A new duct design software tool

This article describes the features and operation of a new duct design software tool. The tool was used in a case study to establish its practicality and performance. This tool is unique in the sense that it employs an optimisation method called the T-method. As far as the authors are aware no commercial duct design software package incorporates optimisation techniques. To enhance user friendliness the program also features a CAD interface for data input and output. By using the new tool an existing duct system was redesigned with the same constraints and specifications set by the original designer. The design program managed to optimise the 30-section system in less than 10 s on a 50 MHz 486 personal computer. In comparison to the existing system the redesigned system yielded savings of 8% on the duct material cost while the energy cost was lowered by 3%. The life-cycle cost decreased by 5%. The redesigned system has nine transition fittings compared to the five of the original system, which will reduce the final savings. Stability problems were encountered in a few sections that had relatively large C-coefficients, which were referenced to upstream velocities. This led to grossly oversized ducts. The problem was overcome by fixing the diameters of the few problem sections at realistic values. This problem was analysed in a previous article by these authors (Building Environ. 33(4) (1998) 173). It must also be said that for this case study the T-method was outperformed marginally by the equal friction method, a traditional duct design method. Notwithstanding the problem with the optimisation method itself the new duct design tool speeds up the design process and provides a user-friendly way of designing duct systems.