Radiative cooling of water to sub-ambient temperature under direct sunlight

Abstract

Radiative cooling uses the cold universe as a heat sink to dissipate heat without consuming electricity. Earlier studies on radiative cooling have been restricted to night-time use only due to solar absorption during the day. However, it is more important to achieve day-time radiative cooling since many energy systems (e.g. air conditioning system) have their peak cooling load during the day. We recently demonstrated a polymer-based radiative cooling material (RadiCold surface) that can generate 93 W/m2 net cooling power at noon time. The employment of this material can be either directly attached to an object that needs to be cooled (e.g. cool roof), or use the material to cool down a heat transfer fluid (e.g. water) and then couple to other energy systems for efficiency improvement. In this study, we show that water can be cooled down to 9.2°C below ambient at noon time under > 700 W/m2 direct sunlight. The use of this technology could generate significant impact on building air conditioning, or supplemental cooling of power plants.