A state-of-art review on concepts, criteria, methods and factors for reaching 'thermal-daylighting balance'

In architectural design, daylight has a contradictory effect on the indoor thermal and visual comfort, and energy use. The resulting need to control or guide the daylight for reaching a balance between thermal and daylighting performance has been emphasized over the years. However, the concept of the 'thermal-daylighting balance' varied depending on various evaluation criteria and research methods, which may confuse designers. To systematically clarify the issue and illustrate the consensus involved in existing research, this study conducted a state-of-the-art review of the thermal-daylighting balance by categorizing and analyzing the concept, metrics, methods, and factors. The differences in the concept expressions were related to the multi-aspects involved (indoor comfort, energy, and view). Methods for reaching the balance could be categorized into five types: separate investigation (M1); separate investigation + overall comparison (M2); one-another (M3); together (M4); and multi-objective optimization (M5). M1 and M2 were frequently applied, while M5 was more effective. Multiple factors for building/facade/control system designs contribute to the balance. Generally, a proper base plan width-to-depth (e.g. 1:1), facade window-wall-ratio (usually around 30%), high transparency and thermal insulation glazing, adjustable shading with control, and efficient lighting equipment were recommended for reaching the balance. The specified optimal values were changed by the variation in locations/climates and factor combinations. Additionally, the uninvolved metrics (for view, non-visual effect, etc.) and factors (e.g. special building functions and climates) were illustrated. The priority among the metrics, factors, or the advanced products/techniques remained future challenges.