Modulating light through arrays of optical MEMS micro-shutters and micro-mirrors could provide enormous energy savings.

Buildings are responsible for 40% of primary energy consumption and 36% of total CO₂ emissions. And, as we know, the CO₂ emissions trigger global warming, sea level rise and profound changes in ocean ecosystems. Replacing inefficient glass surfaces in buildings with energy efficient smart glazing has great potential to reduce energy use for lighting and temperature control.

Harmut Hillmer et al. from the University of Kassel in Germany demonstrate this potential in “MOEMS micromirror arrays in smart windows for daylight management,” an article published recently in the inaugural issue of Journal of Optical Microsystems.

“Our smart glazing is based on millions of micromirrors, invisible to the naked eye, and reflects incoming sunlight based on user actions, sun position, day and seasons, providing a custom light direction inside the building, ”Hillmer said.

(a) If no user is present in summer, all mirrors tilt vertically, keeping solar heat out. This saves a lot of energy by minimizing heat transfer. (b) Once the user’s presence is detected by sensors in the summer, the top mirrors open and reflect daylight towards the ceiling. The room stays cool where no user is standing, saving energy on air conditioning. The parts of the room away from the window can be effectively illuminated by daylight, thus saving energy on artificial light. (c) If no user is present in winter, all mirrors open and collect energy by reflecting solar radiation off a wall, acting as a radiant heater. This saves energy for heating. (d) Once the user’s presence is detected in winter, all mirrors will redirect all solar radiation to the ceiling to minimize glare. The ceiling now acts as a radiant heater, saving heating energy. Credit: Hillmer et al.

The network of micromirrors is invulnerable to wind, window cleaning or all weather conditions because it is located in the space between the windows filled with noble gas such as argon or krypton. Glazing provides free solar heat in winter and overheating prevention in summer, and it allows healthy natural light, huge energy savings (up to 35%), massive CO₂ reduction (up to 30%) and a 10% reduction in steel and concrete in high-rise buildings.

Beyond the energy problem, artificial lighting also has consequences on health and well-being. Various studies have linked artificial lighting to lack of concentration, high susceptibility to disease, disturbed biorhythms, and insomnia. Smart glass can reduce reliance on artificial lighting by optimizing the natural daylight in a room.

State-of-the-art smart glazing is currently optimized for winter or summer and cannot guarantee energy-saving performance all year round. There has been a need for intelligent and automatic technology capable of reacting to the local climate (day, season), using available sunlight, regulating light and temperature, and saving energy.

The researchers’ MEMS micromirror arrays are integrated inside the insulating glass and are operated by an electronic control system. The orientation of the mirrors is controlled by the voltage between the respective electrodes. Room motion sensors detect the number, position and movement of users in the room.

Results include much higher actuation speed in the less than ms range, 40 times lower power consumption than electrochromic or liquid crystal designs, reflection instead of absorption and color neutrality . Rapid aging tests of the micromirror structure were performed to investigate reliability and revealed the durability, robustness and long lifetimes of the micromirror arrays.

And with positive results like this, the benefits of this smart glass are crystal clear.

Reference: “MOEMS micromirror arrays in smart windows for daylight Steering” by Harmut H. Hillmer, Mustaqim Siddi Que Iskhandar, Muhammad Kamrul Hasan, Sapida Akhundzada, Basim Al-Qargholi and Andreas Tatzel, January 26, 2021, Journal of Optical Microsystems.
DOI: 10.1117 / 1.JOM.1.1.014502