Tag Archives: Glazing

Meeting Efficiency Codes without Compromising Design: Technology that Meets Specifications

A full-scale mockup incorporating architectural insulation modules.  [CREDIT] Photo courtesy Dow Corning Corporation

A full-scale mockup incorporating architectural insulation modules. Photo courtesy Dow Corning Corporation

by Stanley Yee, LEED AP

To help overcome concerns about adoption of new technology, a full-scale mockup of a high thermally performing curtain wall incorporating architectural insulation modules was recently successfully tested by an independent third-party. Testing was conducted in accordance with American Architectural Manufacturers Association (AAMA) 501, Methods of Test for Exterior Walls, ensuring acceptable performance for air and water penetration resistance, structural capacity, and vertical and seismic movement requirements.

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Meeting Efficiency Codes without Compromising Design

Photo courtesy of University of Birmingham

Photo courtesy of University of Birmingham

by Stanley Yee, LEED AP

Creating an effectively insulated envelope is necessary for buildings to meet the latest demands of ever-tightening energy codes. Innovative use of high-performance insulation technologies enables architects to achieve improved insulation performance using common building techniques without sacrificing aesthetics.

Thin-profile, high-performance insulation materials that seamlessly integrate into conventional glazing systems now give designers flexibility to better manage and balance thermal performance and façade aesthetics. Materials such as vacuum insulation panels (VIPs), architectural insulation modules (AIMs), and aerogel building insulation blanket materials are becoming more prevalent.

For many years, inexpensive energy made it possible to design buildings without regard for energy performance. The global movement toward sustainability has led to tightening regulations often restricting design freedom.

Local, national, and global organizations continue to develop codes that mandate increased thermal performance in insulation and, in turn, reductions in energy consumption. Construction in the United States can be subject not only to prevailing building codes, but also standards such as American Society of Heating, Refrigerating, and Air-conditioning Engineers (ASHRAE) 90.1, Energy Standard for Buildings Except Low-rise Residential Buildings, with increasing pressure to comply with voluntary standards and certifications such as the United States Green Building Council’s (USGBC’s) Leadership in Energy and Environmental Design (LEED) v4. Other drivers include:

  • 2012 International Energy Conservation Code (IECC);
  • Living Building Challenge;
  • growing demand for net-zero buildings; and
  • American Institute of Architects’ (AIA’s) 2030 Challenge.

From a design standpoint, simply increasing the amount of conventional insulation used in a building is neither practical nor aesthetically pleasing. New insulation technologies provide the performance advantages necessary to achieve effective building envelope insulation without sacrificing design aesthetics.

Integrated use of high-performance insulation in the curtain wall spandrel, in Calgary, Alberta, enables high window-to-wall-ratio designs that meet energy codes. [CREDIT] Photo courtesy BIG

Integrated use of high-performance insulation in the curtain wall spandrel, in Calgary, Alberta, enables high window-to-wall-ratio designs that meet energy codes. Photo courtesy BIG

Thermal performance of commercial insulation materials. [CREDIT] Images courtesy Dow Corning Corporation

Thermal performance of commercial insulation materials. Images courtesy Dow Corning Corporation

 

 

Balancing design trends with energy performance
Cognizant of the need for energy performance, architects are put in a challenging position. Designers are pressured by current building trends to include as much glazing and vision area as possible for optimal aesthetic value, striving to create iconic buildings of aluminum and steel with floor-to-ceiling glass. However, this rise in the use of glass means increasing energy performance can be challenging.

Unfortunately, extensive use of vision glazing is generally lower in thermal performance. To achieve an overall desired level of exterior wall performance, architects and designers must depend on the non-vision spandrel sections.

Used on the façades of commercial buildings, these opaque spandrel sections—typically composed of metal, stone, or glass panels—are used to conceal the floor lines. The spandrels are often designed to visually blend so closely with the vision glass they are not even perceptible, creating the effect of a uniform, all-glass building (Figure 1). They also are manufactured in various colors and designs, adding additional visual interest to the curtain wall’s appearance.

More importantly, the spandrels can be highly insulated to contribute to the façade’s overall thermal performance. Leveraging technical design opportunities in the spandrel sections allows designers to maximize the vision area and still meet prescribed thermal performance requirements of energy conservation codes, such as ASHRAE 90.1 and IECC.

Mineral wool requires eight to 10 times the thickness to provide the equivalent insulation value of a vacuum insulation panel (VIP).

Mineral wool requires eight to 10 times the thickness to provide the equivalent insulation value of a vacuum insulation panel (VIP).

Traditionally, spandrel areas need to be supplemented with an additional layer of thick mineral wool or similar conventional insulation to achieve the necessary thermal value. However, in higher climate zones, such as Climate Zones 4 and 5, this approach may require additional space within the curtain wall to accommodate the required thickness to achieve thermal performance targets. Thin-profile high-performance insulation technologies can solve these challenges.

Beyond the building’s outward aesthetics, architects are also facing the challenge of mitigating uncontrolled thermal losses due to thermal bridging across the building envelope. These heat losses typically occur at transitional conditions in building envelopes, such as:

  • exposed slab edges;
  • where glazing systems meet cavity wall components;
  • where below-grade and above-grade systems meet; and
  • where parapets meet roofs.

Building codes and regulations now require mitigation of thermal bridging conditions. They can make it especially challenging for architects to retrofit existing designs with insulation solutions meeting both performance requirements and available space limitations.

New applications for high-performance insulation technologies
Architects and designers have additional flexibility to respond to insulation performance challenges with high-performance insulation technologies, such as vacuum insulation panels. VIPs can be integrated into architectural insulation modules to enable whole-wall envelope thermal performance improvements; aerogel building insulation blankets can also be included to help address detail-specific thermal bridging issues. These materials not only demonstrate a step-change in thermal performance compared to traditional insulation materials, but also enable designs using current construction techniques to meet demands of the next generation of thermal requirements.

Figure 2 shows the thermal resistance (i.e. RSI, R-value) which is typically expressed as R-value per inch, of various insulation products, including materials typically found on a job site such as expanded polystyrene (EPS), mineral wool, and polyisocyanurate (polyiso). As demonstrated by Figure 2, the change to higher-performing materials is significant, with silica-fume-based vacuum insulation panels as high as RSI 5.63 to RSI 6.16 per 25 mm (R-32 to R-35 per inch) and the aerogel building insulation blanket at RSI 1.73 per 25 mm (R-9.8 per inch).

Composition of vacuum insulation panel.

Composition of vacuum insulation panel.

Thin-profile vacuum insulation panels
Vacuum insulation panel technology provides designers with new options. Offering insulation in a slender profile, a VIP’s thermal performance gives it the equivalency of eight to 10 times the thickness of mineral wool insulation typically used on a construction site (Figure 3).1

Forms of vacuum insulation were invented more than a century ago, and interest has grown over the past several decades in applications where constrained space and weight benefits justify the higher cost, such as commercial applications, as well as in ‘cold-chain’ applications, such as insulated shipping and transport containers. Now, the technology is finding its place in commercial façade insulation applications.

VIP construction (Figure 4) is based on a pressed fumed silica core, which is formed and heated to drive out the moisture. It is then inserted into a handling bag (i.e. core bag) and then into a multilayer, aluminized bag. As that bag is put under full vacuum, its edges are heat-sealed. When the vacuum is released, a full vacuum is contained within the bag. With the vacuum, all the atmospheric gases around the fumed silica are removed, therefore eliminating convective heat transfer from the gases within. With the full vacuum, the unit achieves the initial RSI 5.6 to RSI 6.2 per 25 mm (R-32 to R-35 per inch) center-of-panel (COP) performance. Without the vacuum, the material provides about RSI 1.4 per 25 mm (R-8 per inch), which is approximately twice as good as typical foam insulation—so even if the material loses its vacuum, it continues to provide good insulation performance.2

VIP offers many advantages. It has low nominal thermal conductivity—approximately 4 mW/mK at COP. The metalized bag around the panel is inherently moisture-resistant. The fumed silica core is an ash created by burning a silane. Essentially, the material has already been burned, providing a high degree of fire resistance. The VIP’s thin profile can also allow it to solve various problems; for example, increasing thermal performance requirements not being met by conventional means, or maintaining thermal performance requirements while allowing for increased vision area.

VIP is a pre-engineered product and must be customized by the manufacturer or packaged as part of a system; it cannot be cut to size onsite, as cutting or puncturing the material would cause a vacuum loss and resulting loss of thermal performance.

Cutaway view of architectural insulation modules incorporating VIP technology.

Cutaway view of architectural insulation modules incorporating VIP technology.

Architectural insulation modules are available in various finishes to meet aesthetic requirements.

Architectural insulation modules are available in various finishes to meet aesthetic requirements.

 

AIMs–integrated curtain wall application of VIP
The façades of modern glass curtain walls typify an ideal application for vacuum insulation panel technology. Curtain walls create the iconic artwork and unique character of a building. The ability to maintain a slim façade with a high thermal performance gives the architect the design freedom to maximize the wall’s vision area and/or thermal performance while still meeting local building codes.

For curtain wall applications, VIP technology is provided in an integrated façade module known as an architectural insulation module, which combines a VIP with a protective architectural finish (Figure 5). The module has a back pane of a rigid structural panel material, joined with a warm edge spacer (as used in the insulating glass industry) around the perimeter. VIP is inserted into the space—which typically is the air space in an insulating glass unit—and covered with a finished panel on the front. Modules are available in various architectural options, including opaque, metal, and glass with ceramic frit or ceramic frit patterns (Figure 6).

Performance of architectural insulation modules of various thicknesses.

Performance of architectural insulation modules of various thicknesses.

Modeling and guarded hot-box testing demonstrates the performance characteristics of architectural insulation modules technology (Figure 7). A 25-mm (1-in.) thick unit modeled with a two-dimensional finite element thermal analysis software package, resulting in an effective RSI 1.90 (R-10.84) and a COP value of RSI 3.84 (R-21.8).

A 50-mm (2-in.) thick unit is tested with ASTM C1363, Standard Test Method for Thermal Performance of Building Materials and Envelope Assemblies by Means of a Hot Box Apparatus. Figure 7 shows actual test results of a 50-mm thick structural panel, which includes a 6-mm (1/4-in.) piece of glass on each side and a 38-mm (1.5 in.) VIP in the interspace, sized at 1.5 x 1.5 m (5 x 5 ft), indicating an effective RSI of 3.4 (R-19.05). The effective R-value is lower due to factors including heat losses around the insulating glass spacer assembly.

In addition to demonstrating superior thermal performance, the AIM is designed to meet the physical demands of commercial façade applications, withstanding typical windloads and meeting structural requirements. Constructed to standard or custom spandrel size specifications, the modules require no special installation techniques, eliminating need for specialized installer training.

Effect of VIP on U-value and window-to-wall ratio performance.

Effect of VIP on U-value and window-to-wall ratio performance.

Whole-wall insulation performance
Designing a slim façade with a higher percentage of vision requires the lowest possible U-values for spandrel areas to augment thermal performance characteristics. VIP-integrated façade modules enable additional vision area while still complying with thermal performance requirements, improving the curtain wall’s overall whole-wall performance.

When this technology is applied to a building design, it increases thermal performance by maintaining the same window-to-wall ratio, but its replacing of traditional insulation with architectural insulation modules, increases overall curtain wall thermal performance (Figure 8, Arrow 1).

Further, it increases design freedom as architects gain ability to potentially increase window-to-wall target ratios substantially, without compromising on the insulation value of the curtain wall configuration (Figure 8, Arrow 2X).

Blanket insulation
Like the vacuum insulation technology, aerogel is not a new concept, but it has been optimized for the next generation of building challenges. Invented in the 1930s, the material is composed of 95 to 99 percent air, making it one of the lightest materials. Its nanoporous structure minimizes thermal transport, giving it low thermal conductivity. It has been used in various applications, especially aerospace, but with tightening environmental requirements and increasingly complex building designs, aerogel insulation has now found a new niche providing thermal protection in space-restricted areas.

An aerogel building insulation blanket is made from synthetically produced amorphous silica gel. It features a small particle size, with the diameter of the spaces between aerogel particles similar to the fumed silica in the vacuum insulation panels. Manufacturing this material in a blanket form (Figure 9) creates a usable, flexible, construction-friendly material that can be cut-to-size onsite and applied to reduce the thermal bridging at specific locations in a building envelope assembly. Aerogel building insulation blankets are highly resistant to flame, with an ASTM E84, Standard Test Method for Surface Burning Characteristics of Building Materials, Class A fire rating (flame spread index 5, smoke developed index 10).

Flexible, highly insulating aerogel building insulation blanket.

Flexible, highly insulating aerogel building insulation blanket.

Linear transmittance reductions with aerogel building insulation blankets.

Linear transmittance reductions with aerogel building insulation blankets.

 

Minimizing thermal bridging
Updating architectural details to address thermal bridging concerns has become more common due to increasingly explicit and stringent building codes. The availability of a thin, flexible insulation material reduces the need to make trade-offs in design to meet codes and regulations, and it eliminates bulky or messy insulation from those tight areas of building designs.

Based on ASHRAE Research Project (RP) 1365, Thermal Performance of Building Envelope Details for Mid- and High-rise Buildings, three common construction details were modeled to demonstrate the effect of using aerogel building insulation blankets to minimize thermal bridging. These models are:

  • curtain wall-at-grade detail with the aerogel building insulation blanket applied from the neck of the curtain wall to the below-grade rigid insulation, resulting in a reduction in linear thermal transmittance approaching 25 percent;
  • curtain wall jamb at the exterior and interior insulated steel stud assembly with the aerogel building insulation blanket applied around the adjacent steel stud and at the wall-to-curtain wall transition, resulting in a reduction in linear thermal transmittance approaching 70 percent; and
  • rehabilitated window-wall system with the aerogel building insulation blanket at the slab edge and around vertical and horizontal glazing mullions, resulting in a reduction in linear thermal transmittance approaching 53 percent.

Lineal transmittance values can readily be incorporated into thermal models. This eliminates the guesswork and improves the predictability of the heat loss due to thermal bridging at those locations. (See Figure 10.)

Additionally, two whole-building energy models were created to demonstrate the effect of using aerogel building insulation blanket with conventional and higher-performance assemblies to minimize thermal bridging:

  • for a building with the glazing system covering 100 percent of the façade area, addition of the an aerogel blanket, with conventional assemblies resulted in a 3.56 percent energy savings;3 and
  • for a façade with curtain wall glazing and a steel stud wall assembly, addition of the aerogel blanket and higher-performing assemblies resulted in a 6.78 percent energy savings.4 (See Figure 11)
Annual heating energy savings for Chicago climate.

Annual heating energy savings for Chicago climate.

Conclusion
Vacuum insulation panels, architectural insulation modules, and aerogel building insulation blankets have been introduced in a range of construction projects in the United States and Europe, with positive response.

In an age of increasingly dramatic building design, architects can take comfort in knowing design does not have to take a backseat to performance and energy efficiency issues in current designs can often be addressed with innovative application of high-performance insulation materials.

Notes
1 For more information, see ASHRAE Fundamentals Handbook 2009. (back to top)
2 Visit Vacuum Insulation: Panel Properties and Building Applications at www.ecbcs.org/docs/Annex_39_Report_Summary_Subtask-A-B.pdf. (back to top)

Stanley Yee, LEED AP, is a façade design and construction specialist for Dow Corning High Performance Building Solutions. He joined the company in 2012 with nearly 20 years of experience in the building enclosure industry, working with curtain wall contracting, façade consulting, and enclosure detailing specialists both nationally and internationally. Yee earned a bachelor of engineering degree from Concordia University (Montréal, Québec). An active member of several industry organizations, he is an elected officer of the Board of Directors for the Glass Association of North America (GANA), representing the Energy Division. He can be contacted via e-mail at stanley.yee@dowcorning.com.

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Security Glazing for Safer Schools: Trends in School Safety

Between 1999 and 2009, various school security measures have been implemented:

  • controlled access to the building during school hours (moving from 75 to 92 percent in that decade);
  • controlled access to school grounds during school hours (34 to 46 percent);
  • identification badges for faculty (25 to 63 percent);
  • video cameras to monitor school (19 to 61 percent);
  • telephones in classrooms (45 to 74 percent);
  • student uniforms (12 to 20 percent);
  • restricted social networking websites (now 93 percent); and
  • restricted cell phone use during school hours (now 91 percent).

To read the full article, click here.

 

Security Glazing for Safer Schools

Photo courtesy Graham Architectural Products

Photo courtesy Graham Architectural Products

by Julie Schimmelpenningh

With recent tragedies involving school shootings, parents and administrators across the country are demanding ways to make K−12 facilities more secure. Areas of the schools under significant scrutiny are doors and windows—and more specifically, the glass being specified.

For extra school security, laminated security glass can be an easy and cost-effective measure to assist in resisting forced entry and the threat of bullets. Compared with traditional annealed or tempered glass, this type of material can secure the building more effectively.

Laminated glass is made from a tough plastic interlayer bonded between two pieces of glass. The interlayer is invisible to the naked eye, so laminated glass offers the same clear visual benefits as ordinary glass—an important feature for security. From inside, glass allows occupants to see someone approaching the school. From the outside, it can help responders locate intruders or victims.

Success in other fields
Laminated glass has successfully protected public facilities and major works of art for many years. Security glass has been in use in various forms for generations. Invented in 1903 by French chemist Edouard Benedictus, laminated glass has been employed for decades in car windshields to greatly reduce injuries. It is commonly used in high-risk facilities such as embassies and federal buildings, as well as museums. Laminated glass protects great treasures such as the Mona Lisa, the U.S. Constitution, and the Crown Jewels in London.

After the devastation caused by Hurricane Andrew in 1992, laminated glass became the standard in Florida and other coastal regions. Building code requirements were established to lessen the amount of destruction caused from high winds and to ensure occupant safety.

Enhancements to laminated glass configurations ensure glazing in federal and other public buildings are blast-resistant. Dozens of lives were saved by blast-resistant laminated glass when the Pentagon, newly remodeled, was attacked on September 11, 2001. The shockwaves following an explosion can send glass shards flying for miles and generally cause about 70 percent of the injuries following a blast, as was the case in the 1995 Oklahoma City bombing and many other blast events. It is these qualities that make the material a good candidate for school specifications.

When remodeling an educational facility or building a new school, security should be a major player in the design process. Windows and doors are the easiest point of entry into a school, but they don’t have to be.  Installing laminated security glass for all windows and doors makes forced entry much more difficult. Images courtesy Eastman Chemical Company

When remodeling an educational facility or building a new school, security should be a major player in the design process. Windows and doors are the easiest point of entry into a school, but they don’t have to be. Installing laminated security glass for all windows and doors makes forced entry much more difficult. Images courtesy Eastman Chemical Company

Renewed need for extra security
A school is more than just a facility; it is a place where families send their kids for the majority of their day to learn, participate in sports and clubs, and perform in musicals and plays. Schools can be why families buy a home in a specific neighborhood, and they can be what ties a community together—the buildings are frequently used as emergency management centers or shelters in times of crisis, making security an important attribute, even after teaching hours.

In recent years, however, schools are not being thought of as the safe havens they once were. Since 1992, there have been 387 shootings in U.S. schools, according to www.stoptheshootings.org. One of the most recent involving fatalities occurred last December at Sandy Hook Elementary School, where 20 children and six adults were killed. As no one can predict whether an attack will happen, it is important schools be prepared for anything.

Immediately following the Sandy Hook shooting, discussions across the country started about how this tragedy and future shootings could be prevented. There were conversations about gun control, awareness and care for the mentally ill, as well as improving safety at schools through better communication systems, security measures, and intruder drill training. School districts everywhere are looking at how they can keep their students, teachers, and faculty safe. Design/construction professionals can play an important role as well.

What the school construction industry can do
By installing laminated security glass for all windows and doors, forced entry becomes much more difficult. Laminated glass is fabricated with a tough, protective interlayer, typically of polyvinyl butyral (PVB), which is bonded with heat and pressure between two pieces of glass. The use of thicker interlayers can increase the resistance of the glass to impacts. Upon impact, laminated glass will shatter, but glass shards remain held together by the bonded interlayer. Risks associated with flying or falling glass are minimized.

Laminated security glass stands up to multiple assaults from a blunt or sharp object used to gain entry. If an intruder tries to break through a window or the glass lite of a door, it would take several blows before he or she achieves access through the security glass. This allows valuable time for anyone inside the school to react, enabling more opportunity to call the police, send internal communications about the intruder, lock-down interior doors or classrooms, evacuate, or move students to a safer area.

From a glazing standpoint, school architects and administrators may consider the following when designing new or retrofit glazing systems:

  • glass should provide inherent health, safety, and security benefits that can help mitigate disasters;
  • natural daylight is essential for psychological benefits of students and teachers;1
  • glass should provide visibility for critical passageways and entry areas; and
  • sustained functionality—basic functions of the school can operate following a natural disaster or incident.

Considering threat levels
Entry doors have been the most vulnerable in many school shootings. Hurricane-rated high-impact (i.e. large-missile) glass, or even ballistic glass should be considered. As in the case of Sandy Hook, the shooter penetrated the side lite of the door and then reached through to open it. The ‘break-and-reach’ ability of the intruder must be delayed or stopped. High-performance glass provides resistance, while still providing much needed visibility.

Existing doors may need to be replaced completely if bullet-resistant glazing is specified, as the framing system for such heavy configurations is specialized.

Access doors with a double-entry lobby to the school should be equipped with laminated security glazing having forced entry/burglary resistance capability in accordance with Underwriters Laboratories (UL) 972, Testing for Burglary-resistant Glazing Materials, or Class I of ASTM F1233, Standard Test Method for Security Glazing Materials and Systems.

Today’s schools have an increasing amount of glass windows and doors because of the positive benefits it brings. For extra security, laminated glass is an easy, cost-effective measure in protecting against forced entry and bullet resistance. Compared with traditional annealed or tempered glass, laminated glass can secure the building more effectively.

Today’s schools have an increasing amount of glass windows and doors because of the positive benefits it brings. For extra security, laminated glass is an easy, cost-effective measure in protecting against forced entry and bullet resistance. Compared with traditional annealed or tempered glass, laminated glass can secure the building more effectively.

First-floor glass should be, at a minimum, equipped with basic laminated glass, which typically requires a 0.76-mm (0.03 in.) thick interlayer. This type of glass will deter ingress, retain glass, and slow break-and-reach attempts. Forced ingress glazing will offer greater protection, and uses a thicker interlayer. Laminated glass can be retrofitted into most existing window and door systems and can contribute to compliance for security windows per ASTM E2395, Security Performance of Window and Door Assemblies With and Without Glazing Impact.

If budgets do not permit replacement of windows, security film can be post-applied over the existing windows and doors. This option offers some of the benefits of laminated glass, but provides less resistance against an intruder. Further, like other laminated glass options that are not ballistics-resistant, it will not stop a bullet. Security film also modifies the post breakage behavior of glass, but may allow time to take additional action versus non-enhanced glazing.

During new construction, laminated glass may make economic sense due to its higher performance levels. However, post-applied films can be a good alternative in a retrofit situation where glass replacement is not possible.

It requires several shots from handguns like a 9 mm, .357, or .45 caliber to make a hole large enough to put a fist through to unlock a door or window. In some cases, the intruder may be temporarily confused, as the glass does not ‘behave’ as expected. There are many documented smash-and-grab attempts at a burglary where would-be intruders give up because they are generating too much noise and attention.

Additional benefits
Along with its safety and security enhancing features, laminated glass offers other benefits for schools. Laminated glass dampens sound coming in from the outside, making it an ideal choice for schools located in noisy neighborhoods or urban environments. The interlayer in laminated glass significantly dampens sound, keeping unwanted outside noise at bay.

Numerous studies have shown children concentrate and can learn better in a quiet space. For example, one research project found links between higher achievement and less external noise. Excessive outside sound resulted in increased student dissatisfaction with their classrooms and stress.2

Laminated glass also reduces the amount of solar heat gain and ultraviolet (UV) rays going into a building, making it more comfortable and healthy for students and teachers. Work has been done delving into the importance teachers place on thermal comfort, proving temperature affects both teaching quality and student achievement.3 Interestingly, studies in the 1970s found the best temperature range for learning math and reading is between 20 and 23 C (68 and 74 F).4 Maintaining a specific classroom climate is an essential part of setting students up for success.

CS_February_2014.inddHurricane-rated laminated glass protects against natural disasters. Following Hurricane Andrew in 1992, Florida began to strengthen its building codes to help protect the building envelope. Windborne debris was a major problem during this Category 5 hurricane, and the construction industry began to look for ways to protect the windows in commercial buildings and schools.

Laminated glass proved to be one of the most effective solutions for this problem, and today, is commonplace in buildings in coastal areas of the United States, the Caribbean, and other world areas. Hurricane-resistant glass comprises multiple interlayers; it can be considered for vulnerable areas of a school, such as entry and rear doors, sidelites, and floor-to-ceiling windows.

Laminated glass is versatile, readily available, affordable, and easy to install. Also, it can be used to help a project earn credits within the U.S. Green Building Council (USGBC) Leadership in Energy and Environmental Design (LEED) program. Specifically, designers can secure points toward LEED certification under

  • Energy & Atmosphere (EA) Credit 1, Optimize Energy Performance;
  • Materials & Resources (MR) Credit 4, Recycled Content;
  • Indoor Environmental Quality (EQ) Credit 8, Daylight & Views; and
  • EQ Credit 9, Enhanced Acoustical Performance.

Since laminated glass offers solar, safety, and acoustic benefits, it can help achieve points ordinary glass may not.

Upgrading schools through glazing
In 1998, data collected in surveys conducted by the National Center for Educational Statistics (NCES) suggested the average public school building in the United States was 42 years old.5 This suggests many of the country’s schools may now be at an age where frequent repairs are necessary.

Due to the burst in school construction during the Baby Boom Era, the NECS study reports almost half (i.e. 45 percent) of schools were built between 1950 and 1969. Seventeen percent of public schools were built between 1970 and 1984, and only 10 percent after 1985. These older schools were not envisioned with modern-day security and safety measures in mind; further, they do not offer the physical security level now desirable.

Educator A.C. Ornstein found by the time school is 20 to 30 years old, frequent replacement of equipment is needed.6 Original equipment, including roof and electrical systems, should be replaced between 30 and 40 years old, as rapid deterioration begins after this point. In fact, most schools are abandoned by the time they reach 60 years.

When the NECS study was published, most of those facilities were already about 50 years old and experiencing serious decline. In other words, half of the country’s public schools could be seen as major threats to student safety.

Immediately following the Sandy Hook shooting, discussions across the country started about how this tragedy and future shootings could be prevented. School districts everywhere are looking at how they can keep their students, teachers, and faculty safe. Design and construction professionals can play an important role as well.

Immediately following the Sandy Hook shooting, discussions across the country started about how this tragedy and future shootings could be prevented. School districts everywhere are looking at how they can keep their students, teachers, and faculty safe. Design and construction professionals can play an important role as well.

Today, as the rate of school construction continues to decline, safety is a more serious concern than ever. The existing stock of schools is too old to offer any kind of reliable security systems. Outdated glass, in particular, lacks basic insulation features to control classroom temperature and cannot offer much more than protection from outdoor elements. However, the installation of laminated glass immediately updates an aging school and offers protection to students and teachers.

While there is pressing need for building better schools, many face funding and time constraints. When new buildings cannot be erected, the architectural community must look at available options to modernize, update, and safeguard existing schools. Laminated glass or window film remains one of the easiest and most cost-effective measures available for enhancing student and faculty safety.

Notes
1 For example, a 2002 study by L. Heschong et al (“Daylighting Impacts on Human Performance in School,” Journal of the Illuminating Engineering Society, 31[2])identified effects of natural light on students as evidenced in significantly improved standardized test scores for elementary students. The same study concluded that daylight contributed positively to overall health and well-being of students. (back to top)
2 The G.I. Earthman and L. Lemasters’ paper, “Where Children Learn: A Discussion of How a Facility Affects Learning,” was presented at the 1998 annual meeting of Virginia Educational Facility Planners. (back to top)
3 The 1999 J.A. Lackney report, “Assessing School Facilities for Learning/Assessing the Impact of the Physical Environment on the Educational Process,” was published by Mississippi State’s Educational Design Institute. (back to top)
4 The David P. Harner article, “Effects of Thermal Environment on Learning Skills,” appeared in Educational Facility Planner, 12 (2). (back to top)
5 The NCES report, “How Old Are America’s Public Schools?” was published in January 1999 by the U.S. Department of Education’s Office of Educational Research and Improvement. It can be read online at nces.ed.gov/pubs99/1999048.pdf. (back to top)
6 Ornstein’s article, “School Finance and the Condition of Schools,” appeared in the book, Teaching: Theory into Practice (Allyn and Bacon). (back to top)

Julia Schimmelpenningh is global applications manager, advanced interlayers for Eastman Chemical Company. She is has been a glass industry activist for 25 years with experience in research and development, technical lamination processing, product, applications, and standard development. Schimmelpenningh is a participating member of ASTM, International Organization for Standardization (ISO), and Glass Association of North America (GANA). She can be reached at jcschi@eastman.com.

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Window and Storefront Thermal Performance: What every specifier needs to know

Photos © Benjamin Benschneider

Photos © Benjamin Benschneider

by Brian Stephens

Energy efficiency is becoming an ever-increasing topic in domestic and global markets. However, the scope of effective energy management utilizing fenestration becomes difficult when designing a system that balances performance requirements while remaining economically viable and minimally impacting the environment.

In the commercial building segment, advanced fenestration design is evolving to address growing energy management issues. Although the tools available to influence these designs are readily available, they must be properly employed to achieve the desired result.

The U.S. Department of Energy (DOE) has set a goal to reduce building energy consumption in commercial buildings by 20 percent by 2020. This goal is viable considering current waste levels, but does not have a clear prescriptive path. Examining the components of the fenestration system can help improve a system’s capability to more effectively manage energy and meet thermal requirements.

The need for design evolution is connected to market knowledge, demand, and codes. U.S. code evolution, which follows the international market, is a pressing topic of conversation amongst many organizations in recent years. Building for longevity necessitates specifying with consideration for future standards.

The U.S. Department of Energy’s (DOE’s) Buildings Energy Data Book monitors commercial sector energy consumption. Data courtesy buildingsdatabook.eren.doe.gov/TableView.aspx?table=3.1.4. Image courtesy Technoform Glass Insulation

The U.S. Department of Energy’s (DOE’s) Buildings Energy Data Book monitors commercial sector energy consumption. Data courtesy buildingsdatabook.eren.doe.gov/TableView.aspx?table=3.1.4. Image courtesy Technoform Glass Insulation

Breaking the frame
With consideration to long-lasting, high-performance windows, it is helpful to first understand the components. Improving performance of fenestration products typically begins with a thermally broken frame. According to the American Architectural Manufacturers Association (AAMA) and the Window and Door Manufacturers Association (WDMA) 2012/2013 “U.S. National Statistical Review and Forecast,” 38 percent of all aluminum window and door products in North America have thermally broken frames. This is up from 22 percent in 2005, and projected to increase to more than 50 percent by 2016. The report also states aluminum framing accounts for approximately 91 percent of commercial fenestration systems.

Aluminum is a highly conductive material, so thermally ‘breaking’ the frame improves the fenestration system’s thermal performance. According to the National Fenestration Rating Council (NFRC) 100-2010, Procedure for Determining Fenestration Product U-factors, this means a separation of at least 5.3 mm (0.21 in.) with a low-conductive material. Usually, aluminum-framed commercial fenestration systems are thermally broken using either a pour-and-debridge method or extruded polyamide strips.1

The former method involves a two-part polyurethane mixture poured into an aluminum channel, allowed to cure, and then debridged using a saw blade. ‘Debridging’ refers to separating the interior and exterior assemblies.

Once the conduction (material type and design), convection (system design) through the frame, and the radiation (glass selection) are improved, the limiting factor to the overall system thermal performance is the heat transfer through the edge of glass. Image courtesy Technoform Glass Insulation

Once the conduction (material type and design), convection (system design) through the frame, and the radiation (glass selection) are improved, the limiting factor to the overall system thermal performance is the heat transfer through the edge of glass. Image courtesy Technoform Glass Insulation

However, the majority of thermally broken systems are designed using polyamide due to flexibility in design and recyclability. The strips also separate interior and exterior assemblies, but do so using a mechanical connection. Aluminum pockets designed to hold polyamide strips are knurled to create teeth, which helps create a solid mechanical connection. Polyamide is then slid into these pockets and crimped into place creating a composite profile. The finished assembly is then shear-tested to validate proper assembly. Polyamide has a similar coefficient of expansion and contraction to aluminum ensuring system durability after thermal cycling.

Solar radiation
Once the heat transfer through the window frame has been addressed, the solar radiation through the glass must be improved. Critical to improving glass performance is the management of the solar radiation through it. The glass’ ability to withstand this energy transfer is called its emissivity. As a benchmark, clear glass has an approximate emissivity of 0.84, meaning it allows approximately 84 percent of the energy to pass through.

To reduce the amount of energy transferred through the glass, the fenestration industry developed low-emissivity (low-e) coatings. Low-e coatings can be formulated to have a broad range of solar control characteristics, while maintaining a low U-factor. Dual-pane insulating glass units (IGUs) made with high-performance, low-e coatings can achieve a U-factor of 0.25 Btu/hr·sf·F (1.42 W/m2·K) to 0.30 Btu/hr·sf·F (1.70 W/m2·K), which is a solar heat gain coefficient (SHGC)—fraction of incident solar radiation admitted through a window—of 0.20 to 0.30, while still allowing between 40 to 70 percent visible light transmittance (i.e. amount of light in the visible portion of the spectrum passing through a glazing material). Even lower U-factors are achievable with triple IGUs. The 2012/2013 AAMA/WDMA “U.S. National Statistical Review and Forecast” also noted 42 percent of commercial windows were not thermally improved with either a thermal break in the frame, a low-e coating on the glass, or a high-performance spacer in the IGU.

Heat transfer through glass
Once the conduction (material type and design), convection (system design) through the frame, and the radiation (glass selection) are improved, the limiting factor to the overall system thermal performance is the heat transfer through the edge of glass. To manage this portion of energy loss in a design, systems have evolved from single-lite units to dual-lite IGUs. The IGU, now a sub-assembly in the overall design, comprises several components with the premary influencer on energy management being a warm-edge spacer.

This warm-edge spacer system incorporates a high-performance polymer and low-conductivity stainless steel to provide minimal heat transfer and maximum protection against gas leakage and moisture penetration.

This warm-edge spacer system incorporates a high-performance polymer and low-conductivity stainless steel to provide minimal heat transfer and maximum protection against gas leakage and moisture penetration.

In addition to keeping the glass lites separated and establishing the airspace in the unit, the spacer also serves additional functions in the system. It:

  • accommodates stress induced by thermal expansion and pressure differences;
  • serves as a moisture barrier to prevent passage of water or water vapor that would fog the unit;
  • ensures a gas-tight seal to prevent the loss of low-conductance gas in the air space;
  • creates an insulating barrier to reduce the formation of interior condensation at the edge; and
  • provides a substrate for which adhesive components in the system create the primary and secondary sealant to deliver longevity and performance.

Previously, IGUs were primarily produced with a metal box spacer made of aluminum, filled with a desiccant that absorbs moisture. This assembly has a sealant applied to the edge of the frame, which bonds the glass lites to the spacer. The efficiency of this unit type is relatively low since aluminum is a highly conductive material.

Spacer systems have evolved throughout the years to address this highly conductive component. High-performance, warm-edge spacers were designed to go beyond the standard system. These greatly improve a window unit’s overall U-factor, condensation resistance, and sightline temperature by employing low-conductivity materials and unique design elements. During the fabrication of an IGU, its performance may be further enhanced through the introduction of gas.

Filling the airspace between the lites with a less conductive, more viscous, or slow-moving gas minimizes the convective currents and conduction through the gas within the air space. Manufacturers generally use argon or krypton gas to achieve measurable improvement in thermal performance. Both of these gases are inert, clear, and odorless. Argon and krypton occur naturally in the atmosphere and can help improve the thermal performance, but gas retention and cost can be a concern.

Industry testing (i.e. European Standard [EN] 1279-3, Glass in Building: Insulating Glass Units–Long-term Test Method and Requirements for Gas Leakage Rate and for Gas Concentration Tolerances) has shown less than one percent leakage per year can be achieved if the unit is well-designed and well-fabricated. Again, keeping the gas within the IGU depends largely on the quality of the design, materials, and assembly of the glazing unit seals. Without these, the influence of gas on the system performance can be lost in a short period in spite of the added cost. The Insulating Glass Certification Council (IGCC) offers third-party certification of IGUs for seal durability and gas content in compliance with ASTM E2190, Standard Specification for Insulating Glass Unit Performance and Evaluation.

Sustainability and success
Effectively using some, or all, of these design improvements can aid in the achievement of energy goals for fenestration systems. Another benefit is it allows the designer to maintain flexibility with environmental fenestration design and to reduce use of opaque materials to achieve the energy targets. This approach also responds to owners’ desire for increased daylighting within the building. (The University of Minnesota’s Center for Sustainable Building Research offers more detailed information on this topic.2)

 

Filling the airspace between the lites with a less conductive, more viscous, or slow-moving gas minimizes the convective currents and conduction through the gas within the air space.

Filling the airspace between the lites with a less conductive, more viscous, or slow-moving gas minimizes the convective currents and conduction through the gas within the air space.

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The benefits of daylighting are often overlooked due to other pressing requirements, yet evidence continues to mount in identifying the value expanded daylight adds to a building and its occupants. The Heschong Mahone Group has published three reports with the California Energy Commission (CEC) and the New Buildings Institute (NBI) showing more window area and the corresponding increased daylighting may have a positive influence on productivity, mental function, and physical wellbeing.3

These studies also indicate students in classrooms with more window area have higher test scores, and employees with a window to look out are more productive than their coworkers in cubicles without views. Similarly, the studies demonstrate retail stores with more daylight have higher sales than similar stores with primarily electrical lighting.

The U.S. Green Building Council (USGBC) is one of the many organizations promoting the need for daylighting and high-performance buildings. Its Leadership in Energy and Environmental Design (LEED) rating systems certify projects meet criteria for sustainable design and construction. LEED guidelines are now in their fourth version, known as LEED v4. There are three main changes in v4: market sectors, increased technical rigor, and streamlined services.

Contributing to its Gold certification under the Leadership in Energy and Environmental Design (LEED) program, the RBC Centre in Toronto has a window system relying on a high-performance polyamide thermal break system, as well a low-emissivity (low-e) coating and spacer in its insulating glazing units (IGUs). Photo courtesy AKA Communication Associates

Contributing to its Gold certification under the Leadership in Energy and Environmental Design (LEED) program, the RBC Centre in Toronto has a window system relying on a high-performance polyamide thermal break system, as well a low-emissivity (low-e) coating and spacer in its insulating glazing units (IGUs). Photo courtesy AKA Communication Associates

While high-performance systems cannot achieve LEED credits on their own, they still can contribute to the overall building design in many categories, with respect to energy performance, recycled content, regional materials, and daylighting.

Commercial buildings are adopting many of LEED’s principles and advance system design to improve energy and human performance. The RBC Centre in Toronto, designed by architect firm Kohn Pedersen Fox & Bregman Hamann, incorporates many of these design features to achieve its LEED Gold status. The RBC Centre’s window system relies on a high-performance polyamide thermal break system, as well a high-performance low-e coating and high-performing warm edge spacer in its IGUs. Light shelves also assist in bringing the daylighting more deeply into the building’s interior.

The Living Building Challenge (LBC) seeks to surpass LEED criteria as a green building certification program recognizing the most advanced measure of sustainability in the building environment possible today. Through the International Living Future Institute, LBC certification poses the most rigorous performance standards across the globe.

LBC has seven performance areas, four typologies, and three types of certifications. The seven performance areas are Site, Water, Energy, Health, Materials, Equity, and Beauty, which are then subdivided into 20 ‘Imperatives.’ The four typologies are Renovation, Infrastructure & Landscape, Building, and Neighborhood. LBC provides a framework for design, construction, and the symbiotic relationship between people and all aspects of the built environment.

Its three certification types are Full Certification, Petal Recognition, and Net-zero-energy Building Certification. Validation for Full Certification includes submitting 12 months of post-occupancy data to demonstrate annual operations for net-zero energy and water, plus a zero carbon footprint.

Number one with the Bullitt
Located in Seattle’s Capitol Hill neighborhood, the Bullitt Center strives to become the first U.S. commercial office building to earn LBC Full Certification. The $18.5-million project opened this year on Earth Day—April 22—and intends to last until 2263. The project also serves as a premier example of a successful, collaborative effort between a building’s owner, developer, architect, contractor, specifiers, and manufacturers to incorporate sustainable principles, including energy management levers for fenestration design.

In Seattle, the Bullitt Center (see also page XX) is striving to become the first U.S. commercial office building to earn Full Certification through the Living Building Challenge. Helping achieve its net-zero energy performance goals, the building’s IGUs are triple-paned and weigh up to XX kg (468 lb). Most of these units are 51 mm (2 in.) thick, comprising a spacer and two lites of glass with low-e coating.

In Seattle, the Bullitt Center is striving to become the first U.S. commercial office building to earn Full Certification through the Living Building Challenge. Helping achieve its net-zero energy performance goals, the building’s IGUs are triple-paned and weigh up to 212 kg (468 lb). Most of these units are 51 mm (2 in.) thick, comprising a spacer and two lites of glass with low-e coating. Photos © Benjamin Benschneider

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The six-story, 4831-m2 (52,000-sf) Class A office building’s unusually tall 4.2-m (14-ft) floor-to-floor heights are matched with equally impressive floor-to-ceiling operable window systems. These spacious, daylit areas provide expansive views of the downtown skyline and connect the building’s occupants with their surrounding environment. Prior to fabrication and construction, computer simulations modeled daylight illumination for different window configurations and ceiling heights to optimize energy efficiency.

Further contributing to the building’s energy goals and the occupants’ comfort, the fenestration system not only maximizes thermal performance and condensation resistance, but also enhances acoustic performance for quiet interiors. The IGUs are triple-pane and weigh up to 212 kg (468 lb). The majority of these units are 51 mm (2 in.) thick and comprise a warm-edge spacer plus two lites of glass with low-e coating on the second and fifth surfaces. The spacers vary in size from 12.7 to 15.9 mm (1/2 to 5/8 in.). This composition attains a U-factor of 0.17 Btu/hr·sf·F (.97 W/m2·C), and a condensation rating of 86 can be achieved.

The University of Central Missouri’s renovated Morrow-Garrison Complex (Warrensburg) was able to achieve LEED Gold and the Innovative Architecture & Design Award with its sustainability features. During the design, special spacers were selected to improve the window’s overall efficiencies. Photo © Alistair Tutton Photography

The University of Central Missouri’s renovated Morrow-Garrison Complex (Warrensburg) was able to achieve LEED Gold and the Innovative Architecture & Design Award with its sustainability features. During the design, special spacers were selected to improve the window’s overall efficiencies. Photo © Alistair Tutton Photography

Addressing LBC’s seven performance areas, the Bullitt Center’s operable windows also capitalize on natural ventilation coupled with a heat-recovery system and weather-responsive shading system. The warm-edge spacers were one of thousands of building materials in the Bullitt Center vetted thoroughly for compliance with the LBC “Red List” of 14 potentially toxic substances. Many of these substances, such as polyvinyl chloride (PVC) and formaldehyde, are common in building materials. In striving for a building with essentially no environmental footprint, the Bullitt Center’s collaborative team discovered its high-performance targets could be met with a mix of existing and new technologies, systems, and materials.

Conclusion
Carefully specified components can influence the performance of not only the complete fenestration system, but also the entire building. Integration of thoughtfully selected components can drive system evolution to create successful, sustainable properties that attack building energy mandates, provide effective spaces for building occupants, become valuable structures for building owners, and endure for decades.

Commercial building codes and energy regulation continue to evolve; with these, demand for advanced performing buildings will continue to increase. To support this evolution, it becomes imperative fenestration design moves at a more aggressive pace. To provide value and longevity, these systems should not only meet the current requirements, but also be engineered to respond to future expectations.

The Wisconsin Institutes for Discovery at the University of Wisconsin-Madison received the Innovative Green Building Award and the “Laboratory of the Year” in 2012. The building also achieved LEED Gold certification in 2011. High-performance spacers were used in its IGUs to help improve overall window efficiency.

The Wisconsin Institutes for Discovery at the University of Wisconsin-Madison received the Innovative Green Building Award and the “Laboratory of the Year” in 2012. The building also achieved LEED Gold certification in 2011. High-performance spacers were used in its IGUs to help improve overall window efficiency. Photos courtesy the Wisconsin Alumni Research Foundation

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Notes
1 There are dozens of different kinds of isolation materials, and trade-offs are associated with each. Globally, the majority of projects employ polyamide, which is the focus of this article. (back to top)
2 For more information, visit www.commercialwindows.org/performance.php. (back to top)
3 Visit www.h-m-g.com/downloads/Daylighting/order_daylighting.htm. (back to top)

Brian Stephens, LEED AP, is a product manager with Technoform Glass Insulation North America. He earned a B.Sc. in mechanical engineering from the University of Colorado at Boulder. Within the company, Stephens focuses on strategic market and business development including new product design. Within the industry, he seeks opportunities to share his knowledge of fenestration systems that incorporate thermally broken frames and high-performance warm-edge spacers, as well as the impact of high-performance fenestration on sustainability. Stephens can be reached via e-mail at bstephens@technoform.us.