Sub-ambient radiative cooling and its application in buildings

Radiative cooling can effectively reduce energy consumption for building applications. As a passive cooling technology, a radiative cooling system radiates heat into space via infrared radiation whenever the effective sky temperature is colder than the body surface. Although radiative cooling has been proposed for many years, its application is limited to nighttime operation due to the constraints of the materials and diurnal radiative cooling technology. The radiative cooling surfaces recently developed, which can produce approximately 100 W/m² average daily cooling power, are perfectly applicable for employment in a passive cooling system during the day. This paper reviews the development of radiative cooling techniques and their application in buildings. The existing models for the heat balance of radiative cooling systems are introduced, and the contributions of solar radiation, forced convection, and atmospheric conditions are also discussed in detail. Recent advancements in diurnal cooling approaches and associated radiative cooling surfaces are outlined, and the application prospects are analyzed, accounting for the energy saving potential. In addition, several feasible radiative cooling systems are proposed in this study.