The main reasons for the problems in kitchen ventilation are the disharmony between kitchen process design and ventilation design, and the lack of experience and unreasonable design in domestic kitchen design.
Second, the kitchen ventilation calculation
The ventilation of the kitchen consists of two parts: local ventilation and comprehensive ventilation. Local exhaust air volume should be determined according to the situation of cooking stoves and kitchen range hoods, and the overall exhaust air volume is generally determined by calculation.
1. Calculation of ventilation volume
The ventilation volume of mechanical ventilation should be calculated according to the heat balance, and its calculation formula is:
L=Q/0.337(tp-ti)( 1)
Type, l -- the necessary ventilation, m3/h;
TP- calculated indoor exhaust air temperature, which can adopt the following values: 35 degrees Celsius in summer and 15 degrees Celsius in winter;
Ti—— indoor ventilation calculation temperature, in degrees Celsius;
Q—— total calorific value (sensible heat) in the kitchen, w;
Q=Q 1+Q2+Q3+Q4(2)
Where q1-heat dissipation of kitchen equipment, calculated according to the data provided by the process; If there is no data, please refer to the literature;
Q2 operator heat dissipation, w;
Q3-- heat dissipation of lighting lamps and lanterns, w;
Q4- cooling load of indoor and outdoor enclosure structure, w
2. Local exhaust air volume
Calculate the local exhaust air volume according to the suction wind speed on the surface of the exhaust hood, and the minimum exhaust air volume is L = 1000 p? H
Type, l -- exhaust hood displacement, m3/l;
P- the perimeter of the protective layer (regardless of the length of the wall edge), m;
H- the distance from the cover to the kitchen table, m.
3. Estimation of kitchen ventilation
On the basis of summarizing the engineering design and use, the designer can estimate the ventilation times as follows:
Chinese kitchen n = 40-50h-1;
Western kitchen n = 30-40h-1;
In the estimated ventilation, the local ventilation is considered as 65%, and the overall ventilation is considered as 35%.
Three, local exhaust parts and requirements
In Chinese kitchens, the cooking calorific value and smoke exhaust are generally large, and the exhaust air volume is also large. The exhaust hood is usually a range hood. In order to reduce the impact of oil fume on the environment, smoke hood can be selected.
Cooking room. The requirement for fresh air here is low, but the exhaust effect must be good, otherwise steam will fill the whole workshop and affect the chef's work. The main waste gas is water vapor, which can be directly discharged without using a purification device.
Western kitchen. The amount of cooking is not very large, but the equipment needed is more and more complete, and the exhaust air volume is smaller than that of Chinese kitchen.
The dishwashing room needs a lot of exhaust air.
Fourth, the kitchen air supply requirements
When the kitchen is ventilated, a certain amount of fresh air should be added, and the air supply volume should be considered as 80%-90% of the exhaust air volume.
The negative pressure in the kitchen should not be greater than 5Pa, because if the negative pressure is too large, the furnace will backfire. Therefore, the speed of the blower and the exhaust fan can be increased simultaneously.
30% of the supplementary air volume can be used as rear air supply, and the air supply outlets are directly and evenly arranged above the front side of the exhaust hood.
Outdoor fresh air can be directly used for kitchen air supply, and only a coarse filter is set. In addition, in order to improve the chef's working environment, local or comprehensive cooling devices should be set according to the conditions. The relationship between the heat emitted by kitchen utensils and the cooling load of air conditioning can be calculated by the following formula:
When the heat source of the cooker is gas:
qc=qeF 1F2≈0. 1qe .(3)
Type of QC -- kitchen air conditioning cooling load, kw;
Heat kitchen equipment heat dissipation, kw;
F 1- equipment simultaneous use coefficient, 0.5;
F2—— the proportion of surface radiant heat in the input power of equipment, taking 0.32;
F3- exhaust heat dissipation coefficient, taking 1.6.
When the heat source of the cooker is electricity and steam:
QC = QEF 1 F2/F3≈0. 16qe(4)
In order to prevent the smell of the kitchen from reaching the restaurant, 60% of the air supply can be sent to the restaurant, and then flow from the restaurant to the kitchen. In view of the large ventilation in the kitchen, such a large amount of make-up air flows to the kitchen through the dining room, which is not desirable from the aspects of energy saving and pipeline layout.
Verb (abbreviation of verb) system arrangement
1. The air supply system should adopt DC, and the kitchen ventilation system should adopt variable speed fan or accompanying fan to send and exhaust air.
2. Layout of air supply outlet and exhaust outlet
The layout of the air supply outlet and exhaust outlet in the kitchen should be considered according to the specific position of the cooker, and the air supply jet should not disturb the ventilation of the cooker. When determining the outlet wind speed of the air supply outlet, the regional wind speed is about 2m from the ground.
3. Arrangement of machine room, fan and air duct
The exhaust fan of the kitchen should be located in the upper part of the kitchen. When the kitchen is a part of a public building, the exhaust fan should be located on the roof floor, so that the air duct can be in a negative pressure state and the odor can be prevented from overflowing.
Generally, the exhaust fan of the kitchen should be a centrifugal fan, and the exhaust pipe of the kitchen should try to avoid the horizontal duct being too long. The exhaust shaft in the kitchen should be close to the exhaust pipe to increase the pumping force.
4. Fire prevention and smoke exhaust
The exhaust system of the kitchen should be divided into fire zones, try not to cross the firewall, and fire dampers should be installed when crossing.
The pipes of kitchen ventilation system should be made of incombustible materials.