Evaluating Water and Energy Usage for Greenhouse Cooling Systems in Semiarid Climate

Controlling the growing environment of plants is a major advantage to greenhouse crop production. Air temperature and relative humidity can be manipulated and controlled within a greenhouse, while maintaining high levels of light necessary for the photosynthetic processes of plants. In Southern Arizona light is plentiful; however, the hot, arid summer climate necessitates vigorous cooling of the greenhouse system. Due to the dry climate, evaporative cooling (cooling the air by evaporating water) is extremely effective in Southern Arizona. In this study, two evaporative cooling systems will be analyzed: high-pressure fogging and fan-and-pad. Fan-and-pad cooling is the industry standard, employing an irrigated pad on one wall of the greenhouse and fans on the opposite wall to draw outside air through the pad and into the greenhouse. When hot, dry air is pulled across the wet pad, the water on the pad evaporates, cooling the air as it enters the greenhouse. The second method of evaporative cooling is high-pressure fog, in which water is dispersed from an overhead line at high pressures to produce a fine mist of water. With the addition of mechanical ventilation (fans pulling air through a dry pad) or natural ventilation (opening side and roof vents), the small water droplets are evaporated, cooling the air. This project will determine the total energy and water use of these cooling systems, as well as the effect they have on plant water uptake, evapotranspiration, and overall plant and fruit production.