This document discusses duct design in air conditioning systems and its impact on system performance. It begins with an introduction explaining how duct systems are used to distribute cooled air from central air conditioning equipment to rooms when direct distribution is not possible. Improper duct design can lead to issues like increased friction loss, installation costs, noise, power consumption, and uneven cooling. The document then reviews several other studies that examined topics like air leakage from ducts, methods to minimize leakage and related energy losses, and different duct design optimization methods. It emphasizes the importance of proper duct design for minimizing costs and issues related to air distribution.