| heal.abstract |
A basic problem of greenhouses and particularly of no heated is the weakness of regulation of very high levels of relative humidity that is developed in their interior, during the night, which encourages the growth of fungi diseases. For the confrontation of this problem, the possibility of dehumidification of the greenhouse air was investigated by the use of an air-air heat pump, hydroscopic material CaCl2, as well as their combination, in a hybrid system of dehumidification. Also, the repercussions of dehumidification were studied in the environment of the greenhouse. Two similar tunnel greenhouses were used, in one of these dehumidification was realised according to the above systems and the other one was used as a control. In both greenhouses, cucumber was grown. The dehumidification took place when the greenhouse was closed and when the relative humidity in the space was above 80%. During the night, in the greenhouse in which the dehumidification was functioned, the leaf temperature did not fall under the dew point. In contrast, in the control greenhouse, the leaf temperature was equal or lower than the dew point temperature. The maintenance of relative humidity in the 80% by the dehumidification, created a bigger water vapour pressure deficit, which caused an increase of order to 28% of evapotranspiration and corresponding increase of total water losses. The action of dehumidification had a significant effect on the condensation of water vapours in the internal surface of the greenhouse cover, which is decreased from 90% of the total water losses to 17%. Losses via infiltrations are decreased lightly by the dehumidification. The maintenance of relative humidity up to 80% with the use of heat pump had as a result the temperature in the space of the greenhouse air to be higher up to 2°C, compared to that of the greenhouse without dehumidification. When the combination of heat pump-CaCl2 was used for the dehumidification, the CaCl2 should assemble the 40-90% of total removed water and it had decreased considerably the time of operation. |
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