Assessment of solar radiation distribution in indoor spaces for local thermal comfort evaluation

¹ Department of Mechanics and Bridges, Faculty of Civil Engineering, Silesian University of Technology, Gliwice, Poland
² Department of Heating, Ventilation and Dust Removal Technology, Faculty of Energy and Environmental Engineering, Silesian University of Technology, Gliwice, Poland

^* Corresponding author: This email address is being protected from spambots. You need JavaScript enabled to view it.

Abstract

Shortwave solar radiation significantly influences local thermal comfort in indoor environments, particularly in spaces with large glazed areas. Although building performance simulation tools such as EnergyPlus accurately predict solar gains at the room and surface level, they do not provide information on the spatial distribution of solar radiation incident on the human body. Conversely, ray-tracing tools such as Radiance enable detailed spatial resolution of solar exposure but require high computational effort and complex model setup. This study proposes a hybrid methodology for estimating spatially resolved shortwave solar radiation incident on individual human body segments by combining standard EnergyPlus simulation outputs with geometric analysis. Beam solar radiation is computed using a mesh-based human body model that accounts for solar position, body orientation, surface normal vectors, and self-shading effects. Diffuse solar radiation transmitted through the window is redistributed to body segments using precomputed area view factors. The method was validated against detailed Radiance simulations employing climate-based sky models. A case study of a typical office room in a temperate Central and Eastern European climate with a southwest-facing window was analyzed. Four study cases included two distances of the human body from the window (0.5 m and 1.5 m) and two body orientations toward the window (facing the window or sideways to it). A simplified human body model divided into seven representative segments was adopted. The results show good agreement between the proposed approach and Radiance simulations. Beam solar radiation exhibits strong spatial non-uniformity and is predicted with high accuracy. For diffuse radiation, minor discrepancies were observed, mainly due to differences in sky anisotropy treatment, although high correlations were maintained across all cases. The proposed EnergyPlus-based approach provides a reliable and computationally efficient alternative for estimating local solar radiation exposure on the human body, enabling advanced occupant-level thermal comfort analyses and supporting the evaluation of solar-related discomfort and façade or shading design strategies.