Effect of near-infrared-radiation reflective screen materials on ventilation requirement, crop transpiration and water use efficiency of a greenhouse rose crop

The effect of Near Infrared (NIR)-reflective screen material on ventilation requirement, crop transpiration and water use efficiency of a greenhouse rose crop was investigated in an experiment whereby identical climate was ensured in greenhouse compartments installed with either NIR-reflective or conventional material as internal movable screens. The NIR-filter reduced the energy load of the greenhouse by 8%. The high reflectivity of the canopy in the NIR range caused the energy input of the greenhouse to be reduced by less than the properties of the material would suggest (25%). Both the ventilation requirement of the greenhouse and crop transpiration were reduced by the NIR-selective screen, consistently with the reduction in energy load of the greenhouse and the crop. The potential for commercial application of such material - either as movable screen or semi-permanent screen in addition to cooling - seems limited to high-tech greenhouse production in arid regions, where the reduction in cooling requirement could significantly lower water use for evaporative cooling. The potential for application of a photo-selective paint as alternative to the seasonal whitewash in low-tech greenhouses is obviously much larger. For it to make a difference, however, the NIR-reflectance must be much higher than the value of the present commercially available paints.