Regenerating liquid desiccants with a thermo-responsive solution for energy-efficient indoor humidity control

Indoor humidity management is crucial to human thermal comfort. Liquid desiccant dehumidification as a sustainable technology is promising to manage indoor humidity. However, the significant heat demand for regenerating liquid desiccants remains a long-standing bottleneck, limiting their widespread application in residential and office buildings. This study proposes a forward osmosis process to replace the conventional liquid desiccant regeneration process, where a thermo-responsive solution draws liquid water from the liquid desiccant via the osmotic pressure difference and then regenerates through liquid-liquid separation upon heating. The feasibility of integrating dehumidification and forward osmosis processes (DEH-FO system) is first assessed using solution properties. Results indicate that liquid desiccants must operate at low temperatures below 290 K and concentrations below 20 wt% to meet the humidity requirement for thermal comfort. Furthermore, the DEH-FO system is theoretically assessed in terms of the outlet air humidity ratio, energy efficiency, exergy efficiency, and total cost rate. The DEH-FO system can supply the air with a humidity ratio of 12 g/kg, while reducing heat consumption by an order of magnitude compared to current heat-driven dehumidification techniques. The exergy efficiency of the proposed system can rise from 36 % to 65 %, indicating a significant improvement. The DEH-FO system enables solar energy captured from rooftops to fulfill the heat consumption required for the dehumidification system in high-rise buildings exceeding 30 floors, taking Hong Kong as a case study. This study explores an innovative and energy-efficient strategy to reduce reliance on heat sources for a liquid desiccant dehumidification system, advancing its adoption in residential and office buildings for effective indoor humidity control and thermal comfort.