On the development of an urban passive thermal comfort system in Cairo, Egypt

This paper investigates how urban form can be designed to act as a passive thermal comfort system in Cairo. The system utilizes two main elements, the urban fabric form, with its green structure, and thermal comfort adaptation by introducing urban green scene stimulation with the time of exposure to the urban environment. The courtyard form on a large scale is used to study comfort levels, the effect of compactness on solar access and the local radiant heat island potential in a theoretical neighborhood design using a medium population housing concept as required by Egyptian urban planning laws. Urban canyons in a grid network, with three mid latitude orientations 15 degrees, 45 degrees and 75 degrees from the E-W axis, were examined, with one canyon having virtually no shade. Other canyons had a green structure containing two types of native Egyptian trees. Numerical simulations using ENVI-met were performed for hot climate conditions. Although some very hot conditions were recorded, there were evident examples of more acceptable comfort levels and cooling potential for some orientations and degrees of urban compactness due to the clustered form with green cool islands and wind flow through the main canyons. Some design guidance on how to form urban passive cooling systems is presented. (C) 2009 Elsevier Ltd. All rights reserved.