Comparative analysis of compression-absorption cascade heat pump using various ionic liquid-based working pairs

Abstract

The compression-absorption cascade heat pump (CACHP) is an efficient way for clean heating toward carbon neutrality. Nevertheless, the working pair studied at present is only NH3/LiNO3, it is not always the most suitable fluid when used in different situations. In fact, the performance characteristics of CACHP running other working pairs have not been explored. Ionic liquid (IL) working pair is becoming an alternative to the conventional one. But current studies mainly focus on the selection within the same categories, there are few reports on performance comparison among the optimal IL working pairs which come from different categories. Hence the conclusions drawn at present are inadequate to give comprehensive recommendations about the most suitable IL working pairs. To overcome the mentioned research gaps, this work carries out a comparative analysis of the coefficient of performance (COP) for CACHP running various IL working pairs. The obtained results show that when the runnable range is the most important index, Low-GWP/IL and NH3/Salt are more competitive since they can be operated under more negative conditions. When the efficiency is preferred objective, H2O/ILs and NH3/ILs should be recommended, because their achievable maximum COP is 9.54% ∼ 32.78% higher than other fluids. Noteworthy, the generation temperature is not advised to exceed the critical temperature, no matter what kinds of working pairs are operated, especially when the driving source comes from primary energy consumption. As for the heating capacity of 10 kW, the critical generation temperature is 75.53°C or higher for various working pairs under different heating scenarios.