1, Air Supply Method

Natural ventilation: After the kitchen uses mechanical flue gas exhaust to release the air wrapped in the smoke, the pressure in the kitchen will be reduced. At present, the external pressure is higher than the kitchen pressure, and the gas will naturally flow to the kitchen through various connecting channels to balance the negative pressure generated by the kitchen flue gas exhaust and maintain the air pressure balance. This process is called natural ventilation. Mechanical air supply: In contrast, using a fan to provide a positive pressure air supply in the kitchen is called a mechanical air supply, usually called a fresh air supply.

2, the cause of fresh air supply

In order to maintain the balance and stability of the air pressure in the entire flue gas exhaust system, for kitchens with a large natural air supply and flue gas exhaust, not providing fresh air will cause the following problems: 1. In the air flow through various pipes, the high-speed gas heading for the kitchen flows to the kitchen, generating negative pressure, causing the closure of doors and windows, and blowing hanging doors and windows. 2. At the delivery point, the temperature after the dishes are cooked will drop sharply, affecting the quality of the dishes. 3. Multiple airflows flow to the kitchen, and if it happens to pass under the hood, it will interfere with the smoke on the stove. The wind will blow towards the chef's face, affecting the work and causing smoke to overflow, thereby affecting the smoke exhaust. 4. If fresh air is not provided, the airflow from the restaurant will continue to flow to the kitchen, which will reduce the effectiveness of the air conditioning system. 5. Closed or semi-closed kitchens with insufficient natural air supply will produce negative pressure, and excessive negative pressure will cause the backflow of sewage, severe ceiling suction and the backfire of large stoves.

3, fresh air quantity

According to the "Design Code for Food and Beverage Buildings", the supplementary air volume in the kitchen and the heat treatment room for food and beverage production should be about 70% of the exhaust air volume, and the negative pressure in the room should not exceed 5PA. The negative pressure in the kitchen should be maintained to ensure that the grease generated in the kitchen does not overflow. Generally speaking, if the exhaust volume is small or natural air supplement can meet the demand, it may not be possible to equip fresh air equipment. For example, in a kitchen with 1m x 1m windows and 2m x 80cm doors, if calculated at a natural air supply of 3 m/s, the natural air supply can reach 28000m ^ 3/h. If calculated with 80% fresh air supply, the exhaust volume can reach 35000m ^ 3/h, which can basically cover most small and medium-sized kitchens.

4, air supply precautions

1. The inlet of the fresh air fan should be far away from the outlet of the exhaust fan, and a filter device should be installed at the inlet to prevent rain, snow, dust and other debris from being sucked into the duct. 2. The fresh air diffuser should be evenly distributed near the hood to form a curtain of fresh air to prevent smoke from escaping. At the same time, the incoming air will exchange heat with the heat source in the kitchen, thereby reducing the temperature. 3. The diffuser wind speed is preferably controlled at 0.5-1 m/s. If it is too small, it will not be able to provide air supply, if it is too large, it will cause smoke to overflow. 4. It is recommended to disperse at a speed of 0.5-1 m/s to the air supply part of the air supply duct in front of the hood and two paths of the air converter; the other path of the duct is sent to the ceiling discharged by the diffuser. The air speed is controlled at a height of 0.25 m/s at 2 meters above the ground. 5. According to construction experience, a fresh air system is essential in the kitchen, but it increases the cost of the system. If the kitchen environment is sealed and there is no other way to supplement fresh air, non-powered fresh air can be considered, that is, the duct is installed to the front edge of the smoke hood. According to experience, the fresh air pipe is usually 80% of the cross-sectional area of the main flue gas exhaust pipe, and multiple fresh air shutters can be used (each higher air is recommended because the resistance is too high), or the pipe can be opened directly. It is recommended that Party A use perforated ceiling clips so that fresh air shutters can be omitted.

5. Fresh air in summer and winter

Summer makeup air fan: Currently, it is equipped with a heat exchanger. In summer, turning on the fresh air system can bring fresh outdoor air into the room and maintain the indoor air flow field. Winter air supply or low temperature area air supply usually uses a fan coil unit. The direction of airflow pressure in winter will cause hot air to be discharged, so hot air must be provided to balance the winter exhaust temperature.