What are the two types of fans used in VAV boxes?

• A. Centrifugal and axial.
• B. Inline and roof fans.
• C. Series fan and parallel fan.
• D. Conical and radial.

Answer: (C)

Two configurations are used for the built-in fan in VAV terminals: series and parallel. In a series arrangement, the fan sits in the same airflow path as the space air, effectively pushing air through the VAV box’s damper and coil. This helps move air through the terminal and can improve delivery when the load is high or the duct runs are restrictive. In a parallel arrangement, the fan adds air to the zone from a branch that runs alongside the main VAV path, providing extra delivery without forcing all air through the VAV damper path. The choice between series and parallel changes how the terminal interacts with the central AHU, the energy use of the fan, and the zone’s comfort at partial loads.