1、 Air supply method

Natural ventilation: After the kitchen uses mechanical smoke exhaust to release the air wrapped in smoke, the pressure in the kitchen will decrease. At this time, the external pressure is higher than the kitchen pressure, and the gas will naturally flow to the kitchen through various connecting channels, balancing the negative pressure generated by the kitchen smoke exhaust and keeping the air pressure balanced. This process is called natural ventilation.
Mechanical air supply: In contrast, using a fan to provide positive pressure air supply in the kitchen is called mechanical air supply, commonly known as fresh air supply.

2、 Reason for fresh air supply

In order to maintain the balance and stability of the air pressure in the entire smoke exhaust system, for kitchens with large natural air supply and smoke exhaust, not supplying fresh air will result in the following problems:
1. In the airflow through various pipes, gas flows at high speed towards the kitchen, creating negative pressure that hinders the closure of doors and windows, and also blows up suspended doors and windows.
2. At the delivery point, the temperature of the dish will drop sharply after it is cooked, affecting the quality of the dish.
3. Multiple airflow flows towards the kitchen, and if it happens to pass under the hood, it will interfere with the smoke from the stove. The wind will blow towards the chef's face, affecting work and causing smoke to overflow, affecting smoke exhaust.
4. If fresh air is not supplied, the airflow in the restaurant will continue to flow towards the kitchen, which will reduce the effectiveness of the air conditioning system.
5. A closed or semi closed kitchen with insufficient natural air supply can generate negative pressure, while excessive negative pressure can cause backflow of sewage water, severe ceiling suction, and backfire of the large stove.

3、 Fresh air volume

According to the "Code for Design of Food and Beverage Buildings", the supplementary air volume of the kitchen and the hot processing room for food and beverage production should be about 70% of the exhaust air volume, and the negative pressure of the room should not exceed 5Pa. The negative pressure state of the kitchen should be maintained to ensure that the oil fumes generated in the kitchen will not overflow.
Generally speaking, if the exhaust volume is small or natural air replenishment can meet the demand, it may not be equipped with fresh air equipment.
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 at 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、 Precautions for air replenishment

1. The inlet of the fresh air fan should be kept away from the outlet of the exhaust fan, and a filtering device should be installed at the inlet to prevent rain, snow, dust, and other debris from being sucked into the pipeline.
2. The fresh air diffuser should be evenly distributed near the hood, forming a fresh air curtain to prevent smoke from escaping. At the same time, the incoming air will exchange heat with the kitchen heat source, reducing the temperature.
3. It is best to control the wind speed of the diffuser at 0.5-1m/s. If it is too small, it cannot provide air supply, and if it is too large, it will cause smoke to overflow.
4. Suggest two paths to supplement the air supply
Part of the air supply ducts and air deflectors sent to the front of the hood are dispersed at a speed of 0.5-1m/s;
Another path of pipeline is sent to the ceiling, which is discharged by a diffuser. The air velocity is controlled at 0.25m/s at a height of 2 meters above the ground.
5. According to construction experience, a fresh air system is essential in the kitchen, but it increases the system cost. If the kitchen environment is sealed and there are no other ways to supplement fresh air, non powered fresh air can be considered, that is, installing pipes to the front edge of the smoke hood. Based on experience, the fresh air duct is generally 80% of the cross-sectional area of the main smoke exhaust duct, and multiple fresh air louvers (recommended to be two meters each, as the resistance is too high) can be used, or the duct can be directly opened. It is recommended that Party A use perforated ceiling clamps so that fresh air louvers can be omitted.

5、 Fresh air in summer and winter

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