Development and experimental performance characteristics of composite coated daytime radiative water cooler

The daytime radiative cooling technology may be effectively used to passively cool the water and hence mitigate the undesirable solar water heating of the roof-top storage tank in the summer. Hence, this work presents the radiative water cooler design, development and experimental and numerical performance characteristics. Radiative water cooler surface coating has been developed using the polymer (PMMA)-particle (barium sulfate) composite structure. The effects of various water inlet temperatures and volume flow rates on the water temperature drop and cooling capacity are experimentally and numerically performed. Sub-ambient water cooling throughout the day is observed for a range of 0.1–0.4 L/min water flow rates at the near-ambient inlet temperature conditions. The maximum sub-ambient water temperature drop of 6.1 °C (that of 3.5 °C at noon) is observed with a developed radiative cooler for the flow rate of 0.1 l/min. The usage of the daytime radiative water cooler for sub-ambient water temperature drop is found to be more suitable for above-ambient water inlet temperature. Apart from the solar irradiance, ambient temperature, ambient humidity, wind velocity and coating surface emissivity characteristics, cooling capacity and surface temperature distribution of radiative water cooler also depend on the water inlet conditions.