Exact analytical modeling of a solar-ventilated modernized qanat for atmospheric water harvesting: Decoupling proof and closed-form solutions for Chabahar's humid climate

Ghassemi, Saleh

doi:10.22060/aest.2026.26301.1013

Exact analytical modeling of a solar-ventilated modernized qanat for atmospheric water harvesting: Decoupling proof and closed-form solutions for Chabahar's humid climate

Document Type : Review Article

Author

Saleh Ghassemi

Department of Mechanical Engineering, South Tehran Branch, Islamic Azad University, Tehran, Iran

10.22060/aest.2026.26301.1013

Abstract

Arid-coastal regions face a paradoxical coexistence of acute water scarcity and abundant atmospheric humidity,
demanding low-carbon harvesting solutions. This study develops an exact one-dimensional analytical
framework for a modernized, solar-ventilated underground Qanat equipped with horizontal aluminum fins,
designed for passive atmospheric water harvesting in Chabahar, Iran—a hot-humid coastal city subject to
Indian Ocean monsoons. Moving beyond conventional lumped-parameter and numerical approaches, we
rigorously prove the mathematical decoupling of the sensible heat and species transport equations under
constant ground-temperature boundary conditions, yielding explicit closed-form solutions for the spatial
evolution of air temperature and humidity ratio. Applied to a 500-m finned tunnel at 20 m depth under peak
summer conditions (40°C, 92% RH), the model reveals two critical design parameters: the thermal and
mass penetration depths (𝛿_ℎ ≈ 218 𝑚 𝑎𝑛𝑑 𝛿_𝑚 ≈ 246 𝑚), demonstrating that over 99% of
condensation occurs within the first 250 m of the tunnel. At an optimized airflow velocity of 1.5 m/s—
analytically determined as the thermodynamic optimum balancing residence time and fan power—the system
yields 𝟑𝟕𝟖 𝑳/𝒉 of freshwater, equivalent to 𝟏𝟑𝟔 𝒎³/𝒎𝒐𝒏𝒕𝒉 under 12 h/day operation. The specific energy
consumption is merely 𝟎. 𝟑𝟕 𝑾𝒉/𝑳, over three orders of magnitude lower than conventional vaporcompression
atmospheric water generators. A parametric sensitivity analysis confirms the robustness of the
design and enables rapid optimization without computational fluid dynamics. The proposed modernized
Qanat represents a scalable, off-grid, mathematically optimized solution bridging ancient Persian hydraulic
heritage with modern renewable energy integration for the water-energy nexus in arid-coastal climates
worldwide.

Graphical Abstract

Keywords

Atmospheric

Harvesting

Qanat

Exchanger

Subjects

Energy Storage and Conversion

References

[1] United Nations World Water Development Report, Water for prosperity and peace. UN-Water, 2023.

[2] Iran Meteorological Organization, Annual climate report: Sistan-Baluchestan Province. Tehran, 2023.

[3] H. Kim, S. Lin, N. K. Chaudhary, A. Tiraferri, Y. Xia, and J. Zhang, Energy performance of atmospheric water generators: a review of technologies and thermodynamic cycles. Appl. Energy 268 (2020) 114953.

[4] H. E. Wulff, The qanats of Iran. Sci. Am. 218 (1968) 94–102.

[5] N. K. Bansal, R. D. Mathur, and M. S. Bhandari, A study of underground cross-sections for use as air-heat exchangers. Build. Environ. 20 (1985) 117–125.

[6] A. R. Al-Ajmi, D. L. Loveday, and V. I. Hanby, The cooling potential of earth-to-air heat exchangers for domestic buildings in a desert climate. Energy Build. 38 (2006) 1049–1056.

[7] M. Benkert, K. Olesen, and T. Müller, Ground-coupled air systems for industrial ventilation: a state-of-the-art review. Renew. Sustain. Energy Rev. 145 (2021) 111102.

[8] O. T. Farouki, Thermal properties of soils. Trans Tech Publications, Clausthal-Zellerfeld, 1986.

[9] M. A. Al-Saffar and H. H. Al-Kayiem, Solar-powered forced ventilation for underground cooling ducts in hot-humid climates. Sol. Energy 235 (2022) 412–425.

[10] L. Zhang, H. Wang, and Y. Chen, Battery-integrated PV blowers for off-grid climate control: design and optimization. Energy Convers. Manag. 278 (2023) 116689.

[11] G. Mihalakakou, On the thermal performance of underground pipe systems: parametric and sensitivity analysis. Renew. Energy 26 (2002) 133–143.

[12] V. Badescu, Simple and accurate models for earth-to-air heat exchangers. Energy 29 (2004) 2089–2102.

[13] P. M. Congedo, G. Colangelo, and G. Starace, CFD simulations of horizontal ground-coupled air heat exchangers for building climate control. Energy Build. 54 (2012) 411–419.

[14] D. Wu, Y. Li, and Z. Zhao, Numerical optimization of finned earth-air heat exchangers for humid climates. Appl. Therm. Eng. 178 (2020) 115582.

[15] R. K. Shah and A. L. London, Laminar flow forced convection in ducts. Academic Press, New York, 1978.

[16] J. L. Threlkeld, Thermal environmental engineering, 2nd ed. Prentice-Hall, Englewood Cliffs, 1970.

[17] A. Leroy, M. Alaei, and D. Bross, Radiative atmospheric water harvesting: a review of materials and system designs. Joule 5 (2021) 2748–2775.

[18] ASHRAE, ASHRAE handbook—fundamentals. American Society of Heating, Refrigerating and Air-Conditioning Engineers, Atlanta, 2021.

[19] D. Beysens, I. Milimouk, V. Nikolayev, D. Muselli, and G. Marcillat, Using radiative cooling to harvest atmospheric water. Atmos. Res. 84 (2007) 155–167.

[20] F. P. Incropera, D. P. DeWitt, T. L. Bergman, and A. S. Lavine, Fundamentals of heat and mass transfer, 8th ed. Wiley, Hoboken, 2017.