How to choose the right fan

      Choosing the correct fan is an important condition to ensure the normal and economic operation of the ventilation system. The so-called correct choice, mainly refers to the choice of fan for different uses according to the nature and use of the gas to be transported; The fan selected should meet the air volume required by the system, and the wind pressure should be able to overcome the resistance of the system, and work within the highest efficiency or economic use range.

      Choosing the correct fan is an important condition to ensure the normal and economic operation of the ventilation system. The so-called correct choice, mainly refers to the choice of fan for different uses according to the nature and use of the gas to be transported; The fan selected should meet the air volume required by the system, and the wind pressure should be able to overcome the resistance of the system, and work within the highest efficiency or economic use range. Specific selection methods and steps are as follows:

    1．According to the nature of the gas to be transported, choose different uses of fans. For example, the transportation of clean air, or the dust gas flow through has been purified, dust concentration is not more than 150mg/m3, can choose general ventilation; Transport corrosive gas, to choose anti-corrosion fan; When transporting flammable and explosive gases or dusty gases, explosion-proof or dust exhaust fans should be selected. However, when selecting the specific fan model and specification, it must be determined according to the performance table or characteristic graph on a certain type of product sample.

    2．Considering that the duct system may leak air, some resistance calculation is not accurate. In order to operate reliably, the selected air volume and air pressure should be greater than the calculated air volume and air pressure of the ventilation and dust removal system, that is

    Air volume：　　L′＝KLL　　（1）

    Wind pressure：　　H′=KHH　　（2）

    Where L 'and H' -- selected air volume and air pressure;

    L、H——Calculation of air volume and air pressure for ventilation and dust removal system；

    KL——Air volume additional coefficient, dust removal system KL= 1.1 ~ 1.15；

    KH——Additional coefficient of wind pressure, KH of dust removal system = 1.15 ~ 1.2.

    3．According to the selected air volume L 'wind pressure H', the type of fan is selected on the fan product sample, and the number, speed and motor power of the fan are determined. In order to facilitate the takeover and installation, it is necessary to choose the appropriate fan outlet position and transmission mode. The working point of the selected fan should be within the economic range, preferably on the right side of the highest efficiency point.

　4．The performance parameters of the fan in the standard state (atmospheric pressure 1.013 ×105 Pa, temperature 20℃, relative humidity 50%) are given on the fan sample. If the actual operating state is not the standard state, the actual performance of the fan will change (except the air volume). Therefore, when selecting the fan, the parameters in the actual running state should be converted to the parameters in the standard state, and the conversion relationship is as follows:

　　Pa　　（3）

　　kW　　（4）

Where Hb, Nb, ρb, Pb, TB -- wind pressure, power, air density, gas pressure and temperature of the fan in the standard state (or specified state), that is, the data listed on the fan sample;

　　 H′、N′、ρ、p、t——The wind pressure, power, air density, gas pressure and temperature of the fan under service conditions.

　　In the fan sample, the performance parameters of some boiler induced draft fans are obtained according to the gas temperature of 200℃ or 240℃. When converting, TB in formula (3) and (4) should be substituted into 200℃ or 240℃.

　　5．Unless any one of the fans cannot meet the requirements, or the air pressure and air volume of the fan are required to change greatly during use, it should be avoided to use two or more fans in parallel or series. Because when two or more fans work together, the effect of each fan is different from that of its own use.

　　6．In recent years, due to the continuous improvement of the structure of the fan in China, the efficiency of the fan is constantly improved and the noise is constantly reduced. Some new fans are gradually replacing some old fans. In order to save energy and reduce noise hazards, a new type of fan with high efficiency and low noise should be selected as far as possible on the premise of meeting the required air volume and pressure.