The amount of ventilation depends on the amount of people, the amount of harmful sources, and the relative humidity in a room. At the moment it is possible to measure the amount of people (movement sensors), the CO2 (related to the indoor air quality) and the relative humidity. Measuring other gasses and particulate matters is also possible but more difficult and expensive.
Coupling these sensors to the ventilation control systems ensures the right amount of ventilation at the lowest energy demand for ventilation. As we can see from image below, this house also has a control system for ventilation. But that is not all! This control system can also control the amount of heating depending on the presence of the people and their preferences.
This article explained how to reduce the energy demand for ventilation in winter. But what about cooling in hot countries? If we consider the energy demand for cooling using air conditioning systems in hot countries, it is equally important to ensure the right amount of ventilation so that the energy demand for moving the air and for cooling the fresh air is minimized.