Int. J. Adv. Sci. Eng. Vol.10 No.2 3336-3347 (2023) 3336 E-ISSN: 2349 5359; P-ISSN: 2454-9967 Oraka et al., International Journal of Advanced Science and Engineering www.mahendrapublications.com Numerical Study of the Thermal Performance of Diurnal Passive Radiative Systems for Space Cooling in Owerri – Nigeria C.R. Oraka 1 , G.N. Nwaji 1* , H.O. Okoro 1,2 , C.A. Okoronkwo 3 , N.V. Ogueke 1,4 , E.E. Anyanwu 1 1 Department of Mechanical Engineering, Federal University of Technology, Owerri, Nigeria 2 Department of Mechanical Engineering, Akanu Ibiam Federal Polytechnic, Unwana, Afikpo, Nigeria 3 Department of Mechatronic Engineering, Federal University of Technology, Owerri, Nigeria 4 African Centre of Excellence on Future Energies and Electrochemical Systems (ACE-FUELS), Federal University of Technology, Owerri, Nigeria 1.0 INTRODUCTION Passive radiative cooling technologies have gained research interests in recent times as a viable alternative for cooling [1]. It is simply the process by which a body loses heat by thermal radiation through the atmospheric transparency window [2]. In the case of buildings, radiative cooling results from the thermal radiation exchange between building surfaces on the Earth and the colder atmospheric layers in the sky. The general mechanism is actually by dissipating heat from buildings (heat source) to the sky (heat sink) [3]. Granqvist and Hjortsberg, [4] described passive cooling to far below ambient temperatures by using the clear night sky as a heat sink. A passive daytime radiative cooling system is made of a sky facing surface which can preserve the indoor air temperature below ambient without energy consumption by simultaneously reflecting solar radiation and emitting thermal radiation to the universe through the atmospheric window located between 8–13μm of the electromagnetic spectrum [5]. Radiative cooling occurs because the atmospheric emittance is low in the wavelength interval 8-13μm particularly if the 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. KEYWORDS: Radiative Cooling, Atmospheric Window, Metamaterial, Thermal Radiation, Cooling Power, Numerical Simulation. https://doi.org/10.29294/IJASE.10.2.2023.3336-3347 ©2023 Mahendrapublications.com, All rights reserved *Corresponding Author: godswillmee@gmail.com Received: 16.09.2023 Accepted: 17.10.2023 Published on: 25.11.2023