Understanding Constituent Source Types and Constituent patterns

Applies To
Product(s): WaterGEMS, WaterCAD
Version(s): CONNECT Edition, V8i
Area: Layout and Data Input
Original Author: Scott Kampa, Bentley Technical Support Group

Problem Description

What is the difference between the different Constituent Source Types used in a Constituent analysis?

Steps to Resolve

When using the Constituent analysis, you can set an element to be the source setting "Is Constituent Source?" to True. When you do this, you have additional properties available. This includes Constituent Source Types and a constituent pattern. WaterGEMS and WaterCAD use the following concentration types:

Concentration - this case fixes the concentration of any external inflow entering the network, such as flow from a reservoir or from a negative demand placed at a junction. Basically, whatever comes out of the source will be the value set in the properties.

Flow paced booster - This case corresponds to raising the concentration a set amount even as the flow changes and can be used to model a flow paced chemical feed. It adds a fixed concentration to that resulting from the mixing of all inflow to the node from other points in the network. In this case, there will be some mixing with water coming into the source from other parts of the model. This option can be most useful at a tank (which as mixing) or at a junction where there is flow in and flow out.

Mass boosterThis case is used to represent a feeder, which is manually set to feed a constant mass feed rate. The concentration out of the feeder node is dependent on flow past the feeder node. This option is similar to the flow paced booster, however the key difference is the input. For mass booster, you enter mass rate with units of mass per time, such as mg/s. So the option you would choose (mass booster or flow paced booster) will depend on the type of data you have. 

Setpoint booster - this case represents a feed rate that is controlled to maintain a fixed output concentration from a node and is typical of a feedback control system. It fixes the concentration of any flow leaving the node, as long as the concentration resulting from all inflow to the node is below the setpoint. This is a variation on the "Concentration" method. This type should be used when setting the concentration for a tank. 

Constituent Patterns for time-based variations

A constituent injection can be modeled with a negative demand (inflow), a reservoir, or a tank. If the injection is variable and changes over time, a constituent pattern can be used. For a junction-based constituent injection, “Is constituent source?” should be set to “True,” a base concentration should be entered, and the respective pattern should be selected. For a tank, you would do the same thing, except no negative demand is necessary, and you’ll need to select the appropriate Tank Mixing Model.

Modeling a Chlorine Booster

If you want to model a chlorine booster, the choice of which source type to use depends on how you want to control feed:

  • If you want to continuously feed a known flow and concentration, use Concentration.
  • If you want to feed a constant mass flow rate , use Mass Booster.
  • If you want to modify feed based on flow, use Flow Paced Booster.
  • If you want to maintain a constant outflow concentration, use Setpoint Booster.

Setpoint Booster may be the optimal choice but budget constraints should be considered as it tends to be the most complicated and expensive setup, requiring chlorine sensors and a logic controller. Concentration is usually the simplest and least expensive in terms of equipment but is limited in flexibility.