Effect of ageing on solar spectral reflectance of roofing membranes: Natural exposure in Roma and Milano and the impact on the energy needs of commercial buildings

Abstract Highly reflective roofs, widely known as cool roofs, can reduce peak surface temperatures and the energy required to cool buildings, mitigate urban microclimates, and offset CO 2 . However, weathering, soiling, and biological growth affect their solar reflectance. In this study, the solar spectral reflectances of 12 roofing membranes were measured before the exposure and after 3, 6, 12, 18, and 24 months of natural ageing in Roma and Milano, Italy. The membranes with an initial solar reflectance greater than 0.80, for example, decreased in reflectance by 0.14 in Roma and 0.22 in Milano after two years. Then, for a typical highly insulated commercial building, the annual cooling load savings were calculated to be reduced by 4.1–7.1 MJ m −2  y −1 per 0.1 loss in reflectance. When the buildings are non-insulated, the savings reduction is 58–71 MJ m −2  y −1 in Milano and 70–84 MJ m −2  y −1 in Roma. Ageing yielded a reduction of the cooling load savings that could be achieved with a new white membrane of 14–23% in Roma and of 20–34% in Milano. Moreover, in Milano, an aged, white, highly insulated roof, which has a solar reflectance of 0.56, may reach a surface temperature 16 °C higher than a new roof, which has a solar reflectance of 0.80.

[1]  Ahmed Memon Rizwan,et al.  A review on the generation, determination and mitigation of Urban Heat Island , 2008 .

[2]  Maria Kolokotroni,et al.  THE EFFECT OF THE LONDON URBAN HEAT ISLAND ON BUILDING SUMMER COOLING DEMAND AND NIGHT VENTILATION STRATEGIES , 2006 .

[3]  Anna Laura Pisello,et al.  The thermal effect of an innovative cool roof on residential buildings in Italy: Results from two years of continuous monitoring , 2014 .

[4]  Masayuki Ichinose,et al.  Long-term performance of high-reflectivity exterior panels , 2009 .

[5]  Ana H. Delgado,et al.  Aging and weathering of cool roofing membranes , 2005 .

[6]  Ronnen Levinson,et al.  Effects of soiling and cleaning on the reflectance and solar heat gain of a light-colored roofing membrane , 2005 .

[7]  M. Zinzi.  Self-cleaning ability and cooling effect of TiO2-containing mortars , 2013 .

[8]  M. Zinzi.  Cool materials and cool roofs: Potentialities in Mediterranean buildings , 2010 .

[9]  Mohamad Sleiman,et al.  Soiling of building envelope surfaces and its effect on solar reflectance Part I: Analysis of roofing product databases , 2011 .

[10]  H. Akbari,et al.  Cool surfaces and shade trees to reduce energy use and improve air quality in urban areas , 2001 .

[11]  P. Bacci,et al.  The urban heat island of Milan , 1992 .

[12]  Maria Kolokotroni,et al.  London's urban heat island: Impact on current and future energy consumption in office buildings , 2012 .

[13]  Hashem Akbari,et al.  Aging of reflective roofs: soot deposition. , 2002, Applied optics.

[14]  M. Zinzi,et al.  Cool and green roofs. An energy and comfort comparison between passive cooling and mitigation urban heat island techniques for residential buildings in the Mediterranean region , 2012 .

[15]  C. Romeo,et al.  Impact of a cool roof application on the energy and comfort performance in an existing non-residential building. A Sicilian case study , 2013 .

[16]  Tiziana Poli,et al.  The Influence of the Urban Heat Island over Building Energy Demand: the Case of Milan , 2009 .

[17]  P. Zangheri,et al.  Simplified method for modification of weather data file for energy simulations within urban areas , 2009 .

[18]  Ronnen Levinson,et al.  Three-year weathering tests on asphalt shingles: Solar reflectance , 2012 .

[19]  R. E. Douglass,et al.  Carbon and the optical properties of atmospheric dust. , 1993, Applied optics.

[20]  A. Rosenfeld,et al.  COOL COMMUNITIES: STRATEGIES FOR HEAT ISLAND MITIGATION AND SMOG REDUCTION , 1998 .

[21]  H. Akbari,et al.  Measuring solar reflectance—Part I: Defining a metric that accurately predicts solar heat gain , 2010 .

[22]  David Faulkner,et al.  Measured temperature reductions and energy savings from a cool tile roof on a central California home , 2014 .

[23]  H. Akbari,et al.  Long-term performance of high-albedo roof coatings , 1997 .

[24]  Andrea Giovanni Mainini,et al.  Transparent multilayer ETFE panels for building envelope : thermal transmittance evaluation and assessment of optical and solar performance decay due to soiling. , 2014 .

[25]  R. Betts,et al.  Climate and more sustainable cities: climate information for improved planning and management of cities (producers/capabilities perspective) , 2010 .

[26]  Ronnen Levinson,et al.  Inclusion of cool roofs in nonresidential Title 24 prescriptive requirements - eScholarship , 2002 .

[27]  H. Akbari,et al.  Estimating the effect of using cool coatings on energy loads and thermal comfort in residential buildings in various climatic conditions , 2007 .

[28]  H. Akbari,et al.  Weathering of Roofing Materials-An Overview , 2008 .

[29]  Hashem Akbari,et al.  Impact of the temperature dependency of fiberglass insulation R-value on cooling energy use in buildings , 1996 .

[30]  M. Santamouris,et al.  On the impact of urban climate on the energy consumption of buildings , 2001 .

[31]  H. Akbari,et al.  Soiling of building envelope surfaces and its effect on solar reflectance – Part II: Development of an accelerated aging method for roofing materials , 2014 .

[32]  Gian Marco Revel,et al.  Nanobased coatings with improved NIR reflecting properties for building envelope materials: Development and natural aging effect measurement , 2013 .

[33]  N. Klitsikas,et al.  The effect of the Athens heat island on air conditioning load , 2000 .