Design and calculation of ductwork for variable air volume air conditioning systems

Four commonly used ductwork design and calculation methods for variable air volume air conditioning systems are discussed in this paper. The specified velocity method is currently the most widely used method. The equal friction method is intended to equalize aerodynamic noise across duct sections, so as to reduce the factors that generate duct noise. The static regain method is primarily applied in the calculation of main ducts of variable air volume air conditioning systems, with the goal of maintaining consistent static pressure levels in the main duct acting as a plenum chamber. The balanced capacity method focuses on achieving uniform pressure drop across all paths when volume dampers on branch ducts are fully open, so as to minimize the airflow-induced duct noise and testing workload. It is pointed out that when using a friction chart for round ducts to calculate the friction resistance of rectangular ducts, the attention should be paid to the calculation formula for equivalent diameter.