Energy consumption, energy efficiency and the concept of sustainability are terms that have undoubtedly made their way into the twenty-first century. Therefore, this thesis focuses on energy consumption and energy efficiency in data centers since it is safe to assume that energy consumption in this particular context will increase as well in the near future. The first chapters cover fundamental European and global climate and energy issues. Subsequently, an overview of guidelines and standards for energy efficiency of buildings is provided, as well as an explanation for energy consumption and energy efficiency in data centers. Furthermore thermal guidelines for data processing environments and different cooling technologies for data centers are described. Based on those given general conditions and requirements an energy efficiency model was developed. Subsequently, the calculated data were evaluated and finally used for creating the building- and plant-simulation. In the final section of the thesis, different simulation models were created using the building energy simulation software "DesignBuilder" and "EnergyPlus". The models were created taking relevant and realistic planning parameters and data center characteristics into account. The simulation models considered different cooling technologies at various locations. The consumption of electricity, the electricity costs, the investments costs and the maintenance costs were compared and analysed. Furthermore a profitability analysis was conducted based on the obtained data. Using a reference model additional ways to reduce the consumption of electricity have been determined. The results show that system selection can significantly influence electricity consumption. The worst-case scenario leads to a deviation of approximately 8,0 %. Using a water-side economizer can lead to savings between 3,0 and 6,6 % in total electricity consumption depending on the location and the plant concept. By means of building- and plant-simulation, a range of key issues for data center construction and operation could be identified. Results also suggest that further issues and additional ways of energy saving could potentially be identified by using the applied evaluation methodologies.