Duct flow losses and loss coefficient

[FDS_user]

Hi,

As per the technical reference guide (latest), the total flow loss in the duct, K_j, is the sum of fitting losses in the duct (e.g. elbows, expansion/reduction, orifice plates), K_minor, plus losses due to wall friction, K_wall.

K_total = K_minor + K_wall

I was looking at the verification guide where the pressure drop due to the steady flow in a duct is given by delta_pressure = (K . density . velocity square)/2

Just to be sure, K here denotes K_total here because we are here calculating the overall presure loss happening due to minor (elbows, bends, etc.) and duct roughness (friction factor).  Can anyone please confirm the conclusion or correct it?

Thanks!

[dr_jfloyd]

Yes it is the total loss where K_minor is based on the LOSS input on &HVAC and K_wall is based on the ROUGHNESS input on &HVAC (where ROUGHNESS, LENGTH, DIAMETER, and the velocity are use to compute the friction factor using the approximate form of the Colebrook equations). In the HVAC verification cases only K_minor (LOSS) is set and K_wall=0 (if no ROUGHNESS is given, no friction factor is computed).

[FDS_user]

Thanks, dr_jfloyd, for the clarification!