Hi,
I am running an EPS and I have set up a diurnal pattern for the demands. However, when I look at the demands through time, they do not match the base demand times the multiplier.
In some cases the demands are actually lower than the base demand despite a multiplier greater than 1. What is going on?
I tried using this logic: From
"For example, assume the base demand on a given junction is 500gpm, the equivalent hydraulic time step in the calculation options is set to 1 hour, the pattern multiplier for time step 8 is 1.0 and for time step 9 is 1.945, and the Start Time field would be 8 am (assuming the simulation was started at 12 am). The total calculated demand at the junction shown for time step 8 will be (500 * 1) + (500 * 1.945) / 2 = 736.25."
But that didn't give me the correct demand either:
TImestep 9 hr
[.57gpm(1.9)+.57gpm(1.1)]/2=.855gpm but the model shows 1.01gpm at 9 hours.
Please help me understand.
Thank you,
Nastassja
Hello Nastassja,
I don't see the based demand for J-113 in the screenshot provided. Could send that or a copy of the model to us?
Regards,
Scott
All of the base demands are identical. I will still upload the model.
I do notice that when I change the pattern to stepwise, the demands match the pattern exactly so I must be missing something when it comes to how the model interpolates the demands.
I think the results appear off in the hand calculations because you are using the multiplier at hour 12 in the pattern in the calculation. You would actually use the multiplier at hour 10, which is the next time step that WaterGEMS would consider. You would need to extrapolate the multiplier from the pattern. Based on the pattern, the multiplier at hour 10 would be about 1.6333...
Using this value, the demand at hour 9 would be:
[(0.57 * 1.9) + (0.57 * 1.63)] / 2 = 1.007
This is the same value for the demand as calculated by the program too.
Edit: Related Wiki article: Demand calculation with Continuous vs Stepwise patterns
Answer Verified By: Nastassja Abercrombie
Oh I see, so not the next time step that I defined (3 hour intervals), but the next time step for Hammer, 1 hour.