Simulating invisible light: a model for exploring radiant cooling’s impact on the human body using ray tracing

Radiant systems are an energy-efficient method for providing cooling to building occupants through active surfaces. To assess the impact of the radiant environment on occupants in space, we develop a ray-tracing simulation, which accounts for longwave radiation. Thermal radiation shares many characteristics with visible light, and thus is highly dependent on surface geometry. Much research effort has been dedicated to characterizing the behavior of visible light in the built environment and its impact on the human experience of space. However, longwave infrared radiation’s effect on the human perception of heat is still not well characterized or understood within the design community. In order to make the embodied effect of radiant surfaces’ geometry and configuration legible, we have developed a Mean Radiant Temperature (MRT) simulation method, which is based on a ray-tracing technique. It accounts for the detailed geometry of the human body and its surrounding environment. We use a case study of a pavilion built with an envelope consisting of active cooling panels in Singapore. Using measured data for the surrounding surface temperatures in the pavilion, we explore the impact of both the active panels and the surrounding passive elements and thermal environment on a person’s radiant heat exchange in different postures. The reflectivity and emissivity values of different surfaces are taken into account, and the ray-tracing process allows for multiple-bounce simulation. The model accounts for both longwave and shortwave radiation, and the simulation results are compared with field measurements for validation. The results are expressed both numerically and as spatial radiant-heat-maps. These show a variation of up to 11°C in MRT across the space studied. Furthermore, a digital manikin is used to assess the impact of the radiant cooling panels across the human body. The results show a 10°C variation in radiant temperature perceived by different regions of the body in one position. The findings reveal a significant heterogeneity of radiant heat transfer that current analysis methods typically overlook for both architectural space and the geometry of the human body.