Indoor air quality in low energy schools: the use of CO2 based demand controlled ventilation evaluated

Dutch government encourages with guidelines sustainable design of schools. The guidelines contain requirements regarding the indoor air quality in the schools. In order to evaluate the indoor air quality in the schools, measurements were performed in two new built primary schools. Both schools were designed on classification B of the Dutch government guidelines and have a CO2 based demand controlled ventilation system. To evaluate the indoor air quality, measurements were performed on CO2 level and a questionnaire was held amongst the staff of the schools. Only one of the four measured classrooms met the design criteria while the other classrooms showed exceedances of 46 to 65% during occupancy hours. The measured air flow rates corresponded with the relatively high CO2 levels that were found. At one school, the CO2 levels measured by the local CO2 transmitter were strikingly low. Deviations of 300 to 800 ppm compared to the accurate CO2 transmitter of the measurement setup were found. Resulting high CO2 levels, which were caused by the deviations of the local transmitter, showed that the control strategy at both schools did not meet the design requirements. It is not possible to ensure a good indoor air quality with the current accuracy of the local transmitters.