The ventilation performance of a naturally ventilated classroom was investigated to monitor the CO_2 levels and compare compliance with new guidelines. Measurements of CO_2 levels were taken for 1 week during the heating season while different ventilation modes were investigated. The classroom was shown to have adequate ventilation to provide compliance with current recommendations although thermal comfort was sometimes compromised. Trickle ventilation provided useful ventilation at a rate of 0.75 1 s~(-1) per person. Purge ventilation was shown to reduce the CO_2 concentration by 1000 ppm but would not be sufficient to maintain an acceptable level. Experimental measurements showed that the trickle ventilators provided useful background ventilation at a total classroom rate of 22.91 s~(-1) or approximately 0.75 1 s~(-1) per person which is not enough on its own. Night time use of trickle ventilators for reducing day time CO_2 concentration level is not beneficial since the classroom returns to ambient concentration levels by the time the room is used again. Hence energy savings could be made by reducing the overnight background ventilation during heating period. The teaching staff and pupils control the ventilation into the classrooms by thermal comfort rather than air quality.
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