Hygrothermal performance of cool roofs with reflective coating material subjected to hot, humid and dusty climate

Abstract

The measurements for the short-wave solar reflectivity of a Reflective Coating Material (RCM) with various cleaning operations that were obtained in a previous study were used in this study to conduct numerical simulations in order to assess the moisture and energy performance of cool and black roofs when they were subjected to the weather conditions of Saudi Eastern Province and Kuwait City. The results of the numerical simulations showed that black roofs always work with less moisture than cool roofs. Because the highest relative humidity in the different components of the black and cool roofs was well below 80%, there was no risk of condensation and mold growth in these roofs. For both weather conditions of Saudi Eastern Province and Kuwait City, the results showed that installing cool roofs have resulted in increasing the heating energy loads in relation to black roofs. Conversely, the results showed that the decrease in the cooling energy loads due to installing cool roofs were typically much greater than the increase in the heating energy loads. As such, cool roofs have resulted in net energy savings in relation to black roofs. Replacing black roof by cool roof in Saudi climate, the results showed that the annual energy savings in the total energy load was 25% and 34% as a result of installing cool roof with RCM at no cleaning and weekly homemade cleaning, respectively. Additionally, replacing black roof by cool roof in Kuwaiti climate, the results showed that the annual energy savings in the total energy load was 23% and 31% a result of installing cool roof with RCM at no cleaning and weekly homemade cleaning, respectively.

Review of White Roofing Materials and Emerging Economies with Focus on Energy Performance Cost-Benefit, Maintenance, and Consumer Indifference

“…Currently, there are five strategies that can be applied in order to mitigate the effects of urban heat islands [7][8][9][10][11][12][13]). These strategies include increasing vegetation and trees in urban areas [8], installing reflective pavements on streets, sidewalks and parking lots [9,10], utilizing smart growth practices that help protect the natural environment [11], installing green roofs by growing vegetative layers on the rooftops [12], and installing cool/white/reflective roofing systems [6,[13][14][15][16][17]. Throughout this paper, unless otherwise specified, cool roofs, white roofs and reflective roofs have the same meaning.…”

“…Generally, the external surfaces of different types of roof systems (traditional, green and cool) are exposed to several environmental factors that include dust/dirt, cloud coverage, sunlight, rain, snow, wind, outdoor temperature and relative humidity. The performance of the roofs depends mainly on these factors and the roof specifications [6,[14][15][16][17]29]. The absorbed solar radiation on the external surfaces of the roofing systems causes an increase in the surface temperature of the roof, thereby increasing the cooling load in summer and reducing the heating load in winter [30].…”

“…For PV panels, the dirt/dust accumulations on the panels obstruct or distract light energy from reaching the solar cells, resulting in reduction in PV performance (e.g., see [31,32]) for more details). As provided in [6,16,17] for cool roof applications, dust and dirt accumulations on the reflective materials or coatings installed on the external surfaces of roofs can decrease the short-wave solar reflectivity of these surfaces. This results in increasing the solar heat gains.…”

“…The short-wave solar reflectivity is one of the most important properties for the reflective materials that have a great effect on the amount of energy savings [14,15,36]. Most recently, experimental and numerical studies were conducted to investigate the potential use of reflective roofing technology in hot, humid, dusty and polluted climates such as that in Kuwait and Saudi Arabia [6,16,17]. In these studies, the dust concentration on the surface of a Reflective Coating Material (RCM) that is currently available in the markets was measured in terms of the turbidity when the RCM was subjected to the natural weathering conductions of Jubail Industrial City (JIC).…”

“…Beside dust, this thin layer of the contaminants can contribute to reducing the short-wave solar reflectivity of RCM. Furthermore, technical guide and cleaning processes were developed to increase solar reflectivity of the RCM that would result in high energy savings (see [6,16,17] for more details).…”