Compression-assisted absorption cycles using ammonia and various ionic liquids for cleaner heating

To overcome the shortcomings of the conventional working fluids, ammonia/ionic liquids were analyzed for the compression-assisted absorption heat pump. The property models of different ammonia/ionic liquid mixtures and the thermodynamic model of the proposed cycle were established with verified accuracy. The primary energy efficiency and exergy coefficient of performance under various conditions were compared. N, N-dimethylethanolammonium acetate performed the best under favorable working conditions, while 1,3-dimethylimidazolium dimethylphosphate and 1-ethyl-3-methylimidazolium tetrafluoroborate performed better under other conditions. 1,3-dimethylimidazolium dimethylphosphate can operate under the lowest generation/evaporation temperatures. Compared to ammonia/water, ammonia/N, N-dimethylethanolammonium acetate showed quite similar or slightly higher efficiencies under favorable conditions, ranging in 1.026-1.491. The exergy efficiency generally increased first and decreased later with the increase of the generation/condensation/evaporation temperature and the compression ratio. With optimal compression ratios of 1.8-2.1, the maximum primary energy efficiencies were 1.339-1.382 for different ammonia/ionic liquids. The primary energy efficiencies of the compression-assisted absorption heating were improved by 36-69% compared to gas boilers, by 0.2-54% compared to the conventional absorption cycles.