Product(s):	WaterGEMS, WaterCAD, HAMMER
Version(s):	08.11.XX.XX and higher

Problem

What are the benefits of using the variable speed pump battery (VSPB) element and how do they work?

Background

This article applies to VSPB Type "Target Head". The VSPB Type "Fixed Flow" will behave differently as explained in the following article.

Why is the "lag pump count" field not available when selecting Fixed Flow as the "VSPB Type"?

Solution

Saves time

The VSPB element gives you the ability to model multiple pumps that would otherwise be modeled as parallel variable speed pumps (that use the same pump definition and target nodes) in one element. It saves you time to use this element vs. laying out and inputting pump information for multiple pumps. In the graphic below you can see the difference in setup that makes using the VSPB's easier and quicker for the modeler.

Function

The VSPB allows you to enter one pump definition that applies to all the pumps that are defined in the properties. There is one lead pump and you input the number of lag pumps in the properties that turn on automatically when the lead pump is not able to meet the target head while maintaining a relative speed factor that is below the maximum defined in the properties (default is 1.00 or 100% of the max operating speed). When a lag pump is triggered both it and the lead will run at the same relative speed factor. This process will occur every time a lead and/or lag pump cannot meet the desired head or flow while maintaining a relative speed factor below the maximum.

Note :

Parallel variable speed pump batteries cannot be modeled in WaterGEMS, you can have multiple VSPB's in the model at different locations for different pump stations (for different DMA's), however you cannot model them in parallel. Though you can model variable speed pumps i.e. VSP's in parallel.

When you are using tank as a control node for a VSPB, target head type option will be hidden in that case, since VSPB will attempt to maintain the initial tank level (basically tries to match tank inflow with outflow).

HAMMER Transient Analysis Considerations

It is not generally advisable to use the VSPB element for a transient simulation in HAMMER, as the behavior of wave reflection and interaction can be sensitive to the model network connectivity. Other notable factors include pump impeller configuration and pump inertia. Using individual parallel pumps will provide the most accurate transient results, since the individual parallel piping will be included along with the individual pump inertia, rotational speed and inertia (via the Transient tab of the pump definition)