According to the working principle of fresh air system, fresh air is sent to the room with special equipment on one side of the closed room, and then discharged from the other side to the outside by special equipment, forming a "fresh air flow field" in the room to meet the needs of indoor fresh air ventilation, and the key step is to filter, disinfect and sterilize the air entering the room at the same time. Therefore, the filter becomes indispensable. Usually the primary filter is used to filter dust, PM2.5, etc., and then the composite high-efficiency filter is used to remove the long-term slow release of harmful gases in the room through adsorption and decomposition, so that you can enjoy the fresh air of nature without opening windows.