Duct size = Air volume / Air velocity
Air volume = Room area * Room height * Air change rate
Example: Air volume 40,000 m/s, air velocity 9 m/s
Duct size = 40,000 / 9 / 3,600 = 1.23 square meters
1.23 = 1.5 * 0.82
Therefore, the duct size is 1500 * 800 mm.
Dual-duct diameter design calculation steps:
1. Draw an isometric drawing of the ventilation or air conditioning system, number each duct section, and label its length and air volume. The duct section length is generally calculated based on the centerline length of two fittings, without deducting the length of the fittings themselves (such as tees and elbows).
2. Determine a reasonable air velocity. The air velocity within the duct has a significant impact on the economy of the ventilation and air conditioning system. Higher velocities result in smaller duct cross-sections, less material consumption, and lower construction costs; however, they also increase system resistance, power consumption, and operating costs. For dust removal systems, it increases wear on equipment and pipes; for air conditioning systems, it increases noise. Low flow velocity results in low resistance and low power consumption; however, it also increases the cross-sectional area of the duct, material and construction costs, and the space occupied by the duct. In dust removal systems, excessively low flow velocities can cause dust to accumulate and clog the pipes.
