Abstract This paper proposes a novel and efficient CO2-based demand-controlled ventilation (DCV) strategy for use as an alternative to the proportional-plus-integral (PI) and the proportional-integral-derivative (PID) controls most often used for CO2 control in buildings. The new strategy “Pseudo Session DCV” divides opening hours into pseudo training sessions and breaks. For each pseudo training session, the outdoor airflow rate is calculated through the CO2 mass balance equation to keep indoor CO2 near the set point. For each pseudo break, the outdoor airflow rate is set at either the prescribed ventilation rate or the minimum outdoor air required by industry standards. Simulations were performed for a sports training center using both simulated and experimental CO2 generation rates. The results show that Pseudo Session DCV performs similar to PID for all possible cases, but achieves better energy savings performance than proportional control. For example, the Pseudo Session DCV strategy saves 34–38% of the energy required to condition outdoor air and 62–79% of fan energy compared to a proportional control strategy. Pseudo Session DCV is simple, efficient, capable of utilizing schedules for optimal ventilation control and no tuning is needed. Therefore Pseudo Session DCV control is easier to implement than PI or PID control.