Shading greenhouses to improve the microclimate, energy and water saving in hot regions: A review

Shading greenhouse is an effective method to achieve a suitable environment for crop growth and to enhance crop productivity and quality in hot and sunny regions. This article reviews common shading methods used for greenhouses in summer; their cooling effects on greenhouse air were explored to determine the optimum shading technique for arid regions. Effects of these methods on the overall microclimate as well as the distribution of the microclimatic parameters in greenhouses were discussed. The survey revealed that combining a shading method (e.g., whitewash or shade netting) with ventilation and/or evaporative cooling showed a significant effect on improving overall microclimate as well as the distribution of microclimatic parameters. This consequently reduces the energy and water consumptions and increases the crop productivity and its quality. In sunny regions, incorporating shading with a cooling method is able to maintain greenhouse air temperature at 5-10 degrees C lower than the outside temperature, increases the relative humidity by approximately 15-20% and decreases the transmitted solar radiation by 30-50% compared to a greenhouse without shading. In cold regions, shading materials act as insulators; significantly reduce heat loss from greenhouses at night. Thus, greenhouse air temperature can be maintained at 5 degrees C higher than outside with saving approximately 15-20% of the energy used for heating. The information in this review would be useful for farmers, researchers and greenhouse designers to select the suitable cooling or heating strategy for greenhouses. (C) 2016 Elsevier B.V. All rights reserved.