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 Comparison to Modern Databases (2009, 2021 ASHRAE) The 1994 edition has been superseded, but its influence persists.
All coefficients assume air density is constant. For systems with >2 kPa total pressure (e.g., high-rise buildings), compressibility causes errors, particularly in tees where momentum exchange is modeled incorrectly. duct fitting database -ashrae 1994- pdf
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: Comparison to Modern Databases (2009, 2021 ASHRAE) The
| Table | Fitting Type | Key Parameters | C Range (Typical) | |-------|--------------|----------------|------------------| | T1 | Elbows, 90° Smooth Radius | r/D (radius/diameter) | 0.15 – 0.30 | | T2 | Elbows, Mitered | Number of segments | 1.0 – 1.5 | | T3 | Tees, Converging (Flow into main) | Area ratio, Flow ratio | 0.2 – 4.0 | | T4 | Tees, Diverging | Branch angle (30°-90°) | 0.5 – 6.0 | | T5 | Transitions, Sudden Expansion | Area ratio (A1/A2) | 0.8 – 1.0 (loss factor based on upstream velocity) | | T6 | Transitions, Sudden Contraction | Area ratio (A2/A1) | 0.1 – 0.5 (loss factor based on downstream velocity) | | T7 | Conical Reducers | Included angle (α) | 0.05 – 0.30 | | T8 | Branch Entries (45°, 90°) | Heel vs. Throat radius | 0.4 – 2.5 | | T9 | Damper, Opposed Blade | Blade angle, % open | 0.2 (full open) to >20 (nearly closed) | | T10 | Silencers (Packless) | Length, flow path | 1.5 – 4.0 | The 1994 database exclusively uses IP units (ft, fpm, in