Simulated Effects of Reflective Mulch on Energy and Water Conservation in Semi-Arid Central California Greenhouses

摘要

In addition to the labor, energy and water consumption are the two main cost drivers in current greenhouse systems. Consequently, considerable effort is expended to conserve energy and water, and look for alternative energy sources. Greenhouses in hot and arid regions also require large quantities of water for irrigation. Proper environmental management systems can significantly change the energy and moisture dynamics of greenhouse production systems. This study aims to focus on reducing energy and water consumption in semi-arid California greenhouses. Influences of mulch (having different reflectivities) on energy and water conservation were investigated. The reflectivity of mulch used as a floor cover affects the radiation distribution within the canopy stand, eventually affecting the overall energy and water consumption. A dynamic computer simulation model was used to compare different mulch reflectivities, plant heights, and leaf dimensions to draw a conclusion about energy and water conservation. The results showed that using mulch with less reflectivity (for instance, 20% instead of 80%) reduced energy consumption by as much as 4.2%. With a decrease in reflectivity, the absorptivity of the mulch increases consequently. A high absorptivity results in higher rates of solar energy being absorbed during the day, and released during the night. The mulch functions as a collection device, while the floor itself being the thermal mass. By increasing the reflectivity from 20% to 80%, water savings of up to 8.6% occurred. The savings in energy consumption, therefore, always have to be seen in conjunction with the water consumption. Also, the effect of reflective mulch fades away as shade from canopy stand increases. A complete system analysis is necessary to obtain a complete energy and water balance and to be able to make a viable conclusion.