Numerical investigation of the energy saving potential of flippable electrochromic windows with vacuum structures in severe cold region

Electrochromic smart windows have drawn increasing attention as they can intelligently enhance indoor daylight comfort and decrease building energy consumption. However, electrochromic smart windows generally face the spatiotemporal mismatch between the seasonal heating requirements and diurnal anti-glare requirements, suffering from a light-heat trade-off. Herein, this study proposed a novel flippable vacuum electrochromic (FVEC) window for independent glare and solar heat gain control. As proof, the proposed glazing system can achieve the solar heat gain coefficient (SHGC) variation of 0.103-0.582, with the VIS transmittance variation of 0.154-0.489, and satisfies the indoor daylight quality requirements of buildings across its chromic states. To further investigate energy-saving potential, a transient model was developed to figure out the annual performance of the FVEC window in Harbin. The results demonstrate that, under idealized conditions, each 1 m² FVEC window can reduce the annual cooling and heating loads by 633 MJ and 514 MJ respectively, compared with a triple-glazed clear window. Although these values may decrease when window thermal bridges and sealing performance are considered, these features still demonstrate that the proposed technology can achieve effective switching between low and high solar heat gain, while maintaining daylight comfort during the whole year, showing great promise for buildings located in severe cold regions.