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Considering the Traffic of Airflow Within a Duct System
There are certain prin - ciples of air movement that, once understood, allow you to direct air - flow as needed in an HVAC system. Understanding these principles will allow you to solve comfort problems that have plagued home - owners for decades. The use of the "Coanda Effect" is one of these principles. Once understood, the way you look at duct systems and registers will change forever.
What Is the Coanda Effect?
The Coanda Effect is named in honor of Henri Coanda, a Romanian aerodynamics pioneer and aircraft inventor. This phenomenon is some- times referred to as the surface effect in many publications. The Coanda Effect occurs when airflow is closely projected to a parallel surface, such as a ceiling or the walls of a duct system. When this occurs, airflow is affected by the parallel surface it is flowing with. In simpler terms, air clings to surfaces as it moves.
The Coanda Effect creates a change in pressure at the parallel surface, which allows airflow to cling to the ceiling or duct wall it is flowing with. As the airflow moves along the surface, its movement is extended along that surface and projected farther into a room or down a duct than it would if it were blowing into an open space.
Any disturbance to the airflow pathway has a dramatic impact on the extended airstream being main - tained. The air moving with the surface needs a smooth, obstruc - tion-free pathway to maintain the Coanda Effect. On a ceiling, items such as light fixtures or ceiling variations are obstructions and will interfere with the airflow being maintained. In a duct system, items such as scoop takeoffs, collars, and restrictive duct fittings are consid - ered obstructions...