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Similar to fogging systems, pad and fan systems operate by evaporative cooling: the cooling happens as the heat in the greenhouse air is used to evaporate water to water vapour. These systems consist of fans on one wall, and cooling pads with water circulation on the opposite wall. The fans pull in air from outside the greenhouse, which runs through cooling pads: as the water on the cooling pads evaporates using the energy from the air, the air becomes cooler and humid as it blows over the greenhouse crops and is expelled via the fans on the opposite wall.
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Care should be taken to maintain the fans well, as well as to maintain the permeability of the pads by avoiding blocking them with salt.
Contribution to energy balance and resource use of
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greenhouses:
The evaporative cooling lowers the greenhouse temperature and also affects the humidity inside the greenhouse.
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Depending on how much greenhouse area needs to be cooled, considerable energy may be required to move a huge volume of air across the greenhouse.
Another resource which is consumed in large quantities is water, which can pose problems in hot and dry, water-scarce areas where such cooling might typically be required.
Possible steps towards sustainable, energy-efficient greenhouses
To effectively limit the cooling power of the pad-and-fan system to the interior of the greenhouse, rather than cooling the outside air, natural ventilation should be avoided.
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