Transparent Polymer Coatings for Energy-Efficient Daytime Window Cooling

Solar and thermal management of transparent windows is important for the energy efficiency of human-made structures. Functional layers that partially block solar radiation would also be heated by sunlight, thus accelerating the interior heat exchange and increasing daytime cooling energy consumption. Here, we propose a strategy to improve energy efficiency through window cooling using a transparent double-layer coating, which comprises a near-infrared reflective underlayer and a high mid-infrared emissive top layer. The addition of a top emitter can decrease the temperature of the near-infrared reflective window up to ∼7°C in outdoor tests, and can provide extra cooling energy savings ranging from 20 to 49 MJ ⋅ m−2 ⋅ year−1 for a typical building located in 11 cities worldwide. This accounts for ∼3%–∼8% of their total annual cooling energy consumption and indicates the significant impact of window cooling on interior energy efficiency.