Pressure field and airflow at the opening of a naturally ventilated greenhouse

Direct estimation of airflow at the vent opening by means of differential pressure measurements were performed in a twin-span greenhouse equipped with a continuous vent at the gutter. Application of Bernoulli's equation provided a spatial estimate of mean air velocities and turbulent flows through the opening. In the particular case investigated, a wind blowing parallel to the greenhouse ridge gave rise to an inflow at the downwind end of the ventilator. In qualitative terms, this result is in good agreement with previous measurements performed with sonic anemometers in the same greenhouse with the same wind conditions but, on average, the airflows deduced from the pressure measurements gave higher values. A global wind effect coefficient, deduced from the mean pressure measurements, is in good accord with the sonic anemometer and tracer gas measurements. (C) 1998 Silsoe Research Institute.