Ejector subcooling carbon dioxide combined heating and cooling system driven by waste heat: Energy, exergy, environment and economic evaluation

To address the annual demand for environmentally sustainable space conditioning in the building sector, a novel ejector subcooling transcritical carbon dioxide combined cooling and heating system driven waste heat is proposed. The energy, exergy, environment, economic analysis models are developed, and the energy efficiency is also optimized. Typical residential buildings located in 10 representative cities from 7 different climate zones are chosen as application scenarios. Besides the annual performance indicators, environmental and economic performance indicators are compared with 6 traditional solutions. The results show that in contrast to the baseline system, the discharge pressure can be decreased by 0.47 %∼4.74 %. In both heating and cooling mode, the coefficient of performance improvement ratio of the new proposed system using R1234ze(Z) and R1270 is the highest, reaching 20.65 % and 29.76 %, respectively. Cairo has the highest annual performance coefficient (APF) improvement ratio, with the APF of new system being 10.90 %∼21.05 % higher than the baseline system. APF of new proposed system is generally improved by 21.82 % to 42.81 % compared with the baseline system. In addition, in comparison with the coal-fired boilers and traditional air conditioning combination solution, the carbon emissions are reduced by 38.43 % throughout the lifecycle. In contrast to the direct electric heating and traditional air conditioning combination, the life cycle cost is decreased by 47.95 %. This study can serve as a theoretical reference for optimizing carbon dioxide combined heating and cooling system, as well as a new approach for year-round residential space heating and cooling.