Effective energy solutions using facade materials with highly reflective coatings and aerogel granulate glazing systems
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We are facing an urgent problem of reducing carbon dioxide emissions in order to mitigate climate change. The building sector is a main source of carbon dioxide emissions. This thesis is trying to contribute to the creation of solutions for this problem by investigating the application of relatively new building materials, particularly highly reflective coatings and aerogel granulate glazing facades. Facades have an important role to play in controlling indoor climate and thus building energy use. This thesis investigated which facade properties have an impact on reducing heating and cooling energy demands in a common building type (office building) in Tokyo, Japan. It was shown that walls with high reflectance and windows with low heat gain and low heat transmittance can contribute to achieving energy efficient buildings. In this regard, highly reflective coatings and aerogel granulate glazing systems can make an important difference. These materials are therefore able to serve as an energy solution. Highly reflective coatings and aerogel granulate glazing systems are still new products in the building field. This thesis therefore experimentally provided information concerning their durability. Treated aluminum was investigated as a highly reflective material. New and conventional commercial products were tested through an accelerated aging process, taking into account heat, moisture, and solar radiation. Measurements showed that surface aging due to these aging factors barely affected the optical properties of the treated aluminum. Facades with highly reflective coatings can improve the durability of sealant joints because their lower surface temperatures cause less thermal movement, i.e. less fatigue damage. This has been examined both experimentally and theoretically. Energy performance was simulated for aerogel granulate glazing systems. When the spandrels of a double glazing facade (with shading) were replaced with an aerogel granulate glazing system (without the shade), the energy performance was improved. This was observed in the climates of Oslo, Tokyo, and Singapore, implying that aerogel facades can introduce more daylight and improve energy performance not only in cold regions but also in warm and hot regions. Furthermore, small aerogel granular sizes may be preferable from an energy point of view, because smaller granular sizes feature less solar transmittance without adverse change of thermal performance, and thus contribute to cooling energy reduction. Thus, specific application of this material in spandrels is proposed. It should however be noted that a triple glazing (with the shade) may be better in this regard than an aerogel window in cold climates. The durability of aerogel granulate was investigated experimentally. Although aerogel granules have high permeability, suggesting that convection may occur in the aerogel layer, the experiment showed that thermal performance does not change owing to this process. If aerogel is exposed to moisture over many years (decades), the thermal conductivity of aerogel granules can worsen by ~10%. Building specifications should therefore avoid this aging effect on thermal conductivity by preventing moisture from penetrating into aerogel granules (into the glazing cavity). In order to avoid moisture, aerogel granulate glazing systems have a rim seal. A rim seal is normally hidden in window frames. A main aging factor affecting rim seals is fatigue due to wind pressure. The existence of an optimal rim seal section dimension was indicated experimentally. Ideas to improve durability of the rim seal were also provided. In overall, this thesis investigated energy and durability performance of highly reflective coatings and aerogel granulate glazing systems. The thesis provides useful information for designers considering application of these materials to a facade.