Roof ponds combined with a water-to-air heat exchanger as a passive cooling system: Experimental comparison of two system variants.

This paper evaluates two roof pond configurations combined with a water-to-air heat exchanger (WAHE). Test cells of 1.35 m × 1.35 m x 1.35 m with the same thermal properties, except for the roofs, are built in a hot-dry climate with mild winters. They are connected with a WAHE placed inside the roof pond's water by a pipe through which the indoor air is re-circulated. The first roof consists of a 0.35 m deep water pond covered with a floating polystyrene insulation 0.03 m thick, and a spray system located 0.5 m above it that operates at night. The second roof is covered with an aluminum plate separated by a 0.10 m air gap above a 0.25 m deep water pond. We ran multiple series and compared the results to a control cell that had a California energy code compliant insulated roof. Predictive equations are developed to dimension the WAHE system. Results demonstrate that the cells with roof ponds have better cooling performance than the code compliant control cell. The best performance is obtained in the cell with the WAHE operating continuously. In this case, the indoor temperature stayed below 24 °C even with ambient temperatures above 35 °C. • WAHE systems integrated in roof ponds provide an additional cooling opportunity. • Test cells have been monitored for over two years in a hot and dry climate. • The benefits of integrating WAHE in roof ponds are assessed with promising results. • Predictive equations to dimension the WAHE system are developed. [ABSTRACT FROM AUTHOR]