Due to the increasing amount of new residential and commercial constructions using massive exterior building envelope technologies, it is very important to optimize the mass and insulation distribution in walls. In comparing several massive walls with the same R-value, it can be observed that some wall configurations are more thermally effective than others [1]. This superior thermal performance can be detected only for a specific distribution of mass and insulation inside the wall.
Energy effects of different thermal mass and insulation arrangements in massive exterior walls, have been studied by several authors [2-4]. For multilayer walls, three basic material configurations were considered: insulation either inside or outside the massive layer, and insulation located between two massive layers. The results of extensive parametric analysis have shown explicitly that walls with the insulation outside always performed better than those with the insulation inside. The conclusions of the present study-for the same type of residential building considered by Huang, Byrne, and Ritschard-are generally the same; however, more attention is paid to the dynamic thermal properties of walls themselves and their dependence on structural characteristics.
The annual energy demand of a building for heating and cooling is affected to some extent by the thermal stability of the building itself. Building thermal stability is understood as the ability to hold the internal temperature within a certain interval given normal external temperature oscillations and either with a constant energy supply from the plant or without any plant action. This building thermal stability depends on the dynamic thermal responses of all building envelope components (exterior walls, internal partitions, ceilings, and floors) to external and internal temperature variations. Dynamic responses are determined by the thermal properties of materials, the total amounts of materials used, and their specific arrangement within structures.
The important feature of the ambient temperature course is its diurnal character. It can be relatively well approximated by a harmonic function. Analysis of the simple one-room model of a building exposed to periodic temperature oscillations, for which an analytic solution is available, gives some insight into the complicated stability problems of real buildings. Such a simple model is examined in this paper.
The so-called thermal structure factors are used in selecting and analyzing multilayer walls with essentially different dynamic thermal properties. Six characteristic exterior wall configurations are considered for this study. Walls - of the same R-value and capacity - are composed of the same amount of heavyweight concrete and insulating foam and finished with gypsum board and stucco. They differ only in the arrangement of concrete and insulation layers. Walls with insulation layers on both sides of the concrete core are also included. A material configuration of this kind can be found in insulating concrete forms system (ICF) walls, which generate very specific dynamic thermal properties.
Whole-building dynamic DOE-2.1 E modeling [5] was employed for energy analysis of the one-story residential building. The simulation was performed for six U.S. climatic zones. Three types of whole building performance data were compared for each type of wall: annual heating loads, annual cooling loads, and total annual energy demand.
© Oak Ridge National Labs and Polish Academy of Sciences
Updated August 15, 2001 by Diane McKnight