Energy optimisation of a chemical production site is normally based on pinch analysis of the most important plants. Frequent changes of the production status, i.e. start up and shut down of plants and altering their actual production capacity, lead to a more difficult simulation for the total site analysis as in theory. Moreover, in this case the energy system is strongly interlinked with the plants by material streams. Therefore the development of a total site model is essential. The flexibility of the model allows to generate a program which can be applied for analysis and planning purposes as well. This paper describes the total site model and the use of the program tool. It presents how realistic energy saving potentials can be achieved.