The aim of this study is to model and optimize a district energy system using the city of Geneva as a model. This will be done by using Energy Integration techniques together with efficient actions leading to CO2 emission reductions. This will be done using a number of technologies such as: Wastewater treatment plants, incinerators, gasifiers, solar thermal collectors, solar PV cells, seasonal storage tank. Energy integration techniques will be used to determine way sot reduce losses and increase efficiency system wide, while evolutionary algorithms will be used to find the best combinations of units and processes for an efficient energy system. In order to perform the optimization it will first be necessary to develop an efficient database of Energy Technology models. This will be done using third party and in-house softwares. These databases will then be entered into an optimization algorithm. Once the environomic constraints for the city of Geneva have been defined and implemented, we will be able to perform a case study of the given system. An optimal solution will most probably become apparent; however, a study of the solutions universe will give us a better understanding of the realm of possibilities and will allow us to rigorously justify our solution.