=+12-45 The makeup air duct for a low-velocity system must be sized to handle a maximum of 2000 cfm

(0.94 m3/s). The length of the duet is 40 ft (12.2 m), and it has two mitered elbows (Table 12-

8B, Design 3). The air inlet grille has a lost pressure of 0.25 in. wg (62 Pa) at 2000 cfm (0.94 m3/s), An opposed blade damper is installed in the duct with C = 0.52 when full open. The duct connects to the mixing box, where outdoor air is mixed with recirculated air. Assume an abrupt expansion at the mixing box, A /A, = 2.0.

(a) Size the duct, and compute the lost