Utility and Economic Benefits of Electrochromic Smart Windows

Windows have very significant direct and indirect impacts on building energy consumption, load shape, and peak demand. Electrochromic switchable glazings can potentially provide substantial reductions in all aspects of cooling and lighting electricity usage. The solar-optical properties of electrochromic coatings vary over a wide range in response to an applied electrical signal. This control signal can be driven by a combination of occupant needs, external environmental conditions, building operating strategies, and electricity demand minimization requirements. The impact of an electrochromic glazing depends on the intrinsic properties of the coating, the placement of the coating within a window system, and many parameters related to building type, operating strategy, orientation, and location.

This study explores the potential benefits of electrochromics in comparison to other currently available and emerging glazing technologies. These effects are explored in office buildings in several climates as a function of window size, orientation, and building operating characteristics. The DOE-2 building energy simulation program was used to model the performances of these dynamic coatings, accounting for both thermal and daylighting impacts. Very substantial savings are demonstrated compared to conventional glazings, but specific impacts on component and total energy consumption, peak demand, and HVAC system sizing vary widely among the options analyzed. In a hot, sunny climate, probably the first niche market for electrochromics, simple payback periods of three to ten years were calculated based on an incremental glazing first cost of $15/ft² to $25/ft².

Electrochromic glazings appear to represent a very important future building design option that will allow architects and engineers a high degree of design freedom to meet occupant needs, while minimizing operating costs to building owners and providing a new and important electricity demand control option for utilities. Utility demand-side management programs can accelerate the market penetration of electrochromics by offering incentives to reduce net first cost and payback periods.