Variable Speed Pumps
Variable speed pumps are only intended for use with Real Time Control (RTC).
When defining the pump characteristics, the Switch On Level and Switch Off level define when the pump switches on and off. The Discharge defines the initial discharge of the pump immediately after it switches on. Once the pump is running, its discharge it controlled by the real time control scenario.
You can set these values on the Pump Grid Window of the Links Grid or the Pump Definition Page of the Pump Property Sheet.
For all pump types, including a Variable Speed Pump, the Delay represents the time it takes the pump to reach its full capacity after switch on. The run up to full capacity is linear. So for example a fixed discharge pump with a capacity of 0.1 m3/s and a delay of 120 seconds will be pumping at a rate of 0.05 m3/s after 60 seconds. However during simulation, the time that the pump has been on is only updated every run timestep. This means that if the run timestep is 60 seconds then the discharge is set to 0.05 m3/s for all minor timesteps up to 60 seconds and 0.1 m3/s thereafter.
Three elements are required to control a variable speed pump using real time control.
- A range, to define when the pump should increase or decrease in speed.
- A controller, to define how often the range should be measured.
- A rule, to define the speed or the rate of change of speed of the pump.
The speed or rate of change of speed of the pump, defined in the RTC, always takes priority over that defined as part of the pump definition when defining the network. The Positive Change in Flow and Negative Change in Flow fields defined on the Pump Grid Window of the Links Grid or in the Pump Property Sheet are only used if those in the RTC are left blank.
RTC Rules
In RTC, only one rule can be active at any one time.
Therefore within the RTC generator it is not possible to specify a rule to switch the pump on and a rule to increase or decrease its speed. Therefore the switch on and off of the pump is usually controlled by the pump definition in the network.
When using variable speed pumps, the Override other control check-box on the RTC Window Editor - Regulator Pane should not be ticked, otherwise there will be nothing to switch the pump on.
