Non-linear adaptive temperature and humidity control in animal buildings

Climate control for housed animals is of substantial importance but it is also a difficult and complicated task. The animals in a livestock building affect temperature and humidity conditions inside the building in a nonlinear way, and add long time constants to the system response. Moreover, the inherent coupling of temperature and humidity through psychrometric laws as well as the thermally dynamic, nature of livestock buildings suggest that disturbance attenuation (load control of external environmental conditions, heat emanated by the animals and water-vapour production of animals) is far more important than is the case of other types of buildings. To settle these concerns, a non-linear control design method, resulting in an inherently robust adaptive non-linear proportional integral control law for simultaneous temperature/ humidity control of livestock buildings in both summer and winter conditions, is presented in this paper. The proposed method, successfully tested here through extensive simulation, relies on: (a) a model-based feedback/ feed-forward compensation of measured external disturbances on the basis of input-output linearisation, decoupling and Lyapunov theory; (b) a robust non-linear compensation of unknown external system disturbances and parametric uncertainties, on the basis of non-linear damping terms, to guarantee small output deviations from desired set-point values; and (c) an adaptive non-linear control law incorporating integral action to cope for parametric model uncertainty and unknown disturbances and to guarantee zero steady-state offset in the system response. Its ability to track varying set-points provides the possibility to combine it with higher level control modules useful for the transformation of user-defined settings for temperature and humidity into feasible controller set-points, taking into account the constraints imposed by the capacities of the actuators, the psychrometric laws, animal welfare, etc. The proposed method is applicable to any air-conditioning system and is expected to gain wide acceptance in modern climate control systems. (c) 2005 Published by Elsevier Ltd on behalf of Silsoe Research Institute.