Dependencies of heat transmittance through the ventilated wall system on thermal conductivity of connectors crossing thermal insulation layer

Abstract

The ventilated facade systems are widely used for improvement of energy efficiency and reducing of heat losses of newly built buildings and for existing buildings. To reduce the influence of point thermal bridges on heat transfer through the ventilated facades, previous often used aluminium alloy connectors as a change to stainless steel and reinforced plastic connectors. Different thermal characteristics of connectors using in ventilated facade systems, significantly influence the heat transfer coefficient of building’s walls. Previous empirical calculations of the heat transfer through ventilated facade walls with different connectors according to standard methodology and numerical modelling showed significant differences in results, therefore experimental research with the fragments of the ventilated facade systems were carried out using a guarded hotbox method. The aim of this experimental research was to analyse the heat flows through the ventilated wall system with different kind of heat-conductive connectors. Expanded polystyrene foam (λ – 0,031 W/(m∙K)) was used as thermal insulation material, thickness 300 mm, and three types of heat-conductive connections were installed: aluminum alloy (λ - 160 W/(m∙K)), stainless steel (λ - 17 W/(m∙K)) and glass fiber reinforced plastic (λ – 0,23 W/(m∙K)). The measurements in the guarded hotbox were useful for analysis of differences in results according to the standard and numerical calculations methods. The experimental studies showed that the results are very close to the numerical simulation results. The empirical calculation method gave similar results to the other two methods, except in the case of highly heat-conductive connectors.