As an approach to quantifying this effect, the Air Movement and Control Association (AMCA) developed the concept of the “system effect factor.” Figure 1 includes a family of system effect curves. By entering the chart at the appropriate inlet or outlet velocity on the abscissa, locating the appropriate system effect curve, and reading across to the ordinate, an equivalent pressure loss is obtained for the particular configuration and velocity. This system effect factor is given in inches of water gauge (in. wg) and must be added to the estimated total system pressure losses. Where there will be a “system effect” at the outlet and the inlet, the appropriate factor must be determined separately for each configuration and both must be added to the estimated total system pressure losses.
The complexity of developing appropriate system effect factors will be demonstrated when it is appreciated that AMCA data include more than 100 combinations of blast area/outlet area ratio, outlet duct length, and elbow position.