How to calculate the amount of ventilation duct works?

We do before the installation of ventilation ducts, will calculate the amount of engineering in advance. So, how to calculate the amount of ventilation pipe it? Here we explain to explain.

1, the wind pipe production and installation specifications to the construction plan by the expansion of the area to "m2" for the measurement unit, without deduction of inspection holes, measuring hole, air delivery, suction and other occupied area. Round duct F = π × D ×
L Where: F - circular duct expansion area, m2; D - circular duct diameter, m; L - pipe centerline length, m.
2, the length of the duct shall be based on the length of the construction center line, including the elbow, tee, reducer, Tianyuan place pipe length, but does not include components (control valve, muffler, muffler elbow, Static pressure box) share length. Diameter and perimeter according to the size of the picture shall prevail, overlapping part of the mouth has been included in the corresponding items, shall not be increased.
3, the plastic air duct, composite materials, production and installation of air duct diameter listed in the specifications for the diameter, perimeter for the inner perimeter. The production and installation of ventilation ducts, clean ventilation ducts, FRP ventilation ducts and composite materials ventilation ducts, including flanges, reinforcement frames and sling brackets, shall not be separately calculated.
4, stainless steel ventilation ducts, aluminum ventilation ducts, plastic ventilation pipe production installation does not include lifting bracket, according to the corresponding project to "kg" for the measurement unit, separately.
5, the length of the air duct calculation, the main pipe and branch to the intersection of the center line, the length of the adjustable diameter pipe to the large diameter pipe, the length of meters, the length of the elbow according to the intersection of two air duct center line calculation.
Flexible duct installation according to the center line of the icon to "m" for the measurement unit. The density of galvanized steel sheet is 1.05 times of the density of ordinary thin steel plate.