THE THERMIC EFFECTS OF PLASTIC FILM COVERING AND OF THE STRUCTURE IN THE HYDROTUNNEL

1. the different "quality" of the cover material: we try to optimize the cover so to obtain the highest result of block of long infrared radiations, emitted from soil during the night. For such optimization is an examination the film PE in comparison with the films EVA and PVC, whose shielding action is well known;
2. the use of the "double cover" associated with the use of the layer of flowing water on the external cover, tends to reduce even the thermal losses. The combining of two systems leads to the optimization of benefits for the covered crops, especially in the lower latitudes of Italy where there is "zero demand" of indirect energy;
3. the "shape" and the "volume" of the tunnel: with rectangular shape and with North-South orientation, while as regard the volume, the optimum ratio of tunnel is about 1 m² : 2.5 m³.

The results achieved until today have been the following:

• the inside temperature (Ti) constatement always superior to 4°C, also when the external temperature (Te) reaches values sensitively lower to freezing-point. Such values are enough to protect the crops growing in the cold tunnel, with energetic low cost;
• constancy of the thermal state in the tunnel, caused by flowing water on the cover;
• optimization of the beneficial actions on the crops with the use of plastic films with the reflection as possible of the infra-red, in several films PE, EVA and PVC, and in the model of tunnel most suitable for the purpose;
• economical effectiveness of the system to the traditional heating of help nightly-winter, with cost of exercise and of working from 5 to 10 times cheaper.

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