Performance comparison of air distribution systems for lecture room ventilation and their influence on vertical temperature gradients

High occupant density, intermittent occupancy patterns, and the impact of classroom environment on teaching and learning, make energy efficient classroom air distribution a challenging task. Performance data of different classroom air distribution systems, during their service life, remains
scarce. The current study was hence undertaken to examine performance of three different, demand controlled, air distribution systems, in three in-use lecture rooms: mixed, thermal displacement, and a 50:50 combination of the mixing and displacement schemes. Air temperature and humidity were
measured at 20 different heights, at two different locations, in all three rooms. Occupancy was recorded during each scheduled lecture. The vertical temperature gradients varied with air-distribution system type and actual occupancy. Stratification magnitude was remarkably more for the
displacement system, compared to the other two. For displacement ventilation temperature stratification was primarily limited closer to the floor. Temperature stratification progressively increased through a class hour, gradually returning towards the initial state once students leave. In the occupied zone, temperature gradients stayed within ~4 °C, thus allaying concerns of local discomfort
due to temperature stratification.