Developing Scripts and A Guideline to Mitigate Adverse Effects of Converged Solar Reflection from Curved Façades

Abstract

Converged solar reflection resulting from the curved façades of mid-rise and high-rise buildings has proven to be a uniquely dangerous phenomenon, yet increasingly common. The "death ray" incident at 20 Fenchurch St (the "Walkie Talkie" Building) in London in 2013 was mirrored by a similar occurrence at the Amsterdam University Medical Center (AMC) in 2021, where parts of a car melted from the intense heat produced. This reoccurrence raises a fundamental question as to why this problem keep happening. Several factors may contribute: past studies focused on isolated instances, many building engineers and architects are unaware of the risks, and numerical reproduction of this phenomenon involves numerous parameters and complex scripting.
This thesis aims to provide an algorithm to accurately reconstruct the converged solar reflection phenomenon numerically by analyzing various input parameters, such as the geometry of a façade, the nonlinear reflection rate of glass panels, and the effect of anisotropic sky models. To ensure the validity of the model, on-site solar irradiance measurements were conducted in the parking lot of the AMC building. Additionally, the program was used to reenact the phenomenon at the Walkie Talkie building before improvements to its façade.
Results indicate that the three-dimensional problem can initially be approached with a two-dimensional model using horizontal cross-sections of the façade. The angles at which the most intense focal points occur in both the 3D and 2D models of the AMC building correspond to each other, at 15.24 and 23.04 degrees from the optical axis of the façade (solar azimuth angles of 147.34 and 139.54 degrees from the north). The study also concludes that under the same conditions, replacing a quarter-circle-shaped curved façade with a parabolic-shaped curved façade would significantly worsen the effect, potentially leading to five times higher converged solar reflection on the ground.
In the case of the AMC building, the highest recorded irradiance during measurement was 4834 W/m². This value differed by only 13.45% from the 3D model using the Reindl sky model, which showed 4184 W/m². Conversely, the conventional isotropic sky model produced a larger difference of 23.68%. For the 20 Fenchurch St building, the Reindl sky model also produced more intense results compared to the isotropic model, with the focal point intensity reaching up to 6271 W/m² on August 29, 2013. However, limited access to accurate three-dimensional models and details of the surrounding area may have affected the results.
The study also examined the systematic error due to mismatched curvature of the glass panels with the building's curvature. This mismatch caused irradiance variations, increasing by up to 23.52% at one time and decreasing by 13.09% at another, indicating no constant increase or decrease on the intensity of the focal point.
In conclusion, this thesis successfully captures various variable inputs to recreate an accurate converged solar reflection phenomenon in both the AMC and the "Walkie Talkie" buildings. It integrates these variables into one continuous script without the need to switch between different software, providing a comprehensive tool for assessing and mitigating this dangerous architectural flaw.