Transparent Insulating Materials for building Energy saving: experimental results and performance evaluation

The reduction of energy consumption for heating and air conditioning and electric energy saving in illumination plants could be improved by innovative Transparent Insulating Materials (TIMs), which aim to optimize two opposite requirements: transparency and thermal insulation. Aerogel is one of the more promising for use in highly energy-efficient windows: in addition to the low thermal conductivity (0.010 W/(m K) in evacuated conditions), a high solar energy and daylight transmittance is achieved. Eight samples were manufactured, by assembling several types of glass with monolithic and granular aerogel in the interspace. Measurements of transmission and reflection properties were carried out and the energetic and luminous parameters (light transmittance (τv), solar factor (g) and thermal transmittance (U)) were calculated. U-values slightly higher than 1 W/m2K were obtained for all the samples. The monolithic aerogel introduces a better light transmittance (τv = 0.60) than granular one (τv = 0.27), while U-values are comparable in not evacuated conditions. In order to evaluate the aerogel employing in buildings, a prototype of an aluminium frame window with granular aerogel in interspace was realized. Thermal and acoustic properties of the prototype were evaluated according to the standards. The thermal transmittance of the innovative glazing system was little lower than 1 W/(m2 K) and it showed also good acoustic properties: the Rw index was 3 dB higher than the one of a conventional window with air in interspace.