Uncertainty in airflow rate calculations due to the use of surface-averaged pressure coefficients

Abstract

Abstract Mean wind pressure coefficients ( C p ) are key input parameters for air infiltration and ventilation studies. However, building energy simulation and stand-alone airflow network programs usually only provide and/or use a limited amount of C p data, which are based on several assumptions. An important assumption consists of using surface-averaged C p values instead of local C p values with a high resolution in space. This paper provides information on the uncertainty in the calculated airflow rate due to the use of surface-averaged C p data. The study is performed using published empirical data on pressure coefficients obtained from extensive wind tunnel experiments. The uncertainty is assessed based on the comparison of the airflow rate ( ϕ ) calculated using the surface-averaged C p values ( ϕ AV ) and the airflow rate calculated using local C p values ( ϕ LOC ). The results indicate that the uncertainty with a confidence interval of 95% is high: 0.23 ϕ AV ϕ LOC ϕ AV . In cases with the largest surface-averaged Δ C p , the underestimation or overestimation is smaller but not negligible: 0.52 ϕ AV ϕ LOC ϕ AV . These results provide boundaries for future improvements in C p data quality, and new developments can be evaluated by comparison with the uncertainty of the current methods.