System head curves show the relationship between system head and flow capacity for a booster pump at different time ranges. This relationship represents the variation in total dynamic head against which the pump will be required to operate under various flow conditions throughout the network. While you can select any pump to evaluate, this feature is provided to assist the engineer with determining the expected pump head curve required for delivering flow within the network.
Application Notes: General
The tool adjusts flow through the pump link at the time instant being interrogated. The tool will apply system conditions at that instant and solve the model at varying flow rates to determine the Total Dynamic Head (TDH) required for a pump to deliver that flow rate under the system conditions (that is, the system curve). Think of the tool as simulating the Standard simulation but also ignoring the subject pump data and trying different flow rates for the pump element to determine the TDH required across the pump to deliver that flow rate.
The pump curve that is shown in the resulting graph is from the currently specified hydraulic information for that pump element but is not used in any direct way to calculate the System Curve.
You don't need to complete a Standard simulation prior to running the System Curve, although if the simulation were to fail when running a Standard simulation due to network problems or a lack of data, then it will likely not run when trying the System Curve simulation either.
Application Notes: The network needs somewhere for flow to go
Because the balancing flow must go somewhere, the network requires a downstream tank or emitter to absorb excess flow or supply a shortfall. Without one, the flow has nowhere to come from or go to, and the system curve cannot be solved. Ensure some slack exists in the water flow through the pump before running this analysis.
Application Notes: Steady State Simulation
If the active scenario is set up to run as steady state, then the System Curve simulation will be simulated at steady state, and Steady State (that is, the system curve the initial conditions) will be the only time step you will be able to select.
System conditions during steady state analysis (that is, the system curve all initial tank levels and element status settings, etc.) will be used to develop the system curve. You can adjust these initial conditions and settings in your model to reflect the extremes of performance that the system will experience. This can help you produce an upper and lower limit system curve to aid you in your final pump design.
You can export the data points from these curves to other applications for pump designers and suppliers.
Application Notes: EPS Simulation
If the active scenario is set up to run as an EPS simulation, then the System Curve simulation will be simulated as a normal EPS simulation except that it will pause at the time instants that you specify (up to three) and complete the System Curve simulation as described above.
Note that the pump hydraulic data specified for the subject pump element will be used during all EPS simulation time steps to create system conditions at the time step you specify for system-curve generation. This means that you must use this method with caution at all time steps following the initial time step, since the pump hydraulic information that you have specified for the subject pump in the active scenario may not be very close to your final pump design. Therefore, it may not produce appropriate system conditions at the time step at which you desire to generate a system curve. For this reason, you may want to use the steady state application of this tool while in the pump design process, and then use the EPS application of this tool to test how different pump selections perform in your model.
To develop a system curve for a specific pump, from the InfoWater Pro > Analysis menu, select Run Manager to see the dialog box below. Select the System Curve tab, specify the desired parameters, and choose the Run button.
Target Pump ID
Choose the pump for which you want to evaluate the System Curve by either entering the Target Pump ID or by clicking on the
Browse
button to graphically select the target.
Curve Type
Enter the curve type, Exponential for a system curve generated by single simulation and a curve-fitting function or Multi-Point for a system curve generated by multiple discrete simulations. Multi-Point takes longer to simulate but will give more accurate results over the entire system curve.
Report Data Points
Enter the number of data points or the number of flow increments at which the system curve will be generated and data will be reported.
System Curve Time
For EPS simulations, you can pick up to three simulation time periods (using the Time … buttons) at which system curves will be generated.
We recommend selecting three times that represent times of low demand, average demand, and peak demand in order to evaluate a wide range of operating conditions. All curves will be displayed on the same graph upon successful completion of the simulation.
Interpreting results
A common use of the system curve is to determine "what size pump is needed if demand increases by X?" Interpret these results carefully. The extra flow used to build the curve usually travels to a tank, and that path can differ greatly from the path to the actual new demand location. Because head loss depends on the water's path, a curve built on flow to a tank can misrepresent the head the pump needs to serve higher demand at a specific location. When the demand location matters, add the demand explicitly at that location and evaluate it instead of relying solely on the system curve.