For the past decade, Sargent and Lundy have been designing coal storage ventilation systems using computer-aided duct design methods. Our computer program is not universal, but rather a series of smaller programs. This gives us the flexibility to economically analyze and design portions of systems, modify programs easily, add and update fitting loss coefficients as data becomes available, evaluate balancing techniques, and determine the effect of fittings on the overall resistance of a system.

The major effort during the early development of these programs was the search for fitting data, and the subsequent correlation for computer use. One should note that Chapter 31, Air Duct Design, of the 1977 ASHRAE Handbook of Fundamentals has been revised extensively and includes a greatly expanded section on fitting data. Now that fitting data and computer algorithms are readily available, the use of computer-aided duct design should increase. Is the development of computer-aided duct design a worthwhile investment? To help you judge for yourself, this paper presents a philosophy for designing duct systems utilizing computer-aided techniques. specific examples compare the effect of alternate fitting configurations and design methods on the total system resistance and balancing requirements for a bunker ventilation system. While the examples presented herein are based on a specific type of system, the concepts are applicable to any type of duct system.