QUANTIFICATION OF THE VENTILATION OF A GREENHOUSE WITH A ROOF OPENING

Abstract

Measurements of air exchange rates were performed in situ in a glasshouse equipped with a continuous roof opening. These measurements were carried out using the decay rate method with N2O as tracer gas. Simultaneously, inside and outside air temperatures were recorded as well as wind speed and direction. The experimental data were tested and fitted on a model which estimates the ventilation flux as a function of the temperature difference between inside and outside air (responsible for the chimney effect), of the wind velocity (wind effect) and of the surface of the opening, Results show that: (i) the effectiveness of ventilation decreases as the wind speed increases in a non linear fashion, (ii) the offset used in the linear models is partially a statistical artifact, (iii) the type of the opening and the dimension of the greenhouse affect the determination of the ventilation flux, (iv) wind perturbed by an upwind windbreak seems to be more effective for the ventilation of the greenhouse.