According to a study released by McKinsey & Co. and sponsored in part by the U.S. Green Building Council (USGBC), “investing in energy efficient buildings combined with other non-transportation initiatives could reduce energy consumption in the United States by 23 percent by 2020. This, in turn, would result in an annual savings of $130 billion, reductions in greenhouse gas emissions of 1.1 gigatons, and the creation of approximately 900,000 new jobs.”
When architects, engineers and commercial building owners look to improve the efficiency of their buildings they often look at the building envelope-more specifically at curtain walls, framing systems, doors and windows. And, as the demand for reduced energy consumption and energy costs in a building has increased, so has the need for thermally efficient products.
However, even before energy efficiency and energy costs became a major concern for architects and building owners, windows were a key element in keeping the indoor building environment at a comfortable and easily regulated temperature.
Fundamentals of Thermal Performance
Thermal performance of commercial building products is defined by a key value that measures overall thermal transmission: U-factor
(or U-value). A lower U-factor for a building product represents higher thermal insulating properties.
Besides the inherent energy savings from reduced thermal transfer, more advanced framing systems can help contribute when building owners choose to take advantage of tax incentive programs and green building certifications such as LEED. In addition to savings, energy efficient buildings also provide improved indoor climate and occupant comfort.
Energy codes and U-factor requirements vary by region and climate zone. With the increasing performance demands of energy codes and the need to improve U-factors, high-performance windows are becoming the standard in northern climate zones, and that trend is expected to permeate through the rest of the construction industry.
It’s All Material
Along with building design, material properties influence thermal performance and energy expenditure in commercial buildings. Aluminum windows offer an array of performance, maintenance, aesthetic and sustainable benefits. Aluminum is infinitely recyclable. Windows made from aluminum, like those offered by Norcross, Ga.-based Kawneer and Traco, not only allow for unlimited finish options and installation flexibility, but the window will never rot, warp or buckle due to moisture and weather exposure.
Smarter Windows
Careful consideration must be taken when connecting the protected interior environment with the harsh exterior environment to minimize thermal transfer and meet energy optimization goals. The most common methods for limiting thermal transfer in aluminum windows are with thermal breaks and high-performance glass.
There are primarily two types of thermal breaks used to interrupt the thermal conductance of aluminum windows. The first, pour and debridge, involves pouring liquid polyurethane into a cavity within a single profile, allowing it to harden, then cutting away a small section of aluminum opposite the pour area to fully separate the interior metal from the exterior metal. The second uses polyamide insulating strips installed continuously along the length of two separate aluminum extrusions to form a thermally broken assembly.
One example of a product that leverages thermal break technology is Kawneer’s OptiQ Ultra Thermal Window. Developed as a result of a pioneering partnership with the U.S. Department of Energy, the OptiQ Ultra Thermal Window features a polyamide thermal break. The wider polyamide profiles in this window allow for increased space between interior and exterior metal. Minimized sightlines also decrease thermal conductivity and transfer. Thermal transmission is further reduced by a unique center gasket design, the use of insulating foam strips and the ability to accommodate 1 3/4-inch triple insulated glass.
A Glass Barrier
By using commercially available triple insulating glass, OptiQ Ultra Thermal Windows have the potential to achieve U-factors of 0.17 for fixed and 0.22 for operable while still achieving a structural design pressure of 80 psf.
Glazing elements are critical components to consider when evaluating the thermal capabilities of a window. Insulated glass, warm edge spacer technology and low emissivity (low-E) glass coatings play a major role in enhancing the thermal performance of a window.
Together the thermal break, insulating glass and other glazing elements can greatly improve U-factors of aluminum framing systems, helping to create a more comfortable environment for building occupants and contributing to the overall efficiency of a building.
The Future
Selecting windows for commercial buildings can be challenging; however, “properly designed windows play an important role in achieving these energy and environmental goals and contribute to the comfort, satisfaction and productivity of building occupants.” As the industry continues to move toward more energy efficient building solutions, it may not be long before smart, high-performance products, like the OptiQ Ultra Thermal Window, become the standard versus the option.
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Lisa Jackson, LEED AP, is a product manager, windows for Kawneer North America, Norcross, Ga. For more information, visit www.kawneer.com.