Designing commercial window systems

The Efficient Windows Collaborative website focuses on windows for low-rise residential houses. Many window energy efficiency principles and technologies apply across building types, but some design considerations and window options for commercial and high-rise residential buildings are considerably different from those for low-rise homes:

• Structural strength: Structural glass wall systems and windows in high-rise buildings require strong framing support and strengthened glass. Consequently, the use of metal frames, tempered glass, and other options for structural strength is much more common among commercial than among residential windows.
• Solar heat control: Commercial buildings tend to have significant internal heat gain from occupants, equipment and lighting. Additional heat gain from solar radiation can create hot spots even during colder seasons, so low solar heat gain glazing is preferred in most commercial buildings.
• Optical properties: In schools, offices and similar buildings, lighting is a major energy factor and tasks require glare control. To serve the dual needs of daylighting and glare control, commercial window systems may include features that would not easily find acceptance in residential homes (daylight-redirecting light shelves, tinted glass, etc.).

If you are looking for detailed information on windows for high performance commercial buildings, check out www.commercialwindows.org.

Energy efficiency resources for commercial window design

Windows for High Performance Commercial Buildings: This website offers an overview of window design considerations and technologies for commercial buildings. The site includes a Façade Design Tool that lets you quickly compare the performance of different façade options in terms of annual energy impact, peak demand, carbon, daylight illuminance, glare, and thermal comfort. Results are based on COMFEN simulations.

The COMFEN simulation tool: COMFEN is a software tool developed by Lawrence Berkeley National Laboratory for quick early design scenarios of specific façade, lighting, and shading options using the EnergyPlus simulation engine. COMFEN is available to download for free.

NFRC Energy Ratings: The energy rating and labeling system by the National Fenestration Rating Council (NFRC) has primarily been used for residential windows. For the commercial market, NFRC recently launched the Component Modeling Approach (CMA), a program that provides certified energy ratings of commercial window systems for product validation and code compliance purposes. CMA also allows online analysis of the energy performance of window systems and their components. An introductory fact sheet and detailed information on CMA is available from the NFRC.

ENERGY STAR® The criteria for ENERGY STAR windows are designed for low-rise residential homes. They do not account for the different structural and solar control demands placed on windows in high-rise residential or commercial buildings. ENERGY STAR windows may be a good choice for some commercial buildings, for example some low-rise schools or offices, but before using residential windows make sure to analyze the specific needs of the building.

Tools for Schools: As energy prices increase and school budgets tighten, school districts are looking for cost-effective ways to improve building energy efficiency and operation. The Efficient Windows Collaborative has compiled Tools for Schools, a guide on how efficient window design can help schools save money and enhance the learning environment.