Fire flow calculation using EPANET

[Milan11]

I used to do fire flow calculations by hand previously but now we have to move to software. I work on to ensure sufficient fire flow on small project sites. I tried working using EPANET but it needs to have reservoir in design. But, in my case I just design based on a supply line from city mains. I have Pipe size as 6 in. throughout and the connection to mains have elevation of 159 ft. Static pressure, residual pressure and simulation discharge is 74 psi, 57 psi and 2000 gpm respectively. I have to maintain 20 psi to the furthest hydrant. Please tell me process to do it. Do you know of any manual or videos to design?

 

[Pinwards]

You will have to use a reservoir and pump to simulate the supply from City distribution system. You will need three points of data for the pump curve, generally these are static pressure at zero flow, flow test Q at residual pressure, and then you calculate the available fire flow at minimum pressure (usually 20 psi; NFPA has some publications with the formulas). Set up your new network and use the reservoir/pump at your connection point to simulate the distribution system you are connecting to. If you're just checking a known fire flow, you can enter that as a demand at the appropriate node, or use a multiplier in the demand pattern for that node to bump up the normal demand to the required fire flow. If you want to analyze the maximum available flow at each node, there's an external free program from Optiwater called FireFlow (I have no affiliation with them) that can analyze your EPANET model for max flow at a minimum system pressure.

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[Milan11]

Hi Pinwards,

Thank you for your kind reply. I did create a design as you said. In the pump design, I created two points as (74,0) and (57,2000) but could not figure out the third point. Yes, my minimum requirement is 20 psi. Could you please help me with this? I tried using FireFlow also but do not know what value to give for Flow Interval.

Thnak you!

 

[Pinwards]

Just search for "fire flow calculator" for an easy route of calc'ing available fire flow at 20 psi, or search "hydrant flow test" and most of the results will include the formulas to use. NFPA 291 is also a good resource that has all the formulas you need.

Use 10 gpm or something similar for Flow Interval in FireFlow - essentially it analyzes your model node-by-node, increasing the demand by that Flow Interval until a node in the model violates the Minimum Pressure specified. If you set the interval too small the run takes a lot longer.

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