Correlating thermal transmittance limits of walls and roofs to orientation and solar absorption

The presented research addresses the association of maximum thermal transmittance (U value) of walls and roofs with orientation and solar absorption. The study is performed on walls and a roof typically used in Kuwait when subjected to local hot climate conditions. A computer program employing the total equivalent temperature difference (TETD) method is developed to estimate the U values corresponding to solar absorption coefficients ranging from 0 to 1. At zero solar absorption coefficient, the maximum U values stipulated in the existing national energy code are used to induce the constant total daily heat flux for the developed correlations. Furthermore, the thermal inertia parameters affected by the established U values are also predicted. The results show that the orientation and absorption coefficient have a profound effect on the U value particularly for the roof and west and east wall orientations. Moreover, the decrease in the thermal transmittance significantly enhances the thermal inertia parameters of the aerated autoclaved concrete wall type.The developed correlations can be added to the Kuwait building energy code to extend the application scope of the U value limits based on surface orientation and external solar properties.

► Effect of orientation and solar absorption on thermal transmittance is investigated.
► Computer program is developed to compute the U value and thermal inertia parameters.
► Thermal inertia of aerated autoclaved wall is enhanced with Lower U values.
► Solar absorption has profound effect on roof and west and east wall orientations.
► U value correlations established as a function of solar absorption and orientation.