The Effect of Cloth Characteristics on the Cooling Performance of External Shade Cloths for Greenhouses

Four shade cloths were examined for their ability to reduce temperatures in a greenhouse: (1) a black flat-weave cloth rated by the manufacturer at 30% shade, (2) a black flat-weave cloth rated at 55% shade, (3) a black knitted cloth rated at 50% shade and (4) a white knitted cloth rated at 40% shade. The cloths were examined both dry and wet. The dry, 40% shade, white knitted cloth reduced the rate of energy gain, air temperature rise and electrical energy consumption by more than the dry black cloths. Leaf temperatures were lower under the heavier black cloths (but not the 30% shade) than under the white. When dry the heavier black cloths performed better than the 30% shade black cloth in all respects, except air temperature rise where there was no difference. When wet, both the 55 and 50% shade, black cloths performed better in all respects than either the 40% shade, white or the 30% shade, black. The knitted 50% shade, black cloth performed marginally better than the flat-weave 55% shade, black cloth in several categories, despite a lower shade rating. This was attributed to differences between the two fabrics in the dependence of shade factor on incidence angle.