Fresh air system is a new type of indoor ventilation and exhaust equipment, which belongs to the open system, so that people can breathe fresh, clean and high quality air indoors. The fresh air system is composed of fan, air inlet, exhaust outlet and various pipes and joints. The fan installed in the ceiling is connected with a series of exhaust outlets through the pipe, and the fan starts, indoor polluted air is discharged to the outside by the exhaust outlet and the fan, causes the indoor to form the negative pressure, outside fresh air then installs in the window frame above (between the window frame and the wall body) enters the air inlet to enter the indoor, thus enables the indoor personnel to be able to breathe the high quality fresh atmosphere 1935  Astun in  made the world's first heat-exchanging equipment that can filter air pollution, called "Fresh air system" or "fresh air purifier".