The EMS Guide doesn't define the 'Pump Pressure Rise' actuator and its not entirely clear what this is actuator is controlling. Intuitively, I thought this was the pump head but adjusting this value in the EMS program yields results that lead me to believe this is not a correct assumption. Can someone clarify what this actuator is controlling and if there is a hourly variable I can produce to track it?

For further background, I have an EMS program created (via OpenStudio IDF inject) to control a standard series chiller configuration. The measure controls the chillers appropriately, but now I'm working to adjust the pumping to account for the scenario when the loop bypasses the downstream chiller during low-load conditions (lower overall pressure drop). I'm working in OpenStudio v2.6 / EnergyPlus v8.9.