Flow and pressure demand in a combined standpipe and automatic sprinkler firefighting system

[Giorgos Papakonstantinou]

I am confused in selecting the correct pump for a fire fighting system which has automatic sprinklers and fire hoses.
So in a building where there is already an installed combined system with fire hoses and sprinklers, there is a pump which supplies both, through a manifold with two risers (one for the fire hoses and one for the sprinklers). On this system I am asked to check whether the pump installed, is correct to supply both systems the required pressure and water flow.

I model this scenario in EPANET by choosing the most unfavorable set of 12 sprinklers and the most unfavorable fire hose working simultaneously (each sprinkler with an emitter coefficient and no base demand, and the fire hose with a base demand 380 l/min).

Now I should select a pump which provides at least 4.4bar at the fire hose, and at least 60 l/min and 0.563 bar (5.74 m) at the most distant sprinkler from the set of 12.

Solving the above scenario in EPANET with a certain pump provides the minimum requirements for the sprinklers, but does not satisfy the minimum pressure demand for the fire hose.

Solving the same scenario in EPANET with a bigger pump, satisfies the minimum pressure demand for the fire hose, but it increases substantially the pressure and flow at the sprinklers.

So I doubt myself whether is a good strategy to simulate both sprinkler and fire hose simultaneously.
I have attached my model in EPANET (it uses SI units). If you see I get 47m pressure and 380 l/min but the last sprinkler has double the required pressure and 1.5 the flow (13m pressure and 91 l/min).

What are you suggestions and opinion? Thank you in advance

 

[hateMech]

I believe fire fighting design is based on the "area of operation". This is the area where you expect a fire may break out, and the maximum area a fire fighting system is designed for.

This implies that your most unfavourable area of operation as described above may not always coincide with your most unfavourable set of sprinklers or hose reels when they are considered separately. If that's the case, review the set of sprinklers and hose you assume will operate in case of fire.

If that is not your case, it would seem that there is something wrong somewhere. Maybe that is exactly why you were tasked with reviewing the initial pump selection.

I'm not familiar with EPANET so I could not check out your model.