Water-efficient evaporative cooling by sunlight-reflective radiative-cooling nanofibers

Evaporative cooling, which has the highest potential for energy transfer, is not sustainable without sufficient water. Here we present the membrane that can be used to protect the moisture from unnecessary evaporation. The membrane is composed of nanofiber non-woven fabric that is breathable and has high solar reflectance and high infrared emissivity for water-efficient evaporative cooling applications. The membrane prevents moisture from evaporating unnecessarily by blocking solar absorption and efficient thermal emission. Specifically, the membrane is composed of ∼400 nm diameter polyurethane fiber, which has a high MIE scattering effect on solar radiation (∼2500 nm wavelength), resulting in over 95% solar reflectance as well as over 95% of total infrared (IR) emissivity and IR transmittance at 50 g/m² of membrane. In addition, it has sufficient breathability of over 16 mg•cm²•hr that the maximum evaporative cooling is about 100 W/m². Twice the cooling time and 3 °C cooler surface by tandem of radiative cooling were confirmed in outdoor test of wet fabric covered with nanofiber membrane compared to wet fabric without membrane. This scalable and flexible membrane is applicable where the thermal cooling without energy consumption is required for net-zero energy consumption.