REFINING THE USE OF EVAPORATION IN AN EXPERIMENTAL DOWN-DRAFT COOL TOWER

Direct evaporative cooling has long been recognized as an energy-effic ient and cost-effective means for space conditioning in hot dry areas. In order to extend the use of evaporative cooling to include exterior or semi-enclosed spaces, a down-draft evaporative 'cool tower' was in tegrated in the project of a 500 m(2) glazed courtyard located at the heart of a building complex in the arid Negev Highlands of southern Is rael, designed by the authors. The present article describes the devel opment of the cooling tower system, undertaken in three phases: (i) Pr ototype analysis. Performance of a small-scale tower was monitored, an d comparisons were drawn between varying rates and mechanisms of water and air supply. The results indicated a potential for substantial tem perature reduction in the order of 10 degrees C under summer daytime c onditions, but a meager cooling output when using a natural draft syst em. Mechanical-forced air Bow was thus utilized in the actual tower. ( ii) Field monitoring. The cool tower, approximately 10 m in height and 10 m(2) in cross-sectional area, was operated and monitored during a summer season; its performance was analyzed using a series of water su pply mechanisms and operating modes. The system produced a peak coolin g output of just over 100 kW, with a wet bulb temperature depression o f close to 85-95% during all hours of operation, and a water consumpti on rate of approximately 1-2 m(3)/day. (iii) Refinement. Potential imp rovement in the system's operation was investigated through the develo pment of a wind capture mechanism for increasing inlet pressure and ai r flow to the space. Both fixed and dynamic capture units were investi gated, with wind speed and direction as well as internal air speeds me asured in the small-scale prototype tower. The wind capture unit with the simplest configuration and best performance is recommended for fut ure integration in the full-scale tower.