We have noted that if a small to medium sized restaurant fan using a squirrel-caged blower wheel is installed with the rotation of the wheel reversed form the proper rotation the motor will pull additional current (from 20% to 50% increase). Example: An exhaust fan with a 15" wheel and a 3/4 HP motor will pull 11 amps (at 115 VAC) normally when the wheel is spinning in the correct roatation ("cupping" the air). If the motor is modified to reverse the rotation direction, the current draw is increased to 17 amps, with lower air flow. I am simply curious why the increase in curent draw?

Their will be more resistanse and less flow if ran backwards.
Blades or props are designed to rotate 1 direction, unless intentionally designed to rotate both ways.