Comparative Analysis and Optimization of Passive Radiative Cooling Systems

Passive Radiative Cooling (PRC) is an environmentally friendly technology that reduces building cooling electricity consumption by rejecting heat directly into the sky through the atmospheric window. In this thesis, the performance of a Radiant-Capacitive Cooling System (RCCS) has been analyzed through sensitivity analysis and multi-objective optimization, combining experimental measurements with numerical simulations. The RCCS consists of three main elements: Sky Radiators (SRs) for heat rejection to the sky, Radiant-Capacity Modules (RCMs) installed as ceiling panels for indoor cooling, and Thermal Energy Storage (TES) tanks that regulate system operation. These components are connected through a hydronic circuit, allowing the evaluation of passive radiative cooling materials to maintain indoor thermal comfort. The sensitivity analysis has examined the impact of key parameters, including flow rate, number of RCMs and SRs, tank volume, operating time, and PRC and non-PRC coatings, under various climatic conditions. Results showed that flow rate and surface area of RCMs and SRs are the most critical parameters, while tank volume and coating material have only secondary importance. Climatic conditions strongly influenced performance; milder conditions and cooler nights consistently delivered the best subcooling temperatures and energy savings. The optimization was carried out through different steps: first, a series of sample data was generated to be implemented in surrogate models. Then, surrogate models were trained using these data to approximate system performance. In the subsequent stage, a genetic algorithm was applied to explore the trade-offs between comfort, energy savings, and pumping energy using the predicted performance indicator in the training step. A weighted scoring method was used to select the most balanced solution from the Pareto set. The resulting optimal configuration achieved over 90% comfort together with significant energy savings, while keeping pumping demand at a manageable level. These results are in good agreement with those of the sensitivity analysis. Overall, it can be concluded that although PRC coatings provide uniform but modest improvements, system design (RCM/SR ratio, flow rate, operating time) and local climate are the primary drivers of performance. The combined sensitivity and optimization approaches could provide practical guidelines for designing efficient PRC-based cooling systems applicable to different climatic conditions.