Tag Archives: B2010.40−Fabricated Exterior Wall Assemblies

An Advanced Frame of Mind: The Window-to-wall Ratio Dilemma

Reducing the window-to-wall ratio (WWR) could compromise human views and comfort.

Reducing the window-to-wall ratio (WWR) could compromise human views and comfort.

by Chuck Knickerbocker

In 2013, the American Society of Heating, Refrigerating, and Air-conditioning Engineers (ASHRAE) proposed an addendum to ASHRAE 189.1, Standard for the Design of High-performance Green Buildings. The proposal seeks to reduce the window-to-wall ratio (WWR) area from 40 to 30 percent in small and medium-sized prescriptive-path buildings (buildings fewer than 23,226 m2 [250,000 sf]). ASHRAE 189.1 would allow building and design professionals using the performance-based approach to increase the glazed area.

While the purpose of the

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proposed reduction in glazing is to improve the building envelope’s energy-efficiency, numerous building and design professionals oppose the proposed change. Reducing the glazed area could compromise occupant views, human comfort, and the benefits of natural sunlight. Today, the WWR debate continues, bringing with it a renewed focus on specifying high-performance glazing systems in the building envelope.

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An Advanced Frame of Mind: Steel Framing in the 21st Century

by Chuck Knickerbocker

Using a roll-forming technique in which continuous steel coils are forced through dies and then laser-welded, manufacturers can produce steel window frame members in long lengths and various complex shapes. Compared to traditional steel and aluminum assemblies, this new generation of steel frames provides certain aesthetic benefits:

  • narrower frames;
  • sharp edges rather than rounded profiles;
  • corner joints with no visible weld beads or fasteners; and
  • flexibility to use back mullions of different shapes and sizes.

Since manufacturers can now produce steel frames in long lengths and various complex shapes, design teams can select from hollow-, I-, T-, U-, and L-shaped mullions or custom profiles. Another option is to use the veneer connector to attach the curtain wall to glued-laminated (glulam) beams, I-beams, or round steel tubes, among other structural members.

Advanced steel curtain wall systems use a ‘steel veneer’—or glazing adaptor—to overcome the challenge of fixed back mullions. This component can overlay onto nearly any modular back-mullion system, enabling it to receive glass or any other glazing material.

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An Advanced Frame of Mind: Next-generation framing for energy-efficient glazing

All images courtesy TGP

All images courtesy TGP

by Chuck Knickerbocker

Curtain wall and window framing establishes the total possible area of unobstructed glazing, provides support for high-efficiency glass units, and can help improve thermal performance. With proper specification, it has the potential to help manage a building’s lighting, heating, and cooling energy consumption. However, there is a fine line between good daylighting and increased energy consumption.

A curtain wall with poor thermal and solar heat gain performance in an open, loft-style office building can be problematic. As interior temperatures rise in the afternoon sun, occupants close the window shades and turn on the air-conditioning, increasing HVAC systems loads. The energy consumed to cool the room offsets the lighting loads saved from the curtain wall’s natural light stream.

To avoid this heat exchange dilemma, much of the specification process focuses on the glazing material itself. Glass comprises a large portion of the curtain wall and window area. Bolstering its performance can help prevent adverse side effects like glare, heat loss, and undesired solar heat gain.

Less talked about—though equally important—is framing’s role in energy-efficient daylighting design. Framing anchors the glazing to surrounding building materials and establishes the foundation for numerous performance and design outcomes. With proper specification, it can help create a sound building envelope and support large, high-performance glazing.

Comparing the thermal expansion coefficients of various materials.

Comparing the thermal expansion coefficients of various materials.

Thermal performance
As the connection point between the glazing and the perimeter details, curtain wall and window framing can help combat heat transfer.

Thermal conductivity
Many framing materials and systems have high thermal conductivity compared to other elements of the building envelope, creating assemblies susceptible to summer heat gain and winter heat loss. To overcome this challenge, design professionals often pair framing systems with low-emissivity (low-e) glass or other energy-efficient glazing. While center-of-glass (COG) thermal performance values improve, the system’s overall thermal efficiency remains substantially less effective where the captured or retained glass edge meets the supporting frames.

Incorporating glass with warm-edge spacers and frames with thermal breaks can help address this problem. Containing few, if any, metal components, warm-edge insulating spacers further improve the glazing’s U-value and reduce heat transfer. The spacers also help keep the inside surface of the frames warm to reduce condensation.

Thermal breaks help reduce heat flow by separating the inner and outer frame with low conductivity materials, such as polyester-reinforced nylon. According to the Whole Building Envelope Design Guide,1 a separator is classified as a ‘thermal break’ if it is greater than 6 mm (1/4 in.) thick. Generally, wide thermal breaks outperform narrow ones.

While breaks and separators can improve thermal performance, another important consideration is the conductivity of framing materials. While aluminum has a high thermal conductivity (i.e. approximately 124,500 joule [118 Btus] per hour), it has long remained the standard for commercial fenestration systems because of its lightweight nature. Today, advanced steel frames have emerged as a new, high-performance alternative (see “Steel Framing in the 21st Century“).

Steel’s thermal conductivity is approximately 74 percent less than aluminum (i.e. approximately 32,700 joule [31 Btus] per hour), and is equivalent to that of thermally broken aluminum frames. Due to the design of steel profiles, some advanced steel frames do not necessitate a traditional thermal break. Steel frames without

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a thermal break require less metal to support the glazing than traditional aluminum frames; therefore, they reduce the pathway for heat transfer.

Thermal expansion
Selecting curtain wall and window framing materials with similar expansion and contraction rates can help ensure a sound building envelope as the temperature changes. This is a crucial specification consideration for buildings in climates with extreme morning-to-midday temperature and seasonal changes.

Framing anchors glazing and determines allowable free spans.

Framing anchors glazing and determines allowable free spans.

Between the two main types of curtain wall framing materials—steel and aluminum—the former’s thermal expansion coefficient of about 12 x 10-6 x 1/K is the most comparable to glass and concrete (which are approximately 9 and 10, respectively). Aluminum has a thermal expansion coefficient of about 24. It expands and contracts at a rate about 100 percent greater than steel (Figure 1). This difference can reduce the size of perimeter sealant joints, especially at locations where the expansion is being addressed.

Condensation resistance factor
Another important specification consideration is the condensation resistance factor (CRF), which is a ratio of the surface to ambient temperature difference. Curtain walls and windows with a CRF appropriate for the local climate and building design typically have less interior condensation (or ‘sweating’) on frames.

While the American Architectural Manufacturers Association (AAMA) and other associations provide guidelines for selecting systems with the appropriate CRF, it is important to note the condensation resistance factor is a weighted average. Since it does not take into account cold spots and other peripheral factors, thermal modeling software can prove valuable for projects where condensation control is a concern, including cold-climate, high-humidity applications. These programs factor in numerous variables, including proximity to perimeter heating elements, to help estimate the air temperatures along the inside surfaces of the glass and frames.

In general, thermally broken, thermally improved, and narrow steel frames can help reduce interior condensation by providing a smaller pathway for heat transfer.

Allowable free spans
When factors such as glare and heat gain/loss are adequately addressed, curtain walls and windows with large free spans can provide occupants with increased access to natural light. In turn, this can help reduce electricity consumption for interior lighting.

Aluminum framing can support many of today’s curtain wall free span load demands. Modern steel curtain walls are a suitable alternative for applications requiring greater areas of unobstructed glazing. This performance benefit is the result of steel’s strength. Steel has a Young’s modulus (E) of about 207 million kPa (30 million psi), compared to 69 million kPa (10 million psi) for aluminum. As such, it enables greater free spans than an aluminum system of similar dimensions and applied loads (Figure 2).

For example, given a 1.5-m (5-ft) mullion spacing at a 146-kg-force/m2 (30-lb/sf) wind load, an aluminum mullion of 64 x 191 mm (2 ½ x 7 ½ in.), including the glass and exterior cap, can span a total of 3.8 m (12 ½ ft). Using the same example, if that aluminum mullion was steel, sized at 60 x 192.5 mm (2 2/5 x 7 3/5 in.), it would only deflect one-third as much under the same conditions. In application, the steel mullion’s length can be increased to span almost 5 m (16 1/3 ft)—a 30 percent increase over its aluminum counterpart.

Steel’s strength enables greater free spans than an aluminum system of similar dimensions and applied loads.

Steel’s strength enables greater free spans than an aluminum system of similar dimensions and applied loads.

A second benefit of steel’s strength is the ability to meet curtain wall load and deflection requirements with less material. For example, in a typical two-story curtain wall, unreinforced steel frames can be 44 mm (1 ¾ in.) wide and 146 mm (5 ¾ in.) deep, versus 65 mm (2 ½ in.) wide and 203 mm (8 in.) deep for aluminum. This reduces frame dimension size by approximately 25 percent, and allows for a slight increase in the glazed area.

Support for high-efficiency glass units
Curtain walls incorporating high-performance double- or triple-glazed units can help balance the natural admission of light with energy costs. Due to the size and weight of such glazing, traditional framing may not be able to support the required loads, forcing design teams to reduce the glass lite size and modify free span distances, thus incorporating more framing, not less.

As an inherently strong material, steel can provide the necessary support for heavy triple- or quadruple-glazed units. Depending on product selection, some steel systems can support glazing infills up to 76 mm (3 in.) thick and weights up to 112.3 kg/m2 (23 lb/sf). This far surpasses the typical thickness (i.e. 45 mm [1 ¾ in.]) and weight (i.e. 48.8 kg/m2 10 lb/sf) of triple-glazed units. As a result, steel framing can support high-performance glazing to help offset solar heat gain in large glazed assemblies with marginal effects on the design intent.

A balancing act
While steel curtain wall and window systems can support high-efficiency glass units, it is crucial they account for changing sun angles and solar heat gain. Incorporating shading devices—such as sunshades and sunscreens—can help protect against direct sun penetration. This is important since even strategically positioned curtain wall assemblies are subject to direct sunlight during certain hours of the day.

While selecting the appropriate framing can help optimize a curtain wall or window’s energy performance, it is just one component of a multi-dimensional system. Building layout, site orientation, construction materials, and lighting systems all affect how well a fenestration system transmits light without undesirable side effects.

Large free spans can help reduce electricity consumption for interior lighting.

By allowing the sun’s natural light to penetrate the interior, large free spans can help reduce electricity consumption for interior lighting.

From supplemental devices to glazing options, methods for mitigating heat loss and undesired solar gain include:

  • daylight-optimized footprint;
  • high-performance glazing coatings;
  • triple-glazing;
  • photochromic and electrochromic (EC) glazing;
  • double-skinned façades;
  • daylight-redirection devices;
  • solar-shading systems;
  • daylight-responsive electric lighting controls; and
  • daylight-optimized interior design.

As technology advances, design professionals will increasingly use high-performance curtain walls and windows to do more than create an energy-efficient building envelope. Building-integrated photovoltaic (BIPV) panels, for instance, can harvest daylight and help generate electricity. Manufacturers and suppliers of these specialized products can provide the necessary resources and support during the design and specification process.

Conclusion
With the push towards net zero energy, and with associations such as the American Society of Heating, Refrigerating, and Air-conditioning Engineers (ASHRAE) calling into question the effectiveness of large glazed areas, the benefits of pursuing more efficient fenestration systems extend beyond energy savings (see “The Window-to-wall Ratio Dilemma”). They help ensure future buildings will have large windows and curtain walls, be filled with warm, natural light, and provide occupants with views of cityscapes and nature.

Notes
1 See Nik Vigener, PE; and Mark A. Brown’s “Curtain Walls,” by visiting www.wbdg.org/design/env_fenestration_cw.php. (back to top)

Chuck Knickerbocker is the curtain wall manager for Technical Glass Products (TGP), a supplier of fire-rated glass and framing systems, along with specialty architectural glazing products. With more than 30 years of curtain wall experience, he has successfully worked with numerous architects, building owners, and subcontractors from development of schematic design through installation. Knickerbocker chairs the Glass Association of North America (GANA) Building Envelope Contractors (BEC) Division Technical Committee. He can be contacted via e-mail at chuckk@tgpamerica.com.

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.

Aluminum_FixedWindow

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

WA_BullittCenter_Benschneider4

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.