What is the least efficient method of controlling fan output?

Using dampers to control fan output is considered the least efficient method because dampers work by restricting air flow. When dampers are partially closed, they reduce the volume of air that can pass through the fan, but this creates a pressure drop that requires the fan to work harder to maintain the desired airflow. This excess strain can lead to energy wastage and reduced efficiency overall.

In contrast, other methods such as variable inlet vanes, motor controls, and blade pitch control adjust the flow of air or the fan's speed more directly and efficiently without creating unnecessary pressure losses. For instance, variable inlet vanes can optimize airflow by allowing the fan to adjust the angle of the vanes to suit the operating conditions, while motor controls typically manage fan speed, offering significant energy savings. Blade pitch control allows for the adjustment of the fan blades' angles to achieve optimal efficiency as conditions change. These methods therefore provide a more efficient and effective means of controlling the fan output compared to the simple restriction imposed by dampers.