Open Access Journal Journal of Power Technologies 94 (2) (2014) 1–7 Thermal performance of office building envelopes: the role of window-to-wall ratio and thermal mass in Mediterranean and Oceanic climates Konstantina Leonidaki ∗, a , Elli Kyriaki a , Christina Konstantinidou a , Efrosini Giama a , Agis M. Papadopoulos a a Process Equipment Design Laboratory, Dept. of Mechanical Engineering Aristotle University Thessaloniki, 54124, Greece Abstract Tertiary sector buildings and office buildings in particular are heavy users of energy and hence have the potential to make significant improvements in their energy efficiency. To achieve this there needs to be a rethinking of the building design process leading to an optimization of the building’s energy demand and good indoor environmental quality conditions. The right decisions have to be taken in the early stages of design in order to achieve the best possible energy performance of the building. The main objective of this paper is to present the results of research on the parameters that most influence the building envelope’s energy performance for Mediterranean and Oceanic climatic conditions, according to the Köppen climate classification. The study investigates how two factors—thermal mass and window-to-wall ratio—influence a building’s energy performance. A parametric study on those variables is carried out through a dynamic simulation in order to evaluate their influence for Thessaloniki, Greece, and Nicosia, Cyprus—which both feature a Mediterranean climate—and London, United Kingdom, and Munich, Germany—which both feature an Oceanic climate. The results are discussed and conclusions drawn on the influence of each parameter. Keywords: Office buildings, Window-to-wall ratio, Thermal mass, Energy simulation 1. Introduction Many studies have been carried out over the last forty years to evaluate energy usage by office build- ings from the early design phase. Numerous pa- rameters that influence the design of an urban of- fice building have been considered, accompanied by measures and effective ways to achieve thermal, op- tical and acoustic comfort and indoor air quality, as well as ways to improve conditions in existing build- ings [1, 2]. ∗ Corresponding author Email address: (Konstantina Leonidaki ∗, ) Thermal mass and the window-to-wall ratio are two of the crucial parameters for the energy per- formance of buildings in both Mediterranean and Oceanic climates; therefore a dynamic simulation program has been applied to derive quantitative re- sults and compare these parameters in relation to building envelope and energy performance. A parametric study on those variables was car- ried out through a dynamic simulation in order to evaluate their influence for Thessaloniki, Greece, and Nicosia, Cyprus, (Mediterranean climate) and London, United Kingdom, and Munich, Germany (Oceanic climate). This study is followed by a deeper investigation of them depending on the re-