Assessing airflow rates of a naturally ventilated test facility using a fast and simple algorithm supported by local air velocity measurements

Publication date: 1 August 2016
Source:Building and Environment, Volume 104
Author(s): G. De Vogeleer, P. Van Overbeke, E. Brusselman, L.B. Mendes, J.G. Pieters, P. Demeyer
The high spatial and temporal variations of airflow patterns in ventilation openings of naturally ventilated animal houses make it difficult to accurately measure the airflow rate. This paper focusses on the development of a fast assessment technique for the airflow rate of a naturally ventilated test facility through the combination of a linear algorithm and local air velocity measurements. This assessment technique was validated against detailed measurement results obtained by the measuring method of Van Overbeke et al. (2015) as a reference. The total air velocity $\left|\overline{U}\right|$, the normal $\left|\overline{Y}\right|$ and tangential velocity component $\left|\overline{X}\right|$ and the velocity vector $\overline{U}$ measured at the meteomast were chosen as input variables for the linear algorithms. The airflow rates were split in a group where only uni-directional flows occurred at vent level (no opposite directions of $\left|\overline{Y}\right|$ present in the airflow pattern of the opening), and a group where bi-directional flows occurred (the air goes simultaneously in and out of the opening). For airflow rates with uni-directional flows the input variables $\overline{U}$ and $\left|\overline{Y}\right|$ yielded the most accurate results. For this reason, it was suggested to use the $\left|\overline{Y}\right|$ instead of $\left|\overline{U}\right|$ in ASHRAE’s formula of $Q=E\times A\times \left|\overline{U}\right|$. For bi-directional flows a multiple linear model was suggested where input variable $\overline{U}$ gave the best results to assess the airflow rate.