Thermo-economic and environmental assessment of hybrid vapor compression-absorption refrigeration systems for district cooling

Abstract

District cooling plants are predominantly based on vapor compression refrigeration cycles with detrimental environmental impacts due to fossil-based electricity. Vapor absorption refrigeration cycles promise operating improvements and emission reductions in vapor compression-absorption refrigeration system configurations. However, the use of conventional vapor absorption refrigeration working fluids and the limited studies of systems with capacities that are relevant to district cooling plants, prohibit their scaling-up. This work compares the thermodynamic, environmental, and economic performance of seven configurations of the vapor compression refrigeration cycle with a double-effect vapor absorption refrigeration cycle that employs either the conventional ammonia/water or the novel acetaldehyde-N,N-dimethylformamide working fluid. These three cycles are compared with the cascade and parallel vapor compression-absorption refrigeration system configurations, with ammonia/water or acetaldehyde-N,N-dimethylformamide in the vapor absorption refrigeration. The coefficient of performance of the vapor compression refrigeration unit in the cascade configurations is 252% higher than the stand-alone vapor compression refrigeration configuration. The stand-alone vapor absorption refrigeration coefficient of performance with the novel fluid acetaldehyde-N,N-dimethylformamide is 9.1% higher than that of the vapor absorption refrigeration with ammonia/water. The cost per ton of cooling and the total equivalent warming potential of the cascade vapor compression-absorption refrigeration system with acetaldehyde-N,N-dimethylformamide are 65% and 67.8% lower than those of the stand-alone vapor compression refrigeration. The electrical energy utilization factor is 30.5% lower for the acetaldehyde-N,N-dimethylformamide fluid compared to ammonia/water, in the cascade configuration.