Effect of Insulation Location on Initial Transient Thermal Response of Building Walls

Abstract

The effect of insulation location on the heat transfer characteristics of building wall elements under initial transient conditions is studied. Thermal performance with an insulation layer placed on the inside of a wall is compared to that when the insulation layer is placed on the outside. The investigation is carried out for the climatic conditions of Riyadh, Saudi Arabia, during representative days for July and January using a finite-volume implicit procedure. The initial temperature distribution across the wall is assumed to be uniform and equal to the daily mean external air temperature. The numerical model is validated against a semi-analytic solution developed for a simple test case. The results of model application under the present conditions show that placing the insulation on the inside gives an instantaneous load that is about 20% of the value for outside insulation during the first few hours in the initial transient process. Besides, the duration of the transient process which leads to steady periodic state, and thus, the period of thermal discomfort due to radiation exchange is much shorter for the inside insulation. The average heat transmission over the first 24 hours of air-conditioning operation with the inside insulation is about one-third of that with the outside insulation. The dynamic R-values are averaged over the first 24 hours and compared for various wall orientations, seasons and insulation locations. It is recommended that for spaces where the air-conditioning system is switched on and off intermittently, the insulation should be placed on the inside.