Assessment of green roof benefits on buildings’ energy-saving by cooling outdoor spaces in different urban densities in arid cities

Abstract

Over the last twenty years, Cairo experienced a great rise in temperature by 4–5 K due to the high urban density and lack of vegetation. These factors led to increased air conditioning and electricity usage. This study therefore seeks to evaluate the effect of green roofs on reducing outdoor air temperature and lowering buildings’ cooling energy demand in different urban densities. Group A consisted of the same aspect ratio areas H/W = 1 and different building heights of 12 m, 18 m, and 30 m. Group B contained areas of the same building heights (12 m) and different aspect ratios of H/W = 1, 2, and 3. ENVI-met v.4.4.4 was used to study each area by simulating the reference case and two scenarios: extensive and intensive green roofs. Then, a DesignBuilder model was used to calculate the buildings’ energy demand. This study found that intensive green roofs achieve the maximum reduction in air temperature and buildings’ cooling energy. However, the economic aspect favors using extensive green roofs as they were able to reduce air temperature and buildings’ cooling energy in Group A by 0.1–0.5 K and 1.3–3.2% and in Group B by 0.1–1.7 K and 3.2–13.3%.