For the curve that dropped down from 2000 [ft.sup.3]/min (0.94 [m.sup.3]/s), the PLAF at a partial airflow value was calculated, then used to determine the PLPF. The PLPF was then multiplied by the full-load power (760 W) to determine the power the fan motor would use at the lower airflows.
Using Equation 7 and the coefficients in Table 8, the PLPF would be 0.554 for a PLAF of 0.8.
Because the PLPF and PLAF are normalized to the maximum ECM setting, installing a slightly larger fan/motor than required would mean that at design conditions, the unit would not be operating at a PLAF and PLPF of 1.0, but would be operating at some point down the curve in Figure 7.
Using Equation 7 for part-load operation would yield a PLPF of 0.357 and power requirement of 570 W x 0.357 = 203 W.
Unlike the Knebel (1983) model that went to zero PLPF at zero PLAF, the model for the ECM fan/motor units leveled off near 0.062 for PLAF values less 0.1.