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• Design, optimization of a solar assisted thermal air conditioning system using CO 2. • Optimization examines collector area, inclination and storage tank capacity. • EGTC C2 emerg as the optimal configuration, achieving a seasonal f of 0.649. Traditional air conditioning and refrigeration solutions rely on compressor-driven systems, leading to increased electricity consumption and intensified greenhouse gas (GHG) emissions. These systems primarily utilize synthetic refrigerants such as CFCs, HCFCs, and HFCs. Despite their advantages, these refrigerants are either banned or subject to restricted permissions under the Montreal Protocol (1987) and the Kyoto Protocol (1997) due to environmental concerns. According to the Paris Accord, ratified by 196 parties as of 2017, there is a global shift towards low global warming refrigerants and eco-friendly alternatives. COP27 reaffirmed global commitments to limit temperature rise to 1.5 °C, emphasizing urgent action and stronger climate plans to combat global warming. CO 2 envisaged by ASHRAE is resurrected as a promising natural refrigerant with the advent of high-pressure technologies the design employs a solar evacuated glass tube collector (EGTC) with U-shaped copper tubes and flat plate collector (FPC) to harness solar thermal energy. An immersed heat exchanger's (HX) based thermal storage tank is incorporated to address the intermittency of solar energy. The CO 2 refrigerant offers advantages over other natural refrigerants due to its low critical point. This research conducts a TRNSYS® simulation of a 35.2 kW absorption cooling system with synthetic building load driven by energy captured through FPC and EGTC using R-744, additionally supported by a supplementary boiler for traditional office timing. The system design comprises two solar collectors, the EGTC and FPC, integrated with two different cooling loop configurations (C1 and C2). In C1, the hot water that exits the generator of the absorption chiller is forwarded toward the immersed HX-based hot storage tank, which is connected to the solar and absorption cooling loop. In C2, the working fluid leaving the absorption chiller is diverted directly toward the auxiliary boiler/furnace, if the temperature in the storage tank falls below the necessary level (108.89 °C) and if the tank temperature is greater than this set point temperature, then the flow passes through the storage tank. Both system designs have been developed using TRNSYS, with dynamic simulations conducted throughout the summer. The solar fraction and collector efficiency are considered as key performance indicators to evaluate and compare the system's effectiveness. Then the optimization of system parameters is performed for all four cases (EGTC C1 & C2 and FPC C1 & C2) based on these key performance indicators, all configurations integrated with a fixed synthetic building cooling load. The optimum parameters are found for all four cases, and the optimum parameters for EGTC C1 & C2 are 100 m2, 4 m3, and 11° for collector area, storage tank volume, and collector slope respectively. Similarly, for FPC based configurations, these parameters are 200 m2, 32 m3 for C2 and 4 m3 for C1, and 20° respectively. The results revealed better C2 performance than C1, with EGTC outperforming FPC. The final results were computed for the EGTC based designs due to their high solar fractions, with EGTC C2 emerging as the optimal configuration, achieving a seasonal solar fraction of 0.649. [ABSTRACT FROM AUTHOR]

[Display omitted] Water heating without greenhouse gas emissions is indispensable for sustainable development in low sun regions. The integration of solar energy in domestic water and space heating systems is a sustainable pathway. Kyoto and Montreal protocols have already banned the use of chlorofluorocarbons and hydrofluorocarbons and granted a time limited permission to hydrochlorofluorocarbons. Synthetic refrigerants outperform natural refrigerants, yet 196 countries agreed on phasing out these refrigerants under Paris Accord in 2015. Industries, researchers and policy makers are retrofitting existing heating and cooling systems to integrate natural refrigerants worldwide. In this regard, an evacuated glass tube solar water heating system is simulated in Transient Systems Simulation Program (TRNSYS®) using low global warming potential (GWP) refrigerants. Parametric analysis is carried out to determine optimal sizes and configurations of solar collectors, heat exchangers, tank volumes and heights for annual performance assessment of solar water heaters. The optimized model was dynamically simulated under diverse weather conditions of Pakistan (Karachi), Australia (Melbourne) and China (Beijing). Our results show an optimal selection of solar water heating system parameters using 6 m2 collector area, 0.42 m3 tank volume, and 1.2 m tank height fulfil single family dwelling heating demands. Moreover, use of low global warming potential hydrofluoroolefins (HFOs) R-1234yz and R-1234yf refrigerants shows even superior thermal performance. The highest annual solar fraction values were recorded for CO 2 (0.720289) and R-410a (0.723428) under various weather conditions. Our findings show that use of synthetic refrigerants slightly improves the performance of system, however, giving weightage to environmental benefits the natural refrigerants take precedence over synthetic refrigerants. This research work recommends an adoption of natural refrigerants as an environmentally superior and sustainable option. [ABSTRACT FROM AUTHOR]