Cool roofs can help reduce the heat island effect and also help improving the energy performance of the buildings. A cool roof can reflect the sun’s heat and emits absorbed radiation back into the atmosphere at a higher rate than standard materials. The cool roofs technology has been used for more than 20 years (EPA, 2012). The cool roof basically helps in reflecting sunlight and heat, thus reducing the temperature of the roofs. 20-‐25% of the urban surface is reported to be occupied by roof surface.
The effect of global warming and climate change are matters of concern for the global community, and impacts both rural and urban areas. The world population is expected to increase by 2.3 billion between 2011 and 2050 (United Nations, 2011) and the population living in urban areas is projected to increase from 3.6 billion in 2011 to 6.3 billion 2050. In Asia, it is expected that half of the population will live in urban areas by 2020, while Africa is likely to reach a 50% urbanization rate in 2035 (United Nations, 2012).
One of the more effects in the urban areas is due to the Urban Heat Island (UHI) effect. The UHI can impact issues like public health, environmental hazards, quality of life, etc. The relative warmth of city compared to the rural areas is called as UHI. The changes in landscape i.e. buildings, roads, and other infrastructure replace open land and vegetation causes the surfaces to become impermeable and dry. The UHI effect tends to be strongest during the day when the sun is shining. On a sunny/hot day, the urban space (roofs, pavements) are exposed to sun which can bring the temperature of these areas to around 27–50°C hotter than the air.
The GHG emission reduction potential by the cool roofs is by energy saving which leads to reduced energy demand and hence cutting down the emissions. Akbari et al., 2011 found that changing the black roof to white roof can help in saving of 0.066-‐0.072 kWh/m2/day. The normalized energy saving for per unit of reflectance reduction will be 0.11-‐0.12 kWh/m2/day. It is estimated that white roofs increase solar reflectance by 0.40 helping reducing 100t/100m2 of CO2 emissions. Similarly, colored roofs can help mitigate 5t/100m2 of CO2 emissions which has solar reflectance of about 0.20 (Akbari et al., 2009).
Akbari, H., Tengfang X., Haider T., Craig W., Jayant S., Vishal G., Surekha T., M. Hari Babu, and K. Niranjan Reddy, (2011). Using Cool Roofs to Reduce Energy Use, Greenhouse Gas Emissions, and Urban Heat-‐island Effects: Findings from an India Experiment. Lawrence Berkeley National Laboratory Report.
Akbari, H., Menon, S. and Rosenfeld, A. (2009). Global cooling: increasing world-‐wide urban albedos to offset CO2. Climatic Change. 95 (3–4), doi: 10.1007/s10584-‐ 008-‐9515-‐9.
Akbari, H., and Matthews, H.D. (2012). Global cooling updates: Reflective roofs and pavements. Energy and Buildings.55, pp. 2-‐6.
Akbari, H. & Rosenfelf, A. ( 2008). White Roofs Cool the World, Directly Offset CO2 and Delay Global Warming. LBNL Heat Island Group. Available at: http://www.energy.ca.gov/2008publications/CEC-999-2008-031/CEC-999-2008-...
Akbari, H., Tengfang X., Haider T., Craig W., Jayant S., Vishal G., Surekha T., M. Hari Babu, and Reddy, K. N. (2011). Using Cool Roofs to Reduce Energy Use, Greenhouse Gas Emissions, and Urban Heat-‐island Effects: Findings from an India Experiment. Lawrence Berkeley National Laboratory Report.
APEC. (2011). Cool Roofs In APEC Economies: Review Of Experience, Best Practices And Potential Benefits. Singapore.
Berdahl P. and Bretz, S. (1997). Preliminary survey of the solar reflectance of cool roofing materials. Energy and Buildings. 25:149-‐158.
California Energy Commission. 2008. “2008 Building energy efficiency standards for residential and nonresidential buildings.” December. Available at: http://www.energy.ca.gov/2008publications/CEC-‐400-‐2008-‐001/CEC-‐400-‐2008-‐001-‐ CMF.PDF
Mathews, R., (2012). ‘ Three types of cool roofs’ Available at: http://www.thegreenmarketoracle.com/2012/07/three-‐types-‐of-‐cool-‐roofs.html.
Zinzi, M. and Angoli, S. (2012). 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. Energy and Buildings. Vol. 55, pp. 66–76.
EPA. (2008). Reducing Urban Heat Islands: Compendium of Strategies. Available at: http://www.epa.gov/hiri/resources/pdf/CoolRoofsCompendium.pdf
EPA. (2012). Cool Roofs. Available at: http://www.epa.gov/hiri/mitigation/coolroofs.htm
Konopacki, S., and H. Akbari (2002). Energy Savings for Heat Island Reduction Strategies in Chicago and Houston (Including Updates for Baton Rouge, Sacramento, and Salt Lake City). Paper LBNL-‐49638. Lawrence Berkeley National Laboratory, Berkeley, CA.
Synnefa, A. and Santamouris, M. (2009). ‘Promotion of Cool Roofs in the EU-‐The Cool Roofs Project’, Group Building Environments Studies, Greece. Accesses at: 20 December 2012. Available at: http://heatisland2009.lbl.gov/docs/231120-‐synnefa-‐doc.pdf
Tetali, S. (2011). Assessment of cool roof technology for its energy performance in buildings. (Masters research study, International Institute of Information Technology, 2011). Hyderabad: International Institute of Information Technology.
Urban, B. & Roth, K. (2010). Guidelines for Selecting Cool Roofs. Fraunhofer Center for Sustainable Energy Systems for the U.S. Department of Energy Building Technologies Program and Oak Ridge National Laboratory. Vol. 1.2. Available at: http://www1.eere.energy.gov/femp/pdfs/coolroofguide.pdf
