Performance-based evaluation of artificial shading systems for heat-stress relief in outdoor environments

Tree planting is often regarded as the main urban strategy that can provide extensive distribution of outdoor shade. However, the physical constraints that limit the provision of adequate underground soil volume alongside the slow development of shade-providing tree crowns sometimes make artificial shading elements the only viable option for effective shading. Despite their importance for outdoor climatic design, few studies have assessed the magnitude and quality of heat stress relief provided by common artificial shading systems compared to tree shade, and a widely accepted methodology for evaluating the efficacy of different types of artificial shading systems is still missing. 

In this study, we attempted to develop a systematic analytical method for artificial shading performance based on the geometry and material properties of the elements and the resulting solar transmittance, heat emittance, and overall heat comfort provision in the shade they produce. For this purpose, we monitored the performance of common artificial shading systems under summer, clear-sky conditions in Tel Aviv-Yafo. Monitoring was done using an on-site compact weather station and Chaosense units measuring Mean Radiant Temperature, which enabled us to calculate the degree of thermal stress mitigation using the PET and UTCI indices. The data was collected under a wide variety of artificial shading elements simultaneously with monitoring the conditions at adjacent non-shaded, tree-shaded, and building-shaded locations. 

The monitoring results showed that the performance of non-uniform opaque shading surfaces, such as louvred structures, depended on their geometry and orientation, with optimal performance occurring when the openings in the shading surface are minimal. With uniform shading surfaces, primarily textile-based, we found a large variance in cooling efficacy that mainly resulted from the degree of direct solar transmittance through the shading surface. However, even the least effective uniform artificial elements still demonstrated a considerable reduction in heat stress compared to non-shaded locations.