Computing System Demand Pressure and Flow Fire Sprinkler System

The calculation is tedious and iterative. Fortunately, a number of calculation packages are available for purchase that take the grunt out of the work. A Google search for "piping network calculator" will reveal them.

I wouldn't use Williams & Hazen as I think the Moody chart (it comes under various names) is better.

But I doubt you need to bother with too much detail. The sprinkler nozzles are likely to be rated for design flow at around 2 barg (I looked on the web for a figure, suppliers don't say, understandably, but can work direct off mains water so 2 barg would be typical). You could estimate worst-case pipe pressure drop (it depends on the system layout) and it's likely to be much less than 2 bar, in which case the flow from each nozzle doesn't vary significantly, even in the unlikely event of a major fire and all the sprinklers running.

It doesn't matter exactly how much water is coming from any particular nozzle so long as there is sufficient from them all in aggregate either:

• to douse any fire, or
• to buy time to get all occupants out of the building, or
• to provide a blanket underneath which professional fire fighters can operate effectively.

The facility's fire insurance cover provider will be able to offer advice on system design. Pick up the telephone and make some calls, perhaps? The advantages of the telephone over other methods of contact are:

• its speed
• its interaction potential with people that can help
• its potential for working relationship-building
• it cannot be ignored at the receiving end, particularly in a technical-sales office.

What is the hazard?

0.8 gpm/square ft. is a very high density for a standard sprinkler system.