Validation

There are two options to calculate the power plant model with Ebsilon: simulation and validation. In simulation mode, such an amount of values is specified that the number of variables matches the number of equations and thus (usually) there is a precise solution. Often there are significantly more measured values in actual plants, so that we receive an over determined equation system. It is known that here the measured values are not precise but subject to some uncertainties. In validation mode, statistical methods are used to search for a solution to the over determined equation system where the component equations (“constraints“) are adhered to and “as few as possible“ adjustments (“corrections“) of the measured values have to be carried out. Here “as few as possible“  is to be understood in the sense of minimizing the error sum of squares.

This evaluation, however, depends on the underlying component equations. Thus when limiting to mass and energy balances in the case of heat exchangers solutions may emerge that violate the second law of thermodynamics.

In the context of the certification procedures according to VDI 2048 it was necessary to prove a numerical correlation of the results with the examples in the guideline. This correlation, however, is only possible if the same equations are used. To be able to use the same equations, the option to specify equations manually has been created in Ebsilon. For this, there is a choice box “Input of equations“ under Tools->Model settings->Validation. When you select “Manual input (for validation)” or “Manual input (for raw data analysis)” there, you can enter the desired equations under Calculate->Manual specification of equation.

In this case, the manually entered equations are used for the calculation instead of the component equations usually generated by Ebsilon.

In general, however, in the case of the validation Ebsilon uses the same physical equations for the components as in the simulation, and only additional equations for the redundant measured values are added.

Details are described in the chapter on validation.