There have been increasingly growing concerns over the quality of the air inside buildings and the associated energy use. The CO2-based demand-controlled ventilation DCV is one of the strategies that could offer a great opportunity to reduce energy consumption in HVAC systems. However, implementing CO2-based DCV under ASHRAE Standard 62.1 2004-2010 is not simple as it was under previous versions due to the changes in breathing-zone ventilating rate calculations. Thus, this paper provides insight into the performance of a multi-zone VAV system under different operating and ventilation conditions, discusses the difficulties in the CO2-based DCV, and proposes a robust DCV strategy based on the supply air CO2 concentration. The proposed strategy offers great benefits in terms of better indoor air control and improved energy efficiency. To evaluate the proposed strategy, energy simulations were performed on various USA locations and for a typical two-story office building conditioned by a VAV system. The results show that a significant energy saving could be achieved by implementing the proposed strategy as compared to the design-occupancy ASHRAE Standard 62.1 2010 multi-zone procedure and the amount of saving that could be up to 23% depends mainly on locations and the actual occupancy profile. (C) 2011 Elsevier B.V. All rights reserved.