1. General principles of kitchen ventilation and air conditioning design
1. 1 ventilation
Kitchen ventilation is based on the principle that volatiles and lampblack in each functional area will not pollute the next process. Generally, according to the air quality requirements of facilities and working areas, an oil fume exhaust hood is set to be exhausted to the outside through an exhaust pipe; Local air supply should be set in the chef's operation area to ensure that the chef can breathe fresh air in the environment of high temperature, high humidity and light pollutants; The number of air changes in the kitchen should not be less than 4 times/h.
1.2 air conditioning
The composition of kitchen air has the characteristics of high oil smoke and high water vapor content, so it is advisable to use DC all-air air conditioning system instead of fan coil system. The latter is indoor air circulation mode, which will lead to more dirty air and bacteria breeding due to less ventilation times, increase heat transfer resistance and ventilation resistance, reduce refrigeration effect, and even cause air conditioning equipment to lose refrigeration capacity for a long time. The DC air conditioning system does not use return air, all fresh air comes from the outside, and the indoor air is updated in time.
2. Design form of kitchen ventilation and air conditioning system
2. 1 Layout of air supply system
Kitchen air supply includes post air supply and air conditioning air supply. Rear fresh air supply means that outdoor fresh air is sent to the place near the stove by axial flow or centrifugal fan, and it should be sent vertically downward directly above the chef's cooking position. Diffuser can be used as the air supply outlet, the air supply temperature is generally 20 ~ 23℃, the relative humidity is about 95%, the throat wind speed is less than 2.5m/s, and the diffusion angle θ = 20. The center of the air supply outlet should coincide with the central plane of the single stove, the horizontal distance between the air supply outlet and the fume hood is 200mm, and the height is1.8 ~ 2.3m. Its air intake should be as small as possible, and its coverage should be as large as possible to ensure that the chef is surrounded by fresh air during operation. Air conditioning air comes from fresh air units or combined air conditioners, and is sent to places far away from cookers through air ducts to adjust the indoor temperature in the kitchen. The form and location of the air supply outlet can be arranged reasonably according to the kitchen situation.
2.2 Layout of exhaust system
The ventilation of the kitchen is realized by forced air supply, forced air supply and natural air exhaust. The forced exhaust system consists of fume hood, horizontal exhaust duct, exhaust main pipe and outdoor exhaust shaft. Emissions such as cooking fume generated by chef's thermal processing and kitchen heat are exhausted outdoors through forced exhaust, during which the kitchen is in a negative pressure ventilation state; When there is no hot work task, the pipeline exhaust fan can be turned off, and indoor air can be sent into the fresh air system through air conditioning for positive pressure ventilation, and then discharged outside through doors and windows. The forced exhaust hood and pipeline should be separated and arranged on the principle of consistent opening time and short distance between stoves, so as to avoid the uneconomical operation phenomenon that some stoves have to turn on larger fans. Cookware with large oil fume should be arranged at the end of horizontal drainage pipe as far as possible. In general, the length of the horizontal exhaust pipe should not exceed 15m from the farthest suction port to the main exhaust port. During installation, it is necessary to ensure that more than 2% of the slope leads to the exhaust hood, otherwise, the flue gas cannot be discharged quickly in time, and the oil dirt and condensed water cannot flow back to the exhaust hood smoothly, which will affect the exhaust effect.
Because there is a lot of oil pollution in the exhaust duct, from the perspective of fire prevention, the exhaust duct is generally made of 1.5mm thick steel plate, and the horizontal pipe end of the horizontal exhaust duct is connected with a movable flange, which is convenient for cleaning up the oil pollution. Each air outlet is equipped with a valve to control the air displacement.
2.3 Selection and arrangement of fume hoods
The fume hood should be considered according to the requirements of kitchen technology. Generally, when cooking stoves are placed side by side, they are mainly integrated. The layout of fume hood should be based on the requirements of kitchen technology, understand the overall size of heating and cooking equipment, and determine the size of fume hood. The cross-section of the hood mouth should be similar to the horizontal projection of the oil smoke diffusion area, and it is generally made into an integral rectangular umbrella hood. The included angle between the waist plates on both sides should be a ≤ 120, and the cover should be equipped with a skirt with a certain height, and the height of the skirt is about 0.25m.. The outer edge of the fume hood should not exceed the lower end of the hood of the cooker, and there is a square oil drain tank of about 50 mm, and the lowest part of the tank should be equipped with a drain pipe to drain into the sewer. The cover body is made of stainless steel plate with a thickness of 3 ~ 5 mm, and there is an oil fume filter in the cover, which should be easy to replace and clean to prevent the oil fume from entering the exhaust fan after long-term operation and affecting its normal use. Since the emanation diffuses vertically upward from the emanation source in a cone shape, generally concentrated in the height range of 0.8 ~ 1.0m from the emanation source, the umbrella cover should be lowered as much as possible without affecting the operation.
3. Determination of ventilation volume
3. 1 determination of exhaust air volume
Kitchen exhaust consists of two parts, namely local exhaust and comprehensive exhaust. The exhaust air volume shall be calculated according to the heat balance. The local exhaust air volume accounts for about 65% of the total exhaust air volume, and the actual calculation is generally based on the local exhaust air volume, which is determined according to the situation of cooking stoves and kitchen range hoods. Calculation formula of minimum smoke exhaust volume of various smoke exhaust hoods;
L=3600×V0×F
L -- exhaust air volume, m3/s;
F- cover mouth area (integral cover), m2;
V 0—— suction speed of hood mouth, m/s
The suction speed of the hood is generally not less than 0.5m/s ... Among them, it is recommended to choose a larger value for cooking in the restaurant kitchen, 0.4m/s in the pastry room and 0.3 ~ 0.4m/s in other dishwashing rooms and cooking rooms.
3.2 Determination of air supply volume
In order to prevent the kitchen odor from entering the restaurant, the kitchen should maintain negative pressure, and the negative pressure value should not be greater than 5Pa. The supply air volume (fresh air+air conditioning air) should be considered as 85% ~ 95% of the total exhaust air volume.
4. Auxiliary area air conditioning cooling and other room air conditioning design
The refrigeration of the air conditioner in the cooking auxiliary area must first meet a certain negative pressure value of the whole cooking area, which is generally less than 5Pa. The sum of post air supply and auxiliary area air supply is close to 80% ~ 90% of the exhaust air volume, the air supply temperature is about 65438 09℃, and the relative humidity is about 95%. The temperature in the working environment area is ≤27℃ and the relative humidity is 60 10%. Other rooms without smoke emission can determine their air parameters according to different requirements of their functions and operations.
5. Conclusion
University canteens are the focus of food hygiene supervision. Reasonable design of kitchen ventilation system and air conditioning system, correct installation and use of range hoods and strengthening daily management can effectively improve the air quality of kitchens and restaurants, keep them clean and ensure food safety. Practice has proved that the catering department in colleges and universities independently designed and installed a set of kitchen ventilation and air conditioning system, and the equipment and materials were easily available, which could achieve the expected results.
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