Solving for Friction Factor PDF

The article, "Calculating Pressure Drops in Piping Systems" in the September 2002 issue of ASHRAE Journal, presented a procedure that used the built-in iteration function in spreadsheets to solve the Colebrook Equation. This is fine if an engineer is using the spreadsheet as an lternative to pressure drop tables or graphs. However, there are times when solving for the friction factor is part of a larger solution. That larger solution might benefit from using the iteration function. However, I know of no way to have an iteration embedded in a second iteration. In such a case, it would be helpful to have a direct solution for the friction factor.