by Helen Sanders, PhD
Design teams and glazing contractors are often called in to help solve problems when building owners find there is too much light and/or heat coming in, making interior spaces practically unusable. This author has encountered examples where the sun’s glare is so unbearable in an office building employees were issued sunglasses, and have even covered windows with cardboard.
Electronically tintable, or electrochromic (EC) glass, is a category of dynamic glazing that allows occupants to control the indoor environment by changing the visible light transmission (VLT) and solar heat gain properties of the glass. EC glass can be controlled automatically in response to an external environmental signal (i.e. light, heat, or occupancy) or through integration into a building management system all with manual override capability. Electronically tintable glass has been increasingly adopted as an efficient all-in-one sun management system that provides a view to the outside.1
Many of the commercial projects where dynamic glass is incorporated are ‘fix-its,’ where the existing glass has been replaced with dynamic glazing to make the space work for its intended use. It is not that the existing glass had poor performance—quite the contrary: in some cases, the glass replaced had excellent solar control coatings. Rather, the issue is really the original design concept did not combine the glazing with other elements to adequately address the sun management challenge the exterior environment presents. Perhaps there was too much glass on east and west orientations that caused over-heating, or insufficient consideration of glare control.
For many applications, dynamic methods for solar control and glare control are needed for optimal energy performance and occupant comfort. Dynamic solar control can be achieved conventionally with mechanical movable louver systems or Venetian blinds integrated into double-skin walls. These systems are commonly used in Europe.
Alternatively, electronically tintable glass (i.e. electrochromic) can be used to provide both automatic glare and variable solar control. EC glass can, at the touch of a button or command from an automated system, modulate its solar heat gain coefficient (SHGC) from 0.41 to 0.09 and visible light transmission (VLT) from 60 to one percent2 over a wide range and stopping at points in between (Figure 1).
By achieving a visible light transmission as low as one percent in the tinted state, EC glass provides the ability to block uncomfortable glare while maintaining the view to the outside, unlike the mechanical alternatives which block or obstruct the view. By dynamically controlling the light and heat flow into the building, significantly more energy savings can be captured than when using a static glazed façade solution. Further, occupant comfort is enhanced while maintaining exterior views.
Kimmel Center for the Performing Arts
The renowned Kimmel Center for the Performing Arts in Philadelphia was designed in 2001 by Raphael Viñoly. It is an architectural icon with a vast barrel-vaulted, fully glazed roof housing multiple concert halls, theatres, and large public spaces. However, the Dorrance H. Hamilton rooftop garden—originally designed as a rentable space for private functions with panoramic views of the arts center and the surrounding city—was almost uninhabitable from May to September with temperatures reaching 48 C (120 F). The center’s management had to turn away over a thousand inquiries annually for renting the space.
In a renovation designed by BLT Architects completed in 2012, the rooftop garden has been enclosed in a glass box structure. The design employs dynamic glass in the roof to maintain the views of the center’s vaulted dome, the city, and public spaces, while maintaining a comfortable year-round temperature (Figure 2).3
Ball State University
Ball State University in Indiana (Figure 3) encountered a similar issue with a skylight. A three-sided courtyard in an honors dormitory had been enclosed to create a multi-purpose interior space. To maintain the open feel of the original courtyard, a fully glazed roof was designed. Even though a high-performance, low-emissivity (low-e) coated glass with a 50 percent frit pattern was used, the university realized within three months of the December installation the space was not working. It was too hot and there was too much glare, even during the winter.
Figuring out how to shade a skylight using mechanical shade or blind systems can be challenging and expensive. In fact, the mechanical solutions investigated were more costly than the automated dynamic glass solution which the university implemented only a year after the initial installation. The result was a comfortable space that was open, yet versatile, allowing movies and presentations to be viewed during daylight hours.
Generally, if the original design has not been well planned in terms of addressing the sun management issue, it is hard to come back retrospectively to ‘fix it’ in an elegant way using mechanical solutions that complement the original design intent. Adding sunshades to an existing fenestration system can be challenging, especially when the existing structure is not specified for the additional load.
Sunshades can be effective if included in the design of a new building when used on the south elevation and of an appropriate depth. Often, sunshades can be cut as part of a value engineering exercise and end up being two shallow, causing little or no shade on the window, or removed completely. Also, it is important to appreciate because of the low-angle sun incident on east and west elevations, sunshades are less effective at providing solar control from shading on those orientations.
The compromise solution is frequently to add interior shades or blinds, but this can be a difficult proposition for overhead or sloped glazing where gravity is working against the designer and can cause ongoing maintenance headaches. While this solution can reduce the glare issues, it may not solve the overall heat gain problem, since the heat is already in the building, and the view to the outside is obscured.Dynamic glazing can also provide the glazing contractor with a retrofit solution to simply solve their customers’ heat and light control problems in any climate. If strict privacy is a concern then additional opaque blinds or shades are commended as dynamic glass, while providing some level of privacy to occupants during the day does not offer strict privacy, especially at night.
Buildings with access to natural daylight and views to the outside are desirable because of the positive impact on the health and well-being of occupants, as well as the ability to save energy by turning off electric lights. The access to natural daylight entrains the body’s circadian rhythms, which are critical for the regulating health, attention, and mood—many studies have shown the link between lack of daylight and illhealth.4 Deborah Burnett, a presenter at a daylight symposium last year stated, “daylight is a drug and nature is the prescribing physician.”5 Sustainable design standards and programs—such as Leadership in Energy and Environmental Design (LEED), International Green Construction Code (IgCC), and American Society of Heating, Refrigerating, and Air-conditioning Engineers (ASHRAE) 189.1, Standard for the Design of High-performance Green Buildings Except Low-rise Residential Buildings—all appreciate both high-energy performance and providing a well-lit space with views to the outside.
However, designing with glass and not considering the negative effects of the sun can result in sub-optimal building environments that cause occupants to be uncomfortable and less productive. Moreover, such buildings can give use of glass in buildings a bad name and perpetuate the view that reducing glass in buildings is an appropriate solution and one to be encouraged in building codes.
This has been illustrated most recently when an addendum that would have reduced the allowable window-to-wall ratio in the prescriptive path from 40 to 30 percent was considered for ASHRAE 189.1. Due to numerous comments from many industry sectors, including the daylighting design community and academia, the proposal was withdrawn. However, the discussion is not yet put to bed. The optimization of energy performance, daylight and view, and providing occupant thermal and visual comfort is one of the most significant challenges for high-performance sustainable buildings. Determining how to codify such solutions in building codes and standards is also a challenge. A focus on addressing the three-way optimization may really only begin once as-built performance of buildings is measured not just for energy consumption, but also occupant comfort.Planning ahead
Glass can be a significant contribution in buildings from both an energy and occupant perspective; however, buildings need to be designed well the first time. From a national perspective, it is strategically important to improve the built environment’s quality.
Part of ‘getting it right the first time’ involves understanding how the envelope will interact with the exterior environment throughout the day and from season to season, along with having the tools and products for use in the façade to deal with the dynamic nature of the environment. Some design strategies work well for more southern climates (such as static overhangs) where the sun is intense and the angle does not change as much during the year. However, these strategies may not work as well in northern climates where access to light in the winter is desired, yet the sun angles are sufficiently low to cause glare issues.
There are design tools available that can help determine if perimeter spaces will work prior to building them. For example, the free software tool, DAYSIM, is a daylight simulation tool designed to model the amount of daylight coming into a perimeter space as a function of time of day over the course of a year. It is based on the Radiance software developed by Lawrence Berkeley National Laboratory (LBNL).
By using this tool, designers can easily see if there will be too much glare in a space and experiment with methods of eliminating the problem before the building is constructed. The software can handle both mechanical shades and blinds as well as dynamic glazing and can be helpful in determining if designs have a light control problem before construction.
Integrated design for daylighting
Another important part of a successful initial design is using an integrated approach wherein the daylighting, lighting, and interior design are done in conjunction with envelope design. This provides a holistic approach to optimizing use of daylight, offsetting electric lighting to save energy, and controlling for glare and unwanted heat gain. It also prevents the common occurrence of the envelope being specified and built before the daylighting designer is brought in, by which time he or she has lost most degrees of freedom. Further, because the interior and daylighting designers are involved early, it prevents opaque private offices or 1.8-m (6-ft) cube heights being specified around the perimeter—these negate the benefits of an otherwise good perimeter daylighting design.
Electric lighting accounts for approximately 38 percent of total building electricity use. Up to 80 percent of this electrical energy ends up as heat generated by lights, which then has to be removed by the air-conditioning system.6 In fact, the impact of reducing electrical lighting consumption by using daylight in commercial buildings is far bigger than the energy impact of changing the solar heat gain coefficient and U-factor of the fenestration by a few points.
Contrary to popular belief, a building with no windows is actually not the most energy-efficient structure. Glazed buildings employing high-performance fenestration, with appropriate considerations for solar control, good daylighting designs with a dynamic response for glare, and automated dimmable lighting systems can be more energy-efficient because of the saving in electrical lighting energy.7
The benefits to occupants in buildings with natural daylight and views to the outside should not be overlooked. After all, this is the reason windows are installed in the first place. An integrated design approach, employing daylight modeling and high-performance façade solutions can play an important part in ‘getting it right the first time,’ making even highly glazed buildings both energy-efficient and comfortable for occupants. By demonstrating mastery of the high-performance building challenge, the continued use of glass in buildings can be promoted. It helps make the case for not reducing the maximum allowable amount of glazing in the energy codes.
1 For more, see the white paper by D. Malmquist and N. Sbar’s, The Benefits of Dynamic Glazing. Visit sageglass.com/wp-content/uploads/2013/08/SAGE-benefits_of_dynamic_glazing.pdf. (back to top)
2 Visit sageglass.com/sageglass/sageglass-product. (back to top)
3 Visit pennsylvania.broadwayworld.com/article/Kimmel-Center-Completes-Dorrance-H-Hamilton-Rooftop-Garden-Renovation-20120831. (back to top)
4 For more, see Kathy Velikov and Julie Janiski’s “The Benefits of Glass: A Literature Review on the Qualitative Benefits of Glass on Building Occupants” at na.en.sunguardglass.com/cs/groups/sunguard/documents/native/pro_045179.pdf. (back to top)
5 See Deborah Burnett’s presentation, “Knowledge to practice—Epigenetics design and the built environment,”from the May 2013 Velux Daylighting Symposium in Copenhagen. (back to top)
6 See the 2003 U.S. Department of Energy (DOE), Energy Information Administration’s (EIA’s) “Commercial Building Energy Consumption Survey.” (back to top)
7 See D. Arasteh, S. Selkowitz, J. Apte, and M. LaFrance’s Zero Energy Windows, Proceedings of the 2006 ACEEE Summer Study on Energy Efficiency in Buildings, August 13 to 18, 2006. LBNL report number 60049. (back to top)
Helen Sanders, PhD, is the vice president of technical business development at Sage Electrochromics. She has 17 years of experience in the glass industry, and more than a decade in dynamic glass technology and manufacturing. She is an active member of ASTM, Insulating Glass Manufacturers Association (IGMA), and Glass Association of North America (GANA). Sanders earned her master’s degree in natural sciences and a PhD in surface science from the University of Cambridge. She can be contacted by e-mail at firstname.lastname@example.org.