How are units handled when exporting a WaterGEMS/WaterCAD model to an EPANET model (.inp)?

Product(s): WaterGEMS, WaterCAD
Version(s): 08.11.XX.XX and 10.00.00.XX
Area: Interchange

Problem

When exporting a Bentley water model to an EPANET model, how are the units in the EPANET model determined?

When exporting a Bentley water model to an EPANET model, why are the demands changing?

Note:

  • A "Bentley water model" refers to a model created in WaterGEMS, WaterCAD or HAMMER (.wtg).
  • An "EPANET model" refers to a model that can be opened in EPANET (.inp)

Background

EPANET supports two unit systems.

Bentley water models support the notion of different unit systems, allowing new models to be created in a consistent set of either SI or US Customary units. However, a particular set of units is not required, nor is it required for models continue to use any particular unit for any particular field. A mix of SI and US customary units can be used if you see fit.

Solution

When exporting a Bentley water model to an EPANET model, how are the units in the EPANET model determined?

If the Bentley water model's coordinate field (ie. the unit of distance that is used to represent the model map) is set to SI units, then the exported EPANET model will have SI units (flow will be LPS).

Likewise, if the Bentley water model's coordinate field is set to US Customary units, then the exported EPANET model will have US Customary units (flow will be GPM).

Why are the demands changing after export to EPANET?

In CONNECT Edition versions (10.00.00.XX):

If the Bentley water model has an active demand adjustment set in the calculation options then the individual demands will be adjusted by this factor when exported.

For Example:

  • Demand at a junction in Bentley water model: 0.08 L/s

  • Demand adjustment in Bentley water model: 1.8

  • Demand at the junction in the EPANET model: 0.144 L/s (0.08 L/s * 1.8)

Note: This adjustment can be prevented by removing the demand adjustment before exporting.

In SELECTseries 6 versions (08.11.06.XX) and earlier:

EPANET supports one and only one single global demand multiplier. That is, if there was one demand multiplier in the Bentley water model that was a multiply or divide operation that applied to every demand node (scope: entire network), then that multiplier is used in the exported EPANET model.

The demand adjustment in the Bentley water model is applied by modifying the individual demands in the EPANET model when one of the following is true:

  • There is more than one demand adjustment in the Bentley water model.
  • The demand adjustment in the Bentley water model is not multiply or divide.

The Bentley water model's demand adjustment scope is not system wide.

See Also

When I import my EPANET file (.INP) into WaterGEMs/WaterCAD, the units are not coming in with the optimal units. How do I fix this?

What are the limitations of importing/exporting EPANET files?

Should the EPANET solver and the WaterGEMS/CAD solver give the same results for a model?

What are the difference between WaterGEMS/CAD and EPANET?

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