Thermal-energy and lighting performance of aerogel glazings with hollow silica: Field experimental study and dynamic simulations

The excellent thermal insulation properties of aerogel glazing systems make them an interesting building solution, especially in cold climates. When aerogel glazing systems provide less solar heat gain factor, they could be useful in warm and hot regions (such as Tokyo, Rome and so on) because buildings in such areas are often designed to minimize cooling energy demands. If a sort of opaque powder is mixed with aerogel granules, able to stick to each granule and to cover the aerogel surface discontinuously, the mixture can thus reduce solar transmittance, contributing to daylight usage with less glare risks and cooling energy demand reduction, without shade or blinds, keeping as high thermal performance as aerogel. This innovation is examined in the present paper, by presenting the following solution: a double glazing unit with a mixture of silica granular aerogel and hollow silica powder in the gap (AGS), in order to reduce the solar factor. The solution is tested through in-field experimental campaigns and numerical analyses, making available a set of data not found in literature, where mixtures of aerogel and powder were never studied. The air temperatures in the test Room with AGS, especially the peak values, are lower than the ones in the reference one with installed a standard glazing system (SGS). The same behaviour is observed in several experimental campaigns in different seasons: in mid-season 1 the highest differences are of about 6–7 C, whereas in summer they reach 12–16 C. Significant differences in terms of illuminance are also observed: the calculated Useful Daylight Illuminance (UDI) shows AGS values 57% higher than SGS, highlighting the aerogel ability to diffuse light and to reduce glare. Experimental data were used for energy analyses of a reference building in Tokyo. AGS outperforms a low-e glazing in terms of heating energy demand: the reduction varies in the 22% (North) 62% (South) range. The lighting energy demand is quite similar: electricity demand increases in the 3–6% range. Finally, the internal shade on the reference glazing has a significant impact on the estimated energy demand, both for cooling and heating.