What is difference between the Unit demand control center and the Demand control center?
The concept and input for Unit demands is different from regular demands, hence they have separate "Control Centers" for manipulating demands in bulk.
In the Demand control center, demands are specified for nodes as a base flow with a pattern as shown below. Also, zones to which elements are assigned are also visible here. For V8i versions it can be accessed through Tools>Demand control center and for connect edition versions, it can be accessed through Components>Demand center>Demand control center.
In this Control Center, the hydraulic pattern can be assigned to the node which can be defined under Components>Patterns>Hydraulic Pattern as shown below. To assign patterns to all junctions globally, right click on the Pattern (Demand) column>Global Edit>select the pattern to be assigned.
In the demand control, we apply the total demand (base flow) that will be consumed at that particular junction, irrespective of land unit, population unit or count. In other words, the user must externally determine what the base flow is and enter it.
So when you know the total demand load to be supplied any particular junction, you should use demand control center, otherwise the unit demand control center can be used for greater control and detail (number of units, label of the unit, population, etc.)
Unit loads (SewerCAD/SewerGEMS) or unit demands (WaterCAD/WaterGEMS) are a type of load that is specified by way of the count of a number of something. In the node properties (or control center), the unit count is entered along with the corresponding unit load type. For example a unit load type might be "apartment" for example. Within the unit load type, you specify the population unit corresponding to the unit count, along with the total flow (demand / load) represented by one of those units. For discharge-based unit loads, you would also enter the equivalent population for each unit.
As an example, you may have a unit load type of "Apartment" with population unit of "resident" and unit load of 70 Gal/day, which means that the number you enter for the unit load count in a node (with this unit load type selected) represents the number of apartment residents represented by that node. So, if you have 50 residents, you would enter 50 for the unit load count and "apartment" as the unit load type. The total load/demand for that node would then be 50 residents times 70 Gal/day = 3500 Gal/day.
You can also import demands using tools called Loadbuilder and Modelbuilder. More information about it can be found in the "See Also" section below.
More information about demand control center and unit demand control center can be found in the help documentation, to be searched by phrases "Unit demand control center" and Demand control center".
How do each of the Loadbuilder methods work?
Troubleshooting and Understanding LoadBuilder
Importing Demand and Loading Patterns using ModelBuilder
Importing Demands From A Spreadsheet