Mechanical Cooling

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In high-temperature, high-humidity climates, the possibilities for adiabatic pad-and-fan cooling or cooling by natural ventilation are very limited. In those situations, only mechanical cooling can lower the temperatures in the greenhouse. Such a system works by using a cold surface on which sensible heat is extracted and moisture condenses - this lowers the air temperature and results in a lowered humidity, which provides new adiabatic cooling potential for the crop. Thus such a system performs both cooling and dehumidification.

The cooling power is controlled by lowering the temperature of the cold surface - the colder this surface, the more sensible and latent heat will be extracted. However, there is a limit to the lowest temperature attainable by the cooling water, and hence the cold surface. The cold water can be sourced from a buffer, or can be produced by a chiller. Depending on this, the installed cooling power could refer to the the heat exchange capacity of the heat exchange or the power of the chiller. Eventually an equilibrium greenhouse temperature will be reached where the cooling power equals the cooling load.

The cooling power control is again based on a proportional band along which the cooling power will be increased. The cooler starts working when the greenhouse temperature exceeds the ‘ventilation’ temperature set-point which is the maximum temperature desired for the greenhouse after which cooling needs to be initiated.

Cooling can also be performed using heat pumps.

Contribution to energy balance and resource use of greenhouses:

Mechanical cooling removes the excessive, undesired energy to maintain optimum growing environment. The cooling and dehumidification lowers the need for natural ventilation, preserving dosed CO₂ inside the greenhouse.

Possible steps towards sustainable, energy-efficient greenhouses

Although mechanical cooling requires a high electrical power input, if powered by renewable sources, this can lead to greater sustainability in the greenhouse.