Hybrid Radiative-Evaporative Water-Wall: Integrating Persian Qanat, Badgir Wind-Towers, and Modern CoolWave/Radiative Films for Passive Cooling and Water Harvesting in Semi-Arid Cities

Urban heat and water scarcity intensify in Mediterranean and semi‑arid regions. We revisit three ancienttechnologies—qanat (sub‑surface water galleries), badgir (wind‑catch towers) and step‑well cisterns—andretrofit them with two contemporary materials: a SiO₂‑PVDF daylight‑radiative film (ε₈‑13 μm = 0.97) andCoolWave hydrogel panels (latent heat ≈ 2250 kJ kg⁻¹). We report a 1 m² prototype “Water‑Wall” thatcombines (i) radiative sky cooling, (ii) wind‑induced evaporative chilling and (iii) nocturnal dewcondensation. Outdoor tests (Beer‑Sheva, Israel; July–Sept 2025) show average skin‑temperature reductionof 10.8 °C under 1 Sun and nightly water yield of 12.4 L m⁻². Computational fluid dynamics (CFD) coupledwith WRF micro‑climate data predict up to 25 % HVAC energy savings for a reference 100 m² classroom. Thehybrid system demonstrates how heritage water infrastructures can be upgraded to meet SDG 6 andSDG 13 targets with low‑cost (≈ 45 USD m⁻²) materials.