Investigation of a geothermal-solar cooling unit based on a compressor-assisted absorption chiller

• A hybrid absorption chiller with a mechanical compressor is examined. • Geothermal energy and photovoltaics drive the unit during the cooling season. • The analysis is dynamic for the case study of Lesvos Island in Greece. • The increase of the cooling production is 21.21 % compared to the conventional unit. • The seasonal energy and exergy efficiencies are 28.86 % and 15.41 % respectively. The objective of this work is the design of a hybrid absorption chiller that is fed by renewable energies. A single-effect absorption chiller operating with LiBr/water working pair is the main device of this work which incorporates an extra mechanical compressor between the evaporator and the absorber. The heat input in the hybrid system is given by a geothermal heat source of 92 ο C driving temperature, while the compressor is fed by electricity produced by photovoltaics. The system operates in hybrid mode only when there is available solar irradiation. The analysis is parametric, but there is also dynamic analysis through an hourly-based model. The studied period is from May to September when there is cooling demand, and the studied location is Lesbos Island in Greece. It was found that the hybrid chiller driven by geothermal and solar energy leads to 21.21 % higher cooling production during the season compared to the conventional absorption chiller driven by a geothermal field. The increase is higher in the warmest months, something that indicates the high importance of the compressor assistance in the system. However, the cooling production during the warmest months is lower compared to the other summer periods due to the rise in the system’s heat rejection efficiency and the reduction of PV output during the warmest periods of the day. The seasonal system energy efficiency was found to be 28.86% and the respective exergy efficiency at 15.41 %.