Demand control is particularly energy efficient and reliable when combined with displacement ventilation (DCDV). In order to investigate how much DCDV in practice reduce the ventilation air volumes and the energy demand, two Norwegian schools with CO2-sensor based demand controlled displacement ventilation (DCDV-CO2), Jaer School and Medi (a) over circle School, are analysed and compared with traditional constant air volume (CAV) mixing ventilation. During daytime operation with normal school activity, DCDV-CO2 reduces the ventilation air volume by 65-75% in both schools compared to CAV. For Medi (a) over circle School, both the airflow rates and the energy performance were analysed through measurements and use of a detailed, calibrated simulation model. The analysis period was 11-17 November, 2002. It was found that during this week, DCDV-CO2 daytime operation weekdays reduce the total heating energy demand by 21 %, the amount of unrecovered heat in the exhaust ventilation air by 54%, and the average airflow rate by 50%. Presuming constant fan efficiency it was also found that DCDV-CO2 daytime operation weekdays reduce the fan energy consumption by 87% the analysed week. (c) 2007 Elsevier B.V. All rights reserved.