ReviewFenestration of today and tomorrow: A state-of-the-art review and future research opportunities
Highlights
► Review of fenestration of today and tomorrow. ► State-of-the-art market review of the best performing fenestration products. ► Overview of possible future research opportunities for the fenestration industry.
Introduction
Currently, saving energy and carbon emissions is a top priority for buildings and constructions. With up to 60% [1] of the total energy loss of a building coming from its windows, fenestration products have a huge potential to provide large energy savings. Hence, windows with a low thermal transmittance, or U-value, can substantially reduce energy losses and save costs. In recent years building codes have been requiring lower U-values for new windows, e.g. the Norwegian Building Codes recently restricted the U-value for new windows to 1.2 W/m2 K [2], and this trend is set to continue as governments seek to save energy and reduce emissions.
This work aims to cover all main types of fenestration products, including multilayer glazing [3], vacuum glazing [4], [5], frames [1], [6], electrochromic windows [7], [8], [9], [10], [11], [12], [13], [14], [15], [16], [17], solar cell glazing [18], aerogels [19], [20], low-emissivity (low-e) coatings [21], [22] and spacers [23]. However, mechanically operated fenestration parts, e.g. blinds, shades and awnings, are not part of this study. The focus is on low U-values and solar radiation glazing factors. The first part will be a market review of the best performance state-of-the-art fenestration products available now, while the second part is a review of the research and development being performed and a look at the possible research opportunities and the potential products of the future. The definition of solar radiation glazing factors, e.g. visible solar transmittance (Tvis), solar transmittance (Tsol), ultraviolet solar transmittance (Tuv), solar reflectance (Rsol), solar factor (SF), solar material protection factor (SMPF) and solar skin protection factor (SSPF), may be found in Jelle et al. [14] and Jelle and Gustavsen [24]. When calculating U-values the method used must be noted as there can be up to a 3% difference between the North American (ASHRAE) and European (ISO) methods [25]. For further information on thermal transmittance values and their calculation see works by Gustavsen et al. [1], Gustavsen et al. [26] and Blanusa et al. [25]. Earlier review works on advanced glazing technology [27], advances in window technology [28] and zero energy windows [29] are noted.
This work gives many tables with a lot of information, e.g. manufacturers, product names and various properties, both in the main text and in the appendices. Some of these properties are very important and even crucial to the performance of the various products. Hence, the tables provide the readers with valuable information concerning these products. However, unfortunately it is often hard to obtain all the desired information (e.g. product properties) from all the manufacturers. In general, many property values are often not available at the manufacturers' websites or other open information channels, which is then seen as open spaces in the tables within this work. Hopefully, our addressing of this fact could act as an incentive for the manufacturers to state all the important properties of their products at their websites and other information channels, and also as an incentive and reminder for the consumers and users to demand these values from the manufacturers.
Section snippets
Glazing
Glazing can be considered as the most important part of fenestration products. This is especially true when calculating the U-value of a window as the glazing nearly always has the largest area of the constituent parts, and this greatly affects the overall window Uw-value [26]. Presented within this section are examples of multilayer and vacuum glazing. Multilayer glazing is the most popular commercially available glazing and therefore constitutes the majority of products reviewed. The focus
Future research opportunities
This section aims to outline the research currently being doing into improving fenestration products and creating new innovations. Conclusions will also be drawn on what are regarded as the best solutions for the future of the industry.
Conclusions
This work shows that there are many high performance fenestration products on the market today. With regard to glazing the majority are triple glazed multilayer products, but the vacuum glazing and aerogel solutions are growing and produce competitive U-values. Aerogels in particular have a large potential. They are already in use for translucent applications, and if their clarity could be improved for transparent applications, together with large production cost reductions, the aerogels could
Acknowledgements
This work has partly been funded by the Research Council of Norway, Lian Trevarefabrikk and Lawrence Berkeley National Laboratory (LBNL) through the NTNU and SINTEF research project “Improved Window Technologies for Energy Efficient Buildings” (EffWin), and the Assistant Secretary for Energy Efficiency and Renewable Energy, Office of Building Technology, Building Technologies Program of the U.S. Department of Energy under Contract no. DE-AC02-05CH11231.
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