The study used an average energy

The study used an average energy cost of $0.15. Simple payback calculations used this average energy cost applied to the measured energy savings but did not include maintenance costs or the energy savings associated with heating or cooling makeup air. The shortest payback periods were associated with new construction installations and installations with high fan horsepower systems and high cooking demand diversity. New construction is typically less costly than retrofit installations because of the complexities associated with retrofits. Systems with high horsepower motors and high demand diversity experience the largest savings because of extended periods when large fan systems operate at lower speeds under low cooking demand.  Figure 5 below demonstrates the daily electrical power demand for an exhaust fan for one of the hotels installations. The BLACK curve shows the power used by this fan which operates 24 hours per day without any speed control. The RED curve shows the power required when the fan was modulated to the cooking demand under the hood. The GREEN line is the daily average of the RED curve and represents a 46% reduction in daily power demand.