NATURAL VENTILATION OF A GREENHOUSE WITH RIDGE AND SIDE OPENINGS: SENSITIVITY TO TEMPERATURE AND WIND EFFECTS

Abstract

An air exchange rate model of a Mediterranean greenhouse with ridge and side openings combiningtemperature and wind effects as driving forces of the natural ventilation was developed and tested on experimental data.It is shown that both effects are dependent on the total area of openings, but the temperature effect depends also on theratio of ridge to side openings. The wind effect is related to a global wind effect coefficient, relative to the whole building,which includes both static and turbulent transfers. As far as it concerns the combination of the temperature and windinduced fluxes, it is shown that the vectorial sum of these fluxes, gives a better fit of the experimental data than theiraddition. The relative importance of the thermal buoyancy and wind forces depends on the ratio between wind velocityand the root of the inside-outside temperature difference (u/__). In our experimental conditions the wind effectpredominates on the chimney effect when this ratio u/__becomes greater than 1. The use of the reduced ventilation flux(per unit of ventilator opening area and wind speed) shows that for typical conditions of temperature difference (= 5 K)the roof and side ventilation system is much more efficient than roof ventilation only for wind velocities smaller than2.5 msC1. Finally, a simple design procedure for dimensioning the area of the vents under extreme climatic conditions isproposed and a relative nomograph is given.