A numerical approach to exergy-based sustainability and environmental assessments of solar energy-powered district cooling systems using actual operational data

Abstract

The demand for cooling in buildings has been increasing at a higher rate than heating and more energy is expected to meet this demand. Solar energy can be vital in fulfilling this energy requirement based on its unique renewable energy features. The solar thermal powered absorption cooling (STAC) and solar electrical assisted vapor compression cooling (SEVC) systems are assessed in this study by conducting the conventional and advanced exergy analyses and environmental assessment. Determining the unavoidable part of exergy destruction as in this study provides a unique convenience in design problems where the thermodynamic performances of distinct systems are compared. Under current technological conditions removing the thermodynamically optimized parameters of the designed systems from the minima-maxima dichotomy and rationally evaluating the avoidable part of exergy destruction will protect the researcher from the arbitrariness of the design. The obtained results based on conventional exergy analysis in a component manner showed that priority should be given to solar technologies due to their lowest exergy efficiencies (0.16 for a photovoltaic (PV) and 0.19 for a collector) and sustainability indices (1.20 for the PV and 1.24 for the collector). Advanced exergy analysis results revealed that the exergy destruction significantly originated from the unavoidable part of the total exergy destruction of the components for the solar technologies (93.02 % for the collector and 96.41 % for the PV) cooling (92.12 % for the absorption and 98.42 % for the vapor compression) and overall system (99.92 % for the SEVC and 99.99 % for the STAC). The initial estimated carbon dioxide emissions from the STAC were 0.28 kg CO2-eq attributed to pump power consumption. However these emissions varied dynamically for the SEVC ranging from 0 (when the solar PV field meets the total power) to 5.58 kg CO2-eq (when radiation is not available) depending on the power-consuming components (compressor and pumps).