Dynamic thermal performance of concrete and masonry walls

Modern, massive building envelope technologies (masonry and concrete systems) are gaining acceptance by builders today. All U.S. thermal building standards, including ASHRAE 90.1 and 90.2 and the Model Energy Code, are linked to the steady-state clear wall R-value. They also have separate requirements for high mass walls. Very often, only steady-state R-value is used as a measure of the steady-state thermal performance of the wall. This value does not reflect the dynamic thermal performance of massive building envelope systems. Proper application of thermal mass in buildings can be one of the most effective ways of reducing building heating and cooling loads. However, these systems require application of dynamic thermal performance analysis. The dynamic thermal performance of a series of wall assemblies is analyzed in this paper. Results should enable an approximate dynamic thermal performance evaluation for most popular massive walls. Also, some complex structures are analyzed. Normally, complex three-dimensional building envelope components cannot be accurately simulated using one-dimensional computer models such as DOE-2 or BLAST. Typically, thermal modelers have to use simplified one-dimensional descriptions of complex walls, which may significantly reduce the accuracy of computer modeling. The application of a newly developed equivalent wall theory enabled accurate whole building dynamic energy analysis for complex three-dimensional wall material configurations. A new measure of the wall thermal dynamic performance is proposed in this paper—dynamic benefit for massive systems (DBMS). The thermal mass benefit is a function of the material configuration and climatic conditions. To enable wall performance comparisons, the “R-value equivalent for massive system” is used. The R-value equivalents for massive walls are obtained by comparison of the thermal performance of the massive walls and lightweight wood frame walls.