The Impact of Late Design Choices on Daylight and Energy Use in Buildings

Sammanfattning: Daylight analysis is often carried out when definitive decisions about space characteristics such as materials, colours, window characteristics and furnishing have not yet been made. Such late design choices, which are first introduced or can still be changed late in the design process or even after its conclusion, impact the daylight levels of interior spaces. This study explored the impact of late design choices on interior daylight and energy use of generic office spaces located in the southern Nordics. Nine late design choices, defined as factors introduced by industry professionals after initial decisions about building volume, orientation, window-to-wall ratio and relation to environmental context etc. have been made, or factors decided by interior designers or building occupants after the building has been constructed (floor, ceiling and wall reflectance, visual transmittance of windows, windowsill and head height, the amount and reflectance of furniture as well as height of workspace partitions), and seven daylight metrics (DFAverage, DFMedian, DFPoint, DA, sDA, LD and UDI) were studied for a set of building models of varying orientation, size and WWR with different underlying daylight conditions (nine for static daylight simulations and twelve for dynamic). Daylight simulations were performed according to the 4CM using Honeybee by Ladybug Tools for Grasshopper in Rhinoceros 3D. The energy use of electric lighting with fluorescent and LED lamps was calculated based on simulated LD values. The influence of individual late design choices on each daylight metric was investigated by global sensitivity analysis according to the method of Morris (Elementary Effects Method) using the SALib package for Python. The visual transmittance of windows and amount of furniture were identified as the most impactful factors. Windowsill and head heights, furniture reflectance and partition height had an inconclusive impact, but could be considered medium on average. Floor, ceiling, and wall reflectance displayed the least effect on interior daylight. In certain situations, the variability from late design choices was larger than the difference between target levels in environmental certification schemes. It was concluded that late design choices could have a significant impact on interior daylight. If professionals are aware of this variability, they can take proactive measures to ensure the resilience of interior spaces.