Classroom ventilation with manual opening of windows: Findings from a two-year-long experimental study of a Portuguese secondary school

• Published in: Building and environment 2017-11, Vol.124, p.118-129
• Main Authors: Duarte, Rogério, Glória Gomes, Maria da, Moret Rodrigues, António
• Format: Article
• Language: English
• Subjects: Air quality; Air temperature; Classrooms; Energy conservation; Free-running classrooms; Indoor air pollution; Indoor air quality; Indoor environments; Manual window-airing; Natural ventilation; Running; Secondary schools; Studies; Thermal comfort; Ventilation; Weather; Window opening patterns
• ISSN: 0360-1323; 1873-684X
• DOI: 10.1016/j.buildenv.2017.07.041

Classrooms in Southern Europe are traditionally ventilated with manual opening of windows. This is an energy-sparing and perfectly appropriate way of ventilating classrooms when weather conditions are warm, however, as outdoor air temperatures drop, teaching staff and students tend to leave windows closed and, as a consequence, ventilation rates fall leading to poor indoor air quality. To safeguard classrooms' indoor air quality and promote energy conservation, understanding the conditions for which manual window-airing is appropriate is of great relevance. Yet, given the stochastic nature of window-airing, it is difficult to get hold of this understanding. The main objective of this paper is to find out when manual window-airing of classrooms is appropriate. To achieve this objective, four free-running classrooms of a Portuguese public secondary school were monitored during a two-year period. Ventilation rates were determined and it is concluded that manual opening of windows provides appropriate ventilation for outdoor running mean temperatures larger than 19 °C. When outdoor running mean temperatures are lower than 16 °C, manual window-airing becomes inappropriate and, for outdoor running mean temperatures between 16 and 19 °C, appropriate manual window-airing depends on the indoor air temperature. For the studied classrooms, these results translate into appropriate ventilation for approximately a quarter of the academic year. Because of the significance of this finding, the paper concludes with a review of the ventilation strategy used in the studied classrooms. •Ventilation rates in four free-running classrooms are determined during two full academic years.•Manual window-airing of classrooms is appropriate with outdoor running mean temperatures larger than 19 °C.•For outdoor running mean temperatures between 16 and 19 °C manual window-airing is still appropriate, but depends on indoor air temperature.•When outdoor running mean temperatures are lower than 16 °C, regardless of indoor air temperature, manual window-airing is inappropriate.•For the studied classrooms, manual window-airing provides appropriate indoor air quality and thermal comfort for 25% of the academic year.