First of all, it is impossible for kitchen fumes to flow back to any other room through internal machines. This is because the airflow loops between independent rooms in the central air conditioning system are independent. Generally speaking, there is a return air outlet and an air supply outlet in the room. Under the action of the indoor fan, the cold air is sent out through the air supply outlet, then bypasses the room along the airflow and enters the indoor air return outlet, and there is a coil/refrigerant pipe between the air return outlet and the air outlet. The air coming in from the air return outlet is cooled by the coil/refrigerant pipe, and then sent into the room through the air supply outlet to continue the refrigeration cycle. The air return port, the coil/refrigerant pipe and the air supply port are combined to form an internal unit. For the kitchen, avoiding the oil fume problem is also to prolong the service life of the unit. During the redesign, the air return of the kitchen was designed outside the kitchen. Generally, there is an air-conditioned room next to the kitchen, such as a dining room. In other words, only the air in the room where the air outlet is located can enter the kitchen, and the air (oil fume) in the kitchen will not enter other indoor rooms, such as the guest restaurant.