1. Number of unpowered fans = building capacity * number of air changes per hour / single unpowered fan ventilation capacity.
2. Building volume = length * width * height.
3. Number of air changes per hour: Determine the number of air changes per hour based on the function of the building.
4. Ventilation capacity of a single unpowered fan: According to different annual wind, height, indoor temperature difference, the air exhaust performance of different types of natural ventilators is determined.