Time Lags and Decrement Factors under Air-Conditioned and Free-Floating conditions for Multi-Layer Materials

Time lags and decrement factors for multi-layer materials without air gaps under air-conditioned and free floating conditions were obtained using the response factor and finite volume methods. The definitions under free floating conditions, which are independent of the external environmental conditions, are proposed for the first time. A special version of the finite volume method was employed in which the surfaces of materials were used as computational nodes and temperatures and heat fluxes on surfaces as primitive (state) variables. While the time lag is defined as a phase shift, the decrement factor is defined as the ratio of the amplitude of the temporal evolution of the temperature on the inner surface of the multi-layer material to that of the sol-air temperature or the outer surface temperature. To verify this analytical method, the time lags and decrement factors calculated by the response factor method were compared with the published results. The analytical expressions for the time lag and decrement factor of multi-layer materials under freefloating conditions were then obtained. Recommendations are made for choosing a proper definition for the time lag and decrement factor.