Thermal modelling and optimization of low-grade waste heat driven ejector refrigeration system incorporating a direct ejector model

This paper presents the modeling and optimization of an ejector refrigeration system (ERS). Engineering Equation Solver (EES) has been used for modeling. These models have been validated against published experimental results. Refrigerant R245fa is used as a working fluid. A new analytical model for predicting the optimum (on-design) performance (entrainment ratio) of ejectors is presented. The analytical model of the ejector is validated against two sets of published experimental data and good agreement is established with an average error of 3.4%. The presented ERS model has also been validated with two sets of published experimental results and an average error of 2.9% is obtained. The ERS model is further compared with a model developed in EBSILON (a commercial tool). The results show that for the optimum design of an ERS, the generator pressure increases linearly with heat source temperature while the output (refrigeration effect) increases exponentially. For the case study, the designed ERS produces 1.8 MW of cooling with estimated annual savings of S$0.42 million while operating at 0.3 COP. The presented models can be used for designing ejector and ERS for various applications.