Yes, You Can Use Glass in Cold Climates and Other Myths Debunked
by Ellen Rogers
We’ve all heard (and probably made) our share of excuses, whether the dog ate your homework or your watch broke and made you late. But when it comes to architectural glass, there’s simply no excuse for an excuse, especially given the growing demands for high-performance, energy-efficient buildings. Unfortunately, the industry is not without its share of myths and misrepresentations. This sometimes makes it tough for glass companies and contract glaziers to see their products through, from the drawing board to the façade.
From “less glass is better” to “that will break the bank,” how do you respond to energy-efficient myths? Here’s a debunking breakdown of five myths, in no particular order, that may come in handy.
Less glazing is better.
Fact: Not true—if the glazing/windows are used to effectively bring in daylight, along with dimmable lighting controls to turn down or off the electric lights when there is sufficient daylight.
“Buildings with large glass areas can achieve significantly higher energy performance than ones with no windows – the keys are continuously dimming lighting controls, high-performance fenestration with low U-factor and excellent solar control, and an automatic response for glare,” says Helen Sanders, vice president, technical business development with Sage Electrochromics in Faribault, Minn. “The latter is important to prevent manual blinds being used and resulting in the ‘blinds down – lights on’ syndrome common in buildings today, which negates the daylight harvesting energy savings.”
A related myth involves reducing window-to-wall ratio from, for example, 40 percent to 30 percent. This can result in the use of punched-opening windows rather than continuous-ribbon windows for, what some say, is more energy-efficient and comfortable interior spaces.
Sanders says this is not always the case.
“Punched-opening windows can cause more contrast glare than continuous window walls/ribbon windows because of the difference in luminance between the window itself and the dark walls between them,” she says. “There are a couple of solutions that occupants use to counteract this additional glare, both of which reduce energy performance. One option is to turn the lights on to increase the brightness of the areas around the window. The second option is to pull the blinds on the windows to make them less bright. This causes the occupants to then put the lights on, increasing energy usage.”
She adds that punched-opening windows also have more interfaces with the opaque wall, and thus more opportunities for air leakage and additional heat conduction paths at the boundaries.
The graph demonstrates that when fenestration is combined with dimmable lighting controls, you can change the paradigm of building energy consumption. Instead of building energy increasing with window-to-wall ratio, the building energy decreases as window area increases and electric lighting energy is offset.
Source: SAGE and R. Mistrick at Penn State University.
Myths 2 and 3:
We’re in a cold climate, so we shouldn’t use much glass in this project; We’re in a warm climate, so we don’t need IG.
You’ve probably heard similar concerns, particularly when it comes to hot and cold climates. But according to some in the glass industry, there’s no need to limit the amount of glass due to temperature extremes.
“The key responsibility we have as a glass manufacturer is to work closely with the building and design team, as well as our customers, to make sure they understand not only what glass types are available, but also what products are best suited for each climate zone,” says Alice Dickerson, marketing manager, AGC Glass Company in Alpharetta, Ga. “For example, for colder climates, the focus is to select the best glass configuration (IGU) for keeping more heat inside the building, so U-factor becomes the bigger focus versus choosing a high-performing solar-control solution with the best performance specific to solar heat gain for keeping more heat outside the building—with the balance of a desirable level of visible light transmittance.”
She adds that while many architectural conversations begin with aesthetics, the design ultimately comes down to whether the glazing meets the requirements of IECC or ASHRAE 90.1. “This is where it is important to work closely with the building team to ensure that while we must meet the code requirements, the aesthetics are not compromised.”
Scott Cardwell, architectural representative for AGC Glass Company, says it’s not unusual to assist the building team on how best to evaluate the glazing to ensure that the energy code requirements are met, and not over-prescribed.
“Many times they will simply look at the prescriptive performance characteristics of the fenestration system (or other building components) as the singular method of accomplishing this goal, which can result in over-prescribing the performance necessary to meet the energy code,” he says. “Early on in the design stage of any building, an architect will often consult with a mechanical engineer to determine the performance requirements for a building enclosure. Due to limited details available in these early stages, it is a common practice for the mechanical engineer to share the tables of the prescriptive path to energy code compliance, which establishes component performance values for individual systems. This compliance pathway establishes minimum performance requirements so that energy modeling is not required to ensure code compliance, but generally over-prescribes the performances necessary. In regards to glazing, this over-prescription often limits glazing options and forces the architect to specify a product that may not achieve certain design objectives such as higher visible light transmission. Additionally, the flexibility to choose a lesser-performing glazing may lead to a cost reduction of the overall fenestration system. A better way to achieving energy code compliance is to use software called ComCheck.”
Cardwell explains that ComCheck is a software program available for free through the Department of Energy’s website, energycodes.gov, and is an easy way to model a building enclosure’s energy code compliance.
These high-performance glazing products will bust the budget.
Mark Silverberg, president of Technoform North America and chair of GANA’s Energy Division, points out that a number of climate-engineering firms believe that investing in high-performance glazing offers the biggest payback potential in high-performance building design. This is due to reductions in HVAC and lighting costs, improved productivity and occupant health gains.
He adds that properly designed high-performance glazing offers substantial reductions in condensation, a significant financial risk to buildings.
Silverberg points out that this myth is usually “based on an obsolete financial analysis model based on simple payback and ROI. Sustainable property financial analysis models have evolved significantly. Investments in high-performing glazing allow higher rents, higher retained property values, and higher occupant retention.”
Daylighting and skylighting are the same thing.
While these terms are sometimes used interchangeably, the fact is they are different. According to Neall Digert, Ph.D., MIES, vice president of product enterprise for Solatube International Inc. and a member of the American Architectural Manufacturers Association (AAMA) Skylight Council, daylighting is the art and science behind applying daylight to light in interior, architectural spaces to meet the occupant’s visual and biological needs.
“To that end, a combination of fenestration technologies can be applied to the building’s architecture, including sidelighting through vertical glazing (windows), and/or toplighting technologies as represented by, but not limited to, skylights, tubular daylighting devices, or clerestories,” Digert says. “As a result, ‘skylighting’ would grossly be described as the use of toplighting fenestration strategies to provide daylight to an interior space, and could be one method for daylighting, but it is not necessarily synonymous with daylighting.”
John Westerfield of CrystaLite Inc., who is also a member of the AAMA Skylight Council, adds that skylights are typically used for the dedicated purpose of optimizing the daylighting potential of a building.
“Skylights can be used to daylight the interior spaces of the building, not just the perimeter. Skylight glazing is not limited to clear glass, but can include a wide range of diffusing options to spread the light evenly over the floor area,” he says. “Or, with the use of reflective light conduits and/or tubular daylight devices, daylight can be targeted to specific work areas as needed. Skylights are also exposed to the sun (or bright sky) through the entire day, providing continual daylighting.”
Ellen Rogers is the editor of USGlass magazine. Follow her on Twitter @USGlass and like USGlass on Facebook to receive updates.
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