Falling-Film technique

The pilot is being developed in the Ágora of the Cartuja Qanat Urban Laboratory, a semi-open space of 750 m², bioclimatically conditioned using cold water naturally cooled through passive climate control strategies. This space features the pioneering integration of a falling-film system that enables the production of cold water by using the sky as an environmental heat sink. The system operates by creating a thin water film that flows over photovoltaic panels, enhancing thermal dissipation mainly through longwave radiation and, to a lesser extent, through evaporation.

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The falling-film system is integrated with the photovoltaic installation via a water pumping and storage system known as a qanat. The pilot includes 380 m² of roof area equipped with this technology and an 85 kW photovoltaic plant. Experimental tests conducted during the summer of 2025 show an average thermal drop of 4.9°C in the recirculated water between the qanats and the falling-film system, with an average reduction of 2.65°C over three hours of nighttime operation. These results confirm the system’s high capacity to dissipate heat through combined processes of nocturnal radiation, convection, and evaporation.

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Energy analysis indicates a cooling power of 152.4 kW, equivalent to 907 W/m² of wetted surface area, with a total dissipated energy of approximately 2.72 kWh/m². The system’s electrical consumption is limited to 557 kWh, achieving a coefficient of performance (COP) of up to 32.4, with typical values between 15 and 20 under summer conditions, and water consumption below 3%.

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Overall, these results confirm the high thermal and energy efficiency of the system as a regenerative nocturnal heat sink, enabling daily recharging of the qanat water and ensuring the Ágora’s passive, continuous, and resilient operation during extreme heat events.