Annual space heating and cooling carbon dioxide system based on hybrid techniques of ejector and integrated mechanical subcooling: Optimization and energy, exergy, environment and economic evaluation throughout the world

Abstract

A novel air source transcritical carbon dioxide heating and cooling system employing the techniques of both ejector and integrated mechanical subcooling is suggested. The innovative system is designed to fulfill the annual heating and cooling demands of residential buildings. Different cities from diverse climate zones across the globe are selected as application scenarios. A comprehensive energy, exergy, environment, and economic evaluation model for the system is developed. Coefficient of performance is set as the objective function, and discharge pressure and subcooling degree is optimized using genetic algorithm. The results are compared with the traditional solutions, including baseline system, ejector system, integrated mechanical subcooling system, traditional heating and cooling system using difluoromethane as working fluid, and fossil fuel-fired boiler. The results demonstrate the coefficient of performance and annual performance factor of the new system can be increased by 4.32 ∼ 37.74 % and 7.16 ∼ 38.25 %. The exergy efficiency is 4.24 ∼ 46.02 % and 6.92 ∼ 46.12 % higher than that of the baseline system, ejector system and integrated mechanical subcooling system in heating and cooling mode, respectively. The life cycle climate performance of the new system demonstrates a significant reduction, ranging from 6.67 ∼ 72.90 %, when compared to the other solutions across 10 representative cities. The life cycle cost of the new system can be diminished by 3.44 ∼ 19.11 % in contrast to the baseline system, ejector system and integrated mechanical subcooling system. In comparison with the difluoromethane system, the payback period of the new system is 2.64 ∼ 7.07 years less than that of the ejector system and integrated mechanical subcooling system. This research can serve as a reference for the enhancement and optimization of air source transcritical carbon dioxide heating and cooling systems for residential buildings.