Optimizing the behavior of a total system can be done by engineering by rules of thumb and then do tuning and tweeking. This can be a very time comsuming, expensive process, where the actual optimimum might never be achieved. Damage to the system could also occur, due to wrong settings of PI-regulators, etc. For more complex systems it is therefor safer to model the behavior of each individual component and then tie them up to a whole system in one dynamic, mathematical model. With the model infinite runs can be made to check behavior, proper setting for PI-regulators and proper sizing of components.The build up and proper tuning of the real system can be done much quicker, since good start values for PI-regulators are already known. Tuning taks less time.