rooftop air conditioners installed on the roof for ventilation. There are three main types of roof fans,The first is the axial-flow roof fan, which is often used in low-pressure, large flow occasions. According to the needs of users, it can also be designed as a bidirectional reversible air supply and exhaust fan, that is, the fan with the equivalent characteristics of positive and negative working conditions. The second is the centrifugal roof fan, which is suitable for the occasions with small air volume and high pressure requirements. The third is the non motor turbine exhaust fan, which is an ideal energy-saving ventilation device driven by the indoor and outdoor air pressure difference to drive the special arc-shaped blade to rotate with the axis so as to exhaust the indoor air. The roof fan adopts advanced CAD software and is designed by multi-objective optimization. Among the roof fans, there are eight types of fans in DWT - I series, including 12 ා - 24 ා. The method of changing speed, angle and blade profile is adopted to expand the range of performance parameters to meet the needs of different operating conditions, so as to achieve fan and system allocation, so as to achieve energy saving and noise reduction. The roof fan can also be set as explosion-proof type according to the user's needs, and it can be used for forced exhaust in flammable, explosive and corrosive gas occasions. The roof fan is installed on the roof for ventilation. Due to the particularity of the installation environment, the material and structure of the fan are special. The roof fan is equipped with a device to prevent air backflow after shutdown. Due to the high-speed rotation of the fan under the action of hot pressure, the wind speed in the air duct increases a lot. The fan reverse rotation is very unfavorable to the starting of the motor and may be damaged due to excessive starting current. The roof fan should be designed with reliable rain proof, snow proof and sand proof performance. Unlike rainwater, wind snow and wind sand will not only enter the fan from the top, but also enter the fan from the bottom when the outdoor wind speed reaches a certain strength.
