When a number of exhaust fans are installed on the roof or wall of a building (such as a factory) and the exhaust fans are turned on, a partial vacuum is generated, and the surrounding air naturally fills the vacuum position. As the exhaust fans continue in operation, the partial vacuum is constantly filled with air, thus the flowing air is formed (causing negative pressure in the specific space). When the doors and windows are opened, the inward air flow is generated. In this way, forced convection is formed (air is discharged on one side, and the air is forced to be flowed in on the other side). This is the principle of negative pressure ventilation.
