Air-flow patterns and heat fluxes in roof-ventilated multi-span greenhouse with insect-proof screens

Experiments were performed in a semi-commercial, roof-ventilated, four-span greenhouse with insect-proof screens over its openings, to determine the air-flow patterns, heat fluxes and ventilation rates. The ventilation rate in leeward ventilation increased with wind velocity. A comparison between ventilation rates measured by the tracer gas and energy-balance methods showed good correlation between the two. An indication of the influence of outside wind direction on the ventilation rates and air-flow patterns was observed. The direction of air flow within the greenhouse at plant level was nearly opposite to that of the external wind. Both the mean and turbulent latent heat fluxes through the roof openings were much larger than the sensible heat fluxes. Both the sensible and latent turbulent heat fluxes had high values when the roof openings were opened, and then decayed with time. Their directions at the level of the openings were from the greenhouse towards the outside and at plant level they generally followed the direction of the ambient wind.