Flowsheet equations

About flowsheet equations

Flowsheet equations are equations that you add to your simulation to account for an additional specification or requirement that you want to impose on the simulation.

For example, if you want to define a 5°F approach temperature on one side of a heat exchanger, you can add the following equation to the Canvas:

HX1.Tto - HX2.Tsi = 5/1.8

You must specify the flowsheet equations in internal units of measure (UOMs).

Concepts

• You use flowsheet equations to calculate additional specifications or requirements for your simulation.

• When you create a flowsheet equation, it automatically appears on the Canvas in its own movable box. You can rename the flowsheet equation and define its formula within this box.

• You can use the same functions that Model Writers use in the model equations to define your flowsheet equations. See Equation Functions for more information.

• You must specify any constant coefficients in the flowsheet equations in internal UOMs.

• When you first add a flowsheet equation to the simulation, the simulation is improperly specified (unsquare).

• For each flowsheet equation that you add to your simulation, you must change one variable in the simulation from specified to calculated. This change ensures that your simulation remains properly specified (square).

• If a flowsheet equation calculates the value of a flowsheet variable, you can set the specification status of the flowsheet variable to calculated to make the simulation square.

• You can include or exclude a flowsheet equation based on the simulation mode.

• By default, AVEVA Process Simulation automatically includes a flowsheet equation in only the simulation mode in which you create it.

• If you delete a flowsheet equation from the Canvas, the flowsheet equation is removed from the simulation.

Actions

• Create a flowsheet equation by using the Tools Library or the Simulation Manager.

• Define the mathematical formula for the flowsheet equation either on the Canvas or in the Simulation Manager.

• Rename a flowsheet equation from the Canvas or from the Simulation Manager.

• Copy flowsheet equations between simulations.