Variable Speed Pump (VSP) FAQ's


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

Variable Speed Pump (VSP) FAQ's

After computing a model with variable speed pump batteries, the following user notifications were generated:

"Variable Speed Pump Battery speed unable to be computed; the calculation may be unbalanced. Please review the VSP definition to ensure settings are physically reasonable"

and/or

"Variable Speed Pump Battery has inconsistent results. Calculation may be unbalanced. Please ensure pump batteries are not in parallel."

First, make certain that the VSPB's are not in parallel. If you need them to be in parallel, you should either have combine the VSPB's into one element, or model the pumps individually.

However, if the VSPB's are not in parallel, the issue may be related to other initial settings in the system. Check the initial elevations in any tanks upstream of the VSPB's. If they are initially empty, this may be the cause of the issue. When the tank is empty, the model attempts to close the pipe downstream of the tank. This is normal function in a WaterGEMS or WaterCAD model. This closed pipe could throwing off the network equations, not allowing them to come into balance.

To resolve this, add some insignificant level to the tank. For instance, the minimum and initial levels are 1000.00 feet, change the initial level to 1000.01 feet.

 

What does the user notification, "Variable speed pumping is not suported by Epanet.  Results may not match EPANET.", mean?

Note that this message is only informational. The VSP pump is still analyzed normally for that Engine Compatibility setting, but the message is generated to advise that since EPANET does not support VSPs the results could be different to that which would be simulated in EPANET.

Messages such as this are generated any time you:

  1. Run with an EPANET compatible engine setting, and
  2. The model contains some features or data that is not possible to run in EPANET, and
  3. The model considers (actually runs using) the feature that is noted in the message in the analysis of the results.

 

What does the following user notification mean?

"There is no convergence for the solution of a variable speed pump."

This message is related to the general instability in the model. This message is dependent on the system.

Things to check include pump settings and demands in the system. If the reservoir in is cut off from the demand nodes and there is no other boundary element (tank or reservoir) in the model to supply flow to the pumps. If the pumps are trying to satisfy a small system demand they may not be operating at the optimal operation point on the pump curve.