Articles
MEASUREMENT AND CONTROL OF THE CLIMATE IN A GREENHOUSE, WHERE A HEATED CONCRETE-FLOOR IS USED AS LOW TEMPERATURE ENERGY SOURCE
In the last years much attention has been paid to research in relation with the construction and the heating technique of concrete floors.
When a heated concrete floor has been installed, the climate control is responsible for the amount of heat needed for the plants and released by the floor.
Despite the large time constant of the concrete floor, an acceptable temperature control must be maintained.
Especially this last item didn’t get as much attention as the research mentioned earlier.
It is necessary for the design of a control algorithm to know the physical processes that are taking place in the greenhouse.
The physical processes can be subdivided into a thermal process, a water vapour process and a radiation process.
A discription of these processes will enclose dynamic components and the heat of evaporation of the plants.
Bond Graphs are used to form a discription of physical prosesses based on energy exchange ( Bot et al., 1979). The resulting Bond Graph is converted into a differential equation model and into a model relevant for automatic control.
By means of simulation techniques, control algorithms can be developed, based on the control model and related and fitted to the measurements in an existing greenhouse, that is heated with a concrete floor.
These control algorithms can be implemented in the existing automatic control system of the IMAG greenhouses. (van Meurs, 1980) The control algorithms also will have to take into account plant cultivation demands.