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Initial accelerated durability testing efforts of approximately 12" (0.3 m) x 12" (0.3 m) electrochromic windows (ECWs) suitable for buildings applications are reported. A brief overview is given about using ECWs for saving energy, the concomitant performance criteria, degradative factors that may limit ECW durability, and accelerated life testing (ACL T) methods. The ACLT methods are required because no widely accepted procedures have been established for the real-time testing ofECWs and because we cannot wait 20 or more years for the real-time evaluation for each window design. These methods include (a) the rapid but realistic I-V cyclic tests emphasizing the electrical properties, (b) the ACL T parameters that are typically used in durability tests by standards organizations, (c) the ACLT parameters we have been using to test large-area ECWs, and (d) how the results must be related to real-time testing. We present the quantitative parameters in (a) - (c) and include a detailed description of the procedures for using an Atlas XR-260 chamber with a 4' x 6' horizontal test plane on which the ECWs are positioned. The uniformity of the xenon-produced simulated solar irradiance and UV in the test plane, the variation in ECW temperatures during coloring and bleaching cycles, the stability of the chamber temperature, the methods of temperature and UV measurement, and our rationale for not using high relative humidity during testing is described. The procedures used for continuous and cyclic coloring and bleaching of the ECW s and the electro-optical measurement or the transmittance before and after cycling at 60 ±5°C in the environmental chamber are described. Typical results reported to the manufacturers of the ECW s are illustrated for the trapezoidal voltage waveform for coloring and bleaching, the corresponding luminous transmittance spectra and their changes with cycling, and the decrease in the luminous transmittance ratio resulting from ECW degradation. Keywords: electrochromic windows, accelerated life testing, large-component environmental chambers, durability criteria, largearea devices, degradation factors, degradation stresses, energy savings.
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