If the outside air is humid and hot, the cooling capacity of an evaporative cooling system is very limited to just a couple of degrees Celsius. The high-pressure fog works best in a dry climate, he says. If there isn’t a source of high-quality water, a water treatment system like reverse osmosis is needed. Kacira says another challenge with using high-pressure fogging systems is they require high-quality water (i.e., potable water) so that the nozzles don’t get clogged. Thus proper system design, installation and control strategy are needed.” That is one of the main concerns with fogging systems.
#GREENHOUSE COOLING PAD SYSTEM FREE#
“One of the major concerns with high-pressure fogging systems is free moisture on the plants, which can lead to disease development. “For greenhouse applications, a fine droplet size is best because the water droplets should evaporate as quickly as possible before they can fall onto the canopy and wet the plants,” Kacira says. The fogging system that Kacira used in his research was a variable high-pressure fogging system that delivered fine droplets under a 4.5 to 10.4 MPa operation pressure range. We have not compared the energy and water savings to a mechanically ventilated greenhouse at our facility. With the system operating with variable rate fogging and ventilation rate strategy, we were able to save about 20 to 25 percent of the water and 15 to 20 percent on energy compared to a control strategy using a constant fogging rate and a fixed vent opening. The outside temperatures were about 95✯ to 104✯ (35✬ to 40✬) and 10 to 25 percent relative humidity.
“With the strategies we developed using a naturally ventilated greenhouse with a variable high-pressure fogging system, we were able to maintain the greenhouse climate close to the desired range, around 77✯ (25✬) and 75 percent relative humidity for tomato production. The ultimate goal, he says, was to develop advanced control strategies to maintain the desired greenhouse microclimate while saving water and energy. “Our partners in this project at Technion-Israel Institute of Technology focused on developing climate control strategies using mechanical ventilation with only fans and high pressure fogging.” “With funding from the United States-Israel Binational Agricultural Research and Development Fund, we focused on developing advanced climate control strategies to operate in naturally ventilated greenhouses with high-pressure fogging systems,” Kacira says. For the last three years, Kacira has been involved in an international project to study naturally ventilated greenhouses integrated with a fogging system. Natural ventilation is the other ventilation system for cooling greenhouses. This gradient may affect plant quality and crop yield.” “Another issue is there can be a temperature gradient from the cooler wet pad side to the warmer exhaust fan side. “Water is a precious resource with limited availability, especially in arid and semi-arid regions. “Water is needed for the pad system, and energy is needed to run the pump for water circulation over the pad as well as the energy to run the exhaust fans,” Kacira says. University of Arizona associate professor Murat Kacira says a drawback of using a fan-and-pad type system is that it requires a lot of energy and water.