How is the movement of the pre-rotation vanes controlled?

The movement of the pre-rotation vanes is primarily controlled by chill water temperature control because these vanes are designed to optimize the performance of a cooling system, particularly in variable air volume (VAV) systems. By adjusting the position of the pre-rotation vanes, the system can effectively enhance the airflow characteristics and improve the energy efficiency of the cooling process.

Specifically, when the chilled water temperature is adjusted, the cooling load in the space changes, leading to a need for modifications in air distribution. The pre-rotation vanes help manage this airflow in response to the chilled water temperature to maintain appropriate indoor conditions. This adaptability ensures that the system can efficiently respond to varying cooling demands while maximizing efficiency.

The other options pertain to different aspects of HVAC operation. Fan speed affects airflow but does not directly control the positioning of the vanes. Refrigerant flow is more related to the cooling process and the operation of the compressor and evaporator, rather than directly impacting the vanes. Pressure differential may influence air movement but is not the primary control mechanism for the pre-rotation vanes themselves.