With FHC, you can use Hayes-William or Darcy Weisbach's pressure loss equation and switch easily between the two.
Most often, we will use the Hazen Williams equation Hazen Williams pressure loss equation for our calculation for fire sprinkler sprinklers. However, for water mist systems, we often need to use Darcy Weisbach the pressure loss equation, especially for high-pressure water mist systems, but sometime you may need it for low pressure as well, so you must check with the AHJ and design standards such as NFPA 750.
This document TDS1 - Water mist calculations and FHC will assist you in selecting the correct pressure loss equation.
