The exhaust air volume of kitchen smoke exhaust is the air volume required to maintain the negative pressure place where smoke is captured and discharged through the exhaust hood. The ultimate goal of exhaust volume calculation should be to capture all the smoke generated by kitchen equipment.
Kitchen smoke exhaust is the same as the exhaust of harmful gases from factories and laboratories. It means that all harmful gases must be removed. It is a professional smoke exhaust technology. Based on the above flow field analysis, the key to calculating the most accurate and reasonable exhaust volume is to scientifically and reasonably determine the radius and wind speed of the constant velocity surface of all exhaust gases, so as to use the lowest energy consumption to reduce the generated flue gases. It’s all sucked in and expelled.
Calculation of exhaust air volume of bucket type exhaust hood
Bucket-type hanging exhaust hood is a typical receiving type exhaust hood. How to calculate the exhaust volume is the key to kitchen design. The exhaust volume required by the bucket-type exhaust hood is related to the radius of the constant velocity surface formed by the negative pressure and the wind speed, as shown in the figure. That is, the calculation of the exhaust volume is related to the following parameters: the length a, width of the exhaust hood b. The height h from the stove to the exhaust hood, determine the minimum suction wind speed v on the outer edge of the stove. The exhaust air volume Qp is proportional to the above parameters and can use the formula to calculate exhaust air volume. Because this formula is derived based on the constant velocity surface principle, in order to distinguish it from other calculation methods, it is called the constant velocity surface formula.
Qp=1.4vPhk x 3600
Qp=exhaust air volume (m3/h);
h=Height from smoke exhaust hood to smoke source (m);
v = suction wind speed, generally 0.2~0.5 m/s;
k=pipe leakage coefficient, generally 1.1~1.2;
P=length of the smoking side of the exhaust hood (m), P=an1+bn2 (a and b are the length and width of the exhaust hood respectively, n1 and n2 are the number of open surfaces of the exhaust hood corresponding to a and b respectively)
The above parameters are explained as follows:
(1) Suction wind speed: The wind speed on the constant velocity surface that determines the control range of the exhaust hood. This generally refers to the suction wind speed to be maintained at the edge of the stove. The bucket-type exhaust hood is hung above the stove, taking advantage of the natural lifting effect of hot air, which is conducive to the discharge of hot gases such as oil smoke. When there is no crosswind disturbance, the wind speed can be smaller; when there is crosswind disturbance or when it is far away from the stove, the inhaled wind speed should be slightly larger.
(2) Height: Since the height of most kitchen equipment is the same as the height of the stove, although the rice steaming cabinet, low soup stove and other equipment are of different heights from the stove, the height of the smoke generated is still roughly similar, so it is generally calculated as 800mm.
(3) Pipe leakage coefficient: Since the exhaust pipe may not be sealed, especially the brick-concrete flue, the air leakage coefficient is used to increase the margin in the calculation of the exhaust volume.
(4) Smoking side length of the exhaust hood: In order to ensure effective smoke capture, the size of the constant velocity surface generated by the exhaust hood must be different.