A group of researchers from the Rural Engineering Group of the University of Almeria (UAL), members of the Agri-food International Excellence Campus CeiA3, have implemented a system normally used in the cooling of buildings (evaporator water boxes) to greenhouses in order to analyse its impact on water and energy consumption levels.
The experts found that these evaporation devices are a good option for the cooling of non-airtight greenhouses, just like the ones most often used in the Mediterranean, which are efficient in terms of energy management.
In their article "Energy Efficiency in Greenhouse Evaporative Cooling Techniques: Cooling Boxes versus Cellulose Pads", recently published by the journal Energies, the scientists compare the system of evaporator boxes with ones most commonly used in technified greenhouses, mist propagators and evaporator pads.
As announced on Tuesday by the Descubre Foundation, the first technique makes use of a network of pipes in which pressurised water is injected that then comes out of tiny holes, creating micron-sized drops (one millionth of a meter). Mist propagation systems do not require greenhouses to be air-tight, since the moisture generated inside often requires external air currents. "The problem is that during the summer, due to high temperatures combined occasionally with strong winds, growers must close the windows to prevent the structure from breaking. Closing it will lead to the system no longer working, because the inside becomes saturated with water vapour and no cooling takes place," explains the head of the project, Diego Luis Valera.
For its part, the system using evaporator pads involves covering the windows on one side of the greenhouse with a cellulose material. This cellulose pad is constantly moistened by a pipe running above it. Fans are placed on the opposite side of the greenhouse. Thus, all the air going in does it through the cellulose, which is soaked with droplets that cool the environment. Unlike mist propagation, this method is not affected by higher temperatures or wind; however, it requires air-tight structures.
To overcome the drawbacks of mist propagation and cellulose pads, the system used by the engineers is based on cooling boxes. In this case, the fan and the cellulose pad are together on the same side of the greenhouse, blowing moist air inside. "This system is widely used in buildings, but this is the first time that a scientific analysis is conducted for their application in traditional greenhouses," he stresses.
Following the tests carried out in a wind tunnel at the University of Almería, experts have concluded that evaporator boxes are more efficient than other cooling systems, as they require less energy and water in greenhouses, even in those that are not air-tight. "The results obtained show that the pressure drop with boxes is between 51.27% and 94.87% lower than that produced by cellulose pads. This lower pressure entails a lower specific water and energy consumption."
Experts are already testing the system in experimental greenhouses at the University of Almería, where the ventilation systems are tried out in Almeria-type greenhouses (the traditional one) and in multi-tunnel type ones (the most sophisticated).
Source: fhalmeria.com