Experimental investigation and simulation of water cooling by natural evaporation

Abstract

A setup of water cooling by natural evaporation is investigated. It includes a shallow water tank, insulated and covered with a thin aluminum plate in complete contact with the water. A dark-color fabric was fixed stretched on the plate, which was continuously wetted to cause natural evaporation by solar radiation. The setup was placed on a building rooftop of the University of Patras, Greece. Measurements during a warm period showed significant decrease in water temperature maintained lower than ambient air temperature by 2–16°C, with differences greater than 5°C with 57% probability. Moreover, a computational model was developed and implemented. It is based on energy balance of the water in the tank using local climate recordings (air temperature, relative humidity, wind speed, and solar radiation). The water temperature predictions agree very well with the measurements (3.5% normalized rms deviation). Since the water temperature was always lower than the ambient air temperature, and the operating performance of the setup was high enough, this methodology could be developed for sustainable house cooling during the warmer seasons of the year. This system is environmentally friendly, economically feasible, and sustainable, as it uses water, wind, and solar energy, without emitting greenhouse gases. Statement of Industrial Relevance The proposed technology improves the process of passive water cooling through evaporation of a continuously wetted fabric without losing the cooled water. In parallel, a software was developed that simulated satisfactorily the process. We aim to further improve this technology to make it more easily applicable for mild house cooling, as a renewable and sustainable energy source that saves cooling water and uses wind and solar energy, without emitting greenhouse gases. Moreover, it is environmentally friendly, economically feasible, and operates with high performance. This adds value to the Environmental Engineering Laboratory, the Department of Civil Engineering, and the University of Patras. Novelty or Significance This technology improves the water-cooling process through wet fabric evaporation and is suitable for sustainable house cooling. This is achieved by interposing a thin aluminum plate between fabric and cooling water, in complete contact with them. The evaporating water may be potable or not. The environmentally friendly fabric color allows installations on roofs or in gardens. The structure is simple with common materials, economically feasible with high operating efficiency. The cooling water temperature is maintained from 2 to 16°C lower than ambient air (>5°C with 57% probability). The software developed may be used for designing or assessing such systems.