Experimentally validated CFD analysis on the optimal sensor location for the CO₂-based demand-controlled ventilation

CO₂-based demand-controlled ventilation (DCV) has the potential to achieve energy saving while providing acceptable indoor air quality (IAQ). The spatial distribution of CO₂ concentration could be non-uniform within an occupied space; however, limited information is available on how the sensor location affects the sensing performance of the breathing zone CO₂ concentration. This study used experimentally validated Computational Fluid Dynamic (CFD) models to explore the optimal sensor position for the CO₂-based DCV system considering varied ventilation system (displacement vs. mixing), air change rate, and occupant condition. The results show that the displacement ventilation causes vertical stratification of CO₂, while mixing ventilation can achieve more uniform CO₂ distribution. With mixing ventilation system, CO₂ sensors located at the room return exhaust provide reasonable accuracies that meet the standard requirements. With displacement ventilation strategy, the errors of exhaust CO₂ sensors exceed those requirements due to CO₂ stratification and wall-mounted sensors placed at the breathing height yield smaller errors than the exhaust sensor. The results also indicate the accuracies of the CO₂ sensors placed on the desk are unstable and vary significantly mainly due to impact of occupant thermal plume.