Vent ducting performance mainly contains air leakage rate, wind age, friction coefficient (Darcy Coefficient), pressure-resistant performance and diameter variety rate. Here is a briefly introduction about air leakage rate and wind age.
The national standard “Rubber or Plastic Coated Fabric – Vent Ducting” (GB/T 9900-2008) gives the lowest standard about vent ducting . The wind age and air leakage rate will be measured by “Wind age and Air Leakage Rate of Vent Ducting Measuring Method” (GB/T 15335-2006); and the pressure-resistant performance and diameter variety rate will be measured by “ Tensile Elongation and Elongation at break of Rubber or Plastic Coated Fabric Measuring” (HG/T 2580-2008).
|Size (mm)||Positive pressure vent ducting||Negative pressure vent ducting|
|Air Leakage Rate (%)||Wind age
|Air Leakage Rate (%)|
Materials，connections，processing technology and length of a section of vent ducting have great effect on the air leakage rate of vent ducting. And different ventilation ducts have different air leakage rate in market. The national standard GB/T 9900-2008 proposed that air leakage rate of positive pressure vent ducting should be less than 4% and air leakage rate of negative pressure vent ducting should be less than 5%. But many vent ducting made up by outdated technology could not reach that requirement. Now, the air leakage rate of 10m flexible ventilation ducting with zipper which widely be used in construction site is 1.6%. In domestic market, Jiangsu Sulong Eco-Technologies Co., Ltd could reach this air leakage rate standard.
There are several reasons leading large air leakage rate.
First, the material of vent ducting. As we mentioned in last article, there are many non-environmental pungent vent ducting in domestic market. In order to save cost and industrial equipment, the corrupt producers will produce inferior and pungent vent ducting which the surface is rough and uneven.
Second, connection of ventilation ducting. The connection is also called quick coupling. The end side of each two ventilation ducting are turned up to match together and then fixing the connection joint with quick coupling to ensure no air leakage. Low qualification rate of quick coupling will increase air leakage rate.
Third, increasing ventilation ducting length of every section is the efficient method to lower air leakage rate. Standard length of each ventilation ducting is 100m or 200m. Now Jiangsu Sulong Eco-Technologies Co., Ltd and Guangzhou Plato Chemical Co., Ltd are good manufacturer. Jiangsu Sulong Eco-Technologies specialized in ventilation ducting with lower cost. There are longer ventilation ducting in domestic market, but they are not easy to install and carry and every long ventilation ducting has heavy weight which is not easy to transport.
So there are three measures can reduce air leakage rate.
Generally speaking, air duct is called ventilation ducting according to coal-mining industry. It is used to call ventilation ducting in tunnel construction.
The calculation formula of wind age is:
It is easy to understand that wind age is inversely proportional to the quantic of ventilation ducting diameter and is proportional to coefficient of frictional resistance α (or friction coefficient λ). It reflects resistance characteristic of ventilation ducting. Coefficient of frictional resistance α (or friction coefficient λ) is widely used in calculation of ventilation system.
Friction coefficient (Darcy coefficient) λ depend mainly on the relative smoothness of the ventilation ducting inter wall and it has great effect on wind age. There are three levels S/A/B in Switzerland and λ is changed according to different levels. Now the common parameter is 0.014 in some technical papers which foreign contractor provided to our tunnel construction project like GIA, Howden-Buffalo and Korfmann. The friction coefficient of SL|Tech. vent ducting applied in Karuma Project by SINOHYDRO BUREAU 8 CO., LTD could reach λ 0.015 which is the Swiss S level. So when purchasing ventilation ducting, we need to consider air leakage rate, wind age and friction coefficient.