Desiccant solutions, membrane technologies, and regeneration techniques in liquid desiccant air conditioning system

Liquid desiccant air dehumidification has gained substantial attention recently due to its attractive energy-saving capability, high moisture retention, and low regeneration temperature. However, there are still unresolved limitations in liquid desiccant air conditioning systems (LDACs). Among on-going studies are the search for greener desiccant solvents, high-performance membrane, and regeneration techniques hybridization. This review discusses up-to-date development of the performance influential components of LDACs, such as desiccant properties, regeneration techniques, membranes, energy sources, and hybrid system configurations. The corrosive nature of conventional halide salt solutions, non-biodegradability and high viscosity property of most ionic liquids necessitate the search for alternative solvents in LDACs. Deep eutectic solvents (DES) properties, such as non-corrosive, hygroscopic, biodegradable, and low viscosity idealize promising alternative desiccant solutions. Therefore, DES may be usefully explored and further investigated in LDACs to establish the degree of their capacities in replacing conventional desiccants. Non-thermal regeneration techniques and nanoparticle enhanced membranes were also found to improve the overall energy performance of the LDAC system. Non-thermal regeneration techniques can operate below 40°C and reduce energy utilization between 10% and 50% in indoor space cooling. The coefficient of performance (COP) of this regeneration category is capable of being as high as 6, which is an indication of its promising energy-saving propensity. Highlights: Review on liquid desiccant materials and the potential of deep eutectic solvents as bio-desiccants for air dehumidification. Nanoparticles enhanced ion exchange membrane tendency to eliminate membrane fouling and improve regeneration performance. Non-thermal liquid desiccant regeneration techniques eliminate re-cooling energies requirement in LDACs.