Since HAMMER CONNECT, it is possible to model the behavior of variable speed pumps (VSP), whether they are controlled by variable frequency drives, hydraulic couplings or some other variable speed drive. Workarounds that were previously used, such as pumping through a pressure-reducing valve, are no longer needed.

The parameter that is used to adjust pump speeds is the relative speed. The relative speed is the ratio of the pump’s actual speed to some reference speed. The reference speed generally used is the full speed of the motor. For example, if the pump speed is 1558 rpm while the motor is a 1750-rpm motor, the relative speed is 0.89. This relative speed is used with the pump affinity laws to adjust the pump head characteristic curve to model the pump.

If only a steady state run is being made and the pump relative speed is known, the speed of the variable speed pump can be set in the General tab of the pump dialog box. However, if the conditions that control the pump are not known at the start or an EPS run is being made, then variable speed behavior must be described in more detail.