Coupling sorption and compression chillers in hybrid cascade layout for efficient exploitation of renewables: Sizing, design and optimization

The efficient utilization of renewable energy sources should rely on the exploitation of a mix of thermal and electric energy rather than relying on a single energy source. One way to apply this shared generation concept to space heating/cooling and refrigeration in both residential and industrial sector is through hybrid sorption-compression chillers. However, the experience on these systems is still limited and therefore their design and optimization require some efforts. Starting from the experimental experience on the testing of different hybrid cascade chillers, and integrating the measurement with a dynamic model, some considerations on the sizing, design and optimization of hybrid thermal-electric chillers are reported. In particular, design conditions of pre-commercial or commercial systems are evaluated and optimization at different levels is proposed, i.e. on the core components (through the proper design of relative capacities of the units in the cascade and through proper selection of the refrigerant), on the auxiliaries, to reduce their electricity consumption, and on the overall management of the hybrid chiller. Results demonstrated that the higher is the operating temperature lift between evaporator and condenser the higher are the achievable energy savings of a cascade chiller.