Parametric analysis of an energy-efficient atmospheric water harvesting system (AWHs): Optimizing underground coil configurations for economic water production

Atmospheric water harvesting (AWH) systems have emerged as a critical solution to address global water scarcity, particularly in arid and semi-arid regions where traditional water sources are limited. With over 2 billion people facing water stress worldwide, developing sustainable and energy-efficient water extraction technologies is urgently needed. However, existing AWH methods often suffer from high energy consumption, low yields, or geographical limitations, creating a significant research gap for optimized passive systems. This study investigates an innovative passive AWH system utilizing subsurface geothermal cooling with optimized coil configurations. Four key parameters were analyzed: coil cross-section (rectangular, circular, square, hexagonal), number of coils (8–64), soil type (clay, sandy loam, peat), and coil length (10–40 m). The system employed rectangular stainless-steel coils buried in clay soil at 4.5 m depth, leveraging stable geothermal temperatures for efficient condensation. Results demonstrated that rectangular coils achieved 12.3% higher water yield than circular designs due to superior surface area and drainage. Clay soil enhanced production by 38.5% over peat, while increasing coil length from 10 m to 40 m linearly boosted output by 300%. The system maintained 85.4–85.8% energy savings compared to vapor compression cycles, with peak nighttime efficiency reaching 87.3%. Economically, large-scale configurations (64 coils) achieved a payback period of just 1.2 years. These findings validate passive AWH systems as scalable, low-energy solutions for water-scarce regions, with geometric and soil optimizations significantly improving performance.