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Constructions and related matters relevant to environmental health
Published in Stephen Battersby, Clay's Handbook of Environmental Health, 2023
John Bryson, Stephen Battersby
“Cool” roofs (usually light in colour) are roofing systems that can deliver high solar reflectance (albedo) and have the ability to reflect the visible, infrared and ultra-violet wavelengths of sunlight and reduce heat transfer to the building. They also have high thermal emittance (the ability to radiate absorbed or non-reflected solar energy). “Green roofs”, sometimes known as “living roofs”, are roofs that are partially or wholly covered with vegetation and a growing medium, planted over a waterproofing membrane. It may also include additional layers such as a root barrier and drainage and irrigation systems. They serve several purposes for a building, such as absorbing rainwater, providing insulation, creating a habitat for wildlife, and helping to lower urban air temperatures. Both forms of roof counter the heat island effect. An urban heat island is an urban area that has significantly higher temperatures than surrounding rural or less densely populated areas.
Cool materials in buildings. Roofs as a measure for urban energy rehabilitation
Published in Vincenzo Costanzo, Gianpiero Evola, Luigi Marletta, Urban Heat Stress and Mitigation Solutions, 2021
Noelia Liliana Alchapar, María Florencia Colli, Erica Norma Correa
In the 21st century, environmental and energy problems have become more evident originating a greater interest in investigating the scope, limitations, and potential of high solar reflectance materials as a global warming adaptation and mitigation measure. According to these studies, the main benefits of cool roofs can be summarised in five main points:Reduction of the heat gain of buildings: the temperature of a reflective cool roof is generally similar to outdoor daytime ambient temperature [12]Savings in energy consumption for cooling due to a lower demand in the use of air conditioning during the summer period [13]Improvements in indoor thermal comfort conditions in buildings without air conditioning [14]Increased durability of roofing materials due to less thermal fatigue and less UV degradation, leading to lower material maintenance costs [15]Mitigation of up to 2°C in the heat island effect due to a lower heat transfer to the surrounding ambient air [4]
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Published in Igor Linkov, Emily Moberg, Benjamin D. Trump, Boris Yatsalo, Jeffrey M. Keisler, Multi-Criteria Decision Analysis, 2020
Igor Linkov, Emily Moberg, Benjamin D. Trump, Boris Yatsalo, Jeffrey M. Keisler
Reflective roofs, also known as “cool roofs,” are designed to reflect sunlight. Have you ever felt hotter in a black t-shirt than a white one on a sunny day? That’s not your imagination! Different surfaces absorb and reflect heat differently, and reflective roofs aim to reflect more than absorbed incoming radiation. They absorb considerably less heat than standard roofs; the surrounding air is thus cooler, reducing building heating demand. Cool roofs are characterized by the use of highly reflective or high-albedo materials; these can be reflective paints, sheet coverings, or reflective tiles or shingles. Such reflective materials may be installed (whether in a new roof or as part of a retrofit) at little to no additional upfront cost; they can result in long-term savings as a result of increased roof lifespan and lower energy costs (U.S. Environmental Protection Agency 2016; Urban and Roth 2012; Bretz et al. 1998).
Thermal performance of building prototype with different cool roof structures in composite climate
Published in International Journal of Sustainable Energy, 2022
Generally, Asian countries near the equator receive maximum solar irradiation with an intensity of 800–1000 W/m2 causing thermal discomfort associated with the built environment. It has led to a higher energy demand for thermal comfort in building sectors due to air conditioning systems. Thus, it is necessary to adopt energy-saving techniques (cool and green roofs), which reduce energy demand in buildings to maintain comfort level (Halwatura and Jayasinghe 2008). About 60% of the total energy consumed for heating, cooling, and ventilation in buildings has increased at the rate of 1.8% per annum over the last forty years. Most of the studies focused on improving residential and commercial buildings using the cool paints (Saafi and Daouas 2018; Singh and Rawat 2021; Rawat and Singh 2021a; Rawat, Singh, and Singh 2021). The roof is considered a critical component in all building envelopes because the maximum thermal load (50%–60%) enters through buildings during daytime operation. Cool roofs are one of the solutions to mitigate the urban heat island (UHI) effect and maintain thermal comfort in urban areas. Cool roofs have higher reflectance than conventional roofs, which help to decrease the surface temperature and sensible heat release (Rawat and Singh 2021b).
Developing sustainable design guidelines for roof design in a hot arid climate
Published in Architectural Science Review, 2019
Sama Mahmoud, Walaa S.E. Ismaeel
The cool roof technique reflects the direct solar radiation falling on a roof surface, thus reducing the amount of solar heat gain from outdoor into indoor spaces. This slows down the heat transfer into a building interior by reflective technique, then, removes extra heat from the building through radiation (Al-Obaidi, Ismail, and Abdul Rahman 2014a; Levinson, Akbari, and Reilly 2007; Shittu et al. 2018). It has various benefits e.g. heat retention and prevention, energy savings, as well as added protection against natural impacts (Al-Obaidi, Ismail, and Rahman 2014a; Sheng et al. 2011). Also, it has a global cooling influence (Akbari and Damon Matthews 2012), this is suitable to mitigate urban heat island effect (Bretz, Akbari, and Rosenfeld 1998) and hence, achieve buildings’ energy efficiency (Ganguly, Chowdhury, and Neogi 2015). Previous studies have discussed the thermal performance of reflective building materials and noteworthy for roof tiles (Hernández-Pérez et al. 2014, 2018; Jaffal, Ouldboukhitine, and Belarbi 2012). Some of the studies used an integrated empirical and modelling methodology (Jo et al. 2010). Others have pinpointed the adaptation of a cool roof for the dynamic thermal behaviour of buildings during summer and winter seasons, and its application for small scale residential buildings (Pisello and Cotana 2014; Pisello, Rossi, and Cotana 2014). Accordingly, it has been found suitable for different types of climates; Mediterranean climate (Silva, Gomes, and Silva 2016), hot climate (Ben Cheikh and Bouchair 2004; Suehrcke, Peterson, and Selby 2008) as well as the subtropical and equatorial climates (Brito Filho and Santos 2014).
A numerical study of cool and green roof strategies on indoor energy saving and outdoor cooling impact at pedestrian level in a hot arid climate
Published in Journal of Building Performance Simulation, 2023
Mohamed H. Elnabawi, Esmail Saber
Such reflective surfaces seem to be more promising for several reasons, not only because reflecting incident solar energy is the most direct method of reducing its effect, but also because a solar reflective coating can reflect >90% of the received solar radiation back to the sky. Further, installing reflective coatings or paints on buildings is very simple compared to other passive measures as it can be applied as ordinary paint (Hernández-Pérez et al. 2014), whereas the initial and maintenance costs of a green roof are much higher. When reflective coatings are applied as wall or ground materials, they can elevate the mean radiant temperature and cause discomfort outdoor conditions (Falasca et al. 2019; Middel et al. 2020; Schrijvers et al. 2016); this is why they are commonly used on roofs due to their high and longer sun exposure compared to other building envelope components (Todeschi et al. 2020). This exposure contributes to nearly 50–60% of a building’s overall cooling load in hot, warm, humid and dry climatic zones (Rawat and Singh 2021). The application of a reflective coating to a roof creates what is known as a ‘cool roof’, an expression used to define roofing material with high solar reflectance and albedo, leading to a significant degree of reflection of solar radiation. The cool roof’s high thermal emittance also permits a large amount of absorbed heat to be released, enabling the material to be cooler and contributing to a mitigation of the UHI effect. In hot, arid climates, this may be an optimal solution to higher energy loads for cooling caused by increased air temperatures and to overcome the high rate of heat stress and other heat-related illnesses due to the very high temperature (Harlan et al. 2006). In these zones, 60% of total energy consumption is due to air conditioning loads (Elsarrag and Alhorr 2012).