As the focus of logistics support and safety work in colleges and universities, the processing capacity of main and non-staple foods in colleges and universities is large, which is increasingly valued by managers and operators. The air environment in the kitchen directly affects the quality of food storage and cooking. In the past, due to the lack of information and experience, most kitchen ventilation designs used natural ventilation in ventilation shafts or forced ventilation with axial flow fans and other equipment to remove cooking fume. If the oil stains on ventilation shaft walls and fan blades are not cleaned in time, fires may be caused by careless cooking operations. At present, simple ventilation can no longer meet the needs of modern kitchens, but has developed into a combination of air conditioning and ventilation.
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 facilities and the air quality requirements in the operation area, an oil fume hood is set and discharged to the outside through the 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 adopt direct-flow 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 germ growth due to less ventilation times, increase heat transfer resistance and ventilation resistance, reduce cooling effect, and even lead to the loss of cooling capacity of air conditioning equipment for a long time. The DC air conditioning system does not use return air, and all fresh air comes from the outside, and the indoor air is updated in time.
2. The design of kitchen ventilation and air conditioning system adopts the form
2.1 Air supply system layout
Kitchen air supply includes post air supply and air conditioning air supply. Post fresh air supply means that outdoor fresh air is sent to a place close to the stove through an axial flow or centrifugal fan, and should be vertically supplied downward just above the chef's cooking position. Diffuse diffuser can be used for the air supply outlet, the air supply temperature is generally 21 ~ 23℃, the relative humidity is about 95%, the throat wind speed is less than 2.5m/s, and the tuyere diffusion angle θ = 21. The center of the air supply outlet should coincide with the central plane of a single stove, and the horizontal distance between the tuyere and the oil fume hood is 211mm, and the height is 1.8 ~ 2.3m.. Its volume of 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 when operating. Air conditioning air comes from fresh air unit or combined air conditioner, and is sent to the place far away from the stove through the air duct to adjust the indoor temperature of the kitchen. The form and position of the air supply outlet can be reasonably arranged according to the kitchen situation.
2.2 layout of exhaust system
ventilation in the kitchen is realized by forced air supply and forced air supply and natural air exhaust. The forced exhaust system consists of a fume hood, a horizontal exhaust pipe, an exhaust main pipe and an outdoor exhaust shaft. The fume and other emissions generated by the chef's hot processing and the kitchen heat are exhausted to the outside through forced exhaust, during which the kitchen is in a negative pressure ventilation state; When there is no hot working operation task, the pipeline exhaust fan can be turned off, and the indoor air is sent to the fresh air system through air conditioning for positive pressure ventilation, and then discharged outside through doors and windows. Forced exhaust hood and pipeline should be divided and arranged on the principle of consistent opening time and short distance of stoves, so as to avoid the uneconomical operation phenomenon that some stoves have to turn on larger fans. Cooking stoves with a large amount of oil fume should be arranged at the end of horizontal drainage pipes as far as possible. Generally, the length of horizontal exhaust pipes should be no more than 15m from the farthest suction port to the main exhaust outlet. When installing, it is necessary to ensure that there is a slope of more than 2% to the exhaust hood, otherwise the smoke will not be discharged in time and quickly, and oil dirt and condensate will not flow back to the exhaust hood smoothly, thus affecting the exhaust effect.
Because there are a lot of oil stains in the exhaust duct, from the perspective of fire prevention, the exhaust duct is generally made of 1.5mm thick steel plate, and the end of the horizontal pipe of the horizontal exhaust duct is connected with a movable flange to facilitate the cleaning of oil stains. Each air outlet is equipped with a valve to control the exhaust air volume.
2.3 Selection and layout of oil fume hood
The oil fume hood should be considered in a unified way according to the requirements of kitchen technology. Generally, when the stoves are placed side by side, they are mainly integrated. The layout of the fume hood should be based on the requirements of kitchen technology, understand the overall dimensions of heating and cooking equipment, and determine the size of the fume hood. The cross section of the hood mouth should be similar to the horizontal projection of the oil fume diffusion area, and it is generally made into an overall rectangular umbrella-shaped hood. The included angle between the waist plates on both sides should be a ≤ 1.21, and the hood body should be equipped with a skirt with a certain height of about 1.25m m. The outer edge of the hood mouth should not exceed the stove side. The lower end of the hood mouth should be provided with a square oil drain and sink of about 51mm, and a drain pipe should be arranged at the lowest part of the groove to discharge into the sewer. The cover body is made of stainless steel plate with a thickness of 3 ~ 5 mm. An oil fume filter is arranged in the hood, and it should be easy to replace and clean, so as to prevent the oil fume from entering the exhaust fan after long-term operation and affecting its normal use. Because the emission spreads vertically upward from the emission source in a cone shape, it is generally concentrated within the height of 1.8～1.1m from the emission source, so the umbrella cover should be lowered as much as possible without affecting the operation.
3. Determination of ventilation volume
3.1 Determination of exhaust volume
Kitchen exhaust consists of two parts, namely local exhaust and comprehensive exhaust. The exhaust air volume should be calculated according to the heat balance. Local exhaust air volume accounts for about 65% of the total exhaust air volume, and the actual calculation is generally based on local exhaust air volume, which is determined according to the situation of cooking stoves and kitchen exhaust hoods. The formula for calculating the minimum smoke exhaust volume of various hoods:
L=3611×V1×F
where l-exhaust volume, m3/s;
f-cover mouth area (integral cover), m2;
v1-suction speed of hood mouth, m/s.
the suction speed of the hood mouth shall generally not be less than 1.5m/s. Among them, it is recommended to choose a larger value for cooking in the dining kitchen, 1.4m/s for pastry room, and 1.3 ~ 1.4m/s for other dishwashing rooms and cooking rooms.
3.2 determination of air supply volume
in order to prevent kitchen odor from entering the restaurant, the kitchen should be kept under negative pressure, and the negative pressure value should not be greater than 5Pa. The air supply volume (fresh air+air conditioning air) should be considered as 85% ~ 95% of the total exhaust air volume.
4. air conditioning cooling in auxiliary area and air conditioning design in other rooms
the cooling of air conditioning in cooking auxiliary area should first meet a certain negative pressure value in the whole cooking area, which is generally less than 5Pa. However, the sum of post air supply and auxiliary area air supply is close to 81% ~ 91% of exhaust air, air supply temperature is about 19℃ and relative humidity is about 95%. The temperature in the working environment area is ≤27℃ and the relative humidity is 61 11%. Other rooms with no fume emission can determine their air parameters according to different requirements of their functions and operations.
5. Conclusion
Dining rooms in colleges and universities are the focus of food hygiene supervision. Reasonable design of kitchen air supply and exhaust system and air conditioning system, correct installation and use of oil fume hood, and strengthening daily management can effectively improve the air quality of kitchens and restaurants, keep them clean and tidy, 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 are easy to obtain, which can achieve the expected results.
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