Modelling the heat-balance of greenhouse by use of Matlab

One factor that influences yield is the inside climate of a greenhouse. Cli mate in a greenhouse depends mostly on outside meteorological conditions su ch as temperature, wind, precipitation, and sunshine. In order to create de sirable inside climate conditions we need to know how the processes of ener gy are related to a greenhouse. The knowledge about processes allows to est ablish and use least expensive way of controlling inside climate in accorda nce with the needs of plants. This article describes how MATLAB, SIMULINK a nd Control System Toolbox were used to study the temperatures of a greenhou se equipped with PID-temperature controller. The temperatures of the soil o f the greenhouse, the leaves of the plants and the glass of the greenhouse were studied. During the simulation of the system, a step-function with var ious step sizes was chosen for disturbance. The greenhouse was described by means of a system of differential equations. This system of equations was created on the basis of the electrical substitution scheme of the greenhous e. The distinguished objects of the greenhouse were represented as nodes of the scheme: the soil of the greenhouse, the leaves of the plants, the air in the greenhouse, the glass of the greenhouse, the heating pipes in the gr eenhouse, and the heating floor. The resistance between the nodes correspon ds to thermal resistance between the distinguished objects. The magnitude o f the thermal resistance depends on the temperatures of the distinguished o bjects. Therefore the resistance is non-linear. The laws of heat flow were used to determine this thermal resistance. By using SIMULINK, a simulation model of the greenhouse was created on the basis of differential equations. The model of the greenhouse was used as submodel in the simulation model o f the greenhouse climate control. MATLAB, SIMULINK, and Control System Tool box are useful tools for simulating complicated temperature processes in th e greenhouse.