Derivation of air flow constant 4005?
Derivation of air flow constant 4005?
(OP)
I am looking for a derivation of the constant "4005" that is used in hvac vav's for air flow vs. velocity pressure in a round pipe. Q(cfm) = 4005 * aspect ratio * sqrt [velocity pressure (in h20)]
Thanks!!
Thanks!!





RE: Derivation of air flow constant 4005?
(P1-P2)/Rho = V2/2g (i.e static pressure difference creates flow)
1 lb/sq.ft = 0.1922 inches of wc
1g = 115820 ft/min2
So V = [(2 x 115820)*dP/(0.075 x 0.1922)]1/2
i.e V = 4008.6 x dP1/2 (there may be some conversion problems for the costant to be high by 3.6)
Q = A x V (it is not aspect ratio here but the product of two sides)
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RE: Derivation of air flow constant 4005?
RE: Derivation of air flow constant 4005?
Thus
RE: Derivation of air flow constant 4005?