1. Air supply law

Natural ventilation: After the kitchen uses mechanical smoke exhaust to release the air wrapped in 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 air pressure balance. This process is called natural ventilation. Mechanical air supply: In contrast, the use of fans to provide a positive pressure air supply in the kitchen is called mechanical air supply, often referred to as fresh air supply.

2. Reasons for fresh air supply

In order to maintain the balance and stability of air pressure in the entire flue gas exhaust system, for kitchens with 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 gas traveling to the kitchen at high speed flows to the kitchen, generating negative pressure, causing the doors and windows to close, and blowing the hanging doors and windows. 2. At the delivery point, the temperature of the dish after cooking will drop dramatically, affecting the quality of the dish. 3. Multiple airflows to the kitchen will interfere with the smoke on the stove if it happens to pass under the hood. The wind will blow in the chef's face, disrupting work and causing smoke to escape, thus affecting smoke exhaust. 4. If fresh air is not provided, restaurant airflow will continue to flow toward the kitchen, which will reduce the effectiveness of the air conditioning system. 5. A closed or semi-closed kitchen 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. Amount of fresh air

According to the "Design Code for Food and Beverage Buildings", the amount of supplementary air in the kitchen and the heat treatment room for food and beverage production should be approximately 70% of the exhaust air volume, and the negative pressure in the room should not exceed 5PA. The kitchen should be kept under negative pressure to ensure that grease produced in the kitchen does not overflow. Generally speaking, fresh air equipment may not be available if the exhaust volume is small or if natural air supplementation can meet the demand. For example, in a kitchen with a 1m x 1m window and a 2m x 80cm door, if calculated at a natural air supply of 3m/s, the natural air supply can reach 28000m^3/h. If calculated based on 80% fresh air supply, the exhaust volume can reach 35000m^3/h, which can basically cover the vast majority of small and medium-sized kitchens.

4. Preventive measures for air supply

1. The inlet of the fresh air fan should be away from the outlet of the exhaust fan, and a filter should be installed at the inlet to prevent rain, snow, dust and other debris from being sucked into the duct. 2. Fresh air diffusers should be evenly distributed near the hood to form a fresh air curtain to prevent smoke from escaping. At the same time, the incoming air will exchange heat with the kitchen's heat source, thereby lowering the temperature. 3. It is best to control the diffuser wind speed at 0.5-1m/s. If it is too small, it will fail to provide air supply, if it is too large, it will cause smoke to escape. 4. It is recommended to disperse at a speed of 0.5-1m/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 2 meters above the ground at a height of 0.25m/s. 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, you can consider non-powered fresh air, that is, installing ducts to the front edge of the smoke hood. As a rule of thumb, the fresh air duct is usually 80% of the cross-sectional area of ​​the main flue gas exhaust pipe, and multiple fresh air louvers can be used (each higher air is recommended because the resistance is too high), or the duct can be opened directly. It was recommended that Party A use perforated ceiling clamps so that fresh air blinds could be omitted.

5. Fresh air in summer and winter

Summer Makeup Air Fans: Currently, it is equipped with a heat exchanger. In the 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 fan coil units. The airflow pressure direction in winter causes hot air to be discharged, so hot air must be provided to balance the winter exhaust temperature.