Modeling of optical and energy performance of tungsten-oxide-based electrochromic windows including their intermediate states

Abstract

ACKNOWLEDGEMENTSWe thank Steve Selkowitz, Christian Kohler, and Rueben Mendelsberg (all LBNL) for insightful discussions. This work was supported by the Assistant Secretary for Energy Efficiency and Renewable Energy, Office of Building Technology, of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231, and by the American Reconstruction and Reinvestment Act, under contract DE-EE0003838. DISCLAIMERThis document was prepared as an account of work sponsored by the United States Government. While this document is believed to contain correct information, neither the United States Government nor any agency thereof, nor The Regents of the University of California, nor any of their employees, makes any warranty, express or implied, or assumes any legal responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by its trade name, trademark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof, or The Regents of the University of California. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof or The Regents of the University of California.2 Abstract 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.

Performance and stability of “partly covered” photoelectrochromic devices for energy saving and power production

“…The superior performance of electrochromics compared to other competing technologies has been demonstrated sufficiently [2][3][4][5][6][7]. Furthermore, most performance and stability issues have been addressed [1] and nowadays ECs are on the verge of commercialization, provided that large-scale roll-to-roll processes can be devised for their mass production [1].…”

Green fabrication of a complementary electrochromic device using water-based ink containing nanoparticles of WO3 and Prussian blue

“…Energy-saving smart windows, which control the light coming into buildings, houses, and automobiles, are promising in terms of energy conservation and low environmental impact. [1][2][3][4] Smart windows utilize various technologies, including electrochromic (EC), 5-10 thermochromic, 11,12 gasochromic, 13,14 photochromic, 15,16 and thermotropic 17,18 principles. Among them, the use of EC devices (ECDs) is considered as the most promising technology, because their colour can be switched electrically as needed.…”

Performance requirements for electrochromic smart window

“…A low-emissivity coating on the inner pane (surface 3) will further increase the rejection of the absorbed heat to the outside. Simulation studies show that the SHGC of EC glazing so configured decreases by a factor of approximately 5 in the colouring process reaching values lower than 0.1 [35].…”

“…Recent studies point out how EC devices with high modulation range of the  nir coefficient could realize energy saving for most climates also in the winter season, whereas conventional absorbing EC glazing are poorly efficient. [35,36]. The "ideal smart window" [36] should have  nir =0 in the fully bleached state and  nir =1 in the fully coloured state.…”