The Impact of Courtyard and Street Canyon Surroundings on Global Illuminance and Estimated UV Index in the Tropics

Abstract

Exposing oneself to outdoor daylight in the morning can be healthy and harmful at the same time, due to the risk of ultraviolet exposure. The presence of surrounding buildings in the urban context may also influence the risk. This study aims to identify the impact of courtyard and street canyon surroundings of various size and heights on the peak time and values of global illuminances and ultraviolet index (UVI), for the case of a tropical city. The impact of the surroundings is estimated by performing annual daylighting simulation with Daysim, considering various receiving plane orientations, followed with sensitivity analysis. The results suggest that in the courtyard scenes, on 21 March, 21 June, and 22 December, the maximum horizontal UVI are respectively 9 at 12.00 hrs, 9 at 10.00 hrs, and 5 at 11.00 hrs, while the corresponding, maximum vertical UVI are 6, facing east at 09.00 hrs; 8, northeast at 10.00 hrs; and 3, southeast at 08.00 hrs. In the street canyon scenes, the 5m wide street is more sensitive to height variation, compared to the 10-m wide. The maximum horizontal UVI on the three days are 10, 9, and 5; while the corresponding, maximum vertical UVI are 6, east; 9, northeast; and 4, southeast; all with the same peak time as in the courtyard scenes. Sensitivity analysis results from the three days are found to be more reliable than those from the entire year. The study thus has the main contribution in providing the methodology in estimating UVI under various outdoor scenarios with surrounding buildings, particularly in the tropical region.

Keywords

• global illuminance
• ultraviolet index
• sensitivity analysis
• daylighting simulation