Multi-Criteria Decision Making (MCDM) for optimizing split AC performance: an experimental study on CNT/TiO₂-enhanced POE lubricant

Abstract The rising demand for energy and electricity has led to the exploration of innovative approaches to improve energy efficiency in cooling systems. This study experimentally investigates the performance of a split-type air-conditioning system using R-404A refrigerant and CNT/TiO₂ nanolubricants dispersed in polyol ester (POE) oil at mass concentrations of 0.05, 0.1, 0.2, and 0.3 wt%. The objective is to enhance the thermal and tribological performance of the compressor while reducing overall energy consumption. The incorporation of CNT/TiO₂ nanoparticles into POE oil is expected to improve system performance by reducing compressor power consumption and enhancing heat transfer capacity. To ensure effective utilization and uniform dispersion of the nanoparticles, a two-step preparation method was employed. System performance was evaluated in terms of cooling capacity, compressor power consumption, coefficient of performance (COP), and pull-down time. The experimental results demonstrate that a nanolubricant concentration of 0.2 wt% provides optimal performance, resulting in a 16.5% increase in COP, a 13.8% enhancement in cooling capacity, and an 11.2% reduction in compressor power consumption compared to pure POE oil. In addition, evaporator temperature variation over time, compressor energy consumption, and pressure drop across the evaporator were investigated. The pull-down time was reduced by 18%, while the nanolubricant exhibited excellent suspension stability throughout the experimental duration. Overall, the results confirm that CNT/TiO₂ nanolubricants significantly enhance both the cooling capacity and energy efficiency of air-conditioning systems. However, the long-term stability, durability, and large-scale applicability of the nanolubricant require further investigation. Future research should focus on system optimization and lifecycle performance evaluation.