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Urban heat island is an anthropogenic phenomenon affecting urban outdoor thermal comfort conditions\ud and energy utilization. This is even truer in urban canyon configurations, characterized by low sky view\ud factor and where the effect of short-wave and long-wave solar radiation on construction surfaces is able\ud to produce massive outdoor local overheating. Traditional solutions cannot always be applied in urban\ud historical canyons, where the exteriors of buildings cannot be modified due to preservation. Here, the\ud capability of innovative cool materials to mitigate local microclimate of historical urban canyons is\ud investigated. A preliminary experimental characterization of the materials is performed. A numerical\ud simulation of the microclimate effect generated by the application of such materials is performed. Results\ud show that the proposed materials improve the microclimate without neglecting preservation constrains.\ud Such materials set the best scenarios in terms of thermal comfort, by enhancing albedo on canyon\ud surfaces. Their application on the vertical surfaces of narrow canyons can lead to deleterious effects on\ud outdoor thermal comfort. Such findings are confirmed by PMV and MOCI analyses. Energy efficiency\ud solutions may be effectively implemented in historical districts, opening the doors to other tailored\ud solutions, such as integrated renewables, to make these environments more sustainable and comfortable

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Marble is a natural material, used in the construction field since antiquity. It has always been used to communicate monumentality and solidity. Nowadays new technologies permit marble to express new languages: particularly, translucent marble technology overturns the concept of solidity. The main issue to address is the lack of thermal-energy performance of such a thin stone layer as the only facade component. Conversely, Bianco Carrara and Statuario marbles, for instance, have intrinsic benefits as natural cool materials, due to their high solar reflectance and thermal emissivity. Thus, this paper analyzes the thermal-energy and environmental behavior of marble facade for a new designed building in New York City. An integrated analysis of the energy performance of the marble skin is performed through a preliminary experimental characterization, carried out for two different types of naturally white marble, for comparative purposes. Then, a dynamic simulation model of the building is developed to evaluate year-round benefits and drawbacks of the translucent marble envelope in terms of indoor thermal comfort and air-conditioning requirement. The analysis showed how the proposed marble facade is able to decrease the energy requirement for cooling up to 6%, demonstrating possible relevant perspectives for marble-based facades, even in energy-efficient buildings. OPEN ACCESSSustainability 2014, 6 5440 Keywords: thin translucent marble; building envelope; energy efficiency in buildings; cool natural material; optic-energy and thermal characterization; dynamic thermal-energy simulation of buildings