A two–dimensional particle image velocimetry (PIV) system installed in a large–sized wind tunnel was used to
examine the natural ventilation of fully open roof and Venlo–type multi–span greenhouses. Since the PIV system has rarely
been used for large–scale, low–turbulence airflow conditions, the PIV system was investigated to improve its performance
and accuracy. The PIV accuracy tests were conducted without any greenhouse models in the wind tunnel because it was very
difficult to insert the anemometer sensors in the small–scale greenhouse models, and it was also assumed that the sensor itself
could affect natural airflow patterns inside the models. Good results were obtained in the PIV accuracy test, and the errors
were shown to be mostly in the .5% range. Additionally, the natural airflow in 2– to 10–span greenhouses was investigated
using the PIV system. The PIV results indicated that the PIV technique was an effective method for evaluating the relative
performance of alternative designs of greenhouse and other structures with turbulent interior air distributions.