Urbanization related to population growth is one of the burning issues that the world is facing today. Parallel to this, there is visible evidence of a possible energy crisis in the near future. Thus, scientists have paid attention to sustainable development methods, and in the field of building construction also, several innovations have been proposed. For example, green roof concept is one of such which is considered a viable method mainly to reduce urban heat island effect, to regain lost land spaces in cities, and to increase aesthetics in cities. The present study was aimed at investigating the impact of green roofs on indoor temperature of buildings, the effect of different types of roofs on the air conditioning loads, and the life cycle cost of buildings with different types of roofing. The study was conducted in several phases: initial small-scale models to determine the heat flow characteristics of roof top soil layers with different thicknesses, a large-scale model applying the findings of the small-scale models to determine temperature fluctuations within a building with other common roofing systems, a computer simulation to investigate air conditioning loads in a typical building with cement fiber sheets and green roof slabs, a comparative analysis of the effect of traditional type roofs and green roofs on the air conditioning loads, and finally an analysis to predict the influence of traditional type roofs and green roofs on life cycle cost of the buildings. The main findings of the study were that green roofs are able to reduce the indoor temperature of buildings and are able to achieve better heat transfer through the roof, and, thus a lower cooling load is necessary for air conditioning and has the possibility of reducing life cycle cost of a building. 1. Introduction In the past few decades, scientists have focused greater attention on sustainable development because of the energy crisis which has reached up to an alarming level by now. Energy requirement of urbanized areas is rising rapidly [1, 2]. Since people are becoming much concerned about thermal comfort, the demand for energy has also been at a rise. However, this could lead to an energy crisis with the expected global climatic changes [3]. Moreover, higher consumption of energy may result in urban heat island effect in cities [3]. As the development of cities is coupled with environmental pollution, primarily in the developing countries, environmental friendly constructions are essential [1]. Further to this, the impact of developmental activities on environment forces us to
References
[1]
R. U. Halwatura and M. T. R. Jayasinghe, “Influence of insulated roof slabs on air conditioned spaces in tropical climatic conditions—a life cycle cost approach,” Energy and Buildings, vol. 41, no. 6, pp. 678–686, 2009.
[2]
S. N. Wijerathne and R. U. Halwatura, “Amplification of comfort and the air quality with green roof in cities,” in Proceedings of the International Conference Structural Engineering, Construction and Management, Moratuwa, Sri Lanka, December 2011.
[3]
S. N. Wijerathne and R. U. Halwatura, “The impact of green roofs on urban heat island effect,” in Proceedings of the International Conference on Building Resilience (ICBR '11), Moratuwa, Sri Lanka, July 2011.
[4]
I. Jaffal, S. E. Ouldboukhitine, and R. Belarbi, “A comprehensive study of the impact of green roofs on building energy performance,” Renewable Energy, vol. 43, pp. 157–164, 2012.
[5]
E. Eumorfopoulou and D. Aravantinos, “The contribution of a planted roof to the thermal protection of buildings in Greece,” Energy and Buildings, vol. 27, no. 1, pp. 29–36, 1998.
[6]
T. Takakura, S. Kitade, and E. Goto, “Cooling effect of greenery cover over a building,” Energy and Buildings, vol. 31, no. 1, pp. 1–6, 2000.
[7]
D. Townshend, “Study on green roof application in Hong Kong,” Architectural services department, 2007.
[8]
World Urbanization Prospects, the 2011 Revision, Department of Economic and Social Affairs, United Nation, New York, NY, USA, 2012.
[9]
T. A. Obaid, State of World Population 2007: Unleashing the Potential of Urban Growth, UNFPA, 2007.
[10]
G. Anker, Urbanization Overspeed in Tropical Africa 1970–2000, INUPRESS, Geneva, Switzerland, 1986.
[11]
M. Duneier, Ethnography, the Ecological Fallacy and the 1995 Chicago Heat Wave, Princeton University and CUNY Graduate Center.
[12]
S. Onmura, M. Matsumoto, and S. Hokoi, “Study on evaporative cooling effect of roof lawn gardens,” Energy and Buildings, vol. 33, no. 7, pp. 653–666, 2001.
[13]
R. U. Halwatura and M. T. R. Jayasinghe, “Strategies for improved micro-climates in high-density residential developments in tropical climates,” Energy for Sustainable Development, vol. 11, no. 4, pp. 54–65, 2007.
[14]
R. U. Halwatura and A. A. D. A.J. Perera, “Risk in the use of asbestos roofing sheets in Sri Lanka, Environmental Science and Policy,” in Proceedings of the Annual Symposium, Kothalawala Defence University, Kotte, Sri Lanka, December 2009.
[15]
M. T. R. Jayasinghe and C. Jayasinghe, Sustainable Design of Building, University of Moratuwa, Moratuwa, Sri Lanka, 2009.
[16]
M. T. R. Jayasinghe and D. P. K. Maharachchi, “Use of reinforced brickwork for crack free load bearing construction,” in Proceedings of the Research for Industry, pp. 38–51, Engineering Research Unit, University of Moratuwa, 1998.
[17]
B. L. Ong, “Green plot ratio: an ecological measure for architecture and urban planning,” Landscape and Urban Planning, vol. 63, no. 4, pp. 197–211, 2003.
[18]
R. L. Duble, “Buffalo Grass,” http://aggie-horticulture.tamu.edu/archives/parsons/turf/publications/buffalo.html.
[19]
R. U. Halwatura and M. T. R. Jayasinghe, “Thermal performance of insulated roof slabs in tropical climates,” Energy and Buildings, vol. 40, no. 7, pp. 1153–1160, 2008.
[20]
T. G. Theodosiou, “Summer period analysis of the performance of a planted roof as a passive cooling technique,” Energy and Buildings, vol. 35, no. 9, pp. 909–917, 2003.
[21]
K. K？llblad, “A method to estimate the shading of solar radiation: theory and implementation in a computer program,” in Proceedings of the the Sixth International BPSA Conference, pp. 595–601, Building Performance Simulation Association, 1999.
[22]
C. Ratnaweera and A. G. Hestnes, “Enhanced cooling in typical Sri Lankan dwellings,” Energy and Buildings, vol. 23, no. 3, pp. 183–190, 1996.
[23]
A. I. Jayawardhana, Passive techniques for energy efficiency of building in Sri Lanka [M.S. thesis], Department of Civil Engineering, University of Moratuwa, Moratuwa, Sri Lanka, 2002.
[24]
K. S. Fuller and S. R. Petersen, NIST Handbook 135: Life Cycle Costing Manual for the Federal Energy Management Program, U.S. Government Printing Office, Washington, DC, USA, 1996.
[25]
M. T. R. Jayasinghe and R. A. Athalage, “Passive techniques for residential buildings in low altitudes of Sri Lanka,” vol. 30, no. 2, pp. 18–27, 1999.
[26]
R. Kumar and S. C. Kaushik, “Performance evaluation of green roof and shading for thermal protection of buildings,” Building and Environment, vol. 40, no. 11, pp. 1505–1511, 2005.
[27]
A. Kadirgamar, “Legitimacy and crisis in Sri Lanka,” Economic and Political Weekly, vol. 47, no. 9, pp. 25–29, 2012.
