Global growth in energy use and carbon dioxide emissions have caused serious economic and environmental impact, such as climate change and global warming. The building sector is responsible for 37% of the total carbon dioxide production and 22% of the total energy consumption in Europe. It is therefore imperative to study and optimize the buildings in this direction.

The aim of this paper is to study the energy behavior of buildings and to reduce their energy consumption. For that reason, a methodology was developed that optimizes the building form, in order to minimize the total energy consumption in the four climate zones of Greece.The main factor studied is the shape of the building, which is defined by the shape index, that is the ratio of the sides of the building, the compactness index, that is the volume-to-area ratio and the height of the building. The methodology consists of four steps, modeling the building, simulating its energy behavior, optimizing the process using genetic algorithms, and finally comparing the results.The aforementioned steps are performed in Rhinoceros, an architectural modeling program, along with its graphical algorithm editor Grasshopper and its plug-ins, Ladybug and Honeybee. For the simulation, the Energyplus simulation engine is used and as for the optimization process, the Galapagos solver.

The methodology was applied to three different sizes of residential buildings with 200m², 400m² and 800m² plan, in four Greek cities, Heraklion, Athens, Thessaloniki, Kastoria, that represent the four climate zones. The results of the application revealed that the form significantly affects total energy consumption, especially the energy required for heating. As the need for heating increases, buildings grow large in height and acquire more compact forms.