In a Demand Controlled Ventilation (DCV) system the ventilation airflow rate is continuously matched with the actual demand. By this, the DCV system offers an obvious advantage compared to conventional Constant Air Volume flow (CAV) systems. Due to decreased average airflow rates, less energy is needed for fan operation and for heating and cooling of the supply air. Moreover, a DCV system based on room temperature control also eliminates the need of additional heating in rooms when the cooling capacity of the supply air exceeds the cooling capacity needed, e.g. when the room is unoccupied or when the solar heat load is low. Figure 1 illustrates this situation. This advantage in terms of energy savings is often overlooked. A DCV system based on air-quality control adapts the airflow rate to the actual pollution load, which often is proportional to the occupancy. For example, all the rooms in an office building or in a school are almost never occupied at the same time.