Hybrid Evaporative Radiative Cooling for Large Energy Savings

Passive cooling technologies can be a game changer for addressing global cooling demand, where standalone evaporative or radiative cooling methods have already shown much promise. However, they often face challenges associated with water consumption, solar absorption, parasitic heating, low cooling power, and humidity constraints. Here, we present a hybrid evaporative-radiative cooling architecture that addresses these previous shortcomings. The structure consists of a solar reflector, a water-rich and IR-emitting evaporative layer, and a vapor-permeable, IR-transparent, and solar-reflecting insulation layer. We showcased this concept with the enhanced specular reflector, the polyacrylamide hydrogel, and the polyethylene aerogel as the three layers, respectively. In Cambridge, MA, USA, we demonstrated 9.3 °C below the ambient under direct sunlight. With minimal water expenditure, our sample consistently stayed below the wet bulb temperature, which is not possible with pure evaporation. Under the same weather condition, we showed 300% enhancement over a state-of-the-art radiative cooler in daytime cooling power. Further, we show that hybrid evaporative radiative cooling offers large energy-saving opportunities in food storage and building thermal management applications for a wide range of climate conditions.