Researchers at the University of California’s Berkeley Lab have developed a new type of material which can selectively control the flow of light and/or heat passing through a window, thus potentially enabling major energy savings in large office buildings.

Smart buildings: Photosensitive windows set to reduce energy costs

At a time when total spending on heating, lighting and air conditioning in buildings accounts for close to 40% of the United States’ annual energy bill, researchers at the Lawrence Berkeley National Laboratory have developed a new process for automatically filtering sunlight and controlling heat influx through windows. A glass compound which can be triggered to become more opaque – or more impervious to heat-producing near-infrared light – according to the intensity of the sunlight striking the window has the potential to generate huge energy cost savings. In fact a general trend towards ‘smart’ windows has definitely taken off, and, according to a report from market research and analysis firm NanoMarkets,the overall smart windows market will double from a current value of $2.3 billion to $4.7 billion by 2018.

Composite material that controls both light and heat

Glass which is able to change tint and so adapt to variations in the intensity of natural light has already been on the market for a number of years. However the new process developed by the Berkeley Lab researchers makes use of two electrochromic (i.e. which change color under electrical stimulus) compounds whose combined properties can not only automatically trigger the window glass to turn more opaque but also provide a mechanism for blocking the heat from sunlight while still allowing light to pass through.The glass is made using niobium oxide and then coated or sprayed with nanocrystals of indium tin oxide, which is not only highly conductive of electricity but also exhibits the property of remaining transparent and is already being used in the manufacture of LCDs and touchscreens. A small burst of electricity will induce the glass to allow light to pass through but block the heat, while an increase in the electrical charge will turn the glass completely opaque. This smart economical system can therefore enable more efficient regulation of light and heat levels in the building.

Towards smarter buildings

Against the background of widespread attempts to reduce the world’s energy bill, smart windows appear to offer an efficient alternative for controlling the energy consumed in heating and air conditioning systems. The new process claims to be able to filter up to 35% of UV rays without reducing the light level in a room. However, the materials needed to make such ‘smart windows’ are still very costly and the manufacturing process will need to be simplified if the costs involved are to be justified by the energy savings achieved. Nevertheless the market for smart windows for both commercial/industrial buildings and private homes is rising steadily, and recently the French glassmaking giant Saint-Gobain acquired the Minnesota, US-based start-up Sage Electrochromicsfor €80 million, in a move to diversify into smart glass. Given the considerable cost of the materials involved, Berkeley Lab’s new electrochromic technology will probably currently appeal mainly to corporate customers, who could make estimated savings of over 25% on their firm’s heating and cooling bill. 

By Thomas Meyer
Journalist, Business Analyst