Optimising the performance of passive Downdraught Evaporative Cooling (PDEC) towers for Saudi housing: Investigating the impact of architectural form

Abstract

Saudi Arabia is ranked the number one oil-consuming nation in the Middle East. Buildings consume approximately 75% of the total electricity generated in Saudi Arabia, of which 44% goes to the residential sector, and air conditioning represents about 50% of the aggregate national electrical demand. To improve resource efficiency, reducing this demand by using more energy efficient cooling systems is desirable. Passive cooling techniques could be a sustainable, low-energy alternative to conventional air-conditioning systems when appropriately integrated within a building. Passive Downdraught Evaporative Cooling (PDEC) has the potential to be one of the most efficient and cost-effective passive cooling systems in the hot and arid climate of Saudi Arabia. Despite the emergence of such passive system in the Middle East, there is still a lack of research in the region on the actual performance and applicability of PDEC systems, particularly for residential buildings. Furthermore, there is a shortage of parametric investigations about the impact on PDEC performance when a PDEC tower and a building are integrated together. Therefore, this study firstly investigated the actual performance of an existing PDEC building in Saudi Arabia. Next, a validated computer simulation model was developed of a PDEC tower. Finally, this model was applied to a typical Saudi house to study the integration of a PDEC tower in this type of buildings and to analyse the effect of architectural design on the PDEC performance. The study was addressed in three different stages. The first stage involved field monitoring (1688 recorded hours) and assessment of an existing PDEC building in Saudi Arabia to determine its actual effectiveness. The results indicated that the PDEC towers could deliver significant cooling for library users. The temperature difference between the external dry bulb air temperature and that delivered at the bottom of the PDEC towers ranged from 6°C in the early morning to 22.5°C during the hottest parts of the days (~3.00pm). The PDEC cooling efficiency reached up to 94% during peak times. It was also revealed that the towers' effectiveness was negatively influenced by stronger wind speeds, leading to reduced tower cooling efficiency from above 90% to below 60%. The second stage included the development, modelling, and validation of an initial computational model to study the performance of a spray PDEC tower in Saudi Arabia. In the third stage, a Saudi villa was monitored and computationally modelled in order to virtually assess a PDEC tower’s performance within the house using parametric changes for each case examined. The research found that modifying the window opening design of the cooled spaces could considerably improve the cooling efficiency of the PDEC tower. The results showed that cooling energy savings increased from 22.2% in the first PDEC case to 36.2% in the optimum case.