Ventilation duct is the duct that connects the fan, air treatment equipment and air inlet to transport air, using natural air (called fresh air or new air) to replace indoor air to improve indoor air quality. Ventilation is mainly to improve the office environment, to give employees a good atmosphere, to protect the health of employees, that is, the use of fans to send air or exhaust air, the air will enhance the circulation, so as to maintain a comfortable working environment.