Dynamic performance analysis of an ejector refrigeration system with a direct-expansion solar generator

Ejector Refrigeration Systems (ERS) can obtain their primary energy source from renewable sources such as solar radiation, which transfers heat to the ERS generator to achieve optimal operation. Direct-expansion solar collectors have been gain attention in systems such as solar heat pumps, avoiding the use of additional subsystems and energy sources and reducing costs and electricity consumption. In this study, the dynamic performance of an ERS with direct-expansion solar generator is assessed by means of a validated mathematical model that couples ERS subsystem operation. The proposed model predicts the global behavior of the cycle by describing mass, momentum and energy transport in each subsystem and by coupling their inlet and outlet conditions. An ERS basic design for average meteorological condition with direct-expansion solar generator is numerically analyzed for different transient operating conditions, in terms of solar radiation and ambient temperature, obtained from the typical meteorological year (TMY) of Mexico City. The results show that in favorable environmental conditions, the system can operate 2.3 h longer than the average day because the generator can maintain the refrigerant vapor phase for a longer period. However, refrigerant overheating increases, causing a reduction in the entrainment ratio (ER) and coefficient of performance (COP). This study shows that the ERS with a direct-expansion solar generator can operate for more than 90% of the TMY, reaching ER values of up to 0.6 and COP of up to 0.5, which are close to conventional ERS.