Global energy demand is continuously rising, with building demand accounting for the largest proportion, reaching 30% to 40% of all demand, surpassing that of industry or transportation. Researchers have developed “smart windows” that can save energy and provide warmth in winter and coolness in summer, addressing the main issue of energy consumption in buildings, especially from air conditioning.
Dr. Anurag Roy, a postdoctoral researcher in engineering at the University of Exeter in the UK, highlighted in an article on The Conversation website that windows contribute to heat loss in winter and heat gain in summer, leading to increased energy consumption by air conditioning systems and carbon emissions. Balancing heat transfer without compromising transparency and natural light entry through windows is crucial for people’s well-being and productivity.
Smart windows currently available on the market mostly utilize electrochromic technology, where applying an electric current to a layer of particles or crystals within the glass can make the window opaque or dark, blocking most of the infrared light and keeping rooms warm. This significantly reduces the need for air conditioning in hot climates, retaining 60% to 70% of heat outdoors in high temperatures, and decreasing heat loss by around 40% in colder weather.
Over the past few years, the sales of these windows have performed well in commercial and residential buildings, with the global market estimated at $6.6 billion in 2023. However, there are essential limitations to consider in their use, such as the requirement for electricity to operate. This poses a challenge in remote areas or locations with unstable power supply. Users may need to install alternative power sources like solar panels to utilize these windows in such scenarios.
Additionally, many existing products can only switch between complete darkness and full transparency. This means that during hot weather, you may lose the transparency advantage of glass windows and require artificial lighting in the space.
An alternative solution that does not rely on electricity is photochromic technology, which uses tiny silver halide crystals or compounds like naphthopyran that react to increasing ultraviolet light, causing the glass to darken in bright conditions. This material is identical to that used in light-sensitive sunglasses. Compared to electrochromic windows, photochromic windows offer the additional benefit of blocking harmful UV rays, which can cause cancer and damage furniture and other items.
However, photochromic windows are costly, especially when using silver. They are highly sensitive to weather conditions, reducing their reliability in cloudy or rainy settings. They are also less effective in blocking infrared light and lack manual control features.
Researchers are developing a promising alternative for the future known as thermochromic technology, which reacts to temperature rather than light. These windows incorporate a particle coating that does not require electricity. They are significantly cheaper than photochromic windows and can still block UV rays, with the potential to match electrochromic windows in blocking infrared light. Furthermore, they can gradually darken as outdoor temperatures rise, offering more flexibility than electrochromic windows.
Although glasses using thermochromic technology already exist, they are not yet suitable for windows due to the limitation of the vanadium dioxide layer only fully reflecting infrared radiation at around 67 degrees Celsius, which is much higher than the highest temperatures in the world.
Researchers worldwide are studying ways to improve thermochromic glass, including projects at the Environment and Sustainability Institute at the University of Exeter. By combining successful research and policy support from developed and developing countries, the next generation of “smart windows” should make significant progress and have a significant impact on building carbon emissions in the next ten or twenty years, as summarized by Dr. Roy.