DN85 is a passive air supplement system suitable for kitchens. Its working principle is that when the smoke extractor is working, it creates negative pressure in the kitchen. The outdoor fresh air is sucked in through the controllable air valve inside DN85. Air circulation. Its beneficial effect is to increase the air supply when the fresh air in the kitchen is insufficient, and solve the problem that the oil fume cannot be exhausted due to the insufficient fresh air in the kitchen, and the kitchen oil fume diffuses into the room, causing the air flow in the whole room to be disordered.