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Can you run a VSP with a Control node and Logical Controls at the same time?Problem ID#: 79738
VSP Interactions with Simple and Logical ControlsThe VSP model and APEX have been designed to fully integrate with the simple and rule based control framework within Bentley WaterGEMS V8i .You must keep in mind that the definition of controls requires that the state (On, Off, Fixed Speed Override) and speed setting of a VSP beproperly managed during the simulation. Therefore, the interactions between VSPs and controls can be rather complex. We have tried to everyextent possible to simplify these interactions while maintaining the power and flexibility to model real world behaviors. The paragraphs thatfollow describe guidelines for defining simple and logical controls with VSPs.Pattern Based VSPsThe pattern of relative speed factors specified for a VSP takes precedence over all simple and logical control commands. Therefore, theuse of controls with pattern based VSPs is not recommended. Rather, the pattern of relative speed factors should be defined such that controlobjectives are implicitly met.
VSPs with APEXA VSP can be switched into any one of three different states. When the VSP is On, the APEX will estimate the relative speed sufficient tomaintain a constant pressure head at the control node. When the VSP is Off, the relative speed factor and flow through the pump are set tozero, and the pressure head at the control node is a function of the prevailing network boundary and demand conditions. When the controlstate of a VSP is Fixed Speed Override, the pump will operate at the maximum speed setting and the target head will no longer be maintained.The Temporarily Closed state for a VSP indicates that the check valve (CV) within the pump has closed in response to prevailing hydraulicconditions, and that the target head cannot be maintained. The VSP control node can be specified at any junction node or tank in a networkmodel. As described below, however, the behavior of simple and logical controls depends on the type of control node selected.Junction NodesWhen the VSP control node type selected is a junction node, the VSP will behave according to some automatic behaviors in addition to the controlsdefined for the pump. If the head at the control node is above the target head, the pump state will automatically switch to Off. If thehead at the control node is less then the target head, the pump state will automatically switch to On. The VSP will automatically switch intoand out of the Fixed Speed Override and Temporarily Closed states in order to maintain the fixed head at the control node and prevent reverseflow through the pump. Additional controls can be added to model more complex use cases.
When the VSP control node is a tank, you must manage the state of the pump through control definitions, allowing for flexible modeling ofthe complex control behaviors that may be desired for tanks. If a VSP has a state of On, the pump will maintain the current level of the tank.For example, at the beginning of a simulation, if a VSP has status of on it will maintain the initial level of the tank. As the simulationprogresses and the pump happens to turn off, temporarily close, or go into fixed speed override, the level in the tank will be determined inresponse to the hydraulic conditions prevailing in the network. When the VSP turns on again, it will maintain the current level of the tank, notthe initial level. Thus control statements must be written that dictate what state the pump should switch to depending on the level in the tank.A pump station with a VSP and a fixed-speed pump operating in a coordinated fashion can be used to model tank drain and fill operations.