Grey-box identification of air-handling unit elements

The air-handling units (AHUs) provide complete control of temperature and humidity in air-conditioned spaces. The models of the AHU elements are nonlinear and the controlled variables, temperature and relative humidity, coupled. This paper demonstrates that in the case of sensible heat exchange without moisture removal if the outputs of the electric coils, fluid-filled coils and steam humidifiers of an AHU are considered to be the differences between the air temperature and the humidity ratio of the outlet and the inlet, then the models may be written as the product of a static and a dynamic gain. The parameters of the discrete form of these models are experimentally identified. The dynamics of the elements and of their sensors are very similar. Therefore, the parameter identification of the elements takes into account the model of the sensor, previously identified. This grey-box approach combines theoretical modelling, parameter identification of discrete models and parameter identification of partially known models by using optimization techniques.