Window, Lighting and HVAC System Interactions
Part 2: Windows and Thermal Performance
Part 3: Operable Windows and IAQ
Part 4: Showcase: Windows
Operable Windows and IAQ
By Greg Zimmerman, Executive Editor - August 2009 - Windows & Exterior Walls
Regarding air infiltration, AAMA/WMDA/CSA 101/I.S.2/A440-08, North American Fenestration Standard Specification for Windows, Doors and Skylights is a standard that applies to both operable and inoperable windows. “It includes testing for air infiltration rates and sets applicable standards for performance,” says Lowinski. “Facility executives should require that products be tested and certified to this standard.”
Even so, facility executives who are considering replacing fixed windows with operable windows have an extra layer of detail to attend to. Operable windows can contribute to LEED credits and give occupants the freedom to manage the comfort of their space. Of course, operable windows sometimes create more problems than benefits.
“Generally, if you rely on occupants to control something, it won’t be controlled correctly,” says Lowinski. So facility executives should make sure to produce operational manuals and rules that spell out how the operable windows can be used.
From an energy standpoint, however, there is a problem with replacing fixed windows with operable units: Because buildings are initially designed to account for particular temperature and pressure patterns, operable windows can throw that balance out of whack.
“Open windows in one office could affect air flow in other places,” says Lowinski. “The HVAC system has to pressurize and depressurize certain parts of a building, so it’s important to know how windows affect that balance.”
And that’s the rub: finding a balance. Buildings these days are complicated organisms, with individual product decisions having far-reaching consequences in other areas facility executives may not have initially considered. That’s especially true for windows. Just ask the people who work in the James R. Thompson Center.
Product selection requires a large amount of research and consultation with mechanical engineers, maintenance folks and other experts in the organization who know the building backwards and frontwards. “You don’t just go out and buy windows and hope you made an intelligent choice,” says Lowinski. “You really have to examine the data regarding solar loads, daylighting issues and HVAC systems.”