Abstract
When solar radiation hits a roof surface, a part of solar energy is reflected and another part is absorbed. The absorbed part of solar energy results in an increase of the surface temperature of the roof. Cool (white) roofs use bright surfaces to reflect a significant portion of the incident short-wave solar radiation, which lowers the surface temperature compared to conventional (black) roofs. As such, white roofs help reduce the urban heat island effect during the summer. The questions are: (a) do white roofs lead to moisture-related problems in Saudi climates? (b) what are the amount of energy savings as result of using white roofs instead of black roofs of same insulation amount, and (c) what is the reduction in the amount of insulation in the white roof having the same energy performance level as the black roof? To answer these questions, numerical simulations were conducted for one type of roof that is commonly used in low-rise buildings of Saudi Arabia in order to assess and compare the energy and hygrothermal performance of white and black roofs. The roof was subjected to weather conditions of the Eastern Province of Saudi Arabia. The indoor conditions were taken based ASHRAE recommendations for conditioned space. The main outcome of this study has shown the capabilities of using reflective materials with different short-wave solar absorption coefficients for enhancing the energy performance of roofs and/or reducing the amount of insulation that resulted in same energy performance as black roofs. This study can be used in future for upgrading Saudi Building Code to allow less roof insulation if reflective roof is installed.
Highlights
Buildings are responsible for a large portion of the global and local impacts of climate change
The results showed no moisture accumulation occurred from year-to-year after 6 years and 7 years for the black roof and cool roof, respectively, and the highest relative humidities in the black and cool roofs were well below 80% resulting in no risk of condensation and mold growth occurred in these roofs
We provide the results of the hygrothermal performance of black roofs and cool roofs when these roofs were subjected to the outdoor climates of the Eastern Province of Saudi Arabia
Summary
Buildings are responsible for a large portion of the global and local impacts of climate change. In regions with hot climatic conditions such as that in Saudi Arabia, a considerable part of energy is used for cooling the buildings. Buildings are responsible for about 30–40% of the total energy demand (Al-Homoud, 2005; Vrachopoulos et al, 2012). In Europe, buildings are responsible for 40–50% of energy use (European Commission, 2010). In the Gulf Cooperation Council (GCC) countries, a substantial share of energy is used for cooling. Regarding the distribution of electricity consumption by end-user, Krarti and Hajiah (Krarti and Hajiah, 2011) reported that the building sector represents 90% of the electricity consumption in Kuwait
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