•CFD model is applied to analyse the performance of single-phase ejectors with R134a.•A multi-objective optimisation algorithm is used to improve the ejector performance.•Four ejector cooling cycles are compared against the basic cycle through the SEPR.•Geometrically optimised ejectors are a must to achieve the desired performance.•A thermally-driven sub-cooler with ejector improved the SEPR up to 23%. Global energy consumption for cooling applications is increasing every year, accelerating the fossil fuels consumption and the CO2 emissions. To improve the performance of the vapour compression cycles, ejectors can use the low grade wasted energy as a means of heat recovery. Several proposals have been studied to improve the global Coefficient Of Performance of the ejector cycles. However, very few optimised the ejector geometry to obtain the maximum performance. A CFD-based multi-objective optimization of the ejector geometry and a thermodynamic model of the cooling cycle have been coupled to obtain the best performance of four types of thermally-driven ejector cycles. The results predicted improvements of up to 13% and 23% in the rated Coefficient Of Performance and the Seasonal Energy Performance Ratio, respectively, compared with the basic vapour compression cycle. Using geometrically optimised ejectors makes it possible to achieve a high level of performance that justifies the use of this technology.