What type of control requires less power to drive the fan at reduced loads?

Inlet damper control is particularly effective for adjusting airflow in fans, especially at reduced loads. The primary reason it requires less power compared to other control methods is that it modifies the airflow by regulating the amount of air entering the fan. When the dampers are partially closed, this reduces the volume of air, minimizing the workload on the fan motor. This leads to lower energy consumption.

In contrast, other options, such as variable speed drives, might also effectively control fan speed but generally involve more complex systems that can be less efficient at low speeds. Exhaust fan control and pressure control might also operate at full speed to maintain pressure or remove air, leading to higher power usage without effectively addressing varying load conditions. Hence, inlet damper control emerges as the most efficient option when it comes to power consumption at reduced loads.