Energy and Buildings 92 (2015) 180–187 Contents lists available at ScienceDirect Energy and Buildings j ourna l ho me pa g e: www.elsevier.com/locate/enbuild The energy performance of windows in Mediterranean regions Katerina Tsikaloudaki ∗ , Konstantinos Laskos, Theodoros Theodosiou, Dimitrios Bikas Civil Engineering Department, Aristotle University of Thessaloniki, PO BOX 429, 54124 Thessaloniki, Greece a r t i c l e i n f o Article history: Received 10 December 2014 Received in revised form 16 January 2015 Accepted 23 January 2015 Available online 2 February 2015 Keywords: Windows Energy performance Thermal transmittance of glazed components Solar transmittance of glazed components Energy needs Residential buildings Office buildings a b s t r a c t The paper focuses on the assessment of the windows’ contribution to the energy performance of buildings in the warmer regions of Europe. This is derived by calculating the cooling energy index q c and the area weighted energy needs for different window configurations installed on a reference room for two different building uses, office and residential. The examined window types differed with regard to their thermophysical and optical properties (U- and g-value), geometry (frame and window fractions) and orientations. The energy parameters used for the performance assessment were calculated with the help of a dynamic simulation tool for a location with a representative Mediterranean climate. The extensive multi-parametric analysis exhibited interesting results. It was found that for the cooling mode the energy performance of windows in warm climates is influenced significantly by their thermophysical properties. More specifically, the impact of solar transmittance is significant and its optimal selection can contribute in minimizing the energy consumption, especially in environments with controlled ventilation, such as offices. On the contrary, advanced fenestration products with low thermal transmittance seem to behave unfavorably, since their extremely low thermal transmittance prohibits the dissipation of heat toward the ambient environment and results ultimately in higher cooling energy loads. © 2015 Elsevier B.V. All rights reserved. 1. Introduction The building’s sector – i.e. the buildings of the residential and tertiary sector – is the largest user of energy and CO 2 emitter in the European Union and is responsible for about 40% of the total final energy consumption and greenhouse emissions [1]. The sector has significant potential for cost-effective energy savings which, if realized, would lead to a number of benefits, such as reduced energy needs, reduced import dependency and impact on climate, reduced energy bills, an increase in jobs and the encouragement of local development [2]. Although the transparent elements usually occupy a limited area of the buildings’ fac ¸ ade, their impact on the building per- formance is crucial, as they influence every aspect of the building behavior by providing protection against the environmental con- ditions (sun, cold, wind, noise, safety, etc.), daylight, ventilation, as well as view and interaction with the exterior. These often conflicting and time variant functions of the windows ask for properties that are correspondingly incompatible. In parallel, the heat transfer attributed to the windows accounts for a significant ∗ Corresponding author. Tel.: +30 2310995770; fax: +30 2310995603. E-mail addresses: katgt@civil.auth.gr (K. Tsikaloudaki), klaskos@civil.auth.gr (K. Laskos), tgt@civil.auth.gr (T. Theodosiou), bikasd@civil.auth.gr (D. Bikas). proportion of all energy used for covering both heating and cooling needs [3]. The identification of the window characteristics for achieving the optimum performance constitutes an ongoing pursuit for many researchers; indicatively some of the major published results are reported herein, mainly for showing the plethora of the different aspects examined and results derived. Gasparella et al. [4] have evaluated heating and cooling loads of an office building with regard to the window area, the glazing type and the ventilation patterns. They suggested that the thermal needs can be optimized by utilizing low emissivity glazings, as well as appropriate window areas. In a later study of the same authors, the window energy performance of a well-insulated residential building was analyzed with respect to the glazing type and size, the orientation, as well as the internal gain levels. Among others, they concluded that the use of large glazed surfaces can enhance the winter performance, but may worsen the summer one. Persson et al. [5] studied the influence of the window size on the energy balance of low energy houses in Sweden. After consecutive simulations they concluded that the superior thermal insulation of a house reduces the need for solar radiation to keep the house warm during winter, while during summertime the minimization of southern windows would constitute the optimal solution. Cappelletti et al. [6] have assessed the heating and cooling energy needs of an open-space office with different windows’ characteristics (glazing systems, area, http://dx.doi.org/10.1016/j.enbuild.2015.01.059 0378-7788/© 2015 Elsevier B.V. All rights reserved.