Introduction to Pressure Related Demand in InfoWorks WS Pro

Step-by-step guide

In the InfoWorks WS Pro simulation engine, the flow through pipes is driven by a fixed pre-determined demand. This is because, by default, WS Pro calculates demand without reference to the actual pressure at a demand node. In most cases, you can consider this to be a reasonable assumption, but sometimes this does not reflect reality, as local service pressures have an influence on how customers use water and the losses associated with the network.

EXAMPLE:

If a user consumes a fixed volume of water, such as a load of washing or a dishwasher cycle, then it is easier to reflect that situation in the model.

If the user consumes water based on a task, such as a shower, where the time is more or less fixed, then the pressure in the system would have an influence on the volume removed.

The greater the pressure = the greater the removed volume.

The pressure related demand option is recommended for use in simulations where the hydraulic conditions will make a significant difference to the heads observed in the network, as compared with the calibration model. This is likely to include any kind of incident or design scenario modelling that affects a demand-driven area.

A model calibrated against measured demands indirectly takes into account the effects of pressures in the network. When simulation conditions are similar to calibration conditions, the use of the model without using the Pressure Related Demand option is still valid.

IMPORTANT: Experiment carefully with this option since it is dependent on accurate ground levels and working pressures.

IMPORTANT: With the Pressure Related Demand option activated, total demand depends on the results of the simulation and cannot be predicted accurately.

InfoWorks WS Pro has 8 built-in pressure related demand curves.

To estimate the hydraulic conditions during an incident:

1. From the Model Group, double-click the PRD Network to open the PRD network and control.
2. From the Windows toolbar, click Grid Windows > New Nodes Window.
3. In the Nodes grid view, click the PRD Curve tab to review the PRD curves.
4. To open the properties of one of these curves, right-click it and select Properties.

Optionally:

• You can overlay another curve for comparison.
• You can create custom curves.

5. Close the Grid window.

Before running a pressure related demand simulation, the nominal pressures must be updated. The nominal pressure = the average baseline pressure for the period of a simulation.

To update the nominal pressures from a simulation:

6. Ensure the PRD Network is open in the GeoPlan.
7. Expand the Network menu and select Update nominal pressures.
8. In the Database item selection dialog box, choose the BridgeTown Base > BridgeCon simulation results from which the Nominal Pressure data field is to be populated.

Note: If the simulation icon on the left side of the BridgeTown Base > BridgeCon simulation is grey, then right-click the BridgeTown Base simulation and from the flyout, select Re-run.

9. Commit the changes to the PRD Network.

To begin running a PRD simulation:

10. Double-click the BridgeTown PRD demand diagram.

Set the demand in DMA 0404 to be 100% pressure related:

11. In the Demand Diagram dialog box, expand the Demand Category drop-down and select DOM-0404.
12. Check the Leakage checkbox.
13. Set the Pressure-related (%) to 100.
14. Click Save.

To set up the Pressure Related Demand simulation:

15. From the Model Group, right-click Run Group and select New.
16. In the Schedule Hydraulic Run dialog box, name the run “BridgeTown - Incident with PRD”.
17. Enable Experimental.
18. From the Model Group, drag the PRD Network into the dialog box and drop it into the Network panel; the Control and Demand Diagram group boxes populate as well.
19. In the Demand Diagram box, remove the current demand diagram by clicking the X.
20. Replace it with the BridgeTown PRD demand diagram.
21. In the Scenario tab, deselect the Base scenario.
22. Select the Incident scenario.
23. In the Run Type group box, leave the Run Type as Normal.
24. Enable Pressure Related Demand.
25. The Pressure Related Demand Options dialog box appears. In the Pressure Related Consumption Curves group box, expand the Demand Curve drop-down and select Default Demand.
26. Expand the Leakage Curve drop-down and select Power Law.
27. From the Baseline simulation, drag the PRD Control into the Nominal Pressures from Pressure Profile group box, and drop it into the Sim panel.
28. In the Options group box, deselect Increase Pressure Related Demand on increased pressure.
29. Set the Pressure Related Demand to 100 percent.
30. Click OK.

31. Back in the Schedule Hydraulic Run dialog box, click Save.
32. Click Run.
33. Once the simulation is complete, open the BridgeTown - Incident With PRD simulation on the GeoPlan.
34. Right-click the BridgeTown – Incident Without PRD simulation and select Open As > Alternative Results for Comparison.

35. In the tools toolbar, click the Graph tool.
36. In the Select what to graph for dialog box, click Pressure (m).
37. Click OK.
38. Observe how the results differ when utilizing the PRD functionality.