A parametric analysis of the influence of wind speed and direction on the thermal comfort performance of a Passive Downdraught Evaporative Cooling (PDEC) system – field measurements from a Saudi Arabian library

Abstract

Building energy consumption in the desert climate of Saudi Arabia is dominated by cooling demand. Electricity for this cooling is generated predominantly from finite fossil fuel reserves. To improve resource efficiency and decrease carbon emissions, reducing this demand by using more passive cooling approaches is desirable. One system is the passive downdraught evaporative cooling (PDEC) tower. PDEC captures hot, dry winds at the top of a tower and then cools the air by passing it through or over water. This cooler air then flows out from the base of the tower into the building. In this study, a PDEC system in a small Saudi public library was monitored for two summer months. A key aim of this study was to investigate the relationship between local wind speed and direction and the performance of the PDEC towers. A thermal comfort analysis investigated the acceptability limits of indoor temperature using the adaptive thermal comfort model. A parametric analysis of the wind effects was conducted by grouping wind data in to ranges of wind speed and direction and then correlating them against environmental conditions in the library. The results indicated that the PDEC towers could deliver significant cooling for library users. However, the towers' effectiveness was influenced by changes in wind speed, and in a counter intuitive way – stronger wind speeds tended to reduce the tower cooling efficiency.