Darcy-Weisbach Calculations

Darcy-Weisbach is a formula for calculating friction loss like the Hazen-Williams formula that is usually used for water-based fire sprinkler systems. But whereas Hazen-Williams is used for water in sprinkler pipe, Darcy-Weisbach can be used for any liquid (including water, but NFPA 13 does not permit its use for standard sprinkler systems).

Its use is required in antifreeze systems over 40 gallons of capacity (but not in the non-anti-freeze portions of the system) and in water-mist systems that operate at more than 175 psi. These are, of course, subject to the approving authority.

In order to calculate these systems, you will need to know some things about the fluid being used, specifically the Density and the Viscosity. The Density is in the units of lbs per cubic foot (kg per cubic meter) and the Viscosity is in the units of centipoise*.* These need to be entered in the appropriate spots in the calculation dialog box.

In most cases, two calculations are required. One, the portion of the system containing antifreeze, and two, the portion containing water. This is because Darcy-Weisbach cannot be used for water systems and Hazen-William cannot be used for antifreeze systems.

A two-part example job is available in you \HES\HydraCALC\Ver50\Data\Jobs\Example Jobs folder. It is named Darcy-Weisbach Antifreeze Loop Example - Part One * and * Part Two For more information on Darcy-Weisbach vs. Hazen-Williams see a great comparison article from Scott Martorano of The Viking Group in PDF form at: [Darcy-Weisbach Article](http://www.vikingcorp.com/sites/default/files/documents/Calculating Friction Loss.pdf).