Influence of cavities geometric and emissivity properties on the overall thermal performance of aluminum frames for windows

The increasing attention to energy saving in buildings has led to more accurate analysis of the thermal performance of windows. In particular, the use of aluminum frames has known a rapid development; thanks to the installation of thermal break systems, the performance of aluminum frames is nowadays comparable to the one wooden frames. The numerous air cavities inside aluminum frames suggest a deep investigation of the heat exchange process; the paper, therefore, analyzes the effect of the geometric and surface characteristics of the cavities on the overall performance of the profile. The attention was focused on the emissivity properties of the cavity inner surfaces, since they play a fundamental role on radiation heat transfer; furthermore, the frame thermal performance was evaluated when the geometries of some cavities are changed with the insertion of rubber gaskets.All the analysis were conducted with two different approaches: numerical and experimental, obtaining a good match between the methods; the validation of the CFD model makes it a quick and user-friendly tool for the preliminary design and optimization of aluminum window frames with a high thermal resistance.

► A thermal analysis of aluminum window frames is performed.
► Experimental tests in a hot box setup and numerical simulations are compared.
► The thermal performance of frames is influenced by the emissivity of inner surfaces.
► An optimum air gap depth is found to minimize the frame thermal transmittance.