Energy Performance of Cool Roofs Followed by Development of Practical Design Tool

Abstract

Cool/white roofing systems use paints and membranes with high solar reflectivity to reflect a portion of the incident solar radiation resulting in lowering the temperature of the exterior surfaces in respect of the conventional/black roofing systems. This study focuses on the energy performance of roofing system that is being used in buildings of the Gulf Cooperation Council countries when this roof is exposed to a hot and humid climatic conditions in Saudi Arabia. The long-term moisture performance of the white and black roofing systems were investigated in a previous study in which the results showed that no risk of condensation and mold growth occurred in the roofs with different values of solar reflectivity of the rooftop and different initial construction moisture. With the same environmental conditions that were used in the previous study, the focus of this paper is on assessing the energy performance of white and black roofing systems for a wide range of: (a) thermal insulation thickness, and (b) solar reflectivity of the rooftop. Also, considerations are given in this study to develop a practical design tool that can easily be used by building engineers and architects for determining all pairs of the insulation thickness and the corresponding solar reflectivity of the reflective roofing materials/coatings that resulted in the same levels of the energy performance as those for the black roofing systems of thicker insulation thickness. The results of this study along with the developed practical design tool can be used in future to upgrade the Saudi building code to allow using less insulation in the roofs if white roofing systems are installed.

Energy Performance Analysis of Building Envelopes

“…The proposed roof system included some unsustainable materials that worsen the environmental impacts during the building life cycle. Saber and Maref (2019) analyzed a roof system which consisted of ceramic tile "light color," mortar, sand screed, insulation layer, waterproofing, sand screed, foam concrete, and reinforced concrete slab as shown in Fig. 3-B.…”

“…Not all research has conducted an economic evaluation for these developments despite its importance to homeowners (Mayhoub et al, 2019;Ingrao et al, 2016;Aktemur and Atikol, 2017;Salandin and Soler, 2018;Tejedor et al, 2017;Guillen et al, 2014;Asdrubali et al, 2014) and also the use of sustainable materials are not widely adopted. Many works were also conducted to improve building thermal performance by adding reflective coating and insulation layers but also without economic evaluation of these developments (Mohamed et al, 2016;Saber and Maref, 2019;Radhi et al, 2017;Ascione et al, 2018). On the other hand, adding a plant layer to building envelope systems has been tested which significantly improved building thermal performance during the summer season; however, the side effect of these solutions was recorded in the increase of the relative humidity (Nadia et al, 2013;Gagliano et al, 2015;Bevilacqua et al, 2015;Zhao et al, 2013;Tang and Zheng, 2019).…”

Optimal Combination of External Wall Insulation Thickness and Surface Solar Reflectivity of Non-Residential Buildings in the Korean Peninsula

“…It was concluded that an insulation of 12 to 14 cm must be adopted in all cities to avoid penalties during heating periods. Sabe et al [10] assessed the energy performance according to the insulation thickness and reflectivity (white or black) of the roof in hot, humid climatic conditions in Saudi Arabia. It was observed that if a white roof were applied to a building, the use of insulation on the roof could be reduced.…”

“…As the reflectivity increases, the cooling load decreases [10,11,65]. This phenomenon occurs because the increase in the reflectivity of the solar radiation energy prevents the temperature rise of the external wall, thereby reducing the amount of heat transfer to the indoor space [24,25].…”

The Influence of NIR Pigments on Coil Coatings’ Thermal Behaviors

“…These are called "cool coatings" since they show a high thermal emittance which induces a fast heat release to the surrounding environment. Cool coatings, also for roof applications, have been widely studied [7,[20][21][22][23][24][25][26][27][28][29][30][31].…”