LATENT HEAT TRANSFER IN A LOW ENERGY GREENHOUSE (ZINEG)

The latent heat flux is important for the heat consumption of greenhouses and for the evapotranspiration rate of the crops. The main objective of this research is the development of a simplified heat transfer model to calculate the latent heat flux for any combination of energy saving methods and crops – especially for low energy greenhouses.
A simplified methodological approach using heat transfer coefficients and heat transfer resistances is used to describe the latent heat flux from the leaves to the inner surface of the roof. The latent heat flux is included in the calculation of the heat transfer coefficient (U-value). Furthermore the affiliated amount of condensate allows an estimation of the effect of energy saving on the evapotranspiration of the crop. This is important especially for the use of multiple thermal screen systems. The thermal screens are reducing the latent heat flux to the roof. But as the inner surface tempera¬ture of the roof is reduced, the water vapour difference between the air in the green¬house and the saturation vapour at the roof surface is increased. This will reduce the effect of thermal screens on the latent heat flux.
The accuracy of this approach increases with lower U-values (higher energy saving). The model is valid for night conditions without solar radiation and crops with stomata closed.