Abstract :

Passive radiative cooling does not require any energy input and has a great promise to help address global energy challenges. A 2D mathematical model based on the thermal energy balance approach was developed from the first principle and used to study the feasibility of employing the principles of passive radiative cooling for diurnal comfort space cooling in buildings. The model has been parameterized using Owerri climatic data as a typical tropical climate. The model equation was discretized in a 2D geometry of a scalable Silica-Poymethylpentene (SiO2-TPX) metamaterial with an average emissivity of 0.93 within the atmospheric window (8–13 µm) and reflectivity of 96% within the solar spectrum (0.2–3 µm) using a finite element numerical scheme. The processing was done in FlexPDE Finite Element Model Builder and Numerical Solver version 7.21/W64 3D. The temperature history, underlying energy variables, and cooling potential of the diurnal passive radiative cooler were accurately predicted from simulations for the study location. From the simulation results, which span from the hours of 6:00 a.m. to 6:00 p.m. of the day, the maximum sub-ambient temperature of the cooler was 5oC under direct solar irradiation during the day. The maximum cooling power recorded was 94 W/m2.Therefore, with the development of metamaterials, diurnal passive radiative cooling can enhance the drop in the indoor temperature of buildings when applied as direct fenestration materials, ensure net-zero energy buildings, and aid in offsetting the skyrocketing energy bills arising from increasing space cooling needs in the tropics.