Spectral Selectivity of Electrochromic Windows with Color State for All-Sky Conditions

The optical performance of an electrochromic window is studied for the visible, ultraviolet, and near infrared spectral regions. The performance is found to deviate strongly with window color state and for clear or cloudy skies. A new spectral cloud model (Soule et al) is applied to an electrochromic window recently developed at NREL (Zhang and Benson). A spectral comparison is made between theelectrochromic window and spectrally selective standard windows. Two series of double-glazed window sections, including the electrochromic window with color state and a series of low-E windows, were measured for transmittance and reflectance (300 - 2500nm). With these spectral data, a new near-infrared blocking (reflection + absorption) factor is developed for window application in warm climatesfor cooling load reduction. A chromaticity analysis is presented for both the daylight spectra and the transmitted electrochromic window spectra with color state. Computed daylight correlated color temperatures show a wide range, with values of 5660K for clear global irradiation, 6210K for clouds, and 13, 250K for a zenith blue sky. Chromatic trajectories with color state for transmittedradiation extend further toward the blue to 8180K for the global and 28, 990K for zenith sky irradiation.