Evaluating perceived stuffy air complaints through tracer gas experiments in a modern educational building in Estonia

This paper investigates ventilation-related complaints concerning stuffy air and inadequate air distribution in a modern educational building in Estonia. Ventilation effectiveness was assessed using CO2 tracer gas measurements in a classroom, an office, and two halls. The results highlight key issues related to both the ventilation system design and its air distribution. The classroom demonstrated adequate air change effectiveness (56%), indicative of performance above ideal mixing conditions (50%). The old building hall showed near-mixing performance (43%). In contrast, the new building hall (25%) and particularly the office (13%) exhibited pronounced short-circuiting, where supply air largely bypassed the occupied zone by flowing between the structural slab and suspended ceiling to the extract terminal. The short-circuit effect was caused by horizontal slot diffuser jets combined with decorative wooden slat ceilings — an increasingly common architectural solution in modern Nordic educational buildings, yet one whose impact on ventilation performance has not been systematically documented. These findings confirm occupant complaints, provide quantitative evidence for a previously underreported failure mode, and offer guidance for remedial measures.