A number of glazing mistakes can bedevil a project, including glare, employee behavior, and overglazing.
Let in the light and you’re also letting in heat, free daylight, and potential glare, so it’s both a problem and an opportunity, says William Maiman, marketing manager at MechoSystems.
“If you are selecting a very high light-transmissive glass for your glazing, then you’re really introducing a lot of heat and light, and that will read on the HVAC system as heat and on the occupants as direct solar radiation,” he says.
Letting in a lot of daylight can cause another problem for facility managers: glare. Maiman describes the plight of an office worker at a computer: “You put a wall of desks in front of this glazing you’ve selected. And you now have a very bright sky, which a good part of the southern and western part of our country have, and now you’re trying to resolve a small spreadsheet with fonts that are 10 point on a 16-inch LCD screen. Your eye is going to have a problem with the contrast ratio, and that is going to generate eye fatigue.
“Or worse, somebody gets up and decides to close the shades and then they put the light on, or they close the drapes or window treatment. And an hour later, when the sun has moved, very few people remember to turn off the overhead fluorescent lights and open the window treatment.”
Glare is a common concern among those in the glazing industry. “Designers are told that more light is better, that they can design more occupant-pleasing environments with more light, reducing the need for artificial lighting and saving energy,” DeBusk says. “But what we find is many buildings with high levels of clear, low-e windows with uncomfortable occupants suffering from too much solar heat gain and lots of glare.”
Two other glazing mistakes are a lack of due diligence and overglazing a building:
A lack of due diligence pre- and post-installation: Study a mockup of a proposed project “to be sure it’s going to be what everyone wants,” Maiman advises. Be sure you study the mockup or samples at night as well as in daylight, and from both the inside out and the outside in, he says. And get a thorough explanation of how a system will handle the freeze-thaw cycle.
Sanders notes the importance of getting worker feedback about a new system, tweaking the system, and ensuring that occupants are doing nothing to override it. After installation, for example, is anyone checking that the preferred glass cleaner is being used? Cleaning people can unknowingly use products that ruin scratch-resistant window coatings, Maiman says.
Overglazing a building: Designers can sometimes overdo the glass, Sanders says. She cites the wrongheadedness of believing one can “put in an all-glass atrium, west-facing, and expect it to be comfortable, or to not have high energy consumption.” She sees numerous uses of overhead glass that don’t control enough for heat gain.
“You have to be careful with glazing,” Sanders said. “You can have a very energy-efficient building with a lot of glass on it, but you can also have the reverse. You’ve got to think very carefully about where you put glass, how you’re harvesting energy, and how you’re controlling the solar gain.”
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