Experimental performance evaluation of aerogel glazing systems

Energy savings for heating, air conditioning and illuminating plants could be improved by innovative Transparent Insulation Materials (TIMs), which aim to optimize two opposite requirements: transparency and thermal insulation. Aerogel is one of the most promising materials for use in highly energy-efficient windows: in addition to the low thermal conductivity (down to 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. U-values slightly higher than 1 W/m2 K were obtained for all the samples. The monolithic aerogel introduced a better light transmittance (τv = 0.60) than granular one (τv = 0.27), while U-values were comparable in non-evacuated conditions. With respect to a conventional window (double glazing with a low-e layer), 55% reduction in heat losses was achieved by monolithic aerogel, with only a 25% reduction in light transmittance; for the granular systems, the reduction was about 25% in heat losses, but 66% in light transmission. In order to evaluate the aerogel employing in buildings, a prototype of an aluminum 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.