March 2013 Publication year: 2013 Source:Building and Environment, Volume 61
Computational Fluid Dynamics (CFD) simulations can be used to assess indoor natural ventilation by solving the interaction between the urban wind flow and the indoor airflow. The air exchange rate (ACH) can be obtained from the simulated volume flow rates through the ventilation openings or by the concentration decay method that is often used in experimental studies. This paper presents 3D unsteady Reynolds-averaged Navier–Stokes (RANS) CFD simulations to reproduce the decay of CO2 concentration in a large semi-enclosed stadium. The study focuses on the hours after a concert, when the indoor CO2 concentration generated by the attendants has reached a maximum. The wind flow, indoor airflow and dispersion of heat, water vapour and CO2 are modelled on a high-resolution grid based on a grid-sensitivity analysis. The simulations are validated with on-site measurements of wind velocity and CO2 concentration decay. The validated CFD model is used to analyse the significant horizontal and vertical CO2 concentration gradients in the stadium, showing local differences at t=300s up to 700ppm (i.e. 37% of the maximum of 1900ppm). A specific piecewise-linear technique is applied for the concentration decay method to determine the ACH values for smaller time-intervals. This is needed because the plotted semi-logarithmic decay curve itself is not linear because the ventilation rate changes over time, due to the changing buoyancy forces. It shows that the ACH values decrease from about 2h−1 at the beginning of the concentration decay simulations to about 0.3h−1 at the end.
Graphical abstract
Highlights
► CFD simulations have been performed to model CO2 concentration decay from a large stadium. ► Effects of air temperature and water vapour concentration on flow field are included. ► Coupled modelling approach to model indoor and outdoor airflow simultaneously in one domain. ► CFD model is validated using full-scale measurements of wind velocity and CO2 concentration. ► A piecewise-linear method is applied to obtain ACH values for small time-intervals.
