In any duct system, when the velocity of air is _______, the resistance to air flow is _______________.

In any duct system, as the velocity of air is increased, the resistance to air flow also increases due to several factors. When air moves faster through a duct, it encounters more friction against the duct walls, which leads to a rise in pressure drop or resistance. This can be attributed to the turbulence generated within the airflow; higher velocities create more chaotic patterns in the movement of air molecules, resulting in additional energy losses.

Furthermore, the relationship between air velocity and resistance is defined by the principles of fluid dynamics, particularly the Darcy-Weisbach equation and the principles of laminar and turbulent flow. In turbulent flow, which typically occurs at higher velocities, the flow characteristics change significantly, increasing drag and leading to a greater loss of pressure as air moves through the system.

Therefore, when considering the performance of a duct system, understanding that increasing air velocity correlates directly with increased resistance is critical for engineers and technicians in order to design efficient HVAC systems that adequately manage airflow while minimizing energy loss.