Assessment of the thermal transmittance in ventilated windows

The aim of this paper is to analyze the performance of thermal transmittance of a dynamic glazing system in the real conditions of work. The thermal transmittance of an envelope component, opaque or transparent, is not a constant physical quantity but it depends on the different intrinsic characteristics of the constituent materials. The thermal transmittance is a steady-state calculation and changes as a function of the heat flux, the internal and external temperatures. At the laboratories of ITC-CNR an experimental campaign of a ventilated glazing system has been carried out, in order to assess its behaviour in terms of energy consumption, thermal comfort and energy efficiency in winter and in summer. The experimentation consists in the comparison of two different outdoor test cells, in one of which the ventilated glazing system has been installed and in the other one a traditional windows has been mounted. Starting from the calculation method defined by the Italian regulation, that allows to evaluate the behaviour of a window in standard conditions, the variation of thermal transmittance, due to the air flow passing through the ventilated cavity of the window, has been analysed. The study consists in the following steps: - detection of main parameters (weather, energy consumption and comfort) in the test cells; - assessment of the energy performances of the ventilated glazing system with simulation tools; - comparison between real and calculated data; - validation of the results with the analysis of the energy consumption of the test cells with the Energy Signature method.