where U wind is the far-field wind speed; C p1 is a local pressure drag coefficient for the building, defined at the location of the upstream opening; C p2 is a local pressure drag coefficient for the building, defined at the location of the downstream opening; A 1 is the cross-sectional area of the upstream opening; A 2 is the cross-sectional area of the downstream opening; C 1 is the discharge coefficient of the upstream opening; and C 2 is the discharge coefficient of the downstream opening.