A passive, fan-free condensation cascade for rooftops and cooling-tower retrofit

This document describes a passive condensation cascade for rooftops and for retrofit on cooling towers. Warm, humid air flows downward through a heat exchanger cooled by counter-current water. The air loses heat and water vapor, becomes denser than the outdoor air, and sinks; the density difference can drive the flow without a fan. The system produces distilled water and delivers heated water, for example for preheating tap water in apartment buildings or process water in industry. The cooled air is saturated and requires aftertreatment before use in occupied spaces. Three cases are calculated per square metre of cross-section with verified thermodynamic data (IAPWS-95, CoolProp). As a worked example at an assumed airflow of 0.40 m³/s per m², they give 24, 58 and 170 L/h of distillate and 24, 53 and 136 kW of heat; both scale in proportion to the airflow. An estimate of the passive airflow gives roughly 0.1 to 0.7 m³/s per m² in warm weather and none in cool weather. All figures are calculated, not measured.