Exploring a new approach to ancient Qanat techniques using earth-air and water-air heat exchangers for efficient natural cooling

• New method to cool semi-open urban spaces with Earth-Air and Water-Air exchangers. • Full-scale design of a hybrid 21st century Qanat for passive outdoor cooling. • Soil and water thermal regeneration strategies validated through experimentation. • Nighttime evaporative cooling reduces soil temperature to 23 °C. • The system achieves a drop of 8 °C and provides 20 kWh of cooling during the day. The growing demand for sustainable climate adaptation in cities has intensified interest in passive, energy-efficient cooling systems, especially for semi-open public spaces where conventional air-conditioning solutions are often inefficient. This study proposes a novel reinterpretation of the Persian Qanat system, integrating it with contemporary engineering through Earth-Air and Water-Air Heat Exchangers to create nature-based infrastructure for urban cooling. The experimental set-up is installed at full scale in a public space and includes buried ducts interacting with the soil and submerged ducts connected to a water reservoir named Qanat. The system operates in two phases: daytime cooling by passive heat exchange and nighttime regeneration using evaporative and radiative cooling to restore thermal capacity. Performance was assessed through continuous environmental monitoring, including air, soil and water temperatures, and cooling energy calculations. The results indicate air temperature reductions of up to 8 °C between the inlet and outlet of the ducts during the hottest hours of the day. At night, evaporative regeneration reduced the soil temperature to 23 °C, improving the cooling potential for the following day. The energy analysis showed daily cooling values reaching up to 19 kWh. These findings confirm the potential of the system as a scalable and sustainable climate solution, enhancing thermal comfort in urban environments while recovering ancestral techniques adapted through modern design.