This study utilizes static pressure drop data taken from one manufacturer’s catalog to develop total pressure loss coefficient correlations for single duct VAV terminal units having a circular inlet duct and a rectangular outlet. The control dampers for each box were assumed to be in their wide open position. Separate correlations are presented for cases including a plain box, as well as terminal units that have either hot water reheat coils consisting of one to four tube rows, or an electrical heating element. In every instance the correlations account for static pressure and velocity pressure changes between the box inlet and outlet, based on cross section changes. The correlations are useful for duct designers, since they facilitate the utilization of numerical duct design approaches that require extensive iterative calculations, such as the static regain method. The correlations are proposed for inclusion in duct fitting loss coefficient databases.

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