On the potential of demand-controlled ventilation system to enhance indoor air quality and thermal condition in Australian school classrooms

Abstract

Indoor thermal comfort and air quality in school classrooms are of interest worldwide, primarily because of their potential impacts on students’ health, learning performance and productivity. Further, increasing concerns with changing climate and building energy efficiency highlight the importance of ventilation and comfort in educational settings. The existing literature on indoor air quality (IAQ), ventilation, and thermal comfort in classrooms in subtropical regions of Australia is sparse. Here, we present the results of a field study conducted in secondary school classrooms in Sydney during the school year in 2018 and 2019. We collected data with subjective surveys through questionnaires and with field measurements related to IAQ the thermal comfort in two adjacent similar classrooms. The infiltration and ventilation rates were measured during the non-occupied period using the concentration decay method. We analysed the performance of a cloud-connected demand-controlled mechanical extract ventilation system (DCV), which was installed in one of the two surveyed classrooms during mid-season. Before application of the DCV, CO2 levels were similar in both classrooms with a maximum concentration of approximately 2418 ppm during cold season. The DCV reduced the peak CO2 concentration to 1335 ppm, while CO2 raised to 2981 ppm in the classrooms without DCV during mid-season. Further, Volatile Organic Compounds (VOCs) analysed from air samples show improved air quality in the classroom with DCV. Our results highlight the impact of both indoor temperature and CO2 concentration on students’ feeling of fatigue. Students showed adaptability to indoor temperature change. A period of one week is needed for students’ adaptation to a step change in the mean outdoor temperature. Understanding classroom indoor air quality and thermal environment, as well as students’ perceived comfort, is vital to develop child-based design guidelines for schools.