Hi All,
I'm trying to gain an understanding of how fire hydrant flow data obtained from my local utility provider relates to my model. The data I was given for 2 hydrants is: FH#1: Flow = 820.0 gpm, Static Pressure = 78.0 psi, Residual Pressure = 28.0 psi. FH#2: Flow = 890.0 gpm, Static Pressure = 66.0 psi, Residual Pressure = 34.0 psi. I would like to begin by creating a simple model using 1 reservoir, 1 pipe and 1 junction and calibrate it to one of the sets of flow data. I've created the model with the 3 elements described and I'm now trying to have the results of my fire flow analysis show the same results as the flow data I was given. I adjusted the reservoir elevation and pipe diameter several times but can't seem to zero in on the correct fire flow & residual pressures. Can anyone help explain how I can do this? There is a lot of references to printed information on setting up and fire flow analyses and interpreting the results and on the Darwin Calibrator in the forums but I'm trying to get a very basic view of how the correlation between actual flow data and what the model is doing.
Thank You
First of all, the hydrant test data doesn't make sense. When you conduct a hydrant flow test, you need two hydrants, a flowed hydrant and another hydrant where you measure the static and residual pressure.
As far as Darwin is concerned, you enter the observed static pressure and residual Pressure/flow for the two conditions. Darwin makes adjustments to roughness, demand, closed valves until it minimizes the difference between the observed node pressure and pipe flow.
Darwin assumes you have no connectivity issues in your model and your pump curves, PRV setting and pressure zone boundaries and elevation data are all correct. Before using Darwin, you should sped a few days making sure that your model is correct with regard to these factors. You need to start your calibration with a model that is pretty good.
If you want to test Darwin on a trivial model, you should
1. Build a model with at least two junctions (flowed and residual).
2. Specify the correct C factors on the pipes and demands on the nodes.
3. Use the "correct" model to generate hydrant flow test results, by noting the static pressure at the residual node and the residual pressure when you add a flow to the flowed node.
4. Then make a small change to demand and C, and let Darwin find the correct valves.
Answer Verified By: Walter Medley
Walter, send me you remain address and I'll send you some papers on calibration. tom.Walski@bentley.com
Hello Walter,
Also here are technotes on using Darwin Calibrator and Fire Flow analysis, for your reference, in case you haven't gone through it yet.
Using Darwin Calibrator
How does the Automated Fire Flow analysis work?
Regards,
Sushma Choure
Bentley Technical Suppport