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fire flow analysis at max hour

Hello,

i'm doing the design of potable water and fire fighting network as combined network for a new site, 

we are studying two scenarios (MAx daily + fire) and (Max hourly). because it is too big site (7,000,000 m2) the peak design is the Max hourly flow.

i'm trying to study the fire flow analysis in the scenario of (Max daily + fire) and the hydraulic of the network (pressure and velocities) in the second scenario (Max hourly)

we are proposing three main DMA's, according to my previous study in water losses management we should add the entrance of each DMA with a PRV to sustain the pressure at minimum value for better leakage management. but when i used the PRV's it affected the fire flow analysis

do i follow the right methodology for such case?

note: according to the client requirements, we are assuming fire flow at each junction of the network

Regards 

  • If you can't meet the needed fire flow, then you need to understand why. If it is due to excessive head loss, then you may need to upsize pipes. If it is due to excessive head loss in a control valve, then the valve may need to be upsize or its setting changed.

    I'm not sure what you mean by "run the fire flow analysis in different scenario than the max hourly scenario". In the US, fire flow is usually added to the max day demand. You would use the demands from the max day alternative as the starting point for the fire flow analysis.

    Answer Verified By: ahmed hassan 

  • it affect the fire flow analysis report because the needed fire flow at each node can not be delivered.
    do should i run the fire flow analysis in different scenario than the max hourly scenario?
  • What exactly do you mean by " it affected the fire flow analysis"? If the fire flows decrease because of the PRV, that is expected.

    If fire flow doesn't run, then you need to describe the error messages you received.
  • Hello Ahmed,

    If I understand the issue correctly, you should make sure that the different elements in the model are assigned to the proper pressure zones. When doing the automated fire flow analysis, the program is look at the residual pressure at the fire flow node itself as well as the pressures for the junctions in the same pressure zone as the fire flow node. If you only have one pressure zone, that means that a low pressure at a distance node in a different pressure zone will impact the results.

    In steady, you should make sure you have the junctions assigned to their appropriate pressure zones, in this case likely assigned by their position in relative to the PRVs. This might help with some of the results you are seeing.

    You can find more information on setting up and using the automated fire flow feature at the following TechNote: communities.bentley.com/.../understanding-automated-fire-flow-results

    Regards,
    Scott