Abstract—There is a great deal of interest in constructing Double Skin Facade (DSF) structures which are considered as modern movement in field of Energy Conservation, renewable energies, and Architecture design. This trend provides many conclusive alternatives which are frequently associated with sustainable building. In this paper a building with Double Skin Facade is considered in the semi- arid climate of Tehran, Iran, in order to consider the DSF’s performance during hot seasons. Mathematical formulations calculate solar heat gain by the external skin. Moreover, Computational Fluid Dynamics (CFD) simulations were performed on the case study building to enhance effectiveness of the facade. The conclusion divulged difference of gained energy by the cavity and room with and without blind and louvers. Some solutions were introduced to surge the performance of natural ventilation by plunging the cooling loads in summer. Keywords—Double Skin Façade Buildings, Energy Conservation, Renewable Energy, Natural Ventilation, Semi-arid Climate. I. INTRODUCTION HERE is an increasing demand to improve the efficiency of all glazed skyscrapers and office buildings. Occupants and designers endeavor to make a simulating indoor environment. DSF is considered as applicable solution for this issue [3], [4]. The DSFs are driven by: Decrease of energy consumption by HVAC system which helps the building designs approaches to the concept of green buildings [1], [2]. Increasing transparency; Architects often prefer the envelope to be covered with a high percentage of relatively clear glass which also provides visual comfort within the building around the perimeter [2], [11]. Reduction of energy consumption by relying on natural lighting; DSFs combines a number of features such as low emissivity glasses, argon-filled double-glazed units, triple-glazed units, glazing with selective coating, and V- cool glasses [1], [2], [13]. Improving indoor environment; Sun as a source of natural lighting can materially improve the performance of the human activities that are happening inside the building. This feature also has positive financial effects as well [12]. Enhancing acoustic insulation [11]. In comparison to other building efficiency improvement solutions such as use of ELECTROCHROMIC, F. Vahedi is with the Islamic Azad University, South Tehran Branch, Tehran, Iran, phone: (+98) 912 49 48 715; e-mail: Farid.Vahedi@gmail.com, st_f_vahedi@azad.ac.ir ). THERMOCHROMIC, PHOTOCROMIC panes, which are considered as expensive devices, Double Skin façade relies on lower construction cost. Moreover, DSFs can be available in variable climates and geographical coordinates [11]. By providing natural ventilation, airflow passes through the cavity, so the windows during the night can be opened and indoor environment can benefit the cool outdoor air. As a result the HVAC system performs in low level, however, if the DSF is not designed accurately, so the lack of natural ventilation can cause increase in cooling load during hot seasons in semi-arid conditions such as Tehran [10], [11]. II.SOLAR HEAT GAIN BY A VERTICAL SURFACE IN TEHRAN The Heat Transfer between external skin and air is characteristic which affects forced convection and also natural convection processes. Convection Coefficient as a crucial feature in heat transfer and natural ventilation depends on air velocity as varies by geographical conditions, building orientation and site surroundings. Moreover, heat transfer is most affected by cloud cover, atmospheric humidity, and air pollution [1], [2]. Solar Energy exists at two categories: short wavelength and long wavelength. Long wavelength heat transfer occurs among inside surfaces such as: windows, floors, ceiling, and walls [1]. Total heat gain by the external skin occurs by three components: direct radiation, sky-diffuse, ground-reflected [2]. Additionally convective heat transfer can increase the total amount of heat gain [17], [18]. Conductivity and material thickness must be applied directly in conduction calculations [1]. The amount of radiation out of the Earth’s atmosphere [16]: where is solar constant and δ is the declination angle (the angular solar position at noon): ω is the hour angle at sunrise and sunset: Farid Vahedi Enhancing Thermal Efficiency of Double Skin Façade Buildings in Semi-Arid Climate T World Academy of Science, Engineering and Technology International Journal of Civil and Environmental Engineering Vol:7, No:5, 2013 343 International Scholarly and Scientific Research & Innovation 7(5) 2013 ISNI:0000000091950263 Open Science Index, Civil and Environmental Engineering Vol:7, No:5, 2013 publications.waset.org/4169/pdf