Assessing Environmental Benefits of Twisting Tall Buildings Through Solar Irradiation on Façades

Simon Lay
Director
OFR Consultants, Manchester

Over the last decades and increasingly in recent years, tall buildings geometries have been shifting from straight rectangular boxes towards shapes defined through geometrical transformations such as twisting, bending, shearing and tapering, or their combinations. Twisting geometries, defined by CTBUH as ones that progressively rotate their floor plates or their façade as they gain height, take the lead in this trend. Twisting tall buildings have already spread over continents, varying greatly in their height, floor-to-floor rotation, total rotation, or floor shapes.
From the aesthetical point of view, these twists make them appear more fluid and contemporary, hence defining their distinctive character and identity. From the environmental point of view, however, benefits are not straightforward and vary greatly on climatic and urban conditions. While, some cases have proven via simulations and testing that twisting may help reducing wind loads and consequently saving on structural weight and cost, other environmental aspects such as energy saving, daylighting, glare and views are not well documented neither in academic nor practitioners’ domains.
Therefore, this study aims to assess the global potential of environmental benefits of twisted geometries by finding a correlation between floor-to-floor rotation and façade solar irradiation across all ASHRAE defined climate categories. The study differentiates between beneficial and harmful solar irradiation during Hot and Cold Degree Days to quantify the overall impact of floor-to-floor rotation as a passive solar design strategy. Results show a high sensitivity of solar irradiation benefits revealing positive, negative and neutral scenarios across different climates and various floor-to-floor rotation angles.

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