Thermodynamic, exergy, and life-cycle assessment of a solar-powered air-heated HDH desalination system driven by advanced heat-pump configurations

This study develops a unified thermodynamic–environmental assessment framework for a solar-powered modified air-heated closed-air open-water humidification–dehumidification (AH-HDH) desalination system driven by three heat-pump configurations: a baseline vapor-compression heat pump (BHP), an ejector-expansion heat pump (EEHP), and an ejector-subcooled heat pump with an internal heat exchanger (ESCHP). Unlike previous studies, which typically evaluate thermodynamic, exergy, renewable-energy, or environmental performance separately, the proposed framework integrates first-law and second-law analyses, solar photovoltaic (PV)-battery modeling, solar exergy analysis, life-cycle assessment (LCA), life-cycle climate performance (LCCP), and pollutant emission assessment under identical operating conditions. This enables a comprehensive evaluation of how advanced heat-pump cycle enhancements influence desalination performance, exergy utilization, renewable-energy integration, and environmental sustainability. The heat-pump condenser heats the humid air before dehumidification, while the evaporator simultaneously cools the feed seawater, improving the utilization of both heating and cooling capacities. Model validation showed good agreement with published data, with deviations generally within 1–8% for the heat-pump model and below 2% for the HDH model near the optimum operating region. The ESCHP consistently outperformed the EEHP and BHP, increasing the peak gain output ratio from 6.4 to 8.2, reducing the minimum specific electrical energy consumption from 105 to 83 kWh/m³, and increasing freshwater production from 425 to 460 L/day. Under theoretical upper-bound ideal-component conditions, the ESCHP achieved a maximum GOR of 27.4, a minimum SEEC of 24.5 kWh/m³, and a maximum productivity of 810 L/day across the investigated operating conditions. Total exergy destruction decreased from 1.84 kW in the BHP to 1.43 kW in the ESCHP owing to reduced expansion-device irreversibility. Hourly PV-battery simulations confirmed feasible stand-alone operation with high reliability under the modeled weather, dispatch, and component assumptions, with daytime PV generation supplying the plant load while charging the battery and stored energy maintaining nighttime operation. The LCA, based on 1 m³ of freshwater, showed that the global warming potential decreased from 46.20 to 30.44 kg CO₂-eq/m³, while fossil resource scarcity and fine particulate matter formation were reduced by up to 34% and 36%, respectively. Overall, the results demonstrate that integrating advanced ejector-assisted heat-pump cycles with renewable energy and a comprehensive exergy–life-cycle assessment framework provides an effective pathway for simultaneously improving desalination efficiency, reducing irreversibilities, and minimizing the environmental footprint of decentralized freshwater production systems.