SF-98-08-2 -- The Significance of Bolts in the Thermal Performance of Curtain-Wall Frames for Glazed Facades PDF

Curtain walls are assemblies of glazings and metal frames that commonly form the exterior glass facades of commercial buildings. Evaluating the thermal performance of the bolts that hold curtain wall glazings in place is necessary to accurately rate the overall thermal performance of curtain walls. Using laboratory tests and computer simulations, we assessed the thermal performance of several different configurations of bolts and glazings. Curtain-wall samples were tested at an infrared thermography laboratory. Experimental results were compared to two-dimensional simulations approximating the thermal effect of the bolts using the "parallel path" and the "isothermal planes" calculation methods. It is concluded that stainless steel bolts minimally affect curtain-wall thermal performance (approximately 18%) when spaced at least 230 mm apart, which is the industry standard. Performance is increasingly compromised when there is less than 230 mm between bolts or when steel bolts are used. We also show that the isothermal planes method of approximating curtain wall thermal performance can be used with two-dimensional heat transfer software typical of that used in the window industry to give conservative results for the thermal bridging effect caused by bolts.

Units: SI