Effect of insulation location on thermal performance of building walls under steady periodic conditions

The present study deals with the effect of insulation location on the heat transfer characteristics of building wall elements under steady periodic conditions and for different wall orientations. The thermal performance with an insulation layer placed on the inside of a wall structure is compared to that when the insulation layer is placed on the outside. A numerical model based on a finite-volume implicit procedure is used to determine the detailed and overall thermal characteristics during representative days for the months of July and January in Riyadh, Saudi Arabia. The validation of the numerical model against an analytical solution developed for a three-layered composite wall, accounting for the periodic variations in outdoor ambient temperature and solar insolation, shows excellent agreement. The results of model application reveal that the insulation layer location has a minimal effect on the mean daily cooling and heating loads, with a slight advantage for the outside insulation in summer and the inside insulation in winter. However, the outside insulation gives smaller amplitude of load fluctuation and smaller peak load in both summer and winter for all wall orientations, which could be advantageous in sizing air conditioning systems. Moreover, the outside insulation slightly increases the time lag in summer, compared to the inside insulation, and has practically the same effect on time lag in winter. The dynamic R-values are averaged over a full period and compared for different wall orientations, seasons and insulation locations.