User notification: "Pump Efficiency must be between X% and Y% inclusive."

Product(s): HAMMER
Version(s): V8i, CONNECT Edition
Area:  Modeling

Problem

When computing the transient simulation or using the Validate command in HAMMER, the following red notification appears, preventing calculation:

"Pump Efficiency must be between 0% and 100% inclusive."

However, the pump efficiency is between 0% and 100%.

or:

"Combined pump and motor efficiency should be between 30% and 95% inclusive."

Solution

The transient solver in HAMMER assumes that a pump is operating at or near the best efficiency point. Otherwise, transient results can be skewed because of the way that the initial head and flow are used to construct a four-quadrant representation of the pump. 

The efficiency of a pump is different depending on the operating point. Go to Components > Pump Definitions, click your pump definition and look at the plotted efficiency for each operating point. In the properties of the pump element in question, look at the pump head and flow and compare that operating point with the pump curve to see what the efficiency is. You can also right click on the pump, choose the Pump Curve option and check the box for "efficiency".

Here are some possible causes and solutions:

  1. Incorrectly configured pump startup: If the pump in question is off in the initial conditions and you want to have it start up, make sure you choose "Pump Startup" as the Transient Pump Type, then enter the Nominal Head and Nominal Flow corresponding to a good efficiency from the pump definition.

  2. Unbalanced initial conditions: if you see red colored timesteps in the initial conditions calculation summary and a "network unbalanced" user notification, this means that the initial conditions could not converge on a stable solution and the results are not valid. This could potentially cause invalid results for the pump such as a negative flow that translates to a negative efficiency. Use the advice in this article to troubleshoot and resolve the unbalanced network before attempting to compute the transient simulation.

  3. Zero initial flow: This issue can also occur if the pump is set to be initially on but is unable to turn on for some reason (such as the downstream head being higher than the pump can overcome due to other larger pumps in the pump station already being on). This may cause incorrect efficiency values to be derived based on these erroneous results. 

  4. "Specify initial conditions" calculation option: another possible cause is related to a setting in the transient calculation options. If the field "Specify Initial Conditions" is set to "True", you will need to make sure that nominal head and flow values are entered for any pump in the model. If not, the incorrect head and flow values will be passed to the transient solver and invalid efficiency values as well. In such a case, the simplest solution for such cases is to set "Specify Initial Conditions" to "False". Then you can compute initial conditions and get valid flow and head results. If you need to specify initial conditions, make sure that valid values for nominal head and nominal flow are entered for all pumps in the model.

See Also

WaterGEMS/WaterCAD user notification: "Network Unbalanced"

What is the best way of modeling the best efficiency point (BEP) when modeling a pump in HAMMER?

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