Window-to-wall ratio effects on energy and daylighting in building with dual-band electrochromic glazing across climates

The window-to-wall ratio (WWR) plays a critical role in balancing building energy use and daylighting performance. However, the implications of WWR design for buildings employing dual-band electrochromic (DB-EC) glazing have not been sufficiently clarified. This study investigates the energy and daylighting performance of buildings with DB-EC glazing under different WWRs (0.2–0.8), façade orientations, and climatic conditions using EnergyPlus simulations, and compares DB-EC glazing with EC, Low-E, and double glazing. The results show that when DB-EC glazing is applied in hot-summer and warm-winter regions such as Shenzhen, annual total energy use increases continuously as WWR increases from 0.2 to 0.8, with a maximum increase of 23.3 %. In other climate regions such as Harbin, Beijing, Wuhan, and Kunming, annual total energy use generally initially decreases and then increases with WWR, reaching its minimum at WWRs of 0.3–0.5 and varying overall by 4.6–19.7 %. Increasing WWR improves useful daylight illuminance across climates and façade orientations, whereas excessively large WWRs cause a decline. Compared with static glazing, DB-EC glazing effectively suppresses the increase in total building energy use at large WWRs, particularly in cooling-dominated climates. In Shenzhen, when WWR reaches 0.8, the increase in annual total energy use is limited to 18.3–23.3 % for DB-EC glazing and 11.5–15.6 % for EC glazing, substantially lower than that for Low-E glazing (56.9–57.3 %) and double glazing (68.5–71.1 %). Overall, DB-EC glazing enhances the flexibility of WWR design by effectively limiting the adverse energy impacts of large WWRs. This study provides guidance for WWR design in buildings employing DB-EC glazing.