When I open an .INP file in EPANET the demand on my junctions for a steady state isn't correct


Product(s):Bentley WaterCAD, WaterGEMS
Version(s):V8i
Area:Output and Reporting

Problem

When I open an .INP file, that was created by exporting my WaterCAD file, in EPANET the demand on my junctions for a steady state run isn't correct? Why?

Solution

EPANET and WaterCAD have different handling of patterns for Steady State models because of the way their engines were designed. In WaterCAD, patterns are only applicable in an EPS run, whereas EPANET uses the pattern in an steady state run because their engine is setup a little bit differently than the WaterCAD engine.  For example: Say that you have a junction with ID 432. The actual demand at the node is 657.16 gpm and in WaterCAD you have a pattern applied to this node which would multiply 657.16 * 325 (since the pattern is setup to have a multiplier of 325 at hour 1). You also have a demand adjustment setup in WaterCAD in the calculation options (Analysis > Calculation Options double clik on the calculation option to open it and show the properties) that multiplies all demands in the model by 0.845 in this case. WaterCAD therefore handles the model demands as such: It takes just the demand for the junction of 657.16 gpm and multiplies it by the active demand adjustment of 0.845, which will give you the 555.30 gpm that you see when running the model in WaterCAD. EPANET, however, handles the demands a little bit differently: It takes the demand at the junction of 657.16 gpm and multiplies it by the pattern multiplier of 325, which equals ~213,577 gpm, and then multiplies it by the active demand adjustment of 0.845, which equals ~180,472 gpm. It's done this way in EPANET because it doesn't have an option to set the engine to run a so called "steady state" the way that WaterCAD does. EPANET always runs an EPS run, but if you want to run a "steady state" you set their "Total Duration" = 0 under the Options > Time Area. We actually have a way showing the results you see in EPANET in WaterCAD. What you would do in WaterCAD to see the equivalent results as in EPANET is to go into the calculation options (Analysis > Calculation options) and set the "Is EPS Snapshot?" = to True. Then what you would do is set the "Equivalent Hydraulic Timestep" = to the Hydraulic Time step that is listed in the EPANET "Times Options", which in this case is 1. If you do this then run the WaterCAD model you'll see the same results in WaterCAD that you see in EPANET.

If you want to see the same results in EPANET that you see in WaterCAD with the 555 gpm at the junction then you will need to either

  1. A) remove all the demand patterns associated with the junctions or
  2. B) Create a demand pattern with a multiplier of 1 and assign it to all the junctions.

See Also

What are the limitations of importing/exporting EPANET files?