Jim Paull, ERS, for Zondits. May 23, 2016. Image credit: VetroTech
The first thing attendees saw as they entered the exhibit hall at last week’s American Institute of Architects (AIA) conference in Philadelphia was a large cube showing off Saint Gobain’s SageGlass smart windows. SageGlass was one of three smart window manufacturers exhibiting this year, the others being View and Pleotint’s Suntuitive.
Smart windows have been around for a while. Their ability to change tint by responding to electrical input (electrochromic) or heat from the sun (thermochromic) promises to significantly reduce air-conditioning loads. Moreover, by incorporating smart windows into new buildings, building owners can save considerable capital costs by reducing the size of chillers and rooftop air-conditioning units.
Smart windows may also help glass continue to be the prevalent material used for commercial large office building facades. New building codes and regulations, such as California’s Title 24, paradoxically limit the allowable solar heat gain coefficients – a measure of how much sunlight heats up the interior of a building – while requiring a high percentage of light to be provided from natural sources. While standard low-e insulated glass units (IGUs) may have a hard time conforming to these demanding requirements, smart windows can operate in different tinting modes to satisfy the extremes.
Despite their promise, however, smart windows have not had much traction. This is mainly because of cost: what has been commonly described in building circles as a “non-starter.” Smart windows have thus only seen application in a limited number of “trophy” buildings where cost is no object.
Another issue is size. Smart windows have been too small to meet the specifications for some modern curtain walls. And while thermochromic windows cost less than electrochromic, they can be plagued by tint irregularities due to temperature variations.
All of this appears to be changing for the better. Smart glass window vendors claim that costs have come down to where they are now often only twice as expensive as their low-e IGU counterparts. The number of installations – which used to be counted in the handfuls – are now in the hundreds. Sizes have increased as well, as evidenced by the 6-foot by 10-foot windows that were on display at the AIA exhibit.
Smart windows still represent only a tiny fraction of the overall insulated glass market. But if costs continue to fall, they may reach a point at which they can be widely adopted and have a significant impact on buildings’ air-conditioning loads.