Vegetation in different street orientations of aspect ratio (H/W 1:1) to mitigate UHI and reduce buildings’ energy in arid climate

Abstract

Cairo is characterized by high temperatures compared to the adjacent rural areas. This phenomenon is known as Urban Heat Island (UHI). Due to this phenomenon, high temperatures and the use of air conditioning in the buildings has increased. Outdoor thermal performance is affected by street orientation and aspect ratio (H/W) while Cairo is a mega city, which has different fabrics with different streets (H/W) and orientations. Therefore, this study seeks to find a suitable vegetation ratio for the aspect ratio street (H/W) of 1:1 in order to enhance thermal performance, mitigate UHI and to reduce the energy in buildings in hot arid climates (case study - Cairo). One street was chosen of (H/W) 1:1 as a case study, from downtown Cairo. This street was simulated by using ENVI-met V4.3.2 and by applying four orientations: east-west, north-south, northwest – southeast 310° and northeast – southwest 40°. These orientations were simulated by using the reference case (without vegetation) and three suggested vegetation scenarios (20% trees, 50% trees and 70% grass). The meteorological outputs were discussed in order to know the best vegetation scenario, which enhances thermal performance. In addition, these outputs were used through the DesignBuilder model in order to know the best scenario, which reduces the consumption of energy in buildings. This study found that trees are ineffective in the decreasing of air temperature and the reduction of energy in buildings while they are effective in enhancing thermal performance in the all orientations.