Cool Roofs vs Solar Systems

Abstract:

Well known problem of urban heat island is partly due to the albedo of traditional roofs. Mostexperts of urban climate are convinced that the intensity of urban heat island will be less if theroofs reflect as big part of the solar radiation as possible. Researchers have found or developedappropriate materials of low absorptance in the wavelength spectrum of solar radiation together with high emissivity in the long infrared interval. As a result, roof covering may have such extraparameters as metal roof painted with colored cool coating has 0.8 reflectance and 0.8 emittanceindex or single ply-membrane white (PVC) has 0.7 reflectance and 0.8 emittance index.No doubt taking into account the settlement as a whole cool roofs may decrease the intensity ofurban heat island however some local negative effect should not be forgotten. Approaching the citycenter it is typical that low rise and tall buildings are nearby. In some cases the same buildinghas high and low rise wings, from the point of view of geometry similar is the situation between thefacade and a canopy or a balcony. In this case the radiation reflect by the horizontal surfaceconsiderably increases the load on the facade, in this paper the relevant cases are analysed and thecalculated extra load and its consequences are evaluated.

• Periodical: Applied Mechanics and Materials (Volume 824)
• Pages: 779-785
• DOI: https://doi.org/10.4028/www.scientific.net/AMM.824.779
• Online since: January 2016
• Authors: Dominika Kassai-Szoó, András Zöld
• Keywords: Cool Roof, Cooling Load, Energy Collecting Elements, Reflected Radiation

References

[1] Unger János, Sümeghy Zoltán, Kántor Noémi, Gulyás Ágnes, Kisléptékű Környezeti Klimatológia, Jatepress, Szeged, (2012).

[2] LEED Leadership in Energy and Environmental Design, US Green Building Council, (2005).

[3] J.R. Simpson, E.G. McPherson, The effects of roof albedo modification on cooling loads of scale model residences in Tucson, Arizona, Elsevier Energy and Buildings 25 (1997) 127-137.

DOI: 10.1016/s0378-7788(96)01002-x

[4] Energy Performance of Buildings Directive recast 2010/31/EU of the European Paeliament and of the Council of 19 May 2010. Official Journal of the European Union.

[5] H. Akbari, M. Pomerantz and H. Taha, Cool surfaces and shade trees to reduce energy use and improve air quality in urban area, Elsevier Solar Energy Vol. 70, No. 3. pp (2001) 295-310.

DOI: 10.1016/s0038-092x(00)00089-x

[6] T. Gál, J. Unger, Theoretical and real solar energy gain on roofs in a densely built urban area with trees, Int. Rev. Appl. Sci. Eng. 4 (2013) 1, 13-2.

DOI: 10.1556/irase.4.2013.1.2

[7] Fredrik Lindberg, Per Jonsson, Tsuyoshi Honjo, Dag Wastberg, Solar energy on building envelopes – 3D modelling in a 2D environment, Solar Energy, Volume 115 (2015) 369-378.

DOI: 10.1016/j.solener.2015.03.001

[8] D.N. Asimakopoulos, V.D. Assimakopoulos, N. Chrisomallidou, N. Klitsikas, D. Mangold, P. Michel, M. Santamouris, A. Tsangrassoulis, Energy and Climate in the Urban Built Environment.

[9] A. Synnefa, A. Dandou, M. Santamouris, M. Tombrou, and N. Soulakellis, On the Use of Cool Materials as a Heat Island Mitigation Strategy, J. Appl. Meteor. Climatol., 47, (2008) 2846–2856.

DOI: 10.1175/2008jamc1830.1

[10] ECRC, European Cool Roofs Council An Introduction Guide for Cool Roofing Materials, (2012).