One factor that influences yield is the inside climate of a greenhouse. Climate in a greenhouse depends mostly on outside meteorological conditions such as temperature, wind, precipitation, and sunshine. In order to create desirable inside climate conditions we need to know how the processes of energy are related to a greenhouse. The knowledge about processes allows to establish and use least expensive way of controlling inside climate in accordance with the needs of plants. This article describes how MATLAB, SIMULINK and Control System Toolbox were used to study the temperatures of a greenhouse equipped with PID-temperature controller. The temperatures of the soil of 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 various 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 greenhouse. 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 greenhouse, and the heating floor. The resistance between the nodes corresponds to thermal resistance between the distinguished objects. The magnitude of the thermal resistance depends on the temperatures of the distinguished objects. 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 of the greenhouse climate control. MATLAB, SIMULINK, and Control System Toolbox are useful tools for simulating complicated temperature processes in the greenhouse.
