How to take fire flow conditions into account ?

[EngineeringDaN]

For a project in my 3rd year hydraulics course we have to design a water distribution network for a residential area using EPANET and optimizing it using GAWUP (GANEO).

I have the entire network set up with all the peak flow demands set for each of the required nodes. Using GANEO I can easily optimize this system to give me the best combination of pipe diameters to meet the required pressures and flows at each node. However, I am not sure how I would optimize the system for cases of fire flow. Any fire hydrant in the network at any given time must be able to supply 15 litres/sec in case of a fire, and not more than one fire hydrant must be used in any specific area. I cannot just assign a flow of 15 litres/sec to each fire hydrant and then optimize the system in GANEO. While this would assure I would get the required flow at any fire hydrant at any time, the system would be highly over designed because in reality you would never need more than one fire hydrant open in any specific area.

How can I optimize the network so that any specific hydrant in the system has the required demand of 15 l/s without fixing a flow of 15 l/s to every single fire hydrant ?

Note: This is a rather large network with one reservoir supplying about 180 different nodes and about 50 fire hydrants in total. It would be impossible to analyze the system for different demand flow scenarios without a computer.

 

[Travis_King]

The obvious (albeit long) way is to optimize the system under normal conditions, then assign each hydrant, one by one, the 15 l/s flow and check the pressures at your nodes, upsize system as necessary.