by Katie Daniel | November 7, 2017 2:47 pm
by Rich Rinka
Aluminum is a cost-effective building material option that can support green initiatives without compromising design integrity. With minimal environmental impact throughout its life cycle duration, structural longevity, and high resistance against corrosion, deflection, and wind load, it is frequently specified for various enclosures and fenestration systems. Its use in building envelopes is expected to grow more than six percent per year between now and 2020. (This information comes from the online article, “Aluminum Building, Construction Sector Growing 6% Annually to 2020.” Visit www.proudgreenbuilding.com/news/aluminum-building-construction-sector-growing-6-annually-to-2020.)
The material’s ease of fabrication and extrusion in a variety of shapes and sizes provides designers and architects with a great deal of design flexibility. Aside from its aesthetic and structural qualities, aluminum supports energy-efficient design considerations that lead to potential green building certification.
Aluminum’s versatility means it can be extruded, sheeted, plated, foiled, forged, or cast—even formed into wire, cable, paste, or powder. Its highly reflective surface makes an efficient sunlight reflector, potentially saving on building cooling costs. Additionally, the material provides a clean, modern look to fenestration systems and building skins.
Particularly resistant to temperature extremes, aluminum performs well in a range of climate zones. It increases tensile strength at lower temperatures and excels in humid climates, as it does not absorb moisture or support mold growth or rust. This last point is due to the material’s naturally occurring protective oxide, which can be made even thicker and stronger through anodizing.
Anodizing provides excellent wear and abrasion resistance. The process itself uses little, if any, volatile organic compounds (VOCs) and has little environmental impact. (For more, visit the Aluminum Anodizers Council page at www.anodizing.org/?page=environment.)
Aluminum also weighs about a third of steel. Its lower weight can reduce shipping and handling expenses, and reduce associated carbon dioxide (CO2) emissions during transport. Compared with heavier material, it also may allow easier maneuvering and installation on the jobsite. Thanks to its high strength-to-weight ratio, aluminum is also a critical building material for skyscrapers and other structures where total weight is a factor.
Life cycle considerations
The aluminum industry continues to make strides in streamlining the production and recycling of the material, thus reducing its environmental impact. According to the Aluminum Association, the electrical consumption required to produce new (primary) aluminum has dropped in half over the past 50 years, and is down by 25 percent since 1995. Over the last two decades, electrical energy use in production has decreased about 10 percent. Since the early 1990s, the aluminum industry has achieved an 85 percent reduction in perfluorocarbon (PFC) emissions, and has reduced its overall carbon footprint nearly 40 percent since 1995. (This information comes from the Aluminum Association website, specifically: www.aluminum.org/industries/production/primary-production and www.aluminum.org/sustainability/aluminum-production.)
Further, aluminum is 100 percent recyclable at the end of its service life, with little to no impact on its properties. The Aluminum Association reports nearly 40 percent of the North American aluminum supply is created through the Recycled aluminum production saves about 90 percent of the energy required by primary production.
One of the world’s most widely recycled products, aluminum retains all its original properties in its ‘next life.’ Approximately 75 percent of all the material produced is still in use today. It is estimated that the recycled content of aluminum used in building applications is between 50 and 85 percent.
Ably meeting the heat (and cold) exchange challenge
Despite its many advantages, aluminum has one significant limitation for fenestration systems. On its own, the highly conductive material transfers external temperatures to the internal space unless it has a thermal barrier—
a low-conductivity material placed to reduce or prevent the flow of energy between the building’s interior and exterior. Thermal barriers are also effective in reducing condensation on the interior aluminum frame.
Thermal barrier systems have been in use for decades, but advancements in their development offer even greater insulating factors. One option involves polyamide systems, in which two separate aluminum extrusions are created and preformed, with fiberglass-reinforced polyamide strips inserted into the profiles. The aluminum extrusions are knurled so these ‘teeth’ bite into the inserted strut, and then crimped.
Another strategy involves poured-and-debridged polyurethane barriers—single aluminum sections are separated by the insulating material, typically polyurethane in composition. The void in the aluminum extrusion is filled and the extruded bridge is removed to eliminate metal-to-metal contact.
Determining the ideal U-factor (i.e. heat transfer) and solar heat gain coefficient (SHGC) for a fenestration system in a specific building location is important in selecting the appropriate thermal barrier system. Properties to be considered when choosing a thermal barrier include:
It is important designers understand that external environmental factors, such as exposure to ultraviolet (UV) light, water immersion, humidity levels, temperature extremes, thermal cycling, and cyclic bending (i.e. stresses from positive and negative wind load reversals) affect aluminum differently than other substrate types. Care should be taken to study these factors when making design choices.
The geographic location of a particular project determines the minimum thermal performance of an aluminum fenestration system. The International Energy Conservation Code (IECC) sets the minimum energy efficiency provisions for both residential and commercial buildings. The requirements vary by region, based on the climate. During the design process, manufacturers and design engineers can use thermal modeling or computerized simulations of a fenestration system to determine whether the product will meet the U-factors required for the project.
Integration of renewable energy devices, such as aluminum-framed building-integrated photovoltaic (BIPV) devices used in façades and on rooftops, may help achieve even more energy efficiency and are likely to become more prevalent in the future.
In addition to providing energy efficiency by limiting thermal conductance, daylighting can be enhanced through window systems designed to maximize interior lighting while limiting solar gain or cold transfer. Aluminum framing offers the strength to support larger glazed expanses with narrow sightlines. Additionally, the material provides the flexibility for designers to include, when appropriate, windows that can be manually or automatically opened and closed to promote fresh airflow.
Daylighting has been shown to benefit the health and productivity of occupants. Of the top five healthy building features expected to be used more frequently over the next five years, enhanced air quality, products improving thermal comfort, and better lighting/daylighting exposure lead the list. (Check out Dodge Data & Analytics’ SmartMarket Report, “The Drive Toward Healthier Buildings 2016: Tactical Intelligence to Transform Building Design and Construction,” by visiting www.engineering.com/Portals/0/Stories/14871/Drive_Toward_Healthier_Buildings_2016.pdf.) Each of these factors can be directly and positively affected through the use of aluminum fenestration systems in construction.
Aluminum windows certified to a performance grade of AW are tested to a higher pressure with less allowed leakage for improved air quality and potentially lower HVAC requirements.
Stronger substrates may be able to have thinner profiles, which allow for increased daylighting, particularly in fixed windows.
Use of thermal barriers can lead to better energy efficiency and increased natural daylighting, saving on the energy needed for artificial lighting and HVAC systems, as well as promoting a more comfortable thermal environment for workers. Thermal barrier technology continues to develop, using glass, glazing, and envelope materials to reduce commercial building energy consumption.
Meeting the green challenge
Two case study examples demonstrate the different ways in which aluminum can help project teams meet the green challenge.
For example, the 18-story Edith Green-Wendell Wyatt Federal Building in Portland, Oregon, received funding for renovation that required it to meet the stringent energy and water conservation requirements of the Energy Independence and Security Act (EISA). (Among other things, EISA was enacted to improve the federal government’s energy performance.)
The building, built in 1974, was sheathed in a high-performance skin of shading elements and reflecting aluminum reeds and panels that bounce light and provide shade on the southwest and southeast. West-facing vertical reeds provide relief from low-angle sun without obstructing views.
The exterior renovation, and its updated equipment and systems, reduces the building’s energy consumption by 55 percent compared to the original structure. The building was among the 2014 Top 10 winners named by the American Institute of Architects’ Committee on the Environment (AIA COTE), and recognized as the 2016 Top 10 Plus winner as well. (This comes from the American Institute of Architects [AIA] website.)
In another example, the BAE Systems facility in Sterling Heights, Michigan, was a new construction project made up of a four-story office building and attached 5110-m2 (55,000-sf) prototyping facility. The distinctive structure features a curved and slanted aluminum and glass curtain wall, which provides a state-of-the-art custom exterior, as well as improved thermal performance. The office building was designed and constructed to meet Gold under the Leadership in Energy and Environmental Design (LEED) program. The facility reportedly uses 15 percent less energy than a conventionally designed building. (Visit www.usgbc.org/projects/bae-systems-sterling-heights-facility for more information on the project.)
Taking the LEED
According to the U.S. Green Building Council (USGBC), buildings in the United States account for 38 percent of all CO2 emissions and 73 percent of electricity consumption. Compared to average commercial projects, LEED-certified ones consume a quarter less energy and generate 34 percent fewer greenhouse gas (GHG) emissions.
Using recycled aluminum may allow buildings to satisfy the LEED 2009 Materials and Resources credit (MRc4). This recognizes materials with a specified amount of recycled content, based on cost of the total value of materials in the project. Recycled aluminum can also help reduce energy consumption and meet the new LEED v4 criteria for protecting the health and comfort of building occupants when used to create fenestration systems that help control temperature and daylighting.
Using aluminum in construction may help garner LEED or other third-party green certification because of the material’s:
Pursuing third-party green certification due to concern for the environment and the health and well-being of tenants is not the only consideration, although it is of paramount importance. Owners may benefit financially as well. Several studies have demonstrated LEED-certified buildings may demand higher rents and increased market value. (For more, see articles from Bentall Kennedy Group or San Diego Union Tribune—respectively, www.bentallkennedy.com/news-2015-10-06.php and www.sandiegouniontribune.com/business/growth-development/sdut-green-buildings-outperform-vacancy-rental-rates-2012sep05-htmlstory.html.)
Being able to demonstrate the business and financial benefits of their green building investment is important to owners. Measuring energy efficiency and energy savings in retrofits is one obvious solution, as is achieving LEED certification. However, ‘soft’ measurements also can be of value. For example, asking employees and tenants through surveys specifically about the building’s green initiatives (e.g. thermal comfort, daylighting, and ventilation) may provide anecdotal evidence a green building offers a more pleasant work environment.
Owners and developers who do try to quantify the impact of healthy buildings report improved employee satisfaction and engagement, the ability to lease buildings quicker, and a potential positive impact on the building’s market value.
Determining the optimal combination of building performance and functionality depends heavily on the building’s fenestration system. In turn, the fenestration heavily depends on use of highly engineered framing to meet structural challenges, as well as current and foreseeable stringent energy codes. Aluminum provides the sustainability, structural integrity, and inherent beauty to do the job well.
|THE ANODIZING PROCESS|
|Anodizing is a chemical process that converts the surface of the aluminum to an oxide finish. This is actually a naturally occurring phenomenon, but it can be controlled in manufacturing processes. Anodizing consists of three processing stages.
Rich Rinka serves as the American Architectural Manufacturers Association’s (AAMA’s) technical manager for standards and industry affairs. Before coming to AAMA, Rinka worked in the industry as a field technical engineer for a component supplier, and also served as chair of the AAMA 800 Maintenance Committee. During his time in product development for the automotive industry, he developed (and still holds) four patents related to sealants. He can be reached at email@example.com.
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