Thermal performance of indoor solar shading devices using a thermal nodal model and a lighting simulation model

Various facade designs, such as light shelves, have been proposed to achieve zero emission buildings. However, general thermal load simulation models are unable to properly evaluate the thermal effects of spaces near windows, such as light shelves and counters, which are installed on the interior side of windows for increased daylight utilization. In this study, we propose a method to evaluate the thermal performance of indoor light shelves. The model proposed herein consists of three components: A thermal nodal model of the window area, a lighting simulation model, and a thermal simulation model. The thermal nodal model places a node at each device (glass, ceiling, light shelf, and floor) in the light shelf space. The heat balance equation for each node is then solved. In doing so, the total transmittance of the entire indoor-installed device space, which considers inter-reflections and the solar radiation absorptance of each device, is calculated using the Radiance software. Additionally, the solar heat gain obtained using the thermal nodal model is substituted internally into NewHASP, and the thermal load calculation is performed. Finally, a simulation is performed using an office model, and the indoor-installed light shelf exhibited a 14 % reduction in annual thermal load.