A novel low-grade heat-driven absorption refrigeration system with LiCl–H2O and LiBr–H2O working pairs

• A novel low grade heat-driven absorption refrigeration system using two working pairs is proposed.
• The intermediate pressure is optimized for better system performance in different operation modes.
• Thermodynamic characteristic of the novel absorption system is investigated.

A novel low grade heat-driven absorption refrigeration system is proposed, where LiCl–H2O with higher vapor pressure is used in the high-pressure cycle and LiBr–H2O with lower vapor pressure is employed in the low-pressure cycle. Effects of key parameters on the system performance are analyzed, and different heat source utilization modes are considered: parallel modes (PM-1 and PM-2) and serial mode (SM). What's more, comparisons among the PM-1, PM-2, SM and the traditional double-stage LiBr–H2O absorption system (TDS) are made. Results show that the PM-1 has much higher COP than the TDS under small ranges of working conditions, with the maximum COP improvement 26.7%, while the PM-2 shows prominent advantages under wider ranges, with the maximum COP improvement 35%. In addition, The PM-1 shows much higher COP than the SM under higher condensing temperature and evaporation temperature, while the SM has much lower heat source outlet temperature which is at most 12 °C lower than that of the PM-1. The intermediate pressure is important for the system performance and the optimum value is 2.27 kPa in the PM-1 and 2.5 kPa in the SM. For the PM-2, the intermediate pressure should be chosen to achieve low circulation ratio in the low pressure cycle.