DEVELOPING STREET DESIGN FOR DIRE DAWA CITY TO ENHANCE THERMAL COMFORT

This study discusses the contribution of street design, i.e. aspect ratio or height-to-width ratio (H/W) and solar orientation towards the development of a comfortable microclimate at street level for pedestrians. The investigation was carried out by using the threedimensional numerical model ENVI-met, which simulates the microclimatic changes within urban environments in a high spatial and temporal resolution. Model calculations are run for a typical summer day in May 10, 2016 in Dire Dawa, Ethiopia (9.6 0 N, 41.85 0 E, and 1200 m a.s.l.), a region characterized by a hot and dry climate. Symmetrical urban canyons, with various height-to-width ratios (i.e. H/W 1⁄4 0.5, 1, and 2) and different solar orientations (i.e. E–W, N–S, NE–SW and NW–SE), have been studied. Special emphasis was placed on a human biometeorological assessment of these microclimates by using the physiologcally equivalent temperature (PET). The analysis discussed the hourly temperature variation, humidity, wind speed and solar radiation in detail. Sun path and shadow length calculation for Dire Dawa city was made to compare the comfort of each street. Street width, building height, aspect ratio and street orientation were taken as major variables for the analysis. The results showed contrasting patterns of thermal comfort between shallow and deep urban streets as well as between the various orientations studied in a typical 12m street.