Demand-controlled ventilation (DCV) systems adjust ventilation rates based on occupancy and indoor air quality. CO2 sensors measure occupant density. When CO2 exceeds a setpoint, ventilation increases. When occupancy is low, ventilation reduces saving energy. Outdoor air enthalpy sensors adjust ventilation based on outdoor conditions. When outdoor air is favorable for cooling, ventilation increases. When outdoor air is unfavorable, mechanical cooling is used instead. VOC sensors detect volatile organic compounds indicating air quality problems. Elevated VOC levels trigger ventilation increase. Particle sensors measure indoor air quality. In densely occupied spaces, DCV saves significant energy. Conference rooms without occupancy waste energy with constant ventilation. With occupancy sensors, ventilation activates only when needed. Controls integration with building automation systems enables sophisticated control. Scheduling combines with occupancy sensing for optimized operation. DCV systems require careful commissioning to ensure proper operation. Sensor calibration and setpoint tuning affect performance. Poor commissioning results in inadequate ventilation or wasted energy.