Simulation of classroom modeling on fourfaced windcatcher for optimum indoor natural ventilation rate

Abstract

Natural ventilation, a sustainable alternative to conventional air conditioning systems, has become an attractive solution for providing a good indoor air environment. The importance of maintaining sufficient Ventilation Rate (VR) and Temperature Performance (TP) particularly in schools is recognized as the main contributing factor to health and learning performance of students. One of the oldest natural ventilation systems that is still being used today is the windcatcher. Although many advancements were made in windcatcher design, there are still unexplored areas especially in terms of design parameters including cross-section, height and its placement on the building roof as well as combination with window. Thus, the present study aims to develop a windcatcher configuration that is appropriate for school building in the hot and dry climate of Iran. The research method involved experimental wind tunnel test and computational fluid dynamics (CFD) simulation. Firstly, a smallscale test in a wind tunnel was conducted to compare the CFD simulation with the experimental results. Secondly, to determine the optimum configuration, a four-faced square windcatcher with varied configurations at different locations on the classroom roof was simulated. The results showed that the average difference between CFD and experimental results was 13% which was in the acceptable range. The findings also proved the potential of the windcatcher centrally positioned on the roof in delivering fresh air inside the classroom. Finally, the windcatcher performance in terms of VR and TP was evaluated at different wind speeds and directions along with a closed/open window of a classroom in Yazd climate. It was found that in both window conditions, the windcatcher can meet ASHRAE recommendation of 8 L/s per person ventilation rate at outdoor wind speed of 3 m/s which is the average of wind speed in Yazd. Moreover, the windcatcher was able to provide maximum temperature performance up to 95% at an air incident angle of 15° in open window condition. The study also demonstrated the positive effect of the combination with an openable window on the windcatcher performance. Overall, it can be concluded that the developed windcatcher contributes significantly to improving VR and TP inside the school classroom in the hot and dry climate of Iran.