1. A computer-implemented method for modeling and/or improving operational performance of an energy system, said method comprising: providing a graphical user interface configured to allow a user to manipulate equipment icons into an energy system model representation; using modular, function-based equipment models to simulate behavior of a plurality of physical components represented by the manipulated equipment icons to solve an energy system model represented by said manipulation; receiving a signal from at least one sensor coupled to at least one physical component for receiving data from the at least one physical component, wherein the signal contains information about at least one condition of the at least one physical component; using the information received from the at least one sensor to generate a solution to the energy system model; and displaying the solution of the energy system model.