Today energy-efficient and energy-harvesting buildings experience an ever-increasing interest and demand. Building integrated photovoltaics (BIPV) may in this respect represent a powerful and versatile tool for reaching the goal of zero energy and zero emission buildings. The BIPV systems replace the outer building envelope skin, thus serving simultanously as both a climate screen and a power source generating electricity. However, snow and ice formation on the exterior solar cell surfaces reduce their performance and may also lead to faster deterioration. Hence, if one could find a way to develop solar cells which were able to avoid snow and ice formation on their surfaces, one would have moved a large step ahead. This work presents a review exploring miscellaneous pathways for avoiding snow and ice formation on solar cell surfaces including superhydrophobic and icephobic surfaces.
The recent building practices have shown that aerogel glazings can be used as a multifunctional building envelope component for different purposes. Nevertheless, the distinctive physical properties and energy performance of aerogel glazings suggest that building integration of aerogel glazings may create architectural challenges, aesthetic problems, as well as concerns on their durability and environmental impact, thus highlighting the importance of developing guidelines to regulate the use of aerogel glazings in the building sector. This study discusses various approaches for the building integration of aerogel glazings by presenting a number of successful examples; the advantages of integration are quantified and suggestions are given to address the possible challenges.
Previous studies show that a large part of the net energy demands of an office building is related to window heat loss and cooling demands induced by solar irradiance. Windows with improved thermal transmittance (U-value) and solar heat gain coefficient (SHGC or g-value) are important for reducing the related energy demands.
There is a scarcity of available scientific work addressing multilayer window technologies. Hence, in this study, simulations with the aim of identifying the parameters that play a key role in improving thermal performance of multilayer glazing units have been carried out. A state-of-the-art review is presented, alongside an overview of promising new products and future perspectives and improvement possibilities for multilayer glazing technologies.
It has been found that increasing the number of glass panes in the insulating glazing units (IGU) yields U-value reductions that decrease for each added glass pane. Cavity thicknesses between 8 and 16 mm were found to be optimal for IGUs with four or more panes. Reducing cavity gas thermal conductivity was found to impact IGU U-value. Improving low-emissivity surface coatings beyond the best-available technology has minor effect on U-value reductions.
In addition to the thermal performance of the glazing units, optical properties, aesthetics, ageing properties and robustness should be further studied before the use of such multilayer IGUs may be recommended. Preliminary numerical simulations have demonstrated that thermal stresses to the glazing units due to high cavity temperatures can pose a problem for the robustness and lifetime of such units.
The application perspective of aerogel glazings in energy efficient buildings has been discussed by evaluating their energy efficiency, process economics, and environmental impact. For such a purpose, prototype aerogel glazing units have been assembled by incorporating aerogel granules into the air cavity of corresponding double glazing units, which enables an experimental investigation on their physical properties and a subsequent numerical simulation on their energy performance. The results show that, compared to the double glazing counterparts, aerogel glazings can contribute to about 21% reduction in energy consumptions related to heating, cooling, and lighting; payback time calculations indicate that the return on investment of aerogel glazing is about 4.4 years in a cold climate (Oslo, Norway); moreover, the physical properties and energy performance of aerogel glazings can be controlled by modifying the employed aerogel granules, thus highlighting their potential over other glazing technologies for window retrofitting towards energy efficient buildings. The results also show that aerogel glazings may have a large environmental impact related to the use of silica aerogels with high embodied energies and potential health, safety and environment hazards, indicating the importance of developing guidelines to regulate the use of aerogel glazings.