Robust Control of Greenhouse Temperature and Humidity

Despite the advantages of fogging systems over more traditional cooling methods, this relatively new technique is not widely applied in practice. The major reason for this is the shortage of advanced control algorithm for controlling the fogging system together with ventilation. This work presents a MIMO control formulation of the temperature and humidity tracking problem. The control algorithm is tested inside a small experimental greenhouse. The actuators of the greenhouse consist of variable-speed fans together with two high pressure water lines. By defining the above two actuators to be the control inputs and the outside solar radiation, dry-bulb temperature and relative humidity as the disturbances, a MIMO control problem is formulated and solved under the framework of the H8 loop shaping optimization technique. This yields a robust multivariable (2×2) sub-optimal controller which succeeds to maintain the dry–bulb temperature and relative humidity inside a small experimental greenhouse within ±2°C and ±10% of their respective set points.