Assessing the Fluctuation of Indoor Thermal Conditions in Naturally Ventilated Classrooms Through K-Means Clustering

Abstract

For naturally ventilated classrooms, windows should be constantly open to maintain good indoor air quality during class times. However, it is unknown whether this would result in significant fluctuations in the indoor thermal environment, while the effects of ventilation rate and window operation are still unclear. Therefore, this study assesses the fluctuation of indoor thermal conditions under natural ventilation during class periods, based on the K-means clustering and statistical analysis of data collected in a large measurement campaign in Spanish schools. The results showed that regardless of the heating mode, the indoor thermal parameters remained stable in most cases. High fluctuations were observed only in a few cases: 15% for indoor temperature, 6% for relative humidity, and 3% for indoor air velocity. The variability of the indoor thermal parameters within an hour was less than 1°C for indoor temperature, 3% for relative humidity, and 0.1 m/s for indoor air velocity. Ventilation rate and window operation were found to be related to the fluctuation of the indoor temperature and air velocity, rather than the relative humidity. These findings shed light on the thermal conditions in naturally ventilated classrooms and have practical implications for the implementation of natural ventilation protocols in schools.