VSP Controlled by Discharge Side Tank

The improvement allows users to choose a tank at the downstream side of a pump as the control target. Once a user selects a tank as the control node for a VSP, the control target head is set to the initial tank head by default. The VSP algorithm will calculate the required relative pump speed to maintain the tank level. If the tank level drops below the target level, the VSP will be forced to increase the speed, up to the maximum allowable speed as specified, to meet the target tank level. If the tank level is greater than the target level, the VSP speed will be reduced or shut off to permit the tank supply system demand and thus the tank level can be gradually lowered to the target level.

To set up a discharge side tank as the VSP control node:

Click on a VSP or VPSB.
In the Properties editor, set the attribute Is Variable Speed pump? to True.
Set VSP Type as Fixed Head.
Choose a desired discharge side tank as Control Node.
Specify the maximum relative speed factor and set Is Suction Side Variable Speed Pump to False.

Note: When the target level is missed due to either too high demand or too much inflow into the wet well, the VSP will be operating at the fixed speed until the target level can be reestablished, however, the reestablished target level may not be exactly the same as the initial target head. This is because the VSP is forced back by using the given time step, the pump is operated as a fixed speed pump to move the amount of water within one time step, so that the level cannot be exact unless the time step is small enough to ensure the exact amount of water is moved out the tank to maintain the exact target. The smaller the time step, the closer it will be to returning to the target.