The most important issue facing our planet is climate change which has serious impacts on the environment, flora and fauna and humans. Human’sactivities and modern lifestyle have contributed to the increase of CO2 emissions and enhance of greenhouse effect.

Buildings are the largest consumer of energy in Europe and have the greater responsibility of climate change mitigation. In recent years several attempts took place to improve building’s sector by designing energy efficient buildings. In Greece, the Building Energy Efficiency Regulations, approved and adopted on 30^th March 2010, to improve buildings’ energy efficiency, to save energy and to protect the environment through an integrated building design.

The building design should not only contribute for energy saving but also to provide comfort conditions for the occupants. By ensuring occupant's comfort conditions, we improve their physical condition and we increase their efficiency and productivity.

Occupant is a very important part in the operation of the building and can greatly reduce the building’s energy consumption. This study aims to examine the range of influence of user behaviour in energy consumption. The impact of user behaviour was examined through the manipulation of shading and lighting system. For different use scenarios of shading and lighting system, we examined the energy consumption for heating / cooling and lighting of a typical office in Athens. The results drawn from building’s simulation software presented in this study.