Abstract: There is limited research on the impact of return duct diameters on the performance of air conditioning systems. To investigate the patterns of their influence on performance and summarize design methods, simulation and experimental studies were conducted using return ducts with diameters of φ15.88 mm and φ12.7 mm, thereby obtaining the patterns of how duct diameters affect performance under both cooling and heating conditions. The verification results indicate that using a smaller duct diameter of φ12.7 mm results in a pressure drop approximately 4300 to 4600 Pa greater than that of φ15.88 mm. Due to the different specific volumes of suction under cooling and heating conditions, changes in duct diameter have minimal impact on cooling performance but significantly affect heating performance, reducing capacity by 2%. This verification reveals the key patterns of how return duct diameters affect air conditioning systems, providing important insights for optimizing the selection of return ducts and enhancing system performance.

Key words: Pipe diameter, Performance, Pressure drop