Study on flow characteristics of exhaust shaft with parallel fans in high-rise residential buildings

Abstract

The exhaust shaft is often used to centrally extract cooking fumes captured by parallel fans on each floor of high-rise buildings. Inadequate airflow rate and excessive pressure in the exhaust shaft lead to poor ventilation and unsatisfactory air quality in kitchens. This issue is made worse by mixed installations of exhaust fans with different dynamic performances. In this study, the flow characteristics in the exhaust shaft with parallel fans are investigated by full-scale experiments and computational fluid dynamics (CFD). Based on the orthogonal experimental design, the cross-sectional area, concurrent operating rate, operating position distribution, and P-Q curves are key factors affecting the flow rate distribution significantly. Mixed installation of fans deteriorates the uniformity of the flow distribution along the shaft by even 62.6%. The competition for flow rate between different types of fans is obeying the Matthew effect. Concentration at the bottom and more simultaneous operations exacerbate this problem. An 28% enlargement in the shaft size increases the flow rate by 28.9% and improves the uniformity of the flow distribution by 50%. The stack effect is positive and unstable, with up to a 6.49% increase in system flow rate as a function of the cooking heat intensity. This work can provide guidance for the design of centralized exhaust systems in high-rise residential buildings.