Why are turning vanes added to sheet metal elbows?

Turning vanes are added to sheet metal elbows primarily to improve airflow characteristics in the duct system. By guiding the air smoothly around the bend in the ductwork, turning vanes help to maintain a higher velocity of the air as it changes direction. This improvement in airflow is beneficial because it reduces turbulence and allows the system to operate more efficiently.

In essence, the design and placement of turning vanes minimize the pressure drop associated with turning air in the duct system. When air is forced to change direction suddenly without vanes, it can create turbulent flows that lead to inefficiencies, increased resistance, and potential noise issues. Thus, the use of turning vanes directly supports the objective of achieving higher air velocity at the elbow, which enhances the overall performance of the HVAC system.