Green roofs serve for multiple functions in relevance to the environment, sustainability, aesthetics, visual comfort and energy-efficiency. In hot climates, a green roof can have a crucial role in decreasing cooling loads through thermal mass and evaporative cooling through plant transpiration. It can be implemented on new or existing building constructions.
Currently, a large building stock exists and many new settlements are either newly-built or under construction in Egypt, of which an increasing portion is air-conditioned. The presence of recyclable waste water that can be used for irrigation increases the potential of using green roofs especially in countries with high population. This potential indicated the need to quantitatively explore the effect of green roof parameters on energy consumption in this type of air-conditioned residential buildings located in desert climates.
This study investigated the effect of different green roof parameters on energy consumption of two-storey residential buildings located in desert climates. These included leaf area index, soil thickness, soil conductivity and thermal insulation.
A two-storey residential building was modelled and simulated for energy performance using EnergyPlus. Green roof parameters were tested for their effect on energy consumption. Results were compared to a base case of standard un-insulated roof and to alternatives of roof insulation. Results showed that in desert cities, the green roof achieved savings of up to 30% in Kargah city, 28% in Cairo and 24% in Alexandria. Savings achieved by a green roof in desert cities were more than those achieved by thermal insulation. For comparison a city with a temperate climate, Berlin, was also tested, in which thermal insulation proved to be of more savings than a green roof.