Effectiveness of Green-Roof on Reducing Energy Consumption through Simulation Program for a Residential Building: Cairo, Egypt

Abstract

Green-roofs are becoming a popular breathing roofing alternative to traditional roofing systems. Green-roofs were mentioned as an ecological-economical solution; however, limited work has been carried out on the potential life cycle cost savings of green roofs in arid climates. This paper present costs savings by green roofs in arid climates. The model accounts for energy savings, structural considerations as well as other variables. Detailed thermal simulations for various configurations of green roofs are performed to assess energy savings using DesignBuilder. Experiments are performed for a two story residential building in Egypt with a base case control that uses a traditional roof meeting standard model energy codes. One local sub-climatic zone was simulated while changing the thickness of the green-roof soil, the conductivity of the green roof and building aspect ratio. Costs for green-roof saving potentials were estimated according to Egyptian electricity consumption calculator, other parameters as retrofit potential and structure allowances to withhold the required layers with different thicknesses. The results demonstrate the economic benefits of using green-roofs under different design situations and provide guidance for the selection and design of green-roofs systems in similar climates. Savings varied from 15-32% compared to traditional and un-isolated roofs. It was also found that reducing soil thickness to 15 cm results in 15% annual savings, Moreover, conductivity of soil has significant impact on amount of savings. The research shows that the most energy saving realized when the aspect ratio of the building is 1:1.5.

Impact of Green Roofs on Energy Demand for Cooling in Egyptian Buildings

“…In addition, higher soil thermal conductivity was found to be more efficient in improving the cooling process than the lower soil thermal conductivity. This finding is consistent with that in previous studies [34][35][36] that shows that a higher soil thermal conductivity in the green roof combined with an increased moisture content in the soil contributes to an increase in the evaporation rate, thus reducing the heat flow within the interior spaces. It might, therefore, be concluded that the cooling effectiveness in the building bears a negative relationship with the soil depth that is associated with a high LAI and a positive relationship with the soil thermal conductivity of the green roof.…”

Effectiveness of Green Roofs and Green Walls on Energy Consumption and Indoor Comfort in Arid Climates

“…All simulations will implement a green roof and wall (100% coverage), then, will compare it with a base case (bare wall). A 15cm soil thickness (extensive) is set for any green layer (roof or wall), as it is the most efficient thickness in arid climates [43], Table 2 present the properties of any green layer used in the simulation. Building systems and materials description in DesignBuilder are presented in Table 3…”

Effect of Green Roof Design on Energy Saving in Existing Residential Buildings Under Semi-Arid Mediterranean Climate (Amman as a Case Study (

“…Another model with two stories residential building in Cairo, Egypt with a base case control which uses a traditional roof that meets standard model energy code was simulated while changing the conductivity and the thickness of the green-roof soil. The results showed that savings varied from 15-32% compared to traditional and un-isolated roofs [16]. Other study by Issa Jaffal, Salah-Eddine Ouldboukhitine and Rafik Belarbi, aims to provide a comprehensive study of the influence of a green roof on building energy performance.…”