Sequential optical modulation in smart glazing: A hierarchical thermochromic strategy for climate-adaptive building envelopes

Thermochromic glazing can passively regulate solar gains, but single-response systems often trade solar-heat rejection against daylight preservation. Here we propose a hierarchical response composite window that sequentially activates near-infrared (NIR) and visible-light modulation: a 28 °C VO2 layer first limits NIR heat transmission, whereas a 40 °C hydrogel introduces stronger broadband attenuation only under intense solar thermal stress. Within a simulation-first, prototype-verified reverse-design framework, literature-derived optical spectra were implemented in EnergyPlus, validated against full-scale measurements (indoor-temperature RMSE = 0.45 °C), and assessed across more than 3600 global administrative units, 370 Chinese municipal-level units, and representative hot, mixed, and cold climates. Globally, 96% and 79% of valid units achieved cooling and total energy saving rates above 30%, respectively. In China, the composite window delivered mean cooling and total energy saving rates of 32.18% and 11.45%, with 84.1% of units exceeding 20% cooling savings. Matched-parameter controls further showed that sequencing improves the annual balance among cooling, heating, and lighting rather than maximizing cooling savings alone. It also suppressed over illumination to below 10% and improved useful daylight availability. Prototype spectra verified a VO2-dominated NIR-first state followed by hydrogel-dominated broadband attenuation, while more than 50 thermal cycles confirmed short-term reversible operation. These results establish sequential thermochromic regulation as a climate-aware design principle for reconciling energy and daylighting demands in adaptive glazed façades.