Computer simulation of sunlight concentration due to façade shape: application to the 2013 Death Ray at Fenchurch Street, London

Abstract

In early September 2013, reflected sun light from a building in central London was reported to have caused the melting of metal components of a car parked at street level, and to have created a heating hazard on the local shops opposite the street. The incident was explained by the concave-shaped south facade of the building, which reflects and converges solar radiation into a hotspot on ground level. In this study we attempt to reproduce the phenomenon using a computational backward ray-tracing lighting simulation tool called Radiance (Fuller & McNeil, n.d.). A scene geometry model with material properties and corresponding sky models were created for the simulation. The geometry model, including the building under analysis, as well as 17 surrounding buildings, three roads and pedestrian areas, was created in Rhinoceros (rhino3d.co.uk, 2015). Sky models were established based on the CIE standard sky luminance distribution. Weather situations of clear sky, partly cloudy and overcast sky were modelled to analyse the effect of different weather conditions on the results. Simulations were performed using Radiance. Results are illustrated in the form of irradiance maps showing the phenomenon, indicating the time, duration, position and peak heat lux at the hotspots. The scene corresponding to the afternoon of August 29th 2013, when the hotspot was first observed and reported by media, was replicated. The highest simulated peak flux on that day is 3384 W/m2 . A heat flux of those characteristics can severely injure human skin. Relevant calculations were carried out to proof that damages on surrounding areas could occur. Additionally, the specific time and day when highest heat fluxes occur between June and December was determined by a series of simulations. At this worst scenario simulations showed that the peak heat flux could reach 4176 W/m2.