Fire Hydrant Modeling in EPANET 2.0

[Scott Horowitz]

I am tasked with determining the fire flow in two proposed hydrants, serving two new facilities, that are connected to an existing water system. I am performing this effort in EPANET 2.0, with which I have intermittent experience with; fire flow modeling is not in that category. I have flow tests for three existing hydrants and need to use these results to model the two proposed hydrants, and I am not sure how to correctly build the model(s) and incorporate the existing hydrants. Some of the variables that I have questions regarding are below:

1. Assume only one structure will have a fire demand. I imagine build separate models for each of the proposed hydrants?
2. Do I include all three existing hydrants in the model(s) and input their respective pump curves per their respective flow tests? Or do I include only one existing hydrant, and would this be the hydrant furthest from the new hydrants?

I have built models with three existing hydrants and only one existing hydrant, and the results are different (obviously). I am just not sure if the results can be considered acceptable, and I am hesitant to use them in my engineering report deliverable.

Any guidance on how to correctly build and model fire flows would be helpful!

Thanks to everyone in advance, and have a great weekend!

 

[Pinwards]

Typically I would use the Flow Test nearest to your proposed hydrant(s), and use the curve from that test to simulate the existing system and its response to flow demand. If the two proposed hydrants are near each other and served by the same system, then you could keep them in the same model and just flow them independently for each analysis (with different demand patterns). I used the free add-on FireFlow from OptiWater to analyze available fire flow at each hydrant at minimum system pressure (typically 20 psi).

If the three flow tests are near each other and served by the same distribution system, same diameter mains, etc... then you should have seen similar results from all three. IF they are wildly different, then you may want to look for closed valves or something wrong with the system to cause that difference in results. If the differences are minor, then I would typically use the one closest to the proposed hydrants, or you could use the lowest results to be conservative.

A sketch of your distribution system would be helpful, and descriptions of any major elevation differences or water main size/types.

#