Types of kitchen fans
Centrifugal fan: the airflow moves along the diameter direction of the fan impeller.
Axial fan: the airflow moves along the axial direction of the fan impeller.
The total pressure of centrifugal fan is large, and the motor is isolated from high temperature oil fume gas. Not easy to damage.
Axial flow fan is relatively small, and under normal circumstances, oil fume gas will pass through the motor at high temperature, which is easy to be damaged.
It is generally recommended to use a centrifugal fan in the kitchen.
Centrifugal fans are divided into forward multi-blade impellers and backward impellers.
Advantages of the forward impeller: (Compared with the backward impeller) Choosing a lower speed (low noise) and a smaller diameter can obtain a larger total air pressure.
Disadvantages of forward impeller: low efficiency, high energy consumption and difficult cleaning and descaling.
Advantages of reverse impeller: high efficiency, energy saving and easy cleaning and descaling.
Disadvantages of backward impeller: to obtain the same air volume and total pressure, it needs higher speed (and therefore more noise) and larger diameter.
Selection of fan: The calculation method for selecting the required air volume of fan according to the size of kitchen space and the layout of smoke exhaust hood is as follows:
1, the overall exhaust air volume, according to the kitchen space, ventilation 40-60 times per hour.
For example, the kitchen has a total area of160m2 and a height of 3m. The required ventilation volume is160x3x60 = 28,800 m3/h.
2. According to the windward side of the kitchen exhaust hood (the circumference of the exhaust hood minus the length against the wall), the wind speed per second is about 0.5m ..
For example, the circumference of kitchen range hood is 25m, and the length against the wall is 10m. The required ventilation is 3600 x (25-10) x 0.5 = 27000m3/h 。
2. Calculate the static pressure required by the fan according to the pipeline conditions:
1, according to the air volume and wind speed (wind speed is about 10- 15m/s), determine the cross-sectional area of the air duct. The width-height ratio of air duct shall not exceed 2: 1 (saving materials and reducing wind resistance).
2. Calculate the wind resistance (that is, the static pressure required by the fan) according to the wind speed, cross-sectional area of the air duct, elbow and variable diameter.
Third, according to the calculated air volume and static pressure. Choose the right fan.
Selection points: The main control parameters of smoke exhaust fan selection are working temperature, air volume, total pressure, efficiency, noise, motor power, speed and shaft power. The exhaust fan should be able to run normally for a long time under the condition that the medium temperature is not higher than 85℃. The exhaust fan shall ensure that it can work continuously for 30 minutes when the conveying medium temperature is 280℃, and it can still operate normally when the medium temperature drops to the ambient temperature. At the rated speed, in the working area, the measured pressure curve of the fan and the curve given in the manual should meet the following requirements: the deviation of the corresponding pressure value of the axial flow smoke exhaust fan under the specified flow rate is 5%. Under the specified flow rate, the pressure deviation of centrifugal range hood is 5%. The noise limit of the exhaust fan sound level at the working point given in the manual shall comply with the provisions of JB/T8690- 1998. The exhaust fan can be an ordinary steel centrifugal fan or a special exhaust axial fan. See Code for Fire Protection Design of High-rise Civil Buildings for the specifications of smoke exhaust fans. The minimum air volume of the smoke exhaust fan is 7200m/h, and the maximum air volume should not exceed 60000m/h (referring to the maximum air volume of a smoke exhaust partition). The air volume of the exhaust fan should be increased by not less than 10%~20% according to the required air volume value. The wind pressure value of smoke-proof booster fan should be calculated according to the most unfavorable loop of smoke exhaust system, and the residual pressure value of smoke-proof stairwell should be 40 ~ 50 Pa. The residual pressure of the foreroom, shared foreroom, fire elevator foreroom and refuge floor is 25 ~ 30pa. The fire smoke exhaust fan shall comply with the current standard JB/T10281-2001Technical Conditions for Fire Smoke Exhaust Fan. The fan of the smoke exhaust system should be set separately. The location of the exhaust fan should be on the same floor or higher floor of the exhaust area. Test method: Balance correction of impeller cutting is carried out on the dynamic balancing machine according to the regulations of 7BIT 9 10 1. Impeller overspeed test shall be carried out in accordance with 7BIT 6445. Mechanical operation test of fire smoke exhaust fan low speed continuous operation. After the bearing temperature has stabilized for 20 minutes, measure the M-liter and vibration of the bearing. One liter shall not be higher than 4nC, and the vibration test 99 and its M value shall comply with the relevant provisions of 7Bfr 96V. Aerodynamic performance test The aerodynamic performance test of fire-fighting smoke exhaust fan shall be carried out according to GB+T 1236. The noise measurement method of acoustic test shall be implemented according to the provisions of CB/r 2888. The noise limit shall comply with the provisions of 7BIT 8690. The high temperature resistance test shall be conducted according to GA2 1 1. The performance of high-field crystal should meet the requirements of 4.42. Installation and maintenance: the kitchen fan is an indispensable key equipment in the kitchen. It is suggested that it should not be installed in the ceiling as far as possible, but should be installed in the machine room, roof or external wall and other places convenient for maintenance. Kitchen fans work in high temperature, high humidity and oil fume gas for a long time. Regular maintenance is an essential job. Fault point:
1, the impeller is oily, which leads to the curvature and angle deformation of the blade, and the total air pressure parameter drops obviously, which can not meet the requirements of smoke exhaust.
2. Oil stains on the impeller cause the impeller to lose balance, increase vibration and damage the bearing.
3. Parts are easy to rust and damage the fan in harsh environment.