An Experimental Investigation of the Effect of Thermophysical Properties on Time Lag and Decrement Factor for Building Elements

Abstract

The time lag (TL) and decrement factor (DF) are essential for the heat storage capabilities ofbuilding elements, which strictly depend on the thermophysical properties of the elements.Many investigations are presented in literature arguing to find the influence of eachthermophysical property on TL and DF by keeping the other properties constant. This studyaims to investigate the effect of each property on TL and DF, utilizing relationships betweenthe measurement values of the thermophysical properties of wall materials. Therefore, first,132 new concrete wall samples were produced, and their thermophysical properties weretested. Secondly, TL and DF values for each building element are computed from the solutionof the problem by Complex Finite Fourier Transform (CFFT) technique. Finally, amultivariate regression analysis has been performed, and the variations of eachthermophysical property versus TL and DF are presented, and also the findings are comparedwith literature. The results show that each property alone (keeping the other propertiesconstant) is not adequate to identify the thermal inertia and thermal performance of a wallelement. Besides, 87.3 % decrease in thermal diffusivity corresponds to 6.03 h increase in thevalue of TL and 88.8 % decrease in value of DF; respectively, for W1 wall assembly