Windcatchers are considered as promising passive ventilation and cooling strategy, but the ventilation performance of this system is still of concern in areas with low speed and unpredictable winds. The air short circuiting in windcatchers can reduce its ventilation performance and ability to introduce clean air and remove stale air. The current work aimed to evaluate the indoor environmental quality (IEQ) performance of a two-sided windcatcher fitted with an anti-short-circuit device (ASCD) for improving its performance in low wind speed conditions. Computational Fluid Dynamics (CFD) simulations were performed for different ASCD configurations. The CFD method was verified using grid-sensitivity analysis and validated by comparing the simulation results with wind tunnel data. The results indicated that the average difference between CFD results and previous experimentation was below 10%, therefore indicating good agreement. Building on the findings of the previous research, the study focused on evaluating the impact of the length of ASCD on the achieved fresh air supply rates and air change rate. The length of the ASCD was varied between 5 cm to 50 cm, while the angle was maintained at 80°. The shorter ASCD was still able to minimize the fresh supply airflow short-circuiting to the exhaust stream, and at the same time, it would also require a smaller ceiling space for installation and lower material cost. Hence, the 15 cm ASCD with 80° angle was selected for further analysis in this study. Then, consideration of low wind speed and various directions were studied to evaluate the ventilation performance of windcatcher with ASCD. The study simulated wind speeds between 0.5–2 m/s and two wind directions. Based on the assessment of IEQ factors, including mean age of air and percentage of dead zone, a 0° incident angle demonstrated slightly better results. The achieved fresh air supply rates ranged between 180 L/s to 890 L/s in 45° wind angle, while, for 0°, these values were from 160 L/s to 642 L/s. Likewise, the range of air change rates (ACH) was from 8 ACH to 32 ACH in 0° wind angle and increased to 9 ACH and then to 45 ACH in 45° wind angle.
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