Research Report RP18-1
For building envelope assemblies, thermal bridging through conductive components can greatly reduce the overall thermal resistance of that assembly. Steel stud assemblies are particularly susceptible to thermal bridging due to the high thermal conductivity of the steel components. Being able to accurately capture these impacts can provide designers with more realistic information to drive better design decisions in regards to building thermal performance and building energy use.
The American Iron and Steel Institute (AISI) is developing a simplified calculation methodology for determining the thermal performance of generic steel stud assemblies that includes the impacts of thermal bridging. While hot-box testing and computer simulations can produce accurate thermal performance values, the goal is to provide a practical means of calculating U-factors for these assemblies without the direct need for additional software or testing apparatus. As part of the development process of the AISI simplified calculation methodology, a robust 3D thermal modelling analysis was conducted on a variety of steel stud assemblies. This was done to provide accurate values on which the simplified calculation methodology can be based.
For this project, the thermal modelling was conducted using Siemens NX modelling software and TMG Thermal Solver, following the procedures set forth and calibrated in ASHRAE 1365- RP. The software and procedures were further validated for this project using comparisons between simulated values and hotbox data sets from ASHRAE-785 RP and a compilation of 2011-2012 steady-state hot box tests conducted at ORNL.
A sensitivity analysis of the steel conductivity k-value was also conducted. This analysis investigated the potential impact on the assembly thermal performance if this k-value was varied within the typically reported range for galvanized steel.
For the main body of work for this project, the thermal performance of 27 steel stud assemblies was determined. The assemblies varied by insulation thickness, insulation placement and steel stud depth. Multiple fastener patterns for the insulation and sheathings were also examined.
Overall, 127 simulations were run including validation, sensitivity testing and assembly modelling for this project. This report provides a summary of the model validation, sensitivity analysis and overall thermal performance (effective R- and U-values) of the analyzed steel stud assemblies, as well as key temperature indices.
Civil, Architectural and Environmental Engineering
Wei-Wen Yu Center for Cold-Formed Steel Structures
American Iron and Steel Institute
01 Feb 2018
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American Iron and Steel Institute, "Thermal Analysis of Cold-Formed Steel Wall Assemblies" (2018). AISI-Specifications for the Design of Cold-Formed Steel Structural Members. 158.