Nighttime radiative cooling in hot and humid climates.

Most existing experiments on radiative cooling are conducted in dry climates for better performance. However, many important applications require cooling in hot and humid climates. Here we theoretically analyze the temperature reduction and cooling flux at nighttime with the ambient temperature (Tambient) ranging from 0-40  ∘C and the relative humidity (RH) from 0-100%. Our analysis reveals an interesting crossover: for lower (higher) RH, higher (lower) Tambient results in better cooling. Experimentally, we show that radiative cooling of 5  ∘C below ambient can be achieved even at Tambient = 29  ∘C with RH = 100%.