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The present dissertation deals with the energy performance of hotels and contains a bibliographic and experimental part. Hotels, being one of the most energy consuming parts of a country’s building stock, are one of the most difficult and interesting examples of an energy performance analysis for buildings. What is more, their design is not focused mainly on energy conservation or maximization of a worker’s performance like most similarly huge buildings of the commercial sector. Their focus is depicted on energy use minimization, in parallel with strong reduction of environmental impact. This is reflected on most technical guides, such as ASHRAE and the Greek Regulation for Energy Performance of Buildings. However, the main purpose of the dissertation is not to study a theoretical scenario of a new hotel being built, which would allow the author a great deal of freedom in making assumptions, such as an unlimited theoretical budget, or choosing the most beneficial courses of actions regardless of cost or feasibility, such as choosing the optimal location or having enough available space to install any type of equipment. The main purpose is to evaluate a real life example with all the hindrances and restrictions one would expect from such a case and assess if this hotel building can be transformed into net zero. The hotel which is evaluated is Royal Olympic Hotel, located in the urban environment of Athens. This direction is also reflected on the bibliographical part which is also focused on studies performed on various hotel facilities around the world. The bibliographical part deals with cases of analysis of energy audit in hotels, the assessment of affordable and “cheap” improvements (a methodology which is preferred by the majority of the board of directors and the management in most hotels) and contains case studies of real life hotels which compare different models, methodologies and technologies. The implementation of smart energy management techniques and practices is investigated, as well as case studies of existing net zero energy buildings. The experimental part is focused on the information collected during the audit that was used to perform an energy simulation of the premises through the Energy Plus Simulation Tool, after the initial design of the building in Google Sketchup and Open Studio environment. The financial feasibility of installing Renewable energy Sources Systems is also examined. Using Energy Plus, it was estimated that approximately 130.000 kWh could be produced on an annual basis. The cost was estimated by using retail prices and adding other factors (installation cost and maintenance) the total cost was estimated at 102.000 euros. Of course, this production of renewable energy would not be able to cover the extravagant loads of a medical facility. And since this is a real life study, the financial risk was calculated. Considering a discount rate of 10% and a payback period of 20 years the Net present Value of the cash flows generated by mounted PV array was calculated. Since the result NPV is positive, the installation of photovoltaic is indeed a viable investment. With the help of drawing tools (AutoCAD 2016 for reading and extracting geometrical data from the architectural plans, Google Sketch Up along with the Energy Plus Plug in order to create an input data file for the Energy Plus) as well as finding climatic data for the city of Thessaloniki (in .epw format), the simulation was performed. The results were generally positive since the final energy consumption (including equipment and HVAC) is 183,15 kWh/m2 . This consumption is lower than the average energy consumption of a Greek hotel which ranges from 200 to 300 kWh/m2 /year and even better than some European Countries as seen in the literature review part. This amount is too huge and can not be reduced to such a degree so that the building can be characterized as a Net-Zero Energy Hotel. Even including RES and an efficient management of the building’s energy schedule through automatization the total amount of energy would, at most, reduced by 15-20 %, by inserting improvements towards cooling loads decrease as internal shading blinds. This result can be explained, since buildings located in an urban environment do not, under most circumstances, have the options of independent power plants or enough available land mass for geothermal purposes. However, this study offers the chance to examine a realistic example and proves the imminent need for proper Energy Classification of all Hotels in Greece, as well the accurate detection of the design flaws in already existing buildings.