Gradients of temperature, humidity and CO2 along a fan-ventilated greenhouse

Around the world in warm climates fans are used to ventilate commercial greenhouses. They are usually mounted at one end of the greenhouse and suck ambient air through openings at the opposite end. As the air moves from one end of the greenhouse to the other, gradients of temperature, humidity and CO2 develop along the structure. These gradients result in an inhomogeneous microclimate for the crop and are, therefore, undesirable for growers. Models to predict these gradients were developed for the case of constant (with respect to time) ventilation rate, and were verified by experiments in a greenhouse in which pepper was grown. The experimental results were based on measurements in which the ‘open chamber’ approach was applied to the whole greenhouse. The models were then used to predict changes in temperature, humidity ratio and CO2 concentration in the air along the greenhouse at different hours of the day. The model results show that the largest gradients are to be expected at around midday (11:00–12:00), when the intensity of solar radiation is greatest.