Changes in façade design tend to come about slowly and without much pomp and circumstance. Unlike other industries where new technology can completely reimagine the product (think self-driving cars or 3d printed prosthetic limbs), technological changes related to façade design are often small and incremental. It can often be decades before the impact of these changes is truly felt by architects and engineers or their clients.
Cover Image: Centralised Science Laboratories Chinese, University of Hong Kong – credit RMJM
The biggest, and undoubtedly the most significant, change in façade engineering over the last 50 years has been the shift towards integrating façade design into a building’s energy concept. Curtain walls are no longer solely structural, purposed only with keeping the cold and rain out, and occasionally letting fresh air in. No longer simple architectural features, façades have become an integral part of a project’s sustainable concept.
As sustainable design has evolved from a trend to a ‘golden rule’, glass façades have faced growing vocal criticism from energy experts and architects alike. As one British government advisor put it, why would you want to build a greenhouse in a global warming emergency? The glass-fronted office towers and skyscrapers that make up the skylines of most large cities have been popular over the last few decades because they offer incredible views, create striking silhouettes and let in lots of natural light. However, when using standard glass for these curtain walls, with sunlight comes heat, and in sealed buildings there is nowhere for the heat to escape naturally. The result is significant energy consumption in the cooling of buildings which equates to increasing carbon emissions.
Between 2000 and 2019, the energy consumption related to cooling buildings more than doubled and in the UK accounted for 14% of all energy use. Drastic actions have been taken to combat these energy-draining façades. In New York, the city’s mayor announced a proposal to ban all-glass buildings and require developers to retrofit existing buildings to make them more efficient.
However, there are also scientific arguments in favour of glass façades because they are vitally important to building users. They help create a feeling of openness and connect the people inside to the world around them, an increasingly important feature as most city residents are likely to spend around 90% of their day indoors. Not only this, but exposure to natural light directly affects human circadian rhythm, which is responsible for managing the ‘internal clock’, attention span and memory functions. Studies have shown that office workers and students who experienced longer exposure to natural light experienced higher cognitive function during the day and improved quality of sleep at night.
It has then fallen to façade architects and engineers to find a way to preserve the elegant and graceful aesthetics and the natural light benefits of the typical glass façades while developing new methods for façade design to positively contribute to a building’s overall energy concept. Two of the more exciting façade technologies that have grown out of this need are Electrochromic Glass (also known as Smart Glass) and Kinematic Façade Features.
Smart Glass is electronically tintable glass that can be used for windows, façades and curtain walls. A current is applied to the glass layers, and as the voltage is increased the material turns from transparent to opaque. The earliest usage of this technology within the architecture industry was in office interiors to introduce private spaces upon request. However, the implications for building energy consumption are now encouraging façade engineers to embrace the material.
In the last five years, electrochromic technologies have advanced across three key areas, making Smart Glass a viable option for façade and curtain wall design. New Smart Glass is able to start tinting within 15 seconds and takes less than 3 minutes to enter the darkest tint, meaning that windows can respond more efficiently to the movements of the sun. In its clear state, Smart Glass is also indistinguishable from conventional glass, so façades that embrace the technology do not appear isolated from the architectural narrative in which they are situated. Finally, newer generations of Smart Glass tint so evenly that opacity can be determined shade-by-shade, offering users complete freedom to reap the economic and environmental benefits of the technology.
As well as the aesthetic appeal of Smart Glass in maintaining a clear façade shape unencumbered by additional shadow elements often required in curtain wall design, the ability to block the sun’s heat while still admitting daylight has been proven to reduce the consumption of energy used for air conditioning and electric lighting. In factories and laboratories, which both often house sensitive materials, the use of Smart Glass in the façade means that these properties can reflect solar heat away from the building. By offering building management a means with which to so acutely adjust the temperature of each room by controlling each individual panel of Smart Glass, energy consumption related to heat control is able to be reduced across entire buildings.
At its most opaque, electrochromic Smart Glass can block 90% of solar radiation, drastically reducing the overall energy transfer between building exterior and interior. Not only does this directly reduce energy consumption by up to 20%, it also reduces the size of the HVAC system needed to adequately control the temperature of the building.
In fact, smart-tinting glass can provide solar shading and daylighting control similar to kinematic façades, found on buildings such as the Al-Bahr Tower in Abu Dhabi. These features are mechanical moving structures on the outside of the building on a second layer in front of the curtain wall. Operating almost like two buildings, it gives clients the ability to change the appearance of their building and engage sunlight and shadows efficiently throughout the day.
Studies have shown a building’s façades are responsible for more than 40% of heat loss during winter months and contribute to overheating during the summer, resulting in buildings requiring complex and costly HVAC systems in order to guarantee comfortable interior environments for building users. This is one of the reasons that the building sector consumes more energy than either industry or transport. Almost 50% of all European energy consumption comes from building construction and building management.
It is with these statistics in mind that kinematic façade features have engaged in the use of ‘adaptive shading’. In winter they can be moved to provide additional protection from heat loss, while in summer they can protect façades from solar heat and subsequently drive down the need for high-energy building cooling systems. Some estimates suggest that adaptive shading can reduce annual oil consumption in the construction sector by 10%.
The sustainable possibilities of kinematic façades aren’t limited only to temperature control and regulation. In the last two years, façade engineers have begun to pull together multiple energy-efficient technologies to improve overall energy consumption. Introducing movable photovoltaic cells (solar panels) along vertical façades can ensure that whatever the sun’s position in the sky, the building is optimising its electricity generation.
In a building system designed by a team at the Swiss Federal Institute of Technology Zurich, robotically driven solar panels were oriented by a computer algorithm that factored in electricity generation, passive heating, shading and daylight penetration to determine the optimal position of the panels. Their prototype generated up to 50% more electricity than static, rooftop solar panels. Not only is overall energy consumption reduced, but the energy that is consumed also comes from renewable sources. This will enable buildings to more quickly achieve close to zero net energy consumption.
What both Smart Glass and kinematic façade features have in common is that they embrace a more active role in temperature and sunlight control in a building. It is no longer enough for energy-efficient glass panels to offer passive temperature control benefits to clients. It is not enough for a façade to have no impact on a building’s energy consumption, it needs to be part of the system to reduce energy consumption. What Smart Glass and kinematic façade features offer to architects and their clients is the ability to adopt sustainable design principals with high-precision control without sacrificing visually interesting and exciting developments.
This article was originally published in IGS Magazines Spring 2021 Issue: Read the full Magazine here for more thought-leadership from those spearheading the industry
Author: Thorsten Siller, Facade-Design Specialist at RMJM Façade
Thorsten Siller has more than 25 years of experience in building envelope design and technique. He was involved in projects around the world with a focus on Europe, the Greater China Area, the Middle East, and North America. His vision is not only limited to design and engineering but also focused on the building execution process within the schedule, production, quality assurance and installation method in order to bring the concept idea to reality. Design is like beginning a sentence before you know its ending. The risks are obvious, you may never get to the end without proper planning.