Improving the cost effectiveness of greenhouse climate control

Abstract A control philosophy is described for maximising the financial margin between the value of a greenhouse crop and the cost of controlling the greenhouse climate. This uses physical models, which describe how the conditions inside the greenhouse are influenced by external conditions, to determine the inputs necessary to create the internal climate. Biological models are used to predict the influence of the climate on crop production. Economic models provide input costs and crop market value. These models are used in an optimisation algorithm to determine the values of specific climate variables which maximise the financial margin. The algorithm will operate in real time in the greenhouse climate controller to determine the optimal time trajectory of the controlled climate variable. The paper illustrates this form of control with three examples. Two relate to reducing the cost of greenhouse heating by optimising the closing and opening of thermal screens, and by controlling heating on the basis of integrated, rather than instantaneous, temperature. The third describes the optimal control of carbon dioxide concentration in the greenhouse atmosphere.

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