We are approaching the 50th anniversary of Earth Day, April 1970. As the planet continues to warm, the contributions of glass/building envelope/building design/urban infrastructure to this existential crisis is once again a hot topic. This is not a new debate but it recurs with increasing regularity and now with more intensity and renewed concern across most parts of the planet. History reminds us that speculating on a path forward is fraught with challenges but that prevent us from doing so given the importance of the topic and the consequences of inaction. Ultimately raising these topics is most useful if the exploration contributes in even a small way to a renewed commitment to action and progress.
Glass is not the cause of our environmental problems but it is a contributing factor to the larger challenge of carbon emissions that drive global warming and climate change. Perhaps most importantly we can change the decisions we make about the use of glass in buildings and, properly made, those decisions can help address the problem. Each design decision contributes in some small or large way not just to the design of one building but will influence others and help shape the future we are creating for ourselves and for our children.
Glass is an amazing building material- the transparency and clarity it offers are unique amongst building materials and it allows us to experience the outdoors, from the tranquility of a garden at home to the hustle of an urban street, from the vantage point of cozy, comfortable indoor spaces, in which we spend 80-90% of our time today. Connecting with nature – “biophilia” – is increasingly viewed as an important amenity inside the built environment and glass provides many opportunities. But that transparency from a shimmering sheet of glass comes with a cost- the energetic and environmental consequences of producing the glass and the larger impact of maintaining a comfortable and productive living and working environment within the building behind it.
Authors have written about human impacts on the natural environment for decades but it was the oil embargo of the 1970s and related disruptions in business-as-usual that increased the level of attention paid to our use of energy and the impacts of those patterns. By the 1990s there were clarion calls not only to reduce the use of energy to heat, cool and light our buildings but the environmental impacts, e.g. carbon emissions, of supplying that energy were already under focus. 25 years later those issues and “trends” are clearer to (almost) all and are seen as an existential threat to life as we know it for a planet with almost 8 billion human inhabitants, not to mention all the other living entities on the planet.
In principle we have the intelligence, creativity, willpower and motivation to address these challenges and solve them. In practice, things are more complex and uncertain. It has been said that as a society we overestimate the speed with which we can make these kinds of profound changes, but when they finally arrive we underestimate the complex impacts they have.
At the extreme, buildings wrapped in single sheets of clear glass are clearly a poor solution for those who inhabit them and for the planet. The “Battle for the Wall” has been played out in several venues over the last decade with some useful suggestions and progress, but no consensus or obvious pathway to a widely supported set of solutions.
What follows is one industry observer’s speculation, from the perspective of 2020 but with about 50 years of engagement and insight, of the pathways the glass and building industry might follow, and the potential outcomes.
At the risk of stating the obvious it seems useful to define the context in which we will seeking new façade solutions. This can be outlined with three elements:
- There is a Global Crisis and Aggressive Action in the Building Sector is Needed
- There is a serious problem, that is not self correcting. Delay will likely make matters worse and force more costly, disruptive required actions in the future. Thoughtful, but aggressive action is needed by many players. While “building carbon impacts” is not the only challenge it is one of the top 3 or 4. Time is not our friend as the building industry moves very slowly with the design/build cycle of many buildings from commitment to occupancy at 5 years or more. We don’t have the time or luxury to learn from a long, slow iterative set of solutions.
- The Challenges are Technically Complex and Vary Across the Planet
- The “energy efficiency” challenge of the past is now also a “carbon emissions” challenge. The past focus on minimizing operating energy and carbon is now extended to addressing embodied energy and carbon. Renewables are coming on line rapidly but not yet quickly enough to meet growing demand and to displace the 100 year legacy of fossil fuel powered buildings. Climate, building type, and building size all matter in seeking viable, scalable solutions.
- Viable Solutions and Options are Available Today, but Better, Scalable, More Economical Solutions are Needed
- We can improve tremendously on today’s “state of practice” with pragmatic options that are available now. Globally there are 1000s of buildings that have reached net zero energy or net zero carbon so we have “proof” that they are technically possible. But these buildings are surrounded by tens of millions of more conventional buildings that collective are responsible for about 40% of global energy use. A “skilled architectural/engineering team” with a “motivated client” and a “proper budget” can probablydesign and deliver a zero energy building today. But 99% of new buildings do not achieve these goals and we have a massive infrastructure of existing “legacy” buildings that are largely untouched. In fact if every new building from 2020 onward was a zero energy/carbon we would fall short of the carbon reductions needed to meet the 20C temperature rise goal.
The new buildings we design and build, and the existing buildings we retrofit will impact these planetary balances for the next 50-100 years. With this as context how do we design and specify glass in a building façade in a manner that contributes to a solution rather than exacerbates today’s problems. The simplistic response has been proposals to minimize glass area, given that energy impacts of “conventional glazing” are typically much higher than well insulated opaque walls. But we know – or have heard – that new glass technologies are available today that dramatically outperform their predecessors and that in many instances can meet stringent new, zero net energy goals.
We then have 3 challenges:
1) How do we set these aggressive performance targets,
2) what glass technologies and façade systems are available to choose from to meet them, and
3) how do we ensure that we design and build buildings that meet the targets?
Before we take a deep dive into the products and systems that will deliver these solutions we must first a set of performance goals starting with human needs and ending with planetary impacts:
- Meet occupant needs for comfort, view, connection with the outdoors, daylight
- Provide efficient, economic operations for the building owner/operator
- Support Electric Grid Operation and Optimization
- Use Long lived, recyclable, components to support trends to circular economy
- Minimize energy and carbon impacts on the planet
Vision: We believe we can meet the larger scale societal goals #3-5 while delivering on the promises of #1 and #2. This builds on and extends accomplishments and trends of the last few decades, although we must dramatically amplify, extend and scale them to have the desired global impact.
Since the broad global goal is to target net zero energy and net zero carbon buildings, a starting point is to ensure that the “net zero façade” carries its weight and contributes to that solution. Physics and materials science paints a clear path to a set of technology and systems options that make this not just possible but pragmatic.
So what is the “ideal solution”? Wrong question! There is no “one-size-fits-all” solution and there will never be an “ideal” facades solution that will be best in all climates and orientations, for all building types, sizes and budgets, and for all occupants with diverse tasks and personal needs. Instead we should be looking at a two part solution to match the design solution with the performance needs on a case by case basis.
Thus we need:
1) A technology toolkit or kit of high performance parts from which to draw from, and
2) New tools and business practices that will optimize the design elements, convert them into a specifiable, affordable solution, install and commission them to meet operational goals, and then ensure that they deliver the expected performance over time for occupants and owners.
These are easy to describe but a challenge to implement. Lets look at the two major elements of the challenge: the “façade toolkit” and the “delivery system”.
The toolkit has at least 5 major elements and several minor ones. Each consists of a “Performance Strategy” associated with series of glazing and façade technologies. They span the physical scale from “nano”, e.g. glass coatings to “macro”, e.g. façade shading solutions. fig.1
Strategy # 1: Minimize thermal losses through glass: The largest impact of glass on global energy use is the amount of energy needed to offset heat loss from glass. Even conventional double, low-E glazing (U ~ 1.4 W/m2-K) can have 10 times the heat loss of a highly insulated wall so more improvement is needed here. Fortunately there are at least 3 pathways that can triple the thermal performance of today’s dominant low-E double glazed IGU: 1) variants of triple and quad glazing; 2) vacuum insulating glass, VIG; and 3) aerogel or similar transparent, micro/nanoporous clear solids. fig 2
Conventional triple glazed IGUs can achieve U ~ 0.6; a quad glazing design with low-E coatings and argon gas can reach an insulating value of ~ 0.4. In all but the coldest northern climates, a window with a U in this range becomes energy neutral in winter, as the solar gains available balance out the thermal losses on a seasonal basis. And of course the windows provide daylight year round that can offset electric lighting use. (Note that these windows are also useful in very hot climates where temperatures are often above 40C) Triples and Quad glazed windows can be heavy and will increase the embodied energy of the window. The use of thin glass, ( 0.7mm – 1.3mm) now produced on float lines in vary large volume and at low cost (< $10/m2), combined with krypton gas which optimizes performance at thinner gaps, promised to provide these very low U-values with an IGU of similar size and even lower weight than a conventional triple. VIG technology has advanced in the last decade with several companies offering improved products but they remain costly and have not yet broken into mainstream markets. Their thin section – typically less than 8mm – makes them ideal as a glazing replacement in a single glazed window. Research continues on aerogel variants but we are still awaiting a technical and market breakthrough for window applications. Finally we note that windows, curtain walls and double envelope facades all have glass edge and frame losses which will worsen overall product properties if they are not designed well. The thermally improved materials and designs to minimize these losses for glass edge spacers and frames exist in markets globally – but they are not yet widely utilized in design.
Strategy #2: Dynamically manage solar gain, daylight and glare transmitted through windows: While solar gains are useful in winter in many climates, they are unwelcome in many buildings and climates throughout the year. Given global population growth in hot regions of Asia and Africa and the resultant construction booms there, and given the global warming trends and heat island effects we see in major cities now (major European cities experienced temperatures > 40C in 2019), effective management of cooling loads due to solar energy incident on the windows is a high priority for designers and product suppliers. The deep tinted glass and high reflective glass of the past has been largely replaced with a new generation of higher performing products based on second and third generation low-E coatings. The traditional sputtered low-E coating has a complex multilayer structure that allows it to be tuned to be clear to the eye i.e. it transmits most of the visible light spectrum but reflects the longer wave near-infrared wavelengths. The best of these double silver and triple silver coatings, now widely available from many glass suppliers, transmit about 2.3 times as much daylight as solar heat gain ( e.g. g-value ~ 0.3 and Tv ~ 0.65) and there is no way to improve that performance further with a colorless coating.
However no fixed, static shading solution will ever provide optimal control of daylight, glare and solar gain across hours of the day, seasons, and variable weather. For that level of control and optimization we need dynamic solutions. Interior and exterior shading systems have been in use for a long time, particularly in Europe, including both fixed and manually operable solutions. The current trend is to motorize and automate the operation of these devices and make their performance responsive to occupant or building owner or electric grid needs. This level of “smart” control allows substantial improvement in energy and comfort. fig 3
Motorize blinds, shades and shutters need attention and service with their moving parts. But a different form of solar control can be implemented with new technology at the nano level and incorporated into “smart” active and passive coatings applied directly to glass. These sophisticated coatings may control solar energy and daylight by reflection, by absorption or by scattering, adding a privacy function. Passive coatings change optical properties directly in response to temperature e.g. thermochromic or to light e.g. photochromic. But the future will likely belong to actively controlled coatings where an applied voltage switches the state of the coating, typically based on electrochromic or liquid crystal technologies. Several firms now offer mature products in large sizes suitable for curtain wall designs. A second generation of coatings with enhanced switching speed, more neutral color, gradient switching and lower costs is emerging from both the existing suppliers and new market entrants. fig 4
All of these active coatings systems, as well as automated shading, share two “new” fundamental requirements: 1) the need for a power source, and 2) integration with a sensor and controls infrastructure that drives the operation of the device. Every smart glazing supplier offers these solutions but a lack of interoperable protocols has slowed overall market impact.
All of the active, smart façade solutions are more complex and expensive than conventional static glazing but offer benefits well beyond energy saving, as explained later.
Strategy #3: Extend glare-free daylight impact deeper into spaces: the role of daylight as an energy saving strategy has declined over the last decade as highly efficient LED light sources begin to be deployed but the savings are still real and can be doubled if daylight reaches more than just the classic 5m depth in a traditional daylight room. Skylights are the obvious solution for low rise buildings but getting daylight deeper into the multi-story building floorplate has always been a challenge. But even for multi-story buildings new optical light redirecting coatings placed on high clerestory windows can effectively daylight a 10-15m deep space thus doubling or tripling the daylighted floor area. Market offerings are not yet robust but several active and static options are on the market. The broader health and well being benefits of daylight can be enjoyed by more people working across the floor plate. fig 5
Strategy #4: Convert the window to an HVAC system: Why push air through ducts with fans when a window can provide fresh air requirements? And when the outdoor temperature is right, natural ventilation via operable windows can be an effective cooling strategy in mild climates. In cold climates a conductive film added to the innermost glazing layer becomes a local heat source when electricity is pumped through the coating. This works best when the prime window is highly insulating and can eliminate the expense and floor space taken up by traditional perimeter heating equipment.
Strategy #5 Generate Electric Power from the Window: Building Integrated Photovoltaics (BIPV) employ opaque solar cells to generate electricity and can be integrated into both walls and roofs of buildings, and even shading systems. They work best on parts of the building envelope that receive the most sunlight, and of course from an urban planning point of view cannot be obstructed by adjacent buildings or natural obstacles which will limit applicability in some cities. The newest generation of translucent and transparent BIPV provides light and/or view through the window glazing itself while generating power from the glass. These solutions provide either fully clear views through the glass that generates the power or are partially obscured similar to looking through a screen or blind. However in each case the power per unit window area is lower than with conventional PV systems and vertical orientation of most windows means that power generation will be dependent on orientation and adjacent obstructions. fig 6
Assembling the Kit of Parts: Putting it all Together…
Of course not every building glazing design can or should utilize all these functional elements but it is important to recognize that innovation and investment in the worlds of materials science, engineering, and manufacturing have now provided that kit of parts that we need to achieve a net zero energy/carbon solution while simultaneously delivering a wide range of occupant needs throughout the year.
But there is an enormous gap and tension between the theoretical capability of designing an optimized solution from these technology options and the reality of creating a building that reliably delivers on those performance promises on a daily basis over decades.
These challenges may turn out to be even harder than ensuring that all key technology options are available. Not only is it technically difficult in many cases but time is not on our side- on the one hand the slow pace of a building design-build-operate cycle against the ticking clock of cumulative carbon emissions. We likely won’t get it right the first time or every time but with each iteration – more engagement, more experiments, more feedback we can find the solutions that work and try to scale them.
We describe 6 issues/trends to watch:
Design tools, process: The proliferation of new technology options to consider excites the designer but frustrates the decision makers who must converge to “the” solution. The process from napkin (or cell phone) sketch to completed design is increasingly complex, not just because of the evolving software and tools e.g. BIM (Building Information Modeling, BEM (Building Energy Modeling), LCA (Life Cycle Assessment), and new work flows that manage and coordinate the team, the tools, and design data over time. New project delivery services are integrated into that design process from early in the process.
Manufacture and product delivery: The unitized curtain wall is a first big step away from historical practice of assembling many complex pieces on site. The ability to fabricate what we envision, deliver to the job site, install, integrate and commission is changing, borrowing from other industries that have addressed the challenges of integrating new technologies and processes, as in the automotive and aircraft sectors. We don’t Integrate into systems- factory assembled, site integrated; 3D-printing and additive manufacturing; mass customization, modular production,
Systems Integration Challenges in a “smart world”: We live in a world where the whole must be more than the sum of its parts … Success is often invisible and can be taken for granted- we readily accept comfort and delight in a glare free, thermally comfortable work space with clear views to the outdoors. Measured façade and building performance will only meet expectations if the design produces an integrated systems solution that works reliably over time. If perimeter heating coils at the glass façade were eliminated (saving money and floor space), then the correct highly insulating glazing must be in place to provide comfort. If mechanical cooling is eliminated or downsized (saving money and energy), the smart glazing or shading must work as designed every time not only to manage thermal comfort but to control glare, maximize view and offset electric lighting. Can this control be left to occupants or must it be automated to work reliably? (see fig 7) Can such a system be assembled on site, calibrated and commissioned to work reliably or must it be delivered in a factory pre-assembled package? The balance between manual and automated control is a delicate one, and reliable, occupant responsive operation of the system throughout the year can be a challenge with more complex active systems. Architects often use visual mockups to test appearance before construction begins. There is a small but growing interest in “performance mockups” in which full scale systems are assembled and tested to work out the design details and integration challenges with real hardware and people before final design details are approved. See figs 8 & 9
Grid responsive facades and buildings – the evolving and future decarbonized electric grid will be well integrated with the building energy end uses which today consume about 70% of electric power. A host of technology innovations that have already permeated other aspects of our lives are now entering the building space- wireless communications, ubiquitous cheap sensors collecting real time performance data, machine learning and AI to make that data actionable. Time of day tariffs in which the cost of electricity varies by hour and season may make it profitable to manage an active façade in new ways to save money over the hours of the day. Grid friendly active façade systems may effectively generate new operating income flows that help offset the increased construction cost of these systems. Figure 10 & 11
Materials and The Long View: A renewed focus on Embodied energy/carbon shifts focus to durability, lifetime, reusability and the principles of a circular economy. A material with high embodied energy may be acceptable if it brings very long lifetime and easy reuse and recyclability. While viewed as a constraint it can open new doors (or reopen old ones) for exploration- for example the role of light weight, thin glazing elements in triple and quad units to minimize weight and embodied energy. The long view with a focus on replacement and reuse could lead to more modular façade design solutions where the primary façade structure is designed with a 50-100 year lifetime but where glazing elements could be easily replaced on a 30 year update cycle and new smart controls might be changed out even more frequently. Accompanied by a paradigm of design for disassembly and reuse such an approach could dramatically reduce the assessment of embodied carbon in our buildings.
Standards, Building Codes and Metrics: Very few people are excited about building codes but they serve a purpose, a method to coordinate and standardize at least the set of minimum performance requirements we expect all buildings to meet. Meeting the code is rarely a mark of design excellence- but it provides a platform or floor from which other options can be evaluated on a consistent basis. Updated codes do drive some innovation although operationally most are designed with current practice in mind. New voluntary rating systems, e.g. LEED, etc. have emerged and evolved over time to put continuous pressure on the design community to design and build to better performance levels beyond the codes. Traditional codes focused on prescriptive measures that must be met or exceeded. Newer codes provide performance tradeoffs based on alternative designs that allow “equivalent” energy performance. Many codes have prescriptive limits on window area, e.g. 40% window-to-wall ratio, assuming conventional double glazed windows but these can be increased if higher performance triple glazing and/or smart glazing is used in its place. Numerous research studies and limited field tests have demonstrated that highly glazed facades can equal or outperform code compliant designs, assuming the aggressive design solutions outlined earlier are employed. To reinforce the importance of delivering a result that works, new “outcome-based” codes are in use in some cities where the code is deemed to be met only after a year’s worth of measured performance data in the occupied building demonstrates compliance.
How Do We Pay for the High Performance Facades?
We cannot leave the topic of glass and façades without mentioning the “dismal science”, economics, that drives much of the decision making related to the building envelope, captured most clearly in the elegant design solutions consigned to the circular file in the “value engineering” process. First, cost is often traded against operating cost with some agreed upon payback criteria although these are often too small to justify the larger investments needed to meet aggressive performance goals. Tradeoffs between systems have been noted earlier- a higher performance façade allows a downsized HVAC system which costs less. The brass ring in rethinking costs and cost effectiveness is expanding the concept of performance to include the health, comfort and performance of building occupants, the latter perhaps expressed as productivity or days of sick leave. There is intriguing new performance data that suggests the view from windows, daylight levels supporting circadian rhythm, improved thermal comfort, all increase “productivity”. While the interpretation and application of some of the newest scientific data are still a work in progress, even marginal improvements in occupant performance will have a huge impact on any investment balance sheet as occupant costs are roughly 100 times the cost of energy use on a per meter squared basis of building floor space.
A different solution to the challenge of investment costs is not to directly purchase the façade but rather lease it from others. Increasingly many former purchased “products” are now offered as a lease, often with maintenance built into the lease. Many software vendors lease their software on an annual basis and a large fraction of automobiles are now leased. In buildings, carpets are often leased and then replaced and updated on a regular basis. Why not extend that approach to “Façade as a Service” in which a high performance façade package is designed, financed and delivered as a package to the building, maintained by the lessor and then updated periodically as technology improves. This approach is consistent with the life cycle renewal issue discussed previously. The business case for this approach has been explored in research studies, whether an industry can be built around this concept remains to be seen.
This complex mix of people, technology, industry and finance ultimately impacts most aspects of our lives. We have the opportunity with high performance facades to deliver buildings that are inspiring architecture, market viable and economical for owner/investors; that enhance health, comfort and productivity for occupants, and that ultimately help address the existential environmental challenge we face as a global society. While it is admittedly challenging, we are often at our best when the stakes are highest. This is the classic opportunity to do well by doing good with a new generation of enhanced façade designs in our buildings. The key elements are available and even better ones are emerging. But it will take an extraordinary effort across the building industry, combining passion and skill, to execute solutions at the scale needed to deliver the outcomes we desire and need.
This article was originally published in IGS Magazines Spring 2020 Issue: Read the full Magazine here for more thought-leadership from those spearheading the industry
Author: Stephen Selkowitz Principal, Stephen Selkowitz Consultants Affiliate, Lawrence Berkeley National Laboratory (LBNL)
Selkowitz is recently retired as Senior Advisor for Building Science, LBNL, after leading the Building Technologies Department and the Windows and Daylighting Group for 40 years and is now a consultant and advisor to global building industry clients. He is an internationally recognised expert on sustainable design and high performance green buildings serving as an advisor to governments and business R&D teams globally. Selkowitz has extensive technical expertise on advanced glazing and window technologies, building façade systems, daylighting designs, software tools and integrated building system solutions and he partnered with industry to develop and demonstrate new technologies, systems, processes and design tools that address energy, sustainability and occupant comfort.
He has presented at over 400 scientific, business and industry venues, co/authored over 200 technical papers and 5 books, and holds 3 patents. In 2012 he received LBNL’s first “Lifetime Achievement Award for Societal impact”, in 2014 was awarded McGraw Hill/ENR’s prestigious “Award of Excellence” for “relentlessly working to reduce the carbon footprint of buildings” and in 2016 was elected to the Façade Tectonics Institute College of Fellows.