University of Technology, Mechanical Engineering Department, Baghdad, Iraq


Double skin ventilated roof is one of the important passive cooling techniques to reduce solar heat gain through roofs. In this research, an experimental study was performed to investigate the thermal behaviour of a double skin roof model. The model was made of two parallel galvanized steel plates. Galvanized steel has been used in the roof construction of industrial buildings and storehouses in Iraq. The effect of inclination angle (ϴ) from the horizontal and the spacing (S) between the plates was investigated at different radiation intensities. It is found that using a double skin roof arrangement with a sufficient air gap (S) can reduce the heat gain significantly. The higher the inclination angle (ϴ) the higher the ventilation rate, the lower the heat gain through the roof. In this study, increasing the air gap from 2 cm to 4 cm reduced the heat gain significantly but when the gap was further increased to 6 cm, the reduction in the heat flux was insignificant. A dimensionless correlation was also reduced between Nusselt number ( ) and the single parameter ( ⁄ ) where L is the channel length. This correlation can be handily utilized for designing of engineering applications dealing with high temperature difference natural convection heat transfer.


Main Subjects

[1] J. Hirunlabh, S. Wachirapuwadon, N. Pratinthong, and J. Khedari, “New configurations of a roof solar collector maximizing natural ventilation,” Build. Environ.. Vol. 36, No. 3, pp. 383–391, 2001.
[2].J. Khedari, P. Yimsamerjit, and J. Hirunlabh, “Experimental investigation of free convection in roof solar collector,” Build. Environ. Vol. 37, No. 5, pp. 455–459, 2002.
[3] T. Bunnag, J. Khedari, J. Hirunlabh, and B. Zeghmati, “Experimental Investigation of free convection in an open-ended inclined rectangular channel heated from the top,” Int. J. Ambient Energy, Vol. 25, No. 3, pp. 151–162, 2004.
[4] W. Puangsombut, J. Hirunlabh, J. Khedari, B. Zeghmati, and M. M. Win, “Enhancement of natural ventilation rate and attic heat gain reduction of roof solar collector using radiant barrier,” Build. Environ. Vol. 42, No. 6, pp. 2218–2226, Jun. 2007.
[5] C. ming Lai, J. Y. Huang, and J. S. Chiou, “Optimal spacing for double-skin roofs,” Build. Environ. Vol. 43, No. 10, pp. 1749–1754, 2008.
[6] L. Susanti, H. Homma, H. Matsumoto, Y. Suzuki, and M. Shimizu, “A laboratory experiment on natural ventilation through a roof cavity for reduction of solar heat gain,” Energy Build., Vol. 40, No. 12, pp. 2196–2206, 2008.
[7] Y. K. Salman and H. S. Hamad, “Laminar Natural convection heat transfer between ducted parallel plates,” J. Eng., Vol. 14, No. 3, pp. 2786–2803, 2008.
[8] S. Lee, S. H. Park, M. S. Yeo, and K. W. Kim, “An experimental study on airflow in the cavity of a ventilated roof,” Build. Environ. Vol. 44, No. 7, pp. 1431–1439, 2009.
[9] S. Tong and H. Li, “An efficient model development and experimental study for the heat transfer in naturally ventilated inclined roofs,” Build. Environ. Vol. 81, pp. 296–308, 2014.
[10] B. Bokor, H. Akhan, D. Eryener, and L. Kajtár, “Theoretical and experimental analysis on the passive cooling effect of transpired solar collectors,” Energy Build., Vol. 156, pp. 109–120, 2017.
[11] A. Namin, C. Jivacate, D. Chenvidhya, K. Kirtikara, and J. Thongpron, “ Construction of tungsten halogen, pulsed LED, and combined tungsten halogen-LEd solar simulators for solar cell I - V characterization and electrical parameters determination ,” Int. J. Photoenergy, Vol. 2012, pp. 1–9, 2012.
[12] P. C. Chang, C. M. Chiang, and C. M. Lai, “Development and Preliminary evaluation of double roof prototypes incorporating RBS (radiant barrier system),” Energy Build., Vol. 40, No. 2, pp. 140–147, 2008.
[13] M. C. Yew, N. H. Ramli Sulong, W. T. Chong, S. C. Poh, B. C. Ang, and K. H. Tan, “Integration of Thermal insulation coating and moving-air-cavity in a cool roof system for attic temperature reduction,” Energy Convers. Manag., Vol. 75, pp. 241–248, 2013.
[14] F. P. Incropera, D. P. DeWitt, T. L. Bergman, and A. S. Lavine, "Fundamentals of heat and mass transfer," Wiley, 2007.
[15] S. C. Chapra and R. P. Canale, "Numerical methods for engineers," Seventh, Vol. 33, No. 3. McGraw-Hill Science/Engineering/ Math, 2015.