Carbon-dioxide (CO2) based demand controlled ventilation (DCV) offers the potential for moreenergy efficient building ventilation compared with constant ventilation rates based on designoccupancy. A number of questions related to CO2 DCV exist regarding energy benefits, optimalcontrol strategies, and indoor air quality impacts for contaminants with source strengths that areindependent of the number of occupants. In order to obtain insight into these issues, a simulationstudy was performed in six commercial and institutional building spaces. This paper reports onone of the spaces, a lecture hall, in which six different ventilation strategies were compared,three of them using CO2 DCV. The results depend on occupancy patterns, design ventilation rateand ventilation system operating schedule as well as assumed contaminant source strengths andsystem-off infiltration rates. In these simulations, CO2 DCV resulted in significant decreases inventilation rates and energy loads accompanied by increased indoor CO2 and volatile organiccompound (VOC) concentrations. The increases in CO2 were generally in the range of 300mg/m3. The VOC levels increased by a factor of two or three, but the absolute concentrationswere still low. The annual energy load reductions with CO2 control ranged from about 50 % to75 % depending on the space type, climate and ventilation strategy.