in the winter months, and shaded with moveable shading devices to block out sunlight in the summer months as needed.
Field studies show that people in naturally ventilated buildings accept higher temperatures⁵. This effect of the body adapting to its surroundings is referred to as adaptive thermal comfort. A prerequisite for designing with adaptive thermal comfort in mind is that people can freely adapt their clothing and operate windows.
The consequence of adaptation is that thermal comfort can be achieved in warm climates without air conditioning, by using natural ventilation, solar shading and intelligent building design. In countries with the hottest summers, ceiling fans or mechanical air-conditioning units may be required in addition to natural ventilation and shading.
The Clever Classrooms study (2015) found that better temperature control was achieved in winter when rooms were fitted with radiators with thermostatic controls. In contrast, underfloor heating was associated with poor heating control in individual classrooms due to longer response lag times.
The study also recommended that all methods of temperature control in classrooms be easily operable and readily accessible to teachers.
- Zeiler & Boxem (2009). Effects of thermal activated building systems in schools on thermal comfort in winter. Building and Environment.
- Mendell and Heath (2005). Do Indoor Pollutants and Thermal Conditions in Schools Influence Student Performance? A Critical Review of the Literature. Indoor Air
- Fisk (2017) The ventilation problem in schools: literature review. Indoor Air
- de Dear and Brager (1998). Developing an Adaptive Model of Thermal Comfort and Preference. ASHRAE Transactions
- Clever Classrooms (2015), Summary report of the HEAD project, University of Salford, Manchester