Comparison of experimental and analytical methods to evaluate thermal bridges in wall systems

Twelve ASTM C0236 guarded hot box experiments have been performed on wall systems containing a variety of thermal bridges. All of the wall systems included steel framing. Six walls also had a concrete block wall system and a concrete slab to simulate a wall/floor intersection. Thermal bridges included in the wall systems included steel studs, steel tracks, steel stud/track joints, fasteners (steel framing system), concrete slab, metal bolts and angle iron, and brick ties (concrete block wall). Two-dimensional finite difference modelling was also employed to characterize the wall systems. The experimental test data was used to tune and ultimately validate the computer simulation model. The average variation between the tested and simulated wall system R-Values was 3.3% and ranged from -3.4 to +7.4%. The model was then used to determine the thermal impact of each individual thermal bridge. Beside the standard complement of temperature sensors that are traditionally used for these laboratory experiments, additional sensors were installed near each thermal bridge to define the area and magnitude of the thermal distortion caused by the thermal bridge. These thermal bridges were analytically simulated and the additional heat flux due to each thermal bridge was computed. This paper summarizes the experimental and analytical analyses used to characterize the wall systems and concentrate on the thermal impact each type of thermal bridge has on the overall performance of the wall systems.