CO2-based demand controlled ventilation had been tried and tested in the United States under the old ASHRAE Standard 62 "Ventilation for Acceptable Indoor Air Quality", but this had since been replaced by ASHRAE Standard 62.1 and little is known on the field about the relative performances of CO2-based demand controlled ventilation between the old and new ventilation standards. In view of that, this paper presents a case study for an American elementary school gymnasium in order to compare the implementation of CO2-DCV under the old and new ventilation standards in terms of control strategies involved, the resulting energy savings, and indoor air quality associated with each strategy. The results indicate that, compared to the existing fixed ventilation rate strategy at which the ventilation rate is always 5% of the total supply air flow, a cooling coil energy savings of 0.03% and 1.86% can be achieved using an occupancy detection control strategy under the new ASHRAE 62.1 and old ASHRAE 62 respectively, while preserving thermal comfort and indoor air quality. (C) 2011 Elsevier B.V. All rights reserved.