The fan is mainly composed of blades, belt pulley, blade hub, belt, bearing, blade support, shutters, frame, protection mesh, motor and other components. The motor drives the blades to generate airflow. The movable louver type can be equipped with a louver which can be opened automatically after the start-up and closed automatically when the machine is stopped according to the user’s needs, so as to prevent the entry of outdoor dust, foreign matters, etc., as well as the impact of rain, snow and strong wind