=FORECAST.LINEAR(Your_Aspect_Ratio, Known_Coefficient_Range, Known_Aspect_Ratio_Range) Some coefficients are only valid at turbulent flow (Re > 4000). Add a conditional check:
In Excel: = [@Coefficient] * (0.602 * ([@Velocity_FPM]/4005)^2) for IP units. Use SUMIFS to total all losses for each air handler. This yields your fan selection point instantly. Advanced Tips: Beyond Basic Lookup Once you have the ASHRAE Duct Fitting Database Excel file, you can build advanced features: 1. Automated Interpolation Between Table Values Many fittings lack exact matches for your dimensions. Use FORECAST.LINEAR : ashrae duct fitting database excel
Loss = C * Pv