Effect of two new cover materials on greenhouse energy consumption and cooling load
The aim of this work was to study the effects of a new polyethylene (PE) film with high reflectance and absorption in near infrared radiation (NIR-PE film) and of a PE film with low transmittance in infrared radiation IR (IR-PE film), on the greenhouse microclimate, energy consumption and on growth and yield of a hydroponic tomato crop. Compared to a common PE film (C-PE), the IR-PE film, had 75% lower transmittance in IR, while the NIR-PE had 78% lower transmittance in IR and 42% higher reflectance in NIR. Films were evaluated experimentally in three similar arched roof greenhouses, two covered with the new covering materials and the third one by a C-PE film. The greenhouse and outside microclimate parameters along with crop growth and production were recorded. During the winter period, no significant differences of air temperature and relative air humidity between the tested greenhouses were found. The air vapour pressure deficit (VPD) values observed were relatively low (i.e below 0.5 kPa) during the night period, leading to condensation over the cover. The total energy consumption was 10% lower in the IR-PE covered greenhouse than in the C-PE covered greenhouse. During the summer period, the air temperature in the greenhouse covered by the NIR-PE was 2°C lower than the air temperature of the C-PE covered greenhouse.