Norwegian University of Science and Technology (NTNU),
Keywords: smart window, electrochromic, photochromic, thermochromic, dynamic, controllable, adaptive, solar radiation, energy-efficient, building
Summary:The world of today is experiencing an ever-increasing pressure to shift towards a more sustainable society in order to decrease or ideally avoid the negative impacts of the current climate crisis and energy crisis. Thus, there is an increased interest in the utilization of renewable and non-polluting energy sources alongside improved energy efficiency in miscellaneous sectors. An important sector in this respect is the building sector where there still is a large untapped potential for environmental-friendly energy harvesting and energy-efficient solutions. Here, solar radiation represents a source which could be exploited in several ways, i.e. as daylight, heating and for electricity generation. Building integrated photovoltaics represent one of these areas with a large untapped potential. Another one is the exploitation of smart windows which are able to dynamically change the solar radiation transmittance through the glazing structures according to need, hence enabling savings in heating and cooling demand. Three of these smart window technologies are electrochromic, photochromic and thermochromic windows, which change their transmittance, including colour in the visible wavelength region, by variations in voltage, light intensity, and temperature, respectively. Of these three dynamic window technologies, electrochromic windows represent a controllable smart window technology, whereas photochromic and thermochromic windows represent two adaptive smart window technologies. These different smart window technologies have different advantages and disadvantages regarding both their current practical and commercial realizations and their theoretical possible ideal solutions. In this study we will take a closer look at these smart windows including their energy saving potential. Building energy performance simulations have been conducted with selected commercial smart windows in addition to theoretical cases to investigate the energy saving potential of both the available commercial technologies of today and possible future ones with more ideal solutions. Thus, in addition to comparing real window cases, this study also represents a more general comparison of controllable and adaptive smart window technologies.