Ventilation performance of a large Canarian-type greenhouse equipped with insect-proof nets

This study analyses the ventilation performance of a large Canarian-type greenhouse equipped with insect-proof nets on the vent openings. Air exchange rate measurements were performed in the region of Agadir, Morocco, by means of tracer gas method in a 5600 m(2) greenhouse, planted with a tomato crop and equipped with insect-proof nets. A ventilation model was deduced and the simulations show that: (i) for a given wind direction (parallel or perpendicular to the opening), the ventilation rate increases proportionally with the wind speed and the size of the opening; (ii) the contribution of the chimney effect in ventilation can be neglected when the wind speed has a value greater than 2 in s(-1); (iii) insect-proof net induces a strong additional pressure drop through the opening, which significantly reduces the ventilation rate and generates an important greenhouse air temperature increase. The simulation model was later used to study the effects of anti-thrip and anti-aphid nets on the greenhouse ventilation performance and the resulting climate. In both cases, the induced reduction of aeration was evaluated, as well as the augmentation of the opening area which was needed to maintain the air renewal rate unchanged. The consequences of the use of nets on the interior temperature of the greenhouse were also studied. (C) 2002 Silsoe Research Institute. Published by Elsevier Science Ltd. All rights reserved.