Energy, exergy and economic analysis of an integrated ground source heat pump and anaerobic digestion system for Co-generation of heating, cooling and biogas

Abstract

This study designed and simulated a feasible polygeneration system, which integrated with a ground source heat pump and anaerobic digestion units to co-generate cooling, heating, and biogas for buildings as well as to utilize biomass residues in rural areas. The quantitative investigation of the energy, economics, and exergy of such a system was conducted in a village in Chongqing, China. The results indicated that by incorporating an anaerobic digestion unit, the integrated system could save 21.6% and 32.2% of primary energy, as well as 35.6% and 34.4% of annual costs, when compared to the separated and current systems, respectively. A Sankey diagram of exergy flow showed that exergy efficiency was 32.2%, and the anaerobic digester and heat pump units were the main exergy destruction components. Increasing the operating supplied temperature of the heat pump for the anaerobic digester from 45 °C to 60 °C improved exergy efficiency from 32.2% to 40.7% but decreased the overall energy efficiency ratio from 4.09 to 3.83. In addition, increasing the coefficient of performance (COP) of heat pump units was an effective way to enhance energy and exergy efficiency. The study may aid designers and decision-makers in optimizing the system and its components.