About assigning demand to nodes
Demand can be assigned only to basic nodes, hydrant nodes and reservoirs.
Node demand can be edited in the following places:
- Node Demand page on the Node property sheet
- Customer Points page on the Node property sheet
- Land Use page on the Node property sheet
- Customer Points grid
- Land Use grid view in the Polygons grid
- Demand at Nodes grid view
- Demand Adjustment view
Node demand parameters for individual nodes can be viewed and edited on the Node Demand page.
The Demand at Nodes grid view brings together all the information from the Node Demand page, providing a central location for viewing and editing node demand.
The Demand Adjustment view displays a summary of demand in the water supply model and allows wide scale adjustment of demand for individual demand categories or for the whole model.
Demand can be assigned:
- Manually by entering data in the Node Demand page of the Node property sheet
- Manually by entering data in the Land Use page of the Node property sheet
- By allocation from Customer Points data, which can be imported from GIS or CSV files and allocated using the Static Demand Allocation wizard
- By allocation from land use data
Demand at the node can be specified in three ways:
|
Demand per Property |
Fill in the Specific Consumption and Number of Properties fields for the demand category. The Specific Consumption is the consumption defined as volume per property per day. This is multiplied by the Number of Properties to give total consumption per day
|
|
|
Average Demand |
Fill in the Average Demand box for the demand category. The Average Demand gives a value for the average across all properties in this demand category supplied over a time period, for example litres / second
If Land Use demand is assigned to the node, the Average Demand value will automatically be calculated from allocated Land Use data (displayed on the Land Use page of the property sheet). |
|
|
Direct Demand |
Fill in the Direct Demand Factor box for the demand category. The Direct Demand Factor is a multiplier that can be used to adjust the values in the demand category. This demand type can be used when importing or entering data manually from recorded data. This value will normally be set to 1.0 unless the recorded data is to be adjusted. 
Note
A direct demand factor should only be used with demand categories created as Direct demand. If a direct demand factor is applied to a Factored demand category, it will be ignored. See the demand diagram editor topic for more details.
|
The Demand Category is a 24 hour profile of demand for a particular type of consumer. The demand category is defined by the user in the Demand Diagram editor. The monthly and daily coefficients are also defined using the Demand Diagram editor.
If the Category Type field is blank and the Number of Properties field is blank or zero, the value set for either Direct Demand or Average Demand will be used. If the Category Type field is blank and the Number of Properties is non-zero, the Demand per Property value will be used.
Demand data for as many demand categories as required may be assigned to one node. The same demand category can be added to the list more than once to identify distinct consumers of the same type.
There are two special demand category names:
- If the demand category field is left blank or CONST is entered, a constant demand profile is assumed.
- If CONST_LEAKAGE is entered in this field, a constant leakage profile is assumed.
Scaling demand by area
Demand can also be scaled by area. Individual nodes can be assigned to a particular area and scaling factors set up for each area within the model.
Scaling by area is carried out in the Demand Scaling editor.
Leakage
Leakage values can be set up for individual nodes in the Leakage Loss field on the Node Demand page. This leakage runs at a constant rate during the simulation.
Alternatively, a demand category can be defined in the Demand Diagram editor to represent leakage, with fluctuations to represent changes in leakage loss with changes in pressure through the day. To create a leakage category, select the Leakage box when creating the category in the Demand Diagram editor. Then add an average demand for the category to the node.
Pressure related demand
InfoWorks WS Pro normally calculates demand without reference to the actual pressure at a node. Select the Pressure Related Demandbox on the Schedule Hydraulic Run view to activate the pressure related demand option when running a simulation.
The value of demand corresponds to standard service pressure - average pressure in normal circumstances. You can use the Nominal Pressure field on the Node Demand page to state the likely value of service pressure for each node.
Using the pressure related demand option, if the pressure available at each node differs from its set value during the simulation, all demands will be changed accordingly (the lower the pressure, the lower the consumption or loss on the node).
You are advised to experiment carefully with the pressure related demand option as it is dependent on accurate ground levels and working pressures. The feature has been included since it is obviously important in practice. Bear in mind that with the pressure related demand option activated, total demand cannot be predicted accurately.
