Electronically tintable glass

An architectural enabler
Friday, June 14, 2013
By Helen Sanders

From the very beginning of architecture, man has sought to bring sunlight into buildings; thus, was born the window.

So why are windows so important?

It’s really all about people. People love the view and connection to the outside, the access to natural daylight and the way it makes them feel. The more that’s understood about the impact of changing daylight patterns on the body’s circadian rhythm and the influence of daylighting and views on health, well-being and productivity, the more that’s understood about the importance of windows in buildings.

But windows also come with problems. The environment changes season by season, day by day, and hour by hour, yet the traditional building envelope cannot respond to these ever-changing conditions. The static nature of glass leads to significant problems related to heat and glare control, occupant comfort and productivity, and energy consumption. In winter, the perimeter zone can be too cold; in summer, too hot. And in all seasons occupants are dealing with uncomfortable glare. As such, the benefits of access to natural daylight are offset by thermally and visually uncomfortable spaces. In the case of glare, occupants pull blinds and shades and then block the view to the outside.

Electronically tintable glass offers a dynamic solution to this sun management problem. With the ability to reversibly change its solar heat gain coefficient and visible light transmission at the touch of a button or command from a building energy management system, it provides dynamic control over the amount of heat and light that is admitted to a building.

Having a “heat and light valve” on a building envelope provides the ability to minimize cooling and heating loads and offset electrical lighting as needed without losing the view and connection to the outside. The ability of electrochromic glazings to reach two per cent visible light transmission or less provides sufficient glare control, which, for most situations, eliminates the need for blinds or shades. Eliminating conventional mechanical shading systems such as sun shades and interior blinds not only preserves the unobstructed view to the outside but it provides an architect more design flexibility to produce clean, elegant, highly glazed façade designs without compromising energy performance or occupant thermal or visual comfort. This is also important in the face of increasingly stringent energy codes and the pressure to reduce window areas.

Case study
The LEED (Leadership in Energy and Environmental Design) silver accredited Morgan library expansion at Colorado State University (CSU) is a good example of the architectural design freedom provided by electronically tintable glass. Designed by Studiotrope, the modern glass cube is a focal point of the CSU campus and, as such, preserving the transparency of the glass building was a key design objective for the project.

At the high altitudes of Colorado, the sunlight is intense, especially on the west elevation in the afternoon, which is challenging to mitigate using conventional shading methods. In fact, daylight modeling of the space showed an extremely dense vertical shade solution would be needed to control the western sun, which would have negated the openness and transparency objectives of the design. As a result, making such a highly glazed design work with the conventional solutions would have been extremely difficult.

Electrochromic glass is installed along the entire west elevation in the two-storey curtain wall, including in the doors and operable windows. The glass on the upper and lower floors is zoned so the panes in each area can be controlled separately to provide the optimum balance of energy performance and glare control.

Helen Sanders is vice-president of technical business development at Sage Electrochromics, Inc. Sage is an industry leader in the manufacturing of electrochromic glass. The company has been providing electronically tintable glass to the construction market since 2003. Helen can be reached at 507.331.4909 or helen.sanders@sageglass.com.

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