A classroom of 12m × 25m × 4m requires 3 air changes per

A classroom of 12m × 25m × 4m requires 3 air changes per hour. At an air velocity of 2 m/s, the necessary duct cross section (in m²) is

3 air changes per hour means 3 times the volume of room changes in one hour.
So,

Volume rate per second =	3 × Volume of room	m³/sec
	3600

Volume rate per second =	3 × 12 × 25 × 4	m³/sec
	3600

Volume rate per second = 1 m³/sec
Area = Volume rate per second/ velocity
Area = 1/2
Area = 0.5 m²