Volume 48, Issue 7- July 2013


Blinded by the Lite
Glass May Be Considered an Energy Hog, But Factor in High-Performance Features and Human Comfort and It’s a Real Energy Star
by Ellen Rogers

There’s a reason the corner offices with the views of the city are the most coveted in the building, just like there’s a reason the homes with million-dollar ocean views demand soaring asking prices. The reason is simple: people like that connection to the outdoors. They like sunlight and they like views. They like windows. Now, close your eyes and imagine that highly sought-after corner office; imagine it with only small punched openings. Imagine that house; imagine it without expansive glass openings. Take away the glass and you take away the view. And without a view that property, perhaps, won’t have the same value.

As an example, the American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE) is once again proposing a reduction in window-to-wall (WWR) ratio, this time through a proposed addendum to ASHRAE 189.1, Standard for the Design of High-Performance, Green Buildings, which seeks to reduce the glazing area allowed in the prescriptive path from 40 percent WWR to 30 percent WWR for buildings fewer than 25,000 square feet (see related article on page 20). To put it bluntly, a drop from 40 to 30 percent is a 25-percent reduction in allowable glass usage—25 percent less glass sold annually.

Now consider the corner office and luxury home with the killer views and answer this: why, if we all love windows so much, are some trying to take this away? Why is glazing so frequently viewed as an energy waster, when, in fact, it can very much add to the performance level of a building? It is a simple question; the answers, however, are complex.

The Missing Piece
“There seems to be an oversimplified understanding of the performance of glass. I think this is because glass is viewed as having low performance and it’s the prescriptive parameters driving these criteria,” says Benedict Tranel, senior associate and technical director of the Gensler architectural firm based in San Francisco. “If you reduce the vision area it reduces the amount of solar heat load and U-value of the building envelope, so in a very gross way of measuring building performance, yes less glass gives better performance.”

He continues, “I think what’s missing is a more multi-dimensional understanding of glass performance and how it inter-relates with other building systems, orientation, etc. You can choose high-performance products with U-factors, and a double skin facade and get good performance in combination with great views for people on the inside. You have to be willing to go into these details to appreciate how possible it is to have this. If you look at the prescriptive path and then what you can typically do from the performance approach, you can almost double that [the amount of glass] without going to any great lengths.”

According to Helen Sanders, vice president technical business development with SAGE Electrochromics Inc. in Faribault, Minn., one of the main reasons glazing is thought of negatively in terms of energy performance is because when just comparing the standard parameters of solar heat gain coefficient (SHGC) and U-factor, those of a window are always higher than an opaque wall. This, she is quick to point out, is a very simplistic view.

“If you just focus on these two parameters you’re missing the point that a building with windows can save more energy than opaque walls if the daylight is harvested and used to offset electrical lighting. The key is having an appropriate amount of glass in the appropriate location integrated with dimmable lighting controls as part of a good daylight design,” she says. “The thing about lighting is it also generates heat. If you can use natural daylight, it saves electricity energy and also reduces the load on the HVAC system.”

She adds, “Building modeling studies show that buildings with windows and daylight controls if designed well can be more energy efficient than buildings without windows.”

Thom Zaremba, a code consultant with the Glass Association of Normerica’s (GANA) Glazing Industry Code Committee (GICC), explains that “the whole concept is to distinguish between good uses of energy and things that waste energy. And there are some energy conservation advocates who have lost the distinction of the fundamental concept that it’s not about eliminating what’s a good use of energy, but rather what wastes energy.”

According to Steve Selkowitz with the Lawrence Berkeley National Laboratory Building Technology and Urban Systems Department in Berkeley, Calif., such negative opinions often stem from experiences with poorly performing glazing as well as a lack of understanding about what is possible.

“Most people have experienced discomfort in front of single-glazed windows, sweated uncomfortably behind large expanses of unshaded clear glass in sunlight, or paid large energy bills because of poor performing glass,” he says. “If we simply compare insulating values it is true that typical, older glazing loses more energy than insulated walls. What most people don’t recognize is the degree to which modern fenestration solutions have overcome all of the past performance limitations, and that, in fact, high-performance glazing/fenestration solutions can outperform the best insulated wall or roof.”

Why Windows at All?
“We put windows in buildings for one reason and that is for people,” says Sanders. “So the design should be about making it a great space for people first, giving them access to natural daylight and views, and then next we should do everything we can to make it as energy efficient as possible. If you just focus on energy it can lead you down an inappropriate path.”

She continues, “Designing a high-performance building is a complex problem and needs to balance many competing requirements for windows. The proponents for reducing WWR are focusing on a simplistic approach, which ends up with a reduction in window area. However, what they’re missing is the fact that by using daylight harvesting, innovative designs and new high-performance glazing products you can save a lot of energy without compromising occupant views and comfort.”

She continues, “[The glass industry] needs to understand the arguments in this debate, because it’s an issue for everyone. If the use of glass is reduced in buildings, then the amount of glass sold over time will be reduced and that is not good. This may be one step on the oad to continuing to decrease windows in buildings. That’s not good for business, and from a societal perspective, it’s not good for people, either. Studies have shown the importance of exposure to daylight for entertaining the body’s circadian rhythms and the impact of this on maintaining good health and well-being. The implications of not having access to daylight and having your circadian rhythms out of sync are significant.”

Zaremba adds, “We know, based on history or walking through any downtown area, that people love glass and views. It’s healthy. It increases productivity, it increases daylight, [and] it can reduce electrical loads when coupled with lighting.”

Speaking of the 1891 proposal, he continues, “It is not well-thought-out and violates a number of fundament principles of this code because the one thing it’s supposed to take into account is the human factor.”

Why Care?
For everyone involved, from the architect to the installer, the potential impact a reduction in WWR could have is significant. And experts agree it is a topic everyone in the industry should know and understand. Selkowitz suggests, for example, that the glass industry move away from the minimum area theme and argue for “equal or better overall energy performance,” rather than prescriptive limits on area.

“But that means in colder climates a shift to higher-performance products than the traditional double, low-E, (U ~ .35) windows that are common today,” he says. “If the industry wants to be taken seriously by ASHRAE, the Department of Energy, Environmental Protection Agency and others it needs to support the goal of increasing savings, but doing it more intelligently than by simply reducing window area. We’ve demonstrated that with the proper window technology, increased window area with high-performance units can outperform smaller windows with code-compliant glazings.”

And as Nick Bagatelos, president of Bisem USA in Sacramento, Calif., explains it, “If governing bodies create standards that prescriptively reduce the percentage of glass in a building, everyone in the glass [industry] loses potential sales.”

According to Zaremba, if a proposal such as the latest addendum to 189.1 takes effect, for some, it could very well mean major changes in the way buildings are designed and constructed.

“If you want to use glass you will have to move to a more expensive design and incorporate numerous trade-offs,” he says. “[The industry] needs to know that this will significantly impact their ability to sell glass in the future,” says Zaremba. “The minimum codes (such as ICC) tend to follow the green codes. So there could be a trickle down effort to the minimum codes.”

While many in the glass industry have concerns over what could happen if the ASHRAE proposal goes through, Tranel says it would not likely impact his designs.

“If it’s purely the prescriptive path being tightened, it would have a negliible impact because I always use the performance-based approach because it’s a more holistic approach to how buildings perform and I’m always a proponent of that,” he says.

As an example, Gensler currently is working on PNC Plaza in Pittsburgh. Slated for completion in 2015, the all-glass tower features a double-skin façade and was designed to exceed LEED platinum. The firm is working with PPG, which is supplying 400,000 square feet of Starphire ultra-clear and Sungate 400 passive low-E glasses. J.E. Berkowitz in Pedricktown, N.J., is the fabricator and Permasteelisa North American Corp. in Windsor, Conn., will be the contract glazier.

“We were able to combine a double façade with blinds on the inside of the double-façade cavity and can provide natural ventilation for users, daylight that can be controlled and we’re reducing the solar heat gain coefficient to a theoretical zero,” says Tranel. “The glass itself on the outside is just laminated low-iron as it… doesn’t play a role in actively reducing the solar heat gain coefficient. On the interior, the glass is an argon-filled insulating glass unit (IGU). The net effect is a transparent, all-glass building that is one of the highest-performing façades and one that gives users access to how the façade works.”

Energy Saver
Experts explain that the options are available to use glass and still have an energy-efficient façade. The question is: Where do we start in terms of design? According to Sanders, it begins with making sure glass is used on the appropriate places on the building. For example, this could be using a minimal amount of glass on the west façade.

“You want appropriate glass performance where you have windows and you want to make sure you’re dealing with the dynamic nature of the sun,” she says. “This could mean providing some kind of dynamic glare control and sun management, and ideally, working with the interior design, daylighting/lighting and the façade teams to develop a holistic design for the façade. You have to manage the dynamics of the sun’s heat and glare; you should start with fenestration with an appropriate U-factor (according to the climate zone), develop a method for dynamically controlling glare, a solar control strategy and integrated daylight design with dimmable lighting controls.”

“The simple approach is to use insulating glass with low-E coatings and thermal breaks and insulation at spandrel areas,” adds Bagatelos. “The next step up is to use electrochromic glass for tunable SHGC. The final step is the addition of building integrated photovoltaic panels, so the exterior wall actually creates energy.”

He adds, “There are products that are cost effective now, and with clear planning for energy efficiency an architect can keep high quantities of natural light, and maintain a super-efficient building.”

Zaremaba says another possibility to consider is fourth surface low-E coatings coupled with number-two low-E on the IGU.

“That can significantly reduce the U-factor below what is typically prescribed in the codes and is a very cost-effective way to do so,” he says.

Jon Hughes, director, marketing and business development with AGC Glass Company North America in Alpharetta, Ga., points to the use of triple IGUs as well as double-skin facades as other options.

“Architects like to use glass,” he says. “They are knowledgeable in how to use it, but one limiting factor is the complexity of the design process. When you get into sophisticated designs you need to go to the performance path.”

Selkowitz agrees and says glazing and fenestration have the technical potential to reduce energy losses to zero in most climates.

“In cold climates the strategy is improved insulating value (triple glazing or equivalent); in hot climates it’s proper control of solar gain via coatings, dynamic glazing, shading systems, etc., and for commercial buildings adding dimmable daylight controls to capture the energy benefits of daylight from windows and skylights,” he says. However, he points out that the glazing industry also needs to be active in spreading the word about these capabilities and how these products can help.

“Windows today cost building owners about $40 billion a year in energy costs--that's an inviting target to go after, but it requires design and engineering skills to select the products and systems that will work best in each building, climate and orientation,” he adds. “Fortunately the tools required to optimize façade solutions are available.”

Emerging Technologies
It can be a slow process, though, for new products, design concepts and technologies to gain market acceptance. “It’s like any number of new products: people are conservative so you have to show them it works, it is durable and easily integrates into the way they currently do business,” says Sanders. “You have to have that test data, field data and a number of proof points in buildings where it’s operating successfully.”

Zaremba points out that one of the biggest obstacles is cost. “What will the payback be to use high-performance glass? If it’s ten years or fewer, okay. If it takes 100 years there will be resistance,” he says. “As technologies improve we will see more and more use of these products … as [they become] mandated by codes we will see greater use and lower costs. What slows this down, though, is how fast the codes are adopted and accepted.”

He also points out that there is a business challenge, noting that he sees the window industry as having done a poor job of marketing the value proposition for its products.

Selkowitz adds, “The market focuses too narrowly on cost—cost is always important, but it’s only one of many factors that influence buying decisions. A focus on first cost alone misses the opportunity to capture other market values with high-performance glazing.”

Speaking of such new technologies, there are several with which Tranel would like to work.

“Dynamic facades are really becoming a key part of the solution … [as they can help provide] better building performance,” he says. “I think if you can have operable external sunshades, for example, that can provide a huge improvement to performance. Also interesting, and I think is on the cusp, is phase change material, such as tintable facades and even more passive products that are thermally dynamic controlled so they require no building control or input they just work on their own.”

Spread the Word
It will take a lot of effort and a lot of work, though, to make sure the industry is aware of the potential impact a reduction in WWR could have, as well as the opportunities in support of increasing it.

“I think GANA is doing a lot to get people engaged in the discussion and debate through the work of the energy division and its buildings standards subcommittee. We are generating awareness and education around this topic in the industry, leading the way developing strategies and arguments to address this,” says Sanders. “We’re also reaching out to lighting and daylighting designers and other researchers and architects, and engaging them in the discussion as well. I firmly believe that the next step is to do a better ob of understanding and advocating for the people-related benefits of windows.” This is important, she says “because the energy benefits of daylighting are great now, but as electric lighting moves from fluorescents to solid state lighting, the lighting power density in buildings will go down markedly, and at a certain point you won’t achieve nearly as much energy benefit by just offsetting the lights.”

While Selkowitz says there is still much work before the glazing industry, there is some good news in that the tools and resources are available to help. These can include NFRC ratings, websites and simulation tools that can help facilitate the design of more energy-efficient windows.

“There are tools to help sales reps and architects/engineers select the best window solution that delivers comfort as well as energy efficiency. These tools are backed by measurements in test beds and buildings,” says Selkowitz, who gives an example. “We just completed a field study of the performance of the New York Times building in New York City; this is an all glass façade with high-performance glazing, fixed external glazing, motorized interior shades and daylight dimming. The overall electricity use of typical floors was 24 percent lower than a code-compliant building and the lighting was reduced by 56 percent in dimmable lighting controls. Most importantly, the occupants reported a high level of satisfaction in the thermal and visual comfort in the space.”

And that circles right back to why windows are put in buildings in the first place: people.


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