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Keywords
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Roofing materials, Thermal storage, Heat gain, Cooling load, Time lags
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Abstract
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In this study, thermal performance of three kinds of roofs with different heat capacity and thermal conductivity under different external conditions is investigated by a numerical method. For this purpose, the combined solar radiation, conduction and convection heat transfer were calculated implicitly using a one-dimensional finite difference method. Different high and low solar radiation conditions in two common climates in the Middle East including hot-humid and hot-dry are considered. The effect of roofing materials is investigated in terms of their thermal storage and overall heat transfer coefficient. Also, the time lags and decrement factors are evaluated to compare roofs performance. The numerical model has been validated using EnergyPlus. The results show that the roof with high thermal storage and low thermal conductivity has better performance in comparison to others. However, the total heat gains are not linearly proportional to the overall heat transfer coefficients e.g. here, the ratios of the total load of roof 1 to roofs 2 and 3 are about 12 percent lower than the ratio of overall heat transfer coefficients. Also, the solar radiation intensity had considerable effects on time lags. Finally, the external conditions have no significant effect on the decrement factor.
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