actually the difference between the results for D-W and H-W does not vary consistently (alas there is not a linear relationship). To require using D-W at very high velocities is unnecessarily conservative. At these velocities the pressure loss is so high that it is self regulating so typically occurs only is limited sections of the system. With all the averaging etc that our process entails, why get anal on ONE piece of the puzzle? Having said that, one could argue that one should account for the velocity pressure in the discharge calc at high velocities BUT that is needed only when you really have such velocities (like in a water spray deluge) verses seeing an assigned value from our process.
Roland Huggins, PE - VP Engineering American Fire Sprinkler Assn. --- Fire Sprinklers Saves Lives Dallas, TX http://www.firesprinkler.org On Sep 15, 2014, at 1:56 PM, Damien Shannon <[email protected]> wrote: > So purely along the lines of Andy Rooney's 'have you ever wondered why' :) > ... FM Datasheet 2-0, while not limiting the allowable velocity, does > require that when velocity exceed 30ft/sec, that the calculation be > performed via the Darcy-Weisbach Method rather than the Hazen-Williams. > Entertainment value only, but would seem that the variance between results > in Hazen-Williams versus Darcy-Weisbach become more apparent with higher > velocities. > The 30ft/sec limitation (for application of Hazen-Williams calculations) in > FM 2-0 is strangely close to the 10m/sec (32.8ft/sec) limitation in EN > 12845 Rules for Automatic Sprinkler Installations (previously BS 5306). > > _______________________________________________ Sprinklerforum mailing list [email protected] http://lists.firesprinkler.org/listinfo.cgi/sprinklerforum-firesprinkler.org
