scope:

ABSTRACT

The objective was to develop a simplified U-factor calculation procedure to evaluate an extensive range of cold-formed steel C-shape clear wall assemblies that can be used for energy analysis and code compliance. The scope addresses five wall stud dimensions, four stud spacings, four designation thicknesses, nine cavity insulations, and seven insulated sheathings, for a total of 2128 cases. The technical approach was to (1) analyze each case using the THERM 7.6 two-dimensional heat transfer computer program to determine the U-factors; (2) apply the parallel path calculation procedure for the steel C-shape and cavity insulation paths; (3) calculate the "effective" thermal width of the steel C-shape path, which was defined as the overall thermal zone (OTZ); (4) develop a series of regression equations using Minitab to correlate the OTZ with the key construction variables; (5) develop a Microsoft^® Excel^® spreadsheet that integrates the regression equations with the parallel path procedures; and (6) use the spreadsheet to calculate the U-factors for the 2128 cases. The U-factor results from the spreadsheet were compared to the THERM 7.6 results and the average difference for the 2128 cases was 0.27% with a standard deviation of 3.11%. Based on these results, the simplified U-factor calculation procedure was deemed acceptable for use in energy analysis and developing code compliance criteria for ANSI/ASHRAE/IES Standard 90.1 and the International Energy Conservation Code (IECC).