Nowadays, various systems are used in buildings to maintain a comfortable living and work environment. These building technologies can increase the building energy consumption significantly and could lead to unnecessary greenhouse gas emissions together with a considerable contribution to the global climate change. However, the construction sector has a great potential to decrease the energy usage and significantly reduce carbon dioxide emission. For this aim, Ukraine, as a member of the European Energy Community, is obliged to bring its legislation in the sphere of energy efficiency, in line with European directives and has to implement building energy consumption optimization measures. This Masters Thesis focuses on the evaluation of thermal comfort and indoor air quality in a typical School (No 317) in Kyiv (Kiev), Ukraine. Thermal comfort is assessed by applying different scientific methods including the PMV/PPD model. Results of a monitoring campaign are presented together with a comparison of the objective and subjective evaluation based on a user survey. In a second part, energy efficiency is evaluated, and different thermal performance improvement measures are analysed via simulation. Finally, the values obtained from the simulation are compared with the values presented in the school Energy Certificate and the real measured energy consumption.