Climate and irrigation control

Abstract

This chapter describes the climate and irrigation control problem inside a greenhouse and several control techniques widely used for such purposes, including illustrative results. As greenhouse crop production is influenced by inside climate, control strategies are important to maintain adequate conditions in spite of disturbances acting on the system. The controlled variables are usually PAR radiation, temperature, relative humidity and CO2 concentration. The usual actuators are natural ventilation, shading screen, heating, CO2 injection and fogging. Fertigation control systems are also required to provide the required quantity of different fertilizers, taking into account the pH and electrical conductivity of the drain and reference nutritive solutions. The disturbances affecting the system are outside ones like temperature, relative humidity, solar irradiance, wind speed and direction, sky temperature, and rain. Furthermore, crop transpiration can be considered as a disturbance, as well as a set of variables describing other elements of the greenhouse like cover and soil temperature. This chapter overviews different control techniques developed by the authors for temperature control using natural ventilation and heating, covering PID control, feedforward control, adaptive control, model-based predictive control, event-based control, and fuzzy logic control. A model-based irrigation strategy is also included.