Urban daylight model with open-source and GIS-based tools: A case study in Italy

This paper presents a detailed analysis of the daylighting performance of buildings in the centre of Catania, in southern Italy. The proposed methodology employs a set of ‘facade-room’ archetypes representing rooms with typical floor and window dimensions, adjacent to an external facade characterized by predefined features: orientation, sky view factor, presence of balconies, window to floor-ratio, building age, windows facing. These parameters are extracted from georeferenced datasets in QGIS, with geometries modelled in Blender and daylighting performance metrics calculated using the Radiance®-based VI-Suite plugin. The daylighting performance of each archetype is then linked to the corresponding building facades within QGIS, enabling rapid analysis of large urban areas. One hundred archetypes were defined and associated with 29’000 georeferenced facade planes. Focusing on the impact of urban densification on daylight, the study reveals an average Sky View Factor of 0.28 for the case study area, resulting in a 50% mean reduction in Useful Daylight Illuminance autonomy, a 40% decrease in Daylight Factor and a loss of 1’550 hours of daylight compared to scenarios without buildings obstructions. Conversely, urban dense environment reduces the probability of excessive sunlight and reflects sunlight towards buildings increasing daylight autonomy. The proposed methodology enables the assessment of likely daylighting performance for individual rooms in urban buildings, storing these data within a GIS framework to support urban planning, property valuation and urban energy assessment.