Windows on Sustainability  

With world net electricity generation estimated to soar 77 percent by 2030, powered by fossil fuels that will generate a 39 percent rise in carbon dioxide emissions, the move is on to net-zero buildings—structures that generate as much energy as they consume. Often considered the next wave in architecture, net-zero buildings dispense with heating bills, electricity expenses, air-conditioning costs and other energy uses—and can potentially be independent of the energy grid supply. The American Institute of Architects has set a goal of net-zero buildings by 2030 and some parts of the country, notably California, will require that a building generates as much energy as it uses by that date. This article will focus on the significant role advanced glazing systems play in getting buildings toward net zero. High-performance glazings will be defined, their benefits and recent advances discussed, as well as how they fit into the rapidly emerging fields of building integrated photovoltaics (BIPV) and pre-wired curtain walls, which incorporate advanced glazings into the building envelope, replacing traditional materials with those that serve as both building skin and solar power generator.

Advanced Glazings for a Net-Zero Envelope Solution

The U.S. Department of Energy estimates that buildings account for some 40 percent of all energy use in the United States—more than either the transportation or industrial sectors—and 70 percent of its power plant-generated electricity. Over 30 percent of this energy is lost through poor building efficiency. Nearly every country has passed regulations to reduce buildings' energy consumption, and manufacturers are racing to develop products that meet those demands.

Windows are commonly regarded as one of the least energy-efficient building components, responsible for up to 40 percent of the total heating, cooling and lighting consumption. According to the National Research Energy Laboratory, the potential energy savings from the wide-scale use of advanced windows is nearly 6 percent of national energy consumption. Window manufacturers and glazing contractors are embracing new technologies to achieve ever higher energy performance through low solar heat gain coefficients (SHGC) to reduce air-conditioning loads and through low U-factors to reduce thermal transfer—key goals of commercial buildings.

A UL-approved BIPV curtain-wall retrofit on the Sacramento Municipal Utility District (SMUD) Headquarters in Sacramento, California. Photo by David Bush, courtesy of BISEM USA

 

Advanced Glazings for a Net-Zero Envelope Solution

The U.S. Department of Energy estimates that buildings account for some 40 percent of all energy use in the United States—more than either the transportation or industrial sectors—and 70 percent of its power plant-generated electricity. Over 30 percent of this energy is lost through poor building efficiency. Nearly every country has passed regulations to reduce buildings' energy consumption, and manufacturers are racing to develop products that meet those demands.

Windows are commonly regarded as one of the least energy-efficient building components, responsible for up to 40 percent of the total heating, cooling and lighting consumption. According to the National Research Energy Laboratory, the potential energy savings from the wide-scale use of advanced windows is nearly 6 percent of national energy consumption. Window manufacturers and glazing contractors are embracing new technologies to achieve ever higher energy performance through low solar heat gain coefficients (SHGC) to reduce air-conditioning loads and through low U-factors to reduce thermal transfer—key goals of commercial buildings.

Definition of Terms

U-factor and U-value are interchangeable terms referring to a measure of the heat gain or loss through glass due to the difference between indoor and outdoor air temperatures. U-factor or U-value is also referred to as the overall coefficient of heat transfer. A lower U-value indicates better insulating R-value equals a measure of the resistance of the glazing to heat flow. It is determined by dividing the U-value into 1, (R-value = 1/U-value). A higher R-value indicates better insulating properties of the glazing. R-value is not typically used as a measurement for glazing products. Both U-value and R-value are a measure of resistance to heat flow and are referenced here to help understand U-factor. The solar heat gain coefficient (SHGC) is the percent of solar energy incident on the glass that is transferred indoors both directly and indirectly through the glass. The direct gain portion is the solar energy transmittance, while the indirect is the fraction of solar energy incident on the glass that is absorbed and re-radiated or transmitted through convection indoors. For example, 1/8-inch (3.1 mm) uncoated clear glass has an SHGC of approximately 0.86, of which 0.84 is direct gain (solar transmittance) and 0.02 is indirect The shading coefficient (SC ) is a measure of the heat gain through glass from solar radiation. Specifically, the shading coefficient is the ratio between the solar heat gain for a particular type of glass and that of double-strength clear glass, that is 1/8-inch glass. A lower shading coefficient indicates lower solar heat gain. For reference, 1/8-inch (3.1 mm) clear glass has a value of 1.00 (SC is an older term being replaced by the SHGC). In either case, a lower number indicates improved solar control over the 1/8-inch clear glass baseline. With a long air-conditioning season, it is most important to reduce solar gain and therefore reduce air-conditioning loads.

High-Performance Low-E Glass

First introduced in the 1980s, low-E commercial coatings refer to glass with low-emissivity coatings, microscopically thin metal layers that are deposited on a window surface to help keep heat on the same side of the glass from which it originated. Low-E glass reduces heat gain or loss by reflecting long-wave infrared energy, or heat, and therefore, decreases the U-value and solar heat gain, and in doing so, improves the energy efficiency of the glazing. Because of its relative neutrality in appearance and energy efficiency, low-E glass is widely used in residential and commercial buildings and is expected to continue to increase in usage in the coming years. If a higher solar gain low-E coating is specified, the higher heat load from solar transmission can burden the cooling system, causing energy costs to rise more than necessary as the air-conditioning system overworks to maintain a comfortable temperature throughout all sections of the building. In addition to controlling the solar heat gain inside a building, the correct glass can affect the size and efficiency of the HVAC equipment as well as daylighting systems. Minimizing solar heat gain through low-E coatings can actually significantly reduce the size of an HVAC unit.

The first low-E glasses had SHGCs of between 0.4 and 0.7, the SHGC being the fraction of the heat from the sun that enters through a window, expressed as a number between 0 and 1, with the lower a window's SHGC, the less solar heat it transmits. Over the years the energy codes have gotten stricter. Both ASHRAE 90.1-2010 and the 2012 International Energy Conservation Code require a maximum 0.25 SHGC in zones 1-3 (resourcecenter.pnl.gov/cocoon/morf/
ResourceCenter/graphic/973) for any window-to-wall ratio up to 40 percent. Glass manufacturers keep improving on those numbers through new higher-performing low-E technologies that balance energy performance of glass and the aesthetics.

A recent study by engineering company Enermodal Engineering Inc. compared the energy savings of a new high-performance low-E coating to a standard commercial low-E coating widely used in recent years. Simulating a 175,000-square-foot 10-story office building, the study found the low-E glass to have the potential to save $2.50 per square foot of glass by downsizing the chilled water and air distribution systems. In terms of operational cost savings, annual energy costs are lowered by as much as $1.60 per square foot of glass in a building with glare and daylighting controls. In total, the higher-performance coating offered a 30 percent improvement in energy performance for a very small increase in glass cost. The return on investment would be realized in one to two years. The simulated coating offered a neutral appearance, glare control and a lower solar heat gain that enabled the downsizing of the building's HVAC system upfront, in addition to ongoing energy savings.

In general there are two ways to apply coatings to glass, through either a pyrolytic or sputter process.

Advanced architectural glass helps architects create striking building designs while significantly reducing energy costs. Chihuly Garden and Glass House, Owen Richards Architects. Photo by Ben Benschneider, Artwork © Copyright, Chihuly Studio, 2012, all rights reserved

 

Pyrolytic

Pyrolytic low-E glass is glass with low-E coating applied at high temperatures and fired into the glass surface during the “on-line” float glass manufacturing process. The high solar heat gain of pyrolytic low-E glass is good for cold climates, though it may not meet energy codes in other climes, and can be less crisp in appearance compared to other coatings.

Sputter Coatings

By contrast, sputter low-E glass is glass with low-E coating applied through an “off-line” coating process. The off-line process occurs after the float glass is produced, using a Magnetron Sputter Vacuum Deposition (MSVD) coater. Glass is put into a vacuum chamber, where ionized gas bombards the surface of a metal cathode (silver) with ions. Atoms of the desired metal are vaporized and then deposited in a thin film on the surface of the glass. The MSVD works at the molecular level to produce superior performance and offers significant advantages over “hard” (pyrolytic) and traditional “soft” coatings. By using different gasses, such as argon or nitrogen and oxygen, and by layering metallic and dielectric layers in different sequences, a wide variety of coatings can be produced to meet many design and performance requirements. In general, the MSVD process offers more coating options and improved solar, thermal and light-to-solar gain options than the pyrolytic process. Sputter coatings, offered in a wide variety of color and performance options, including post-temperable versions that can be produced efficiently in stock sizes and then fabricated nearer to the job site, can meet and exceed energy code requirements, dramatically lowering heat gain or loss while providing high visible light transmission and optimal transparency.

The commercial market for coated glass is predominantly sputter coatings, and continues to grow as the pyrolytic coatings have seen limited increases in demand.

Sputter Low-E Spectrally Selective Coatings

These coatings reflect both long-wave IR and solar near-infrared rays. In other words, they transmit a higher ratio of daylight compared to the amount of solar heat transmission. By blocking solar heat and making maximum use of daylight, spectrally selective glass can now provide a range of visible light transmission on clear float glass between 40 and 70 percent, while also offering lower reflectivity than was possible in the past, as well as a low U-factor and solar heat gain coefficient. Spectrally selective coatings, defined by the U.S. Department of Energy as glass with a light to solar gain of 1.25 or better, can significantly improve building heating, cooling and electric lighting, to the point of downsizing HVAC equipment, which reduces initial capital investment and ongoing energy costs. Spectrally selective coatings can be applied on clear or low-iron glass as well as various types of tinted glass to produce “customized” glazing systems capable of either increasing or decreasing solar gains according to the aesthetic and climatic effects desired. The Department of Energy further maintains that computer simulations have shown that advanced window glazing with spectrally selective coatings can reduce the electric space cooling requirements of new buildings in hot climates by more than 40 percent. Spectrally selective low-E coatings are available with one, two or three layers of silver; each layer improves the coatings selectivity.

Sputter Low-E Hybrid Coatings

These multifunction coatings have medium reflectivity but with higher light transmission which provides improved transparency. In comparison to older, low light-transmitting reflective coatings, manufacturers have added low-E performance and brightened the exterior appearance while still transmitting considerable light and achieving a low SHGC. Originally developed for residential markets, low-E coatings had low color, reflection and high transmission. Manufacturers modified those films to increase the exterior reflection, which can be an asset in the commercial marketplace, while lowering the transmission, which can increase the heat loads. In short, hybrids were modified to have lower transmission, higher reflection and very good solar properties including low U-values and low shading coefficients.

The sputter coating process occurs after the float glass is produced, using a Magnetron Sputter Vacuum Deposition (MSVD) coater. Source: Guardian Industries Corp.

 

Many Coating Options

Sputter low-E and hybrid coatings come in many color and performance options utilizing one, two and three layers of silver, sandwiched within other metal layers. These coatings represent the best available performance in high light transmission and low solar heat gain coefficient.

Depending on how it is fabricated, low-E glass can have a neutral clear appearance and very high light-to-solar gain rations. High-performance products offer a variety of appearance and light transmission options with superior solar energy control. These products can save thousands in upfront and ongoing costs. For a comparison of various low-E products, see the chart above.

Low-voltage electrical current is applied to the optically active layers in the electrochromic coating, which adjusts the level of tint. Source: Guardian Industries Corp.

 

Electrochromic Glass

Dynamic glass is a category of next-generation windows that can change traditionally static performance characteristics such as visible light transmittance and solar heat gain coefficient. Technologies include electrochromic (EC), thermochromic, photochromic, liquid crystal (LC) and suspended particle devices (SPD). Thermochromic and photochromic technologies change their properties based on ambient temperature and light respectively. EC, LC and SPD technologies have the advantage of electronic control of glass performance, enabling intelligent controls that can be integrated with occupant schedules, lighting levels or algorithms to increase building energy efficiency.

Probably the most energy efficient, and the only one of these technologies to have passed the ASTM standard for accelerated environmental durability, is electrochromic glass, which adapts to changing conditions—somewhat like sunglasses for a building—switching from clear to tinted on demand. With the flip of a switch, electrochromic glass can change from fully transparent to a fully darkened state and potentially in between states as well, allowing control of heat and glare in buildings without the need for shades, blinds or any type of window treatment or external shading device. Unlike permanently tinted windows, occupants enjoy unobstructed views. Whether automated, or manual, the tint level of the window can be adjusted to settings that match changing needs. It should be noted that electrochromic glass can take a short period of time to change, with the time required increasing as the glass size increases. Typical times would range between 10 and 30 minutes for commercial glass sizes.

Depending on project design, this glass technology has the potential to dramatically reduce HVAC energy consumption and peak power usage, which can result in a significant reduction in operating costs. Office lights can be dimmed in the mornings, further reducing costs. In short, electrochromic technologies enable designers to use more glass while still meeting or exceeding building energy codes and standards and improving occupant comfort.

In an electrochromic glass, a thin assembly of several layers is sandwiched between two pieces of glass, which are transparent electronic conductors. Low voltage applied to the conductors moves the ions between layers, which sparks the color change. Reversing the voltage restores transparency to the window. The power required to operate one 60-watt incandescent light bulb is enough power to operate more than 1,800 square feet of electrochromic glass.

Photovoltaic Glass Units

Photovoltaic glass (PV) has a significant part to play in getting buildings to net zero. Traditionally the building roof has been the province of PV products in the form of PV panels that needed their own support system and were limited by the space available. Most PV materials used in roofs are crystalline silicon; they have conversion efficiency of up to 13 percent and are typically opaque and rigid. Newer, thin-film PV cells are manufactured by depositing ultra-thin layers of semiconducting materials on glass or stainless steel sheets, and are a better fit for integration into building glazing materials. Thin-film PV is being integrated into vision glass for windows, skylights and facades, and opaque PV glass can also be produced for use as spandrel glass that, when coupled with PV vision glass, effectively turns the entire building envelope into an electric power generator, without the need to install PV panels separately on the roof.

 

PVGUs incorporate advanced optics to turn sunlight into electricity. Image courtesy of Guardian Industries Corp.

 

In a new category of green building material, manufacturers have combined proprietary optics, high-efficiency crystalline silicon, advanced materials science and simulation software to create a highly efficient photovoltaic glass unit (PVGU), essentially photovoltaics in a standard double-pane window form, known in the industry as an insulating glass unit or IGU. Virtually an insulated window with integrated photovoltaics, the PVGU is an energy-generating alternative to the IGU, while leveraging its modularity, ease of installation and acceptance by the design and building industry. This technology can offer high light transmission, significant up-front savings on HVAC systems and on-going energy costs, all while generating electricity for the building.

Opaque PV glass can also be produced to use as spandrel glass which shields structural building components such as columns, floors, HVAC systems, electrical wiring and plumbing from view. With intense market competition, the price of opaque PV spandrel has come down to a level that begins to approach insulated glass, making it a cost-effective solution especially on a sunny southern exposure. Manufacturers are offering an increasing range of glass configurations in both PV vision and spandrel glass. When combined, PV vision glass and opaque spandrel glass effectively turn the entire building envelope into an electric power generator.

The most advanced example of a PVGU is a high-density unit that uses prisms to collect direct sunlight by having a thin layer of monocrystalline silicon solar cells sandwiched horizontally between two layers of glass to form an individual tile, which acts as a cell. An internal plastic reflective prism directs sunlight onto the solar cells. Softer daylight and less intense horizontal rays are admitted through the window, minimizing glare and heat, creating a view for occupants and generating the same level of power of a roof top solar panel at the same orientation—in short, breaking the existing trade-off between high module efficiency and low transparency.

PVGUs offer a serious alternative to IGUs, and can have up to three times the power density while achieving low solar heat gain and a very high light-to-solar gain while optimizing daylighting and improving U-values. Optimal PVGU potential would be on the south, east and west facades of a building.

In November 2011, two existing windows on the south side of North America's tallest building, the Willis Tower, formerly the Sears Tower, were replaced by PVGUs. Each window is about one square meter and capable of generating 120W of power. Energy harnessed by the transparent solar windows is expected to reduce heat gain, and therefore cooling costs as well. If the experiment succeeds, the Willis Tower may increase its PVGU installation, becoming a virtual vertical solar generation farm.

High-Performance Glass and LEED

Various types of high-performance glass contribute to LEED points in four categories. Following are the number of points possible in specific categories and examples of glazing systems that can contribute to those points. EAc1: 1-19 points for NC or 3-21 for CS. Optimize Energy Performance. Thermally broken window and curtain-wall systems with optional thermal upgrades. EAc2: 1-7 points for NC, 4 for CS. On-Site Renewable Energy. Fully integrated solar energy systems to produce electricity. MRc4.1: 1-2 for NC, 1-2 for CS. Recycled Content – 10% (post consumer + ½ pre-consumer) MRc4.2: NA. Recycled Content – 20% (post consumer + ½ pre-consumer). Aluminum extrusions for windows can be made of at least 30 percent recycled material. MRc5.1: 1-2 for NC, 1-2 for CS. Regional Materials – 10% Extracted, Processed and Manufactured within 500 miles of project site. MRc5.2: NA. Regional Materials – 20% Extracted, Processed and Manufactured within 500 miles of project site. EQc2: 1 for NC, 1 for CS. Increased Ventilation. Window operation types can help to create airflow patterns. EQc6.2: 1 for NC, 1 for CS. Controllability of Systems (Thermal Comfort). Automated windows; operable window systems. EQc7.1: 1 for NC, 1 for CS. Thermal Comfort – Design. Operable and automated window systems. EQc8.1: 1 for NC, 1 for CS. Daylight and Views. Sun control systems can optimize day-lighting and exterior views. EQc8.2: 1 point 1 for NC, 1 for CS. Daylight and Views. Glazing options can optimize views to the outside while satisfying the project’s structural and thermal needs. IDc1.1-1.4: 1-5 for NC, 1-5 for CS. Innovation in Design. High-performing façade systems could help to provide performance that exceeds LEED-NC requirements.

Putting it All Together—BIPVs and Pre-Wired Curtain Walls

While the contribution of high-performance glazing is key, it can be even more successfully leveraged as part of a whole system approach to the energy design of a building. Industry experts say that significant energy reduction in a building—up to 60 percent—can be achieved from factors like early planning, high-efficiency HVAC systems, extra insulation, daylighting, energy-efficient lighting, rooftop energy production, and energy storage. Achieving the final 40 percent of energy reduction is the real challenge and requires a paradigm shift and/or new technologies.

Building Integrated Photovoltaics (BIPV)

Current technology is creating an opportunity to integrate PV into residential and commercial structures in an important new way allowing the entire building exterior to become a power generator. A building integrated photovoltaic (BIPV) system consists of integrating photovoltaic modules into the building envelope, such as the roof or the façade. By simultaneously serving as building envelope material and power generator, BIPV systems can provide savings in materials and electricity costs, reduce the use of fossil fuels and emission of ozone depleting gases, and add architectural interest to the building.

Leveraging PVGU and advanced architectural glazings, the BIPV product replaces the standard vision glass or skylights, with a glass product that converts direct sunlight into energy. BIPV systems are incorporated into the design of a building in the early planning stages. The architect works with photovoltaic engineers and other experts to create an aesthetically pleasing, effective design. BIPV technology can be installed in lieu of regular building materials, thereby saving money on construction. For example, glass with specialized solar cells embedded can be used on the facade of a building instead of conventional glass.

Still in its infancy, the global market for BIPV technology was estimated by market firm BCC Research at 1.2 GW in 2010 and was poised to more than double in size for several years to 11 GW by 2015. Another research firm, NanoMarkets, estimates that the total market for BIPV glass will reach $6.4 billion (USD) in revenues in 2016 compared to $1.5 billion in 2012. The report estimates that global appetite for BIPV curtain wall will grow dramatically through 2020, when the EU will require all new construction to be net-zero energy buildings.

According to research from Jesse Wolf Corsi Henson, AIA, LEED AP, BIPV spandrel applications can contribute more than 15 percent of annual electricity needs for highly efficient office buildings throughout major U.S. climate zones—an amount that existing roof-mounted PV systems for tall buildings do not achieve. While current research reveals the energy production limits associated with their vertical application, the net-zero energy goal suggests a reconsideration of BIPV facades. Currently available PV module products can allow building planners, architects, engineers and contractors the option of employing façades as major energy generators. Potential future studies could include the impact of additional BIPV spandrel on the east and west building facades. Further development of BIPV strategies and products is required in order to create and adapt tall buildings into net-zero annual energy consumers.

Cost may be a consideration. Yet BIPV projects are eligible to earn substantial federal tax credits. The BIPV Federal Tax Credit allows a 30 percent direct tax credit in the first year after installation. President Bush signed this into law in 2003, and President Obama again signed the bill and extended it until 2017. The second tax advantage is the MACRS accelerated depreciation. This reduces full depreciation time from the 39-year class life to the 5-year class life. In addition, most cities in the U.S. have local utility subsidies that differ per municipality but may also add to the financial benefit of these systems.

Holistic Solution

The net-zero envelope can accept multiple glazed cassettes that allow a design team to tune the building for different orientations or climate zones. Photo courtesy of BISEM USA Another energy-saving scenario is a building that features a combination of a wired curtain wall and a non-wired curtain wall that incorporates the full range of energy-efficient glazings—PV GU, spandrel PV , electrochromic and highperformance low-E. The wired portion of the curtain wall would incorporate the electricity-producing PV glass, and the non-wired would include low-E coated glass. Manufacturers and glazing contractors maintain that there is a place for low-E glass on the same building as advanced glazings. For example, low-E can be used on the north elevation with PV GU on the south and west for optimal energy efficiency.

BIPV also offers a favorable life-cycle cost profile. Research from Columbia University and Brookhaven National Laboratory states that “the value of building integrated photovoltaics in façade applications lies in the fact that these systems entirely replace facade-cladding systems that do not have the added benefit of generating power that offsets expensive, nonrenewable and polluting sources from the surrounding electrical grid.” This study confirmed this through life-cycle analysis via the metrics of energy payback time, energy return on investment, global warming potential and carbon-equivalent payback time. Based on firsthand life-cycle inventory data from the designer, architect and supply chain partners involved in the construction of curtain-wall facade arrays in Manhattan, the researchers found despite lower incident radiation from sub-optimal orientation and shading obstructions, facade-integrated BIPV was shown to have “an environmental impact comparable to that of optimally oriented roof or ground mounted PV systems.” This environmental benefit was due to “the avoided environmental burden associated with the materials that facade BIPV replaces.” The researchers' primary findings indicated that when completely replacing an alternative cladding system, a facade BIPV system has a competitive energy payback time of 3.8 years.

Pre-Wired Curtain Walls

Pre-wired curtain-wall systems provide a simple solution which integrates a number of diverse disciplines: design, engineering, manufacturing procurement, installation, monitoring and final commissioning. If the envelope strategy is developed early in the design process, the cost increases can be kept to a minimum. In a pre-wired curtain-wall sun-lighting, SHGC, U-value, R-value energy production and fresh air can be mixed and matched to develop a complete skin solution that will generate electricity and help to achieve a net-zero energy building. Designs are more cost effective on a large south-facing curtain wall by incorporating the latest photovoltaic technology into conventional envelope technology. The Federal Tax Credits (ITC – 30%) and MACRS accelerated depreciation will pay for 80 percent of the cost in the first year, and the remaining 20 percent of the cost in the second year. After that, the savings multiply due to the energy production of the façade. See the IRS curtain wall tax ruling at www.novoco.com/energy/resource_files/irs_guidance/plr/plr_201043023.pdf. Tax laws are subject to change, so consult your tax advisor for the most up-to-date tax advantages.

The curtain-wall product takes the form of a flexible aluminum chassis that seamlessly incorporates multiple sustainable products at once. These include photovoltaic curtain-wall panels, electrochromic glass, UL-approved wiring, super high R-value glass, and sunlighting options that bring natural light 50 feet into the building. Simple manipulation of this kit of parts allows the designer to fine-tune the building for an individual lot or different climate zones, and dramatically reduce the buildings energy usage.

Designers have the flexibility of purchasing BIPV systems as a “Plans and Specifications” package as well as having the system installed. In certain cases, the manufacturer will provide an expert on BIPV curtain-wall installations to coordinate the complete installation. For mid- and high-rise products, the most advanced pre-wired curtain-wall options come as complete packages that combine four usually separate trades: photovoltaic design, electrical engineering, curtain-wall manufacturing and waterproofing. The photovoltaic design component calculates system size and determines PV module selection, DC wiring, UL-rated harnesses, inverter size, life-cycle replacement, and the monitoring solution for the project. The UL-rated wiring harness is shop installed, which reduces field labor by 85 percent. The final curtain-wall design and installation includes energy modeling and AAMA water testing procedures.

Curtain-wall retrofit systems also exist. A curtain-wall retrofit system for SMUD (Sacramento Municipal Utility District) Corporate Headquarters that was AAMA tested and UL approved demonstrates the benefits that can be expected. The retrofit eliminated the problem of harsh direct sunlight and dramatic solar heat gain. The installation retrofitted opaque PV panels in front of the existing curtain wall, without interrupting the original glazing and warranty. This solution dramatically improves SHGC and harvests electricity in an area that was unavailable before. The opaque PV panels generate electricity to run the DC-powered HVAC systems, so the brighter the sun shines, the harder the air-conditioning runs.

Glass for Net Zero

When it comes to windows, architects have numerous tools to achieve solar control while increasing occupant comfort, improving building aesthetics and reducing building energy costs both up front and in energy-related costs for typical commercial buildings. Building integrated photovoltaic units and pre-wired curtain walls have the potential to turn entire buildings into power producers. The reality of ubiquitous net-zero buildings may still be a way off, but today's glass solutions are making a clear contribution to achieving that goal for motivated architects and owners.

 

A pre-wired curtain-wall retrofit system and waterproof outriggers for SMUD (Sacramento Municipal Utility District) Corporate Headquarters. Photo by David Bush, courtesy of BISEM USA

 

 

Guardian Industries is a diversified global manufacturing company headquartered in Michigan, with leading positions in float glass, coatings and fabricated glass products. Guardian’s most recognizable products are its energy-saving architectural glass products SunGuard® for commercial and ClimaGuard® for residential applications. www.guardian.com