1 Proceedings of 3rd Conference: People and Buildings held at Westminster University, School of Architecture and the Built Environment, London, UK, 20th September 2013. Network for Comfort and Energy Use in Buildings: http://www.nceub.org.uk Impact of concave and convex façades on building solar and energy performance Binaee Raof 1 and Mohamed B Gadi 2 1 Student, MSc course Renewable Energy and Architecture, Department of Architecture and Built Environment, Faculty of Engineering, The University of Nottingham, UK, laxbr2@nottingham.ac.uk 2 Associate Professor, Department of Architecture and Built Environment, Faculty of Engineering, The University of Nottingham, UK, mohamed.gadi@nottingham.ac.uk Abstract: It is well known that façades play a crucial role in buildings’ energy efficiency. Modern architects have designed a wide range of concave and convex building façades which are often prompted only by building aesthetics rather than energy requirements. Predicting solar radiation and energy performance of buildings incorporating flat façades have been widely published. In contrast, curved façades still need more attention from researchers in the field. The lack of published research into concave and convex façades is mostly due to the complex nature of their curvature and the consequent complex physics involved. This paper assesses the solar and energy performance of concave and convex façades by using (Energy plus) software. Three groups of forms were modeled according to their curvatures (curvature in plan, in section and in both plan and section). DSR received by each façade and building energy demand were calculated, it proves that for east orientation the performance of curved façades is better than flat . Keywords: Concave and convex façades, solar performance, energy efficiency, modern architecture, curved surfaces. Abbreviations: DSR Direct solar radiation, CSR Horizontal cross-section –ratio, CSRe Vertical cross- section-ratio 1. Introduction: A form is the most noticeable characteristic in any building; a curved form is one of the common forms in modern architecture. It has a remarkable impact on the solar and energy performance of the building and it can increase the energy efficiency of the building, improve indoor comfort (Mashina ,Gadi 2010). Façade as the fundamental part of buildings envelope have effect on the indoor environmental conditions, the energy performance of buildings and the occupants comfort, providing natural light, preventing unwanted solar heat gain are some of their function (Aksamija, 2013). In this context the paper aims to evaluate the solar and thermal behavior of buildings that have concave and convex façades in their outer skin, and Kuwait city with latitude 29.22° and longitude 47.98°is chosen. The reasons for simulating different forms with curved façades and their solar and energy performance are compared with the flat façades for showing the effect of the façades design on passive design strategies, to investigate the average DSR received by elevations of curved and rectangular forms. In addition, the