Due to limited energy sources, countries are looking for alternative solutions to decrease energy needs. In that context, natural ventilation can be seen as a very attractive sustainable technique in building design. However, understanding of ventilation dynamics is needed to provide an efficient control. Ventilation rate has to be determined not only in terms of energy, but also for controlling indoor air quality and emissions. For these reasons, agricultural buildings (livestock houses, greenhouses, etc.), naturally ventilated industrial buildings, and residences require a reliable ventilation rate measuring technique. Measuring techniques suffer from the problem of imperfect mixing of air within the ventilated structure. Therefore, a new technique should be developed that uses direct measuring techniques in combination with mathematical models to identify the total ventilation through large air openings.