Influence of two new greenhouse covering materials on greenhouse microclimate and cooling load

Aim of this paper was to study the effects of a new polyethylene (PE) film with high reflectance and absorption in near infrared radiation (NIR-PE) and of a new PE film with low transmittance in infrared radiation IR (IR-PE), on greenhouse microclimate and cooling load of a hydroponic tomato crop. Films were evaluated in the laboratory and experimentally in three similar arched roof greenhouses, two covered with the new covering materials and the third one by a common PE film (CPE). The greenhouse and outside microclimate parameters along with crop growth and production were recorded. Laboratory measurements show that in the total radiation band the NIR-PE film has 13% lower transmissivity than the other two films and 57% higher absorptivity than the C-PE film. Experimental results show that the NIR-PE covering material reduces significantly the solar radiation entering the greenhouse and resulted in a temperature drop up to 2°C than the air temperature of the C-PE covered greenhouse. The total production per m2 was 12.12 kg, 12.00 kg and 10.25 kg under the IR-PE, the NIR-PE and the C-PE covered greenhouses, respectively with no significant differences between the three greenhouses