Paper Conference

Proceedings of Building Simulation 2017: 15th Conference of IBPSA


A New Method of Representing Highly-Conducting Window Frames in Building Simulation Models

Peter R. Lyons1and D. Charlie Curcija2
1Peter Lyons & Associates, Canberra, Australian Capital Territory, Australia Email
2Lawrence Berkeley National Laboratory, Berkeley, CA, USA Email

Abstract: Highly conducting metal window frames are still common in many countries. At standard NFRC environmental conditions (NFRC 2016), such metal frames can exhibit U-factors exceeding 15 W/(m2K). Window frames are inhomogeneous window elements where heat transfer is two- and three-dimensional. Their thermal performance is represented through a frame Ufactor, Uf, which is calculated for projected frame surface area. However, it is currently not possible to correctly represent such frames in building simulation models. This is because surface film coefficients (outdoor and indoor) are based on the usual assumption that heat flow across the building envelope is onedimensional. This is generally true for a window’s parent wall or glazing surface, but not for the window frame itself. The upper limit to the simple, 1-D U-factor is about 6 W/(m2K). We present a simple method for correcting surface heat transfer coefficients in building models, so that highly conducting metal frames can be correctly modeled and also to provide more accurate surface heat transfer coefficients for more insulating frames. To demonstrate robustness of the technique, the process is repeated at various boundary conditions.
Pages: 1728 - 1731