Influence of application of accurate airflow resistance on openings with different configurations of shading devices on the building thermal performance

With large cooling potentials, natural ventilation is the main passive technique applied to tropical buildings. In computational simulations studies, the discharge coefficient (Cd) is required as a parameter to characterize the resistance the opening imposes to the airflow. As shape and angle of shading devices influence the airflow through the openings, accurate setting of Cd has a significant impact on the characterization of the cooling phenomena. This study investigates the effect of accurate Cd of five different configurations of shading devices. Using a classroom as a generic case, corrected Cd obtained from CFD models were used to simulations on the software EnergyPlus identifying airflow levels and periods of thermal comfort under the climate conditions of São Paulo. Results indicate that using 0.6 as a Cd value in the simulations is adequate for openings with shading devices that have a lower level of obstruction on the façade. However, for geometries with several slats and low angles, Cd values can be as low as 0.34. In this case, the airflow through the room decreases in average 15% in relation to the model that used usual Cd. The outcomes contribute to a more precise prediction of natural ventilation of buildings with shaded openings.