GREENHOUSE COOLING DURING WARM PERIODS

ISHS Acta Horticulturae 357: III International Symposium on Protected Cultivation in Mild Winter Climates

GREENHOUSE COOLING DURING WARM PERIODS

Authors:

J.I. Montero, A. Antón

Abstract:
During the majority of the productive cycle, greenhouse temperature is too high, both for good crop performance and for the health of greenhouse workers. Reducing temperatures is one of main problems facing greenhouse management in mild climates. Cooling is more expensive and more difficult than heating and most greenhouses are not adequately structured for installing cooling systems.

There are four factors which permit temperature reduction:

Ventilation or air renewal
Crop evapotranspiration.
Reduction of solar radiation which affects plants (shading)
Water evaporation inside the greenhouse (fog system,ooling system, etc.)

These four factors are interlinked in the balance of energy equation. For the air in a permanent greenhouse, a simplified version can be written as follows:

Rint + Hci = Vent + LE + Evap.

Where

Rint = Solar energy transmitted to and absorbed in
the greenhouse.

Hci = Heat transferred by convection to the
greenhouse air from the cover.

Vent = Energy transferred out of the greenhouse by
ventilation.

LE = Energy used in transpiration from the crop.

Evap = Energy consumed to evaporate water from the
evaporative cooling devices.

A change in any one of these factors affects all the others, For example, on reducing solar radiation by means of shading, transpiration usually decreases and the ventilation rate is changed by the change in temperature.

This paper includes some results of the cooling tests carried out in Mediterranean greenhouses and the calculations of a simulation programme which combines different cooling methods for achieving the best possible climate.

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