Transparent insulating materials: experimental data and buildings energy saving evaluation

摘要

The aim of the present paper is the study of the thermal and optical properties of innovative transparent materials for glazing systems. Thus, some innovative transparent solutions concerning Transparent Insulating Materials (TIM) were considered: monolithic silica aerogel and capillary geometric media. Initially, the optical properties of the single pane of aerogel were measured with a spectrophotometer, evaluating spectral transmittance vs. wavelength. Then, eleven different samples were realized, by assembling several types of glass (simple, float glass with various thickness, reflecting glass, low-e coated glass), in various combinations, with a pane of aerogel. Each sample could be considered as a double glass with aerogel in the interspace. In the same way, the capillary layers of TIM were inserted between two glass plates. Measurements of transmission and reflection coefficients vs. wavelength were carried out. The results were employed to calculate the energetic and luminous parameters: light transmittance (τ_v), light reflectance (ρ_v), solar direct transmittance (τ_e), solar direct reflectance (ρ_e), solar factor g and thermal transmittance (U). The performances of the different samples were compared. U-values slightly higher than 1 W/m~2K were obtained for all the samples; the values of light transmittance are in the 0.04 - 0.61 range, while the solar factor is in the 0.12-0.65 range, depending on the nature of the glass panes. The innovative glazing systems were compared with the conventional windows, characterized by the same type of inner and external glass pane, but with air in the interspace; results show a 25-30% reduction in light transmittance, but the heat losses are reduced to 1/2 or 1/3. The best of the two materials is aerogel because it introduces a better light transmittance and, if inserted in a double glaing, it allows one to obtain optimal insulation with lower thickness.