TY - JOUR T1 - Modeling of optical and energy performance of tungsten-oxide-based electrochromic windows including their intermediate states JF - Solar Energy Materials and Solar Cells Y1 - 2013/ SP - 129 EP - 135 A1 - Sunnie H.N. Lim A1 - Jan Isidorsson A1 - Lizhong Sun A1 - B. Leo Kwak A1 - André Anders KW - Electrochromic windows KW - Energy efficient window modeling KW - Energy simulation KW - Smart windows AB - Tungsten-oxide-based electrochromic (EC) windows are currently the most robust and matured dynamic windows where the transmittance of visual light and near-infrared radiation can be controlled by a small applied voltage. In its standard application, the window is commonly either in its clear or colored state. In this contribution, we study the optical and energy performance of such window in the fully bleached and fully colored state as well as when it is kept in intermediate states. Different configurations in terms of placement of the EC layer stack and possible additional low-emissivity (low-E) coating within the insulated glass unit are considered. Using optical data and software tools we find that even a small coloration has a significant effect on the energy performance because the solar heat gain coefficient is readily reduced by the absorption of the EC layer stack. We compare the performance of the EC windows to commercially available solar-control (spectrally selective) low-E windows. VL - 108 JO - Solar Energy Materials and Solar Cells DO - 10.1016/j.solmat.2012.09.010 ER -