Fenestration Innovations for Leaner, Greener Times
Fenestration Performance Factors
Underlying the codes and standards is a well-established foundation of building science related to glazing and fenestration design. A number of those help design teams calculate energy performance, while others relate to safety and fire performance. Among the most important to consider are:
Air leakage
The energy codes and green standards offer guidance to protect buildings from excessive air leakage, often given as maximum levels of air movement in cubic feet per minute (cfm). Poorly designed window-wall interfaces and leaky curtain wall assemblies, for example, transfer heat via air movement in an uncontrolled manner.
U-factor
“Air infiltration is important but distinct from U-factor, which describes the heat transfer rate or insulating ability of an entire fenestration assembly, glazing panel or a window frame,” says Erik S. Sutton, Assoc. AIA, manager of product marketing with EFCO, a Pella Company. “When the temperature inside is different from outside the building, heat will be lost or gained directly through a window. U-factor is the overall rate of heat movement.”
Courtesy of EFCO, a Pella Company |
High-performance low-E glass was specified for Ashton Judiciary Square, Washington, D.C. Photo courtesy of Guardian Industries |
Solar heat-gain coefficient
Direct sunlight on fenestration also adds heat to the building interior through solar radiation, even on the coldest winter day. Glass and window assemblies can control this heat gain to a predictable extent, says Guardian Industries' Dolan, defined as solar heat-gain coefficient, or SHGC.
Visible light transmittance
To calculate how much daylight will be available inside a building to offset electrical lighting needs or to address potential glare, the measure visible light transmittance (VLT) provides a basis for comparison.
Fire-protective and fire-resistive glass ratings
While not associated directly with energy consumption, fire ratings for glass provide a means for comparing the ability of fenestration to protect building occupants and property against fire.
To allow for daylight opportunities and maximize lines of sight, for example, fire-protective and fire-resistive glass can be applied in areas where traditionally only opaque, fire-rated construction materials have been used. “We are seeing fire-rated glass used in stairwells, occupancy separations, exit corridors and property line applications,” says Diana San Diego, director of marketing for SAFTIFIRST, a U.S. manufacturer of specialized glass for fire-rated applications. “Now, designers can use fire-rated glass to bring natural light into a space, allow it to penetrate further into the building, and even lessen electrical lighting loads by sharing artificial lighting between spaces separated by glass, while still meeting all the fire-rated requirements of the application.”
Electrochromic glazing provides a range of operating conditions, including lower VLT (transmittance) and lower SHGC in its tinted, or activated, state. Image courtesy of Guardian Industries |
These performance indicators help describe the control of fire, light, heat and air movement in the building envelope and interior separations. The ability of fenestration systems and materials to control environmental factors is an important criterion for successful building designs.
Notice
www.sunguardglass.com
www.safti.com
www.efcocorp.com