Abstract
In year-round hot climatic conditions, conventional air conditioning systems consume significant amounts of electricity primarily generated by conventional power plants. A compression-assisted, multi-ejector space cooling system driven by low-grade solar thermal energy is investigated in terms of energy and exergy performance, using a real gas property-based ejector model for a 36 kW-scale air conditioning application, exposed to annually high outdoor temperatures (i.e., up to 42 °C), for four working fluids (R11, R141b, R245fa, R600a). Using R245fa, the multi-ejector system effectively triples the operating condenser temperature range of a single ejector system to cover the range of annual outdoor conditions, while compression boosting reduces the generator heat input requirement and improves the overall refrigeration coefficient of performance (COP) by factors of ~3–8 at medium- to high-bound condenser temperatures, relative to simple ejector cycles. The system solar fraction varies from ~0.2 to 0.9 in summer and winter, respectively, with annual average mechanical and overall COPs of 24.5 and 0.21, respectively. Exergy destruction primarily takes place in the ejector assembly, but ejector exergy efficiency improves with compression boosting. The system could reduce annual electric cooling loads by over 40% compared with a conventional local split air conditioner, with corresponding savings in electricity expenditure and GHG emissions.
Highlights
C were sized to meet medium- and high-bound ejector critical temperatures/pressures, respectively, which is at the expense of a reduced ejector entrainment ratio and overall refrigeration sub-system coefficient of performance (COP)
The multi-ejector refrigeration system effectively triples the operating condenser temperature range of a single ejector system to cover the range of annual outdoor conditions, while avoiding a severe degradation in performance at high condenser temperatures through compression boosting
The multi-ejector system effectively triples the operating condenser temperature range of a single ejector system to cover the range of annual outdoor conditions while maintaining comparable performance through compression boosting
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. Solar ejector-based refrigeration systems, which are the focus of this study, can convert low-grade thermal energy gained using solar collectors into mechanical work to compress the working fluid of a thermodynamic refrigeration cycle, and can deliver refrigerant evaporation temperatures in the 5–10 ◦ C range [6]. The performance assessment of ejector-based refrigeration systems has generally focused on fixed boundary conditions and either parametric analysis or mathematical optimization, rather than annual or seasonal performance evaluation with time-variable conditions in practical space cooling applications A few such studies have been reported [18,19] with attention to harsh climatic conditions, such as are representative of the Middle East and North Africa (MENA).
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
