Several features of architectural aluminum building products can be combined to enhance the overall sustainability of metal building projects today, and for years to come. The good news is although some of these products have slightly higher initial cost than their more common counterparts, the payback from improved efficiencies is seen in a relatively short time. These “green” products also attract potential tenants and buyers.
One important factor to consider in the initial building design is the window-to-wall ratio, or the total area of a façade which is comprised of vision glass and framing. The climate surrounding the project location will influence the optimum ratio for the building.
In cold weather locations, like the Great Lakes area, heating energy use increases with window area and decreases because of daylighting advantages. The target range for WWR is 0.15 to 0.30, varying by the orientation of the window. Warmer climates, like the Gulf Coast, strive to balance increased cooling cost with larger windows versus the decreased need for electric lighting. WWR ranges between 0.30 and 0.45 are desirable within this region.
Accessories for glass and aluminum framing systems, like sun shades and light shelves, contribute toward the reduction of electrical energy use. Furthermore, these may contribute to buildings seeking to meet green building rating systems’ criteria such as the U.S. Green Building Council’s LEED program.
Sun shades function like a permanent exterior awning, but are designed to withstand the elements year-around. They shade the glass area underneath the unit and block direct sunlight’s infrared radiation, or solar heat gain, from unnecessarily warming the inside of the building during peak summer months. As the sun’s position lowers during the winter months, more sunlight enters the building, which helps reduce heating costs/energy use. Many variations in size, shape and color are available.
Light shelves are internal fixtures mounted on glass walls above occupied areas. They catch the free, abundant, sunlight on the building perimeter and redirect it to areas normally lit by electric lighting. Energy efficiencies are gained with automatic electric lighting controls. This diffused, natural light not only reduces electric energy use, but also contributes to occupant comfort and well-being.
Within the 2009 LEED Green Rating System’s Indoor Environmental Quality category, Daylight and Views’ credits are available for incorporating the use of natural lighting in new construction.
IEQ 8.1 offers one point for lighting 75 percent of interior spaces using sunlight. Schools may earn up to two additional points if 90 percent of classroom spaces achieve specified daylighting levels.
IEQ 8.2 is one additional point for increased daylighting to 90 percent of interior spaces
Another potential point is available for Thermal Comfort (IEQ 7.1). This credit is earned by providing a comfortable thermal environment that supports the productivity and well-being of building occupants.
LEED credits in the Energy and Atmosphere category also are possible through Optimize Energy Performance (EA 1), up to 19 points for new construction projects. These points achieve increasing levels of energy performance above the baseline in the prerequisite standard to reduce environmental and economic impacts associated with excessive energy use.
Using high-content, recycled, aluminum extrusions for framing of vision glass areas is an easy and cost-effective way to boost credits for the LEED Materials and Resources category, while providing for thermal improvement at the same time. Recycled, aluminum, extruded systems are available from many suppliers and in as many variations.
LEED MR 4 allows one point for a total recycled content of 10 percent, and awards an additional point for a total recycled content of 20 percent. Total recycled content refers to all reclaimed building product materials used on the project from the roofing overhead to the concrete foundations and site-work below. All of the post-consumer and one-half of the pre-consumer content can be counted. The recycled content value of a material assembly is determined by its weight compared to the total building materials’ weight. The recycled fraction of the assembly is then multiplied by the cost of assembly to determine the recycled content value.
Key points to consider in pursuing LEED MR points include:
Post-consumer content—Qualifying, aluminum material includes that which is diverted from landfills after their previous lifecycle. This content is made from such items as beverage cans, home siding and automotive wheels. Rigorous selection of recycled material during the “smelting” stage is critical to the output quality of recycled aluminum.
Pre-consumer content—Qualifying, aluminum material includes that which is reclaimed from manufacturing production processes. It is more abundant than its post-consumer counterpart.
Please note that reusing material reclaimed from the same process in which it was generated does not contribute toward its recycled content. Examples are glass culls re-used in the making of new glass, and metal scrap re-used for new product within same facility.
Prime aluminum—Primary billet aluminum generally is included in the overall recipe of recycled aluminum, as well.
Available combinations of these three components vary per supplier. Higher post-consumer content contributes more toward MR 4. Pre- and post-consumer content totaling 100 percent is possible, but typically requires special ordering.
New anodizing processes for aluminum reduce the amount of waste by-product and produce high-quality finishes when used with recycled aluminum. The anodizing process involves multiple baths. The first of these baths is an etching tank that removes a portion of the aluminum extrusion surface to clean it before an electrolytic hard-coat is applied. Use of low-pH, chemical bath for etching only removes five percent of the surface that higher pH chemicals do. The lower pH bath also works better with recycled aluminum and produces a more consistent finish with a lower reflectivity.
Painted finishes for aluminum framing also add an attractive dimension that can be environmentally sensitive. Whether spray or powder-coat, responsible paint applicators remove all Volatile Organic Compounds during the drying process before materials leave the manufacturing facility. Because the VOCs are removed before reaching the job site, they do not apply to low-emitting materials outlined in LEED.
Features of the anodizing or painting of aluminum framing systems do not contribute directly toward any LEED points; however, they are generally considered as beneficial aspects of overall, sustainable design.
Energy efficiency is increasingly seen in specifications and construction product features. Aluminum framing systems for storefronts, curtainwalls and entrances offer a variety of thermal barrier designs with varying degrees of performance. Materials include simple, rubber insulator pads and gaskets; polyurethane filled pockets; and high-performance, polyamide glass, fiber struts.
The U-value provided by these thermal breaks is the measure of temperature transmitted or conducted through glass and aluminum framing members. The lower the number, the less temperature is transmitted to the building’s interior. A good range of performance is 0.43–0.48 U-value.
Condensation Resistance Factor is another industry measurement to help reduce the occurrence of frost on interior aluminum frame surfaces. Sub-zero outside temperatures combined with high winds versus comfortable indoor conditions with high temperatures and humidity levels require framing systems that stop the transfer of cold. For CRF, the higher the number is, the higher the product’s resistance to condensation. Look for ratings between 64 and 69 CRF.
Glass selection plays an important role in the overall performance of the framing system’s U-value. Glass is a natural, thermal insulator and performs better than the aluminum framing system holding it. Because of the large surface area of glass compared to the framing system holding it, the glass has a great influence on the overall performance of the system. This ratio of glass vision area to the total surface area, including the framing system, is used in calculating the performance of U-values and CRF.
Coated glass products, such as low-E on insulated glass units, help to block infrared radiation, or solar heat gain from reaching the building interior. Reduction of this excess heat lessens the need for air conditioning during the summer months. Allowing more heat from sunlight reduces the energy required for heating during the winter months. A balance of these two factors is needed to achieve the optimum combination.
Features of high-performance glass that provide higher U-values are focused on the space between insulated panes. Typical insulated units are made from two, 1/4-inch (6-mm) glass sheets separated by 1/2-inch (13-mm) of air or gas filled space. The spacer creating this half-inch void is sometimes made from metal, which also can transmit temperature. This spacer can be produced with its own thermal barrier to reduce the potential for transference of temperature. The insulated space between glass panes can be filled with special, rarified gases like Argon, and are inserted at a negative pressure for increased thermal properties.
LEED credits for the glass and aluminum glazing system have been identified earlier as Optimize Energy Performance (EA 1), and Thermal Comfort (IEQ 7.1).Another aspect of Thermal Comfort involves contributing to LEED points by allowing occupants’ control of their environment through products like operable windows. Fresh air can be accessed, when desired, at the discretion of the individual.
Sustainable building features are now more available and more affordable than ever. Sunlight, temperature, energy use, occupant comfort, aesthetics, recycling and profitability can be combined through a little research and planning. Whether preparing for new construction, or looking for ways to renovate and upgrade an existing property, the products and practices to assist with success are easily accessible.
Walt Lutzke works for Walker, Mich.-based Tubelite Inc. Drawing from 28 years in the industry, his experience includes development and distribution of print and electronic product information for contract glaziers and architects. Continuing his professional development, he represents Tubelite’s involvement with the American Institute of Architects, Construction Specifications Institute and the U.S. Green Building Council. For more information on Tubelite, visit www.tubeliteinc.com.