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Identification of a continuous time model of the heat dynamics of a greenhouse


, : Identification of a continuous time model of the heat dynamics of a greenhouse. Acta Horticulturae 406: 39-48

In order to use model based optimal control strategy for the heat supply to greenhouses, a reasonable description of the heat dynamics is required. This paper describes the identification of a stochastic model for the heat dynamics of a greenhouse which takes the global radiation, outdoor air temperature and the heat supply as input variables. The model is a lumped parameter model formulated in state space form in continuous time. The formulation contains physically interpretable parameters. For the identification, data from an experiment conducted in the winter of 1992 have been used. In the experiment data were sampled every two minutes. Obviously, a greenhouse is a distributed system. However, the fundamental assumption used in the lumped parameter system is that the heat capacity can be collected at certain nodes of the system. Physical knowledge as well as statistical methods are used to validate the model. Considering the physical validation, the estimated parameters show reasonable agreement with physically suggested parameters. Furthermore, the model has been used to simulate the air temperature on independent data. The simulation shows that the first node fits reasonably to the measured air temperature in the greenhouse. The second node seems to describe the temperature of the soil in the pots and few centimetres of the ground. The interpretation of third node is more doubtful but it describes most likely the temperature of a deeper part of the ground.

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