Integration of reversible absorption heat pumps in cogeneration systems: Exergy and economic assessment

Polygeneration energy systems in building applications are widely recognized as an effective way to reduce primary energy consumption and greenhouse gas emissions, thanks to high energy efficiencies and optimal integration of different energy technologies and sources. In the present work, the integration of a reversible absorption heat pump and an internal combustion engine in a novel trigeneration system is proposed. The reversible absorption heat pump, which employs a water-ammonia mixture, is driven by the exhaust gas of the engine, and can produce heating and cooling, alternately. The proposed trigeneration system is presented, and the energy services provided under the heating and cooling operating modes are evaluated. A levelized cost of energy analysis is conducted to evaluate the economic viability of the proposed system. Next, a second-law analysis compares its overall exergy efficiency to those of conventional systems. Finally, the novel trigeneration system is implemented in a case study, namely a large office building located in Pisa, Italy. The integrated optimal sizing and operation are evaluated by using a genetic algorithm-based procedure. The findings show that the system integrating reversible absorption heat pump and cogeneration unit provides valuable economic and energy performance. The exergy efficiency of the system can reach 43%, and cost savings of around 5% and 10% are achieved compared to traditional cogeneration and separate-production system, respectively.