Aerodynamic-assisted plenum windows for improved natural ventilation

Abstract

The COVID-19 pandemic that began in early 2020 has had a significant impact on our lives over the past few years. It has taken many lives and brought a heavy burden of memories to the entire world; this compels us to pay attention to indoor air quality (IAQ). In regard to indoor air quality (IAQ), adequate ventilation is essential for reducing the risk of airborne transmission of various viruses, including influenza, respiratory syncytial virus, and MERS-CoV. Ensuring proper ventilation can help to mitigate the spread of these diseases and promote a healthier indoor environment. Natural ventilation is an ideal way compared with mechanical ventilation as it’s energy-saving. In densely occupied cities like Hong Kong, the noise pollution is quite severe, so there is a growing demand for sound-proof windows with sufficient natural ventilation performance to supply high-quality indoor environment. Among those sound-proof windows, there are sufficient studies on acoustic performance of plenum windows while lacking systematic study on their natural ventilation performance. Especially, there is parametric research on plenum windows installed with rigid cylindrical scatterer arrays to improve their acoustic performance with their influence on natural ventilation unknown. To address the ventilation performance of these plenum windows, we present CFD simulations of nine different layouts of rigid cylinder arrays in a generic isolated building model. This includes one plenum window without a rigid cylinder installed, followed by four distinct layouts of cylindrical scatterer arrays, each consisting of four or six cylinders. The dimensionless cross-ventilation rate (DFR) induced by wind, air changes efficiency (AEE), and factor-optimization were calculated and analysed from the simulations. The benchmark building model was validated using a set of published experimental data and one set of published simulation data. Based on the results, with the increase of number of cylinders, their natural ventilation performance will deteriorate. Among those with same equivalent number of cylinders, the ds type performs the best. The most aero-dynamic optimized design for plenum windows is the one installed with 4 rigid cylinders named (j)V(2, 2)ds. To improve the natural performance of plenum windows further, guide vanes are added in the plenum windows with the rigid cylinders. At first, a comparison was conducted between the scenarios without and with guide vanes in the corner of the front window opening, in order to assess their impact. This consists of cross-ventilation dimensionless flow rate (DFR) induced by wind, air change efficiency (AEE), and factor-optimization (α). The factor-optimization approach shows a 10% improvement can be achieved for the plenum window with a 2x2 cylindrical scatterer array and two guide vanes, considering both the increase in DFR and AEE. The analysis of U/Uref, W/Uref, and vorticity contours and velocity streamlines generated from the aforementioned CFD simulations elucidates the underlying mechanisms involved. A preliminary analysis has been conducted on the potential mechanisms by which the installation of cylinders and guide vanes in plenum windows affects ventilation performance, with a particular focus on flow velocity, the strength of vortices generated indoors, and the shear layer.