Numerical optimization and experimental study of an active chilled beam with high entrainment efficiency

Abstract

Active chilled beams are increasingly being applied in indoor environments due to their enhanced thermal comfort and quieter environment. However, their relatively low cooling capacity per unit area necessitates more building space. Previous investigations have aimed to enhance the cooling capacity by increasing the entrainment ratio through optimizing single factors such as the nozzle design or the shape of the chilled beam. Additionally, the loss coefficient of the heat exchanger used for simulations was generally simplified to a constant value, potentially causing errors since the induced airflow velocity was typically low and fell within a nonquadratic resistance region. A simulation method for chilled beams that uses the inertial resistance coefficient and viscous resistance coefficient is proposed herein to more accurately reflect the variation in coil resistance with airflow velocity. In addition, the effects of the nozzle position, mixing room length, heat exchanger angle, and guide vanes on the entrainment ratio of the chilled beam were systemically optimized based on the proposed simulation method. To validate the effectiveness of this new simulation method, full-scale experiments were conducted. The results showed that the average error between the simulation and experimental values was approximately 5 %, confirming the accuracy of the simulation method. Under different primary air velocities (ranging from 4 m/s to 13 m/s), the optimized active chilled beam improved the entrainment ratio by 27.23–84.70 %, thereby enhancing the cooling capacity by 23.78–82.97 %. Additionally, the optimal nozzle spacing was determined to be 60 mm. These findings underscore the potential for significant design optimizations in active chilled beams to enhance their cooling efficiency and overall performance in indoor environments.