NFPA 96 Duct Velocity
NFPA 96 Duct Velocity
(OP)
When calculating the minimum grease duct exhaust velocity in a square duct, am I to use the circular round equivalent to calculate the duct area or just multiply the length by width? For HVAC systems, I was taught to use circular equivalent, but I've seen equipment manufacturers use the straight-forward length * width approach.
Example: 1,800 cfm in a 12"x12" duct. Per NFPA, is the velocity 1,800 ft/min [1,800 cfm / 1 sq. ft] or is the velocity 1,917 ft/min [1,800 cfm / (PI* 13.12 inches^2 / 4]?
Thanks in advance.
Example: 1,800 cfm in a 12"x12" duct. Per NFPA, is the velocity 1,800 ft/min [1,800 cfm / 1 sq. ft] or is the velocity 1,917 ft/min [1,800 cfm / (PI* 13.12 inches^2 / 4]?
Thanks in advance.





RE: NFPA 96 Duct Velocity
RE: NFPA 96 Duct Velocity
RE: NFPA 96 Duct Velocity
I recall a senior engineer telling me that the ductalator takes into effect the minimal velocities around the edges of the rectangular duct, when calculating the velocity.
I have compared your equation to this and found them to be off, especially when the cfm gets up over 5000 cfm.
I have not considered using the circular equivalent (but probably should)
knowledge is power