Dual-window spectrally engineered passive radiative coating for efficient year-round building thermal management

Year-round passive radiative thermal management of buildings offers a promising path to reduce heating, ventilation and air conditioning (HVAC) energy demand without active energy input. However, most existing approaches only exploit the primary atmospheric window (8−13 μm) while overlooking the second window (16−25 μm), thereby limiting their seasonal performance. In this work, we present a novel dual-mode passive radiative coating with switchable emissivity for on-demand building cooling and heating. The coating features a flexible, multi-layered architecture composed of poly(vinylidene fluoride) (PVDF)@SiO2/Al/multi-walled carbon nano-tube (MWCNT). In cooling mode, the coating achieves exceptional solar reflectance (98.1 %) and high emissivity (0.93 and 0.89) across both atmospheric windows, enabling efficient sub-ambient daytime cooling during summer. In heating mode, it exhibits strong solar absorption (93.5 %) and ultra-low emissivity (0.15) across the mid-infrared range of 2.5–25 μm, delivering effective above-ambient warming in winter. Simulations indicate an annual energy saving of up to 9.2 % (67.5 MJ m−2) in building energy use with this coating. Widespread adoption could potentially reduce global CO2 emissions by approximately 1.14 billion tons and yield annual cost savings of $205.99 billion. This flexible dual-mode coating presents a promising passive solution for all-season thermal management of building envelopes, contributing significantly to global sustainability and carbon neutrality goals.