Trying to balance natural light and distracting influences like glare and solar heat gain is a major challenge for buildings with many windows. In recent years, electrochromic windows have emerged in the marketplace, affording facilities managers the ability to electronically modulate the amount of light admitted into a building.
As technology has progressed, so too have the best practices for implementation. The General Services Administration (GSA) reported on two case studies of buildings implementing electrochromic windows through its Green Proving Ground (GPG). Learn how to best leverage electrochromic windows in your workplace.
Electrochromic in Practice
The HVAC benefits electrochromic windows have on buildings has been well-documented. This study, conducted by Lawrence Berkeley National Laboratory, looked at occupant satisfaction in two different locations: the 911 Federal Building in Portland, OR, and the Moss Federal Building in Sacramento, CA. Both buildings have curtain wall designs with high window-to-wall ratios.
Before retrofits, the 911 Federal Building had dark-tinted, dual-pane, low-e windows with fitted venetian blinds. Electrochromic windows were installed adjacent to the south facade in the sixth and seventh floors and later to the third, fourth and fifth floors after receiving positive feedback from occupants.
In Sacramento, the Moss Federal Building received electrochromic windows in the south facade of the sixth floor, which replaced 84 double-pane low-e units.
In both facilities, most building occupants were satisfied with the change. In Portland, 85% of occupants in private offices and 92% in open offices preferred electrochromic windows from the previous ones. In Sacramento, 63% of occupants preferred electrochromic windows to the previous options.
Reception to the new windows obviously wasn’t without some reservations. Some occupants indicated that the time it takes to fully tint wasn’t adequate. For some manufacturers, this problem is exacerbated by the fact that users cannot abort a transition with an override function without finishing the current tint process.
Getting the Most out of Electrochromic Windows
In addition to finding out how many occupants liked the change to electrochromic, GSA made some key conclusions about the best practices for installation and operation, including:
- Select clear windows to facilitate a broad switching range. Because they tried to match the legacy windows aesthetically, the Portland facility added a blue-tinted layer of glass to the electrochromic windows. As a result, the windows were limited in being able to let light into the building. Therefore, electrochromic windows with a clear inboard glass layer are best.
- Configure electrochromic window installations into zones. The two buildings installed their electrochromic windows in the south-facing facade, but it can get too dark if all the windows are electrochromic and set for the darkest tint. Installing them in zones or equipping them with individual controls can help mitigate this.
- Test before you install to avoid any surprises.
- Educate occupants and manage expectations. Let occupants know how electrochromic windows operate, whether they have override controls and how to use them. If occupants understand how the new windows work, they will more likely be satisfied with them.
What’s the Best Fit for Electrochromic Windows?
Based on the findings from the reports, GSA determined these were among the best applications of electrochromic windows.
- Facilities where outside views are critical. A previous GSA study at the Land Port of Entry (LPOE) in Donna, TX, found that electrochromic windows worked well in locations where glare compromises mission critical outdoor visibility. The electrochromic windows at the Donna LPOE had a 100% user preference over previous conventional windows.
- Facilities with seasonal thermal comfort challenges. For buildings that experience seasonal discomfort, electrochromic windows help to provide dark tinted glass in the summer and clearer glass in the winter.
- Facilities with atriums and skylights. The heat gain that atriums and skylights can bring to a building can neutralize the positive effects they might otherwise have on building occupants. Although it hasn’t been evaluated yet, the evaluation team believes electrochromic windows would work well with atriums and skylights.
- Facilities needing to reduce peak cooling load. Electrochromic windows can help reduce peak cooling load. Like in Portland, this ability to reduce HVAC energy requires occupants to accept darker tint levels.
- Facilities with radiant cooling. Buildings with radiant cooling and other low-energy cooling systems benefit from the control that electrochromic windows provide, since HVAC systems take time to respond to atmospheric conditions.
For more information on the electrochromic installations in Portland and Sacramento, as well as other key findings and lessons learned, visit www.gsa.gov.