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The paper describes the methodology followed for the development of new cool products in order to widen the range of existing solutions both including coloured (even dark) materials and extending the application also to building vertical components. Cool coloured ceramic tiles and acrylic paints for façades and roof membranes have been developed and tested at lab scale. Spectral reflectance measurements have been performed demonstrating a significant improvement of reflectance in the Near InfraRed (NIR) range (up to. +0.40) while keeping dark colour and high absorbance in the visible. The development of new products has been also oriented to the improvement of durability properties, being this aspect of relevance for high reflecting materials that have to keep their cooling properties over the time. While ceramic tiles naturally offer superior resistance to outdoor ageing, a significant increase of biological growth resistance has been achieved also for roof membranes by including ZnO nanoparticles. The approach followed by the authors aimed at delivering products, that besides having higher NIR reflectance, were capable of satisfying industrial and market requirements being compatible with standard manufacturing processes and offering additional functionalities. A complementary paper will be dedicated to the extensive experimental and numerical evaluation of new materials' thermal performances. © 2014 Elsevier Ltd.

A significant contribution to the reduction of the Urban Heat Island effect and cooling energy demand is given today by the so called cool materials for the building envelope with enhanced reflecting and emitting properties. The present study shows some preliminary results of the EU project COOL-Coverings aiming at developing innovative nanobased coatings with improved Near InfraRed reflecting capabilities. The key idea is to work on a nanoscale by tuning the crystal size and distribution of selected nanostructured oxides. Cool prototypes of brown colored ceramic tiles and green acrylic paints have been developed and compared to conventional ones showing an improvement in solar reflectance without any perceptual difference in color. The material characterization has been based on the measurement of spectral reflectance on a wide wavelength range (300–2200 nm) using a UV/Vis/NIR spectrophotometer. In parallel with the development of nanostructured cool materials, natural aging tests on ceramic and painted concrete tiles have been performed with the goal of identifying and measuring the effects of the main aging factors affecting reflective properties. A significant drop of solar reflectance for paints has been noticed from the very beginning of the testing period while ceramic tiles have confirmed excellent resistance to weathering. However, both for paints and tiles the effect of soiling cannot be neglected and, if combined to weathering, it can lead to a solar reflectance reduction as high as 10%. This preliminary study will pave the way to a future development of dedicated accelerated aging testing procedures for cool materials.

International audience; A laboratory method to simulate natural exposure of roofing materials has been reported in a companion article. In the current article, we describe the results of an international, nine-participant interlaboratory study (ILS) conducted in accordance with ASTM Standard E691-09 to establish the precision and reproducibility of this protocol. The accelerated soiling and weathering method was applied four times by each laboratory to replicate coupons of 12 products representing a wide variety of roofing categories (single-ply membrane, factory-applied coating (on metal), bare metal, field-applied coating, asphalt shingle, modified-bitumen cap sheet, clay tile, and concrete tile). Participants reported initial and laboratory-aged values of solar reflectance and thermal emittance. Measured solar reflectances were consistent within and across eight of the nine participating laboratories. Measured thermal emittances reported by six participants exhibited comparable consistency. For solar reflectance, the accelerated aging method is both repeatable and reproducible within an acceptable range of standard deviations: the repeatability standard deviation sr ranged from 0.008 to 0.015 (relative standard deviation of 1.2–2.1%) and the reproducibility standard deviation sR ranged from 0.022 to 0.036 (relative standard deviation of 3.2–5.8%). The ILS confirmed that the accelerated aging method can be reproduced by multiple independent laboratories with acceptable precision. This study supports the adoption of the accelerated aging practice to speed the evaluation and performance rating of new cool roofing materials.

Cool materials have a large potential as cost-effective solution for reducing cooling energy consumption in hot summer and mild winter regions like Mediterranean countries. A previous paper has described in detail the development of cool coloured ceramic tiles, acrylic paints and bituminous membranes for the building envelope taking into account both roof and façade application. This paper proposes an experimental and numerical approach for evaluating thermal performances of these materials on calibrated middle scale units and the energy impact on real buildings. This twofold analysis aims at describing a method that can help manufacturers to accurately compare new products against existing ones taking into account also new potential applications (e.g. building façades). Five dedicated test cells have been realized in Algete, near Madrid, fully instrumented and calibrated before being covered with traditional and cool systems of the same colour. Thermal performances have been then monitored during summer 2012 and May 2013 showing a net reduction of heat flux through the building envelope (up to 50% of peak value) and wall temperature (up to 4.7°C) in the case of cool materials. An uncertainty analysis was also performed to validate results. In parallel with the testing campaign a 3D numerical model of the mock-up has been implemented and fine-tuned with experimental data. This model has been then used as virtual scenario on which coverings with different radiative properties can be accurately evaluated and compared. For a full characterization of new materials complementary simulations have been performed with the ESP-r software. Yearly cooling energy reductions ranging from 0.6 to 3.5kWh/m2 have been estimated on different European localities. This preliminary study also demonstrates how cool façades can have a positive impact on yearly energy savings especially in the case of multi-storeys buildings and hot climates. The results shown in the paper have been achieved within the EU project COOL-Coverings aiming at developing new cool coloured products for the building envelope. © 2014 Elsevier Ltd.