Water Tank Max Inflow and Draw & Min Inflow Rates

[ahijazi]

I need to find out the Maximum Fill Rate, the Minimum Fill Rate, and the Maximum Draw Rate (Peak Demand + Fire Flow) on a elevated Water Tank that has numerous supplies, but doesn't have a direct feed pump, but it is fed off the system pressure coming in from higher pressure zones. The tank has a capacity of 2.5 million gallons and a HWL of 400' in elevation. The water main supplying the tank is at an elevation of 316'. The outlet line has a manifold with a check valve that acts as the inlet line into the tank. The outlet line has a altitude valve that controls the tank inflow start and stop. Both the inflow and outflow lines are 12" in diameter. What is the best way to calculate the needed rates considering the worst case scenarios in each case. I am assuming my fire flow demand is 2000 gpm becasue that is the maximum required fire flow in the system and I still don't know my system's peak demand.

Thanks in advance

 

[BigInch]

You need to break the tasks down into fill related and draw related and analyze these things separately.

Each fill scenario flowrate needs to be determined independently against the worst tank condition of Hi Water Level. Then you will know the maximum sustained flowrate that can enter the tank from each source. Then consider which fill systems are working independently and when and if any work together at various times. For a fire supply to the tank, you must determine which is the scenario(s) that yields the smallest flowrate that will be entering the tank at any and all times and the reliability of that supply scenario, combining reliabilities as necessary.

Each emptying scenario is analyzed in the same manner, determining minimum flowrate independently, and usually that will be at the lowest allowed tank level. Then consider if it is possible that fire supplies can come from only one or can be supplied by a number of outlet systems. Then consider the lowest combined reliability of each of those systems in making up that lowest possible flowrate for each of those cases, consumption demand and fire demand that can be reliably supplied.

Highest Demand, either consumption or for fire, is determined by what is required by all the facilities in the service territory. You must do a survey and count the number and types of facilities to know their maximum demand rates and add up all demands that could be under a fire emergency situation at the same time. The largest value is the maximum fire demand. The fire department will usually be able to give you some requirements for, or guidence in how to determine the maximum fire demand flowrate.

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"Pumping accounts for 20% of the world’s energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies)

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