The database implicitly assumes galvanized steel with absolute roughness ε = 0.09 mm (0.0003 ft). For flexible duct or internally lined duct, no modification is given—engineers must add separate friction loss. 5. Comparison to Modern Databases (2009, 2021 ASHRAE) The 1994 edition has been superseded, but its influence persists.
The 1994 database exclusively uses IP units (ft, fpm, in. w.g.) in tables. A conversion to SI is provided in an appendix, but rounding errors (e.g., 1 in. w.g. = 248.8 Pa) often lead to 1-2% discrepancies. 4. Mathematical Model & Assumptions The core equation implemented in the database’s companion software (a DOS executable) is: duct fitting database -ashrae 1994- pdf
[ C = \frac\Delta P_measured0.5 \rho V_ref^2 ] but rounding errors (e.g.