What is the relationship between static pressure, velocity pressure, and total pressure in a duct system?

In a duct system, total pressure is the sum of static pressure and velocity pressure. Static pressure is the pressure exerted by the air on the walls of the duct. It represents the potential energy of the air. Velocity pressure is the pressure exerted by the moving air due to its velocity. It represents the kinetic energy of the air. Total pressure remains constant in a closed duct system if no energy is added or removed. In other words, if the velocity pressure increases, the static pressure must decrease, and vice versa, to maintain a constant total pressure. This relationship is described by Bernoulli's principle. For example, when a duct narrows, the air velocity increases, and the velocity pressure increases. As a result, the static pressure decreases. Conversely, when a duct widens, the air velocity decreases, and the velocity pressure decreases. As a result, the static pressure increases. Understanding the relationship between static pressure, velocity pressure, and total pressure is essential for designing and balancing duct systems to ensure proper airflow and efficient system operation. Measuring these pressures at various points in the duct system can help diagnose problems such as restrictions or leaks.