Modeling of a daytime radiative cooling performance testbed

The aim of this master thesis is to analyze the daytime radiative cooling performance of a Passive Radiative Cooling (PRC) system, a technology able to deliver cooling without any electrical input. Due to this property, PRC technology finds significant application in the field of climate change mitigation. Global cooling demand is expected to rise from 36% in 2022 to 60% by 2050, leading to an increase in electricity consumption in the residential sector. This latter ranks as the second-most energy-intensive sector following the industrial one. Reducing energy demand means reducing the greenhouse gas (GHGs) emissions caused by fossil fuels combustion, which is the main source of heat and electricity production. Limiting GHG concentrations, especially carbon dioxide (CO2), is essential to mitigate the intensifying greenhouse effect and global warming. PRC is a process through which a surface, exposed to the sky, can reach below ambient temperature by emitting infrared radiation to the deep sky. The wavelength range through which the PRC works is called atmospheric window, in particular it goes between 8μm and 13μm. For effective daytime cooling, a thermal-selective emitter is required with a high solar reflectivity and a high emissivity within the atmospheric window. The PRC system analyzed here consists of an emitter with selective properties designed to enable effective daytime radiative cooling. This emitting panel is placed above water channels through whose water flows. The analysis are conducted using COMSOL Multiphisics exploiting meteorological conditions of summer 2023 in Turin extracted from the ERA5 database. In this work will be explored how to exploit PRC through a custom design system and how performances are affected by design choices and external conditions. The most impactful factors in the system are the water mass flow rate and water inlet temperature as the meteorological conditions. Those parameters directly influence the cooling efficiency, thus the reduction of the water temperature with respect to the inlet power. An increase in the mass flow rate or in the inlet water temperature causes an increase in the cooling power, thus the increase of the cooling efficiency. A maximum daily cooling efficiency of 47% can be achieved on a clear-sky day with an inlet water temperature of 30◦C. However, under these conditions, the subambient temperature of the outlet water is less pronounced. Therefore, optimal conditions represent a trade-off between achieving a lower outlet water temperature and maximizing cooling power. Passive Radiative Cooling offers an innovative, energy-efficient cooling solution with broad applications. In buildings, PRC reduces energy consumption and mitigates urban heat islands while in power generation, it improves photovoltaic panels efficiency by lowering operating temperature. However, unlocking PRC’s full potential requires further research on advanced emitter materials and optimized system designs.