Evaluation of thermal comfort in a classroom under stratum ventilation with various air change rates

Ensuring thermal comfort in classrooms is critical for student well-being and learning performance, particularly in tropical climates where high temperatures and humidity frequently compromise indoor conditions. Conventional ventilation systems often fail to balance indoor air quality with thermal comfort, leading to issues of inadequate mixing at low air change rates (ACH) and overcooling at higher rates. While stratum ventilation has been proposed as a promising alternative, limited studies have quantitatively assessed its performance across different air change rate levels in educational environments. This study addresses this gap by evaluating thermal comfort in a classroom equipped with stratum ventilation under five ventilation scenarios (0.5, 2.0, 3.5, 5.0 and 6.5 ACH). A combined approach of computational fluid dynamics and experimental validation was employed, with the Predicted Mean Vote (PMV) and velocity distributions analysed at 0.8 m above the floor to represent seated occupants. The results reveal a strong inverse correlation between air change rates and Predicted Mean Vote (R² = 0.91), with mean Predicted Mean Vote decreasing from −0.75 at 0.5 ACH to −1.8 at 6.5 ACH. Zone-level analysis highlights non-uniformity, with front zones near supply diffusers showing greater cooling sensitivity (PMV −1.45 at 2 ACH; standard deviation 0.35). Contour maps further indicate that at ≥5 ACH, local air jets exceed 0.12 m/s, increasing draught risk despite improved mixing. An optimal balance was observed at 2–4 ACH, where the mean Predicted Mean Vote stabilised between −1.2 and −1.5 with moderate variability, offering a practical compromise between air quality and comfort. These findings advance current knowledge by quantifying the trade-off between ventilation effectiveness and thermal comfort in stratum-ventilated classrooms, providing design guidance applicable to other high-occupancy indoor environments.