The effect of occupancy and environmental physical variables on classrooms’ natural ventilation: a path modeling approach

In this paper, we use a path model to study natural ventilation in classrooms and research the link between air change rate, occupancy, and both outdoor and indoor physical variables. In general, the path model is derived from the building physics and occupant behavioral considerations via structural equation modeling (SEM), and allows for the use of continuous observable and unobservable factors. The latter are often employed in behavioral and social sciences to represent personal and group attributes. The path model is validated with data gathered during two consecutive academic years from four classrooms of a Portuguese school. The results confirm indoor and outdoor air temperature as major drivers of classroom ventilation, with standardized total path coefficients of approximately 0.55. Solar energy, precipitation, and occupancy are also significant drivers of classroom ventilation, with standardized total path coefficients of 0.24, −0.18, and 0.17, respectively. These results contribute to our understanding of the relative importance of occupancy as well as to identifying the most relevant environmental determinants of natural classroom ventilation. In spite of the statistical significance of the path model as a whole and its detailed causal relationships (direct, indirect, and feedback), only 58% of classroom ventilation variance is explained by the selected input variables. Because naturally ventilated classrooms depend significantly on occupants’ interactions with the built environment, i.e., opening/closing windows and blinds, extending path modeling to include additional personal and context-related drivers of occupants’ behavior would allow for further insights into the complex multi-domain topic of natural classroom ventilation.