Close Coupled Ductwork Fitting Pressure Drop

Abstract

The impact of close coupled ductwork fittings on system pressure drop is the central thrust of this paper. The configuration selected for in-depth research was taken from the engineering mechanical plans and specifications for a college library building under construction. The mechanical room is small and the ductwork leaving the air handling unit consists of very close coupled ductwork fittings. Design engineers currently have very little in the way of industry standards or design tools to quantify the impact of such arrangements. In order to better understand the magnitude and direction of close coupling on overall system pressure loss, the following research tools were employed: computational fluid dynamic (CFD) analysis, scaled fitting and arrangement testing in the laboratory, and full-scale arrangement field testing. Overall, each of these different approaches supported one another. The research revealed that close coupling of fittings can be either complementary or detrimental, depending upon the specific circumstance. For the specific set of fittings investigated, close coupling resulted in an approximately 27% higher pressure loss than predicted using conventional procedures. This led the authors to conclude that further research and better design tools are needed.