Experimental and Numerical Energy Assessment of a Monolithic Aerogel Glazing Unit for Building Applications

Abstract

In the last few decades, the attention of researchers has been focused on the characterization of aerogels in order to improve the thermal performance of transparent building envelopes. Granular aerogel is already spread in the market thanks to the easy manufacturing system, whereas the difficulty in producing monoliths without defects, cracks, and inhomogeneity limited the diffusion of monolithic aerogel systems. A new production process for the monolithic panels was developed at Union College (Schenectady, NY, USA); it is a rapid supercritical extraction technique which allows a reduction in production time (only a few hours) and results in less solvent waste. Panes with maximum dimensions of about 100 × 100 mm were fabricated and composed in a unique glazing system, with external dimensions 300 × 300 mm. The thermal characterization of the innovative monolithic aerogel glazing system (simple float glazing 4.7-mm-thick monolithic aerogel pane 15-mm-thick simple float glazing 4.7 mm thick), which was carried out by means of a Small Hot Box apparatus, showed a thermal transmittance value of about 1.1 W/(m 2 K). Data was used in dynamic simulations of a typical non-residential building. They showed that the new investigated solution allows a valuable reduction with respect to a low-e double glazing system in terms of heating energy demand (about 5-7% for Helsinki, 8-12% for Paris, and 10-15% for Turin), for different window-to-wall ratios. monolithic form is the difficulty in fabrication of samples without defects, cracks, and inhomogeneity, and their high cost [5]. In the last years, a rapid supercritical extraction method was developed at Union College (Schenectady-NY), allowing a significant reduction in fabrication times (6-8 hours) and in solvent waste. Good optical properties can be obtained (τ v > 80%); when assembled with two glasses (total thickness 22 and 12.7 mm of aerogel), a thermal resistance of 0.86 and 1.55 m 2 K/W is obtained at atmospheric pressure and in evacuated conditions, respectively [6,7].Guoqing Zu et al. evaluated the thermal performance of monolithic alumina aerogel systems, prepared by a sol-gel method combined with the ethanol supercritical drying technique [8]. The thermal conductivities at 30 • C and 400 • C were 0.028 and 0.065 W/mK, respectively [8]. Duer and Svendsen [9] presented the main results of a research project founded by the European Commission. They discussed an aerogel pane prototype of 450×450x15 mm 3 , made under vacuum conditions and sandwiched between two glasses; a conductivity value of about 0.010 W/mK was measured at ambient temperature.Another interesting study presents a detailed investigation of the mechanical microstructural and thermal properties of monolithic aerogels made from polyethoxydisiloxane [10]. The thermal conductivity is highly dependent on the densities of monolithic panes; a minimum value of 0.0135 W/mK was measured for a density of 120 kg/m 3 , a maximum value of 0.024 W/mK for about 300 kg/m 3 . Similar values of thermal conductivity were fo...

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