Ceiling radiant cooling: Comparison of ARMAX and subspace identification modelling methods

The building of the Faculty of Mechanical Engineering, Czech Technical University in Prague – Dejvice, has been heated by a ceiling radiant heating system (“Crittall” system) since 1961. One building block has been equipped by means which enable the use of the pipes of the radiant heating system for ceiling radiant cooling. As optimization of this system is desired, the first step to be performed is the identification. Because of a complicated physical description of the entire system, and a set of measured data which is large enough to perform statistical identification, a decision was made to identify the system by ARMAX model identification and subspace identification methods. The resulting identified model shows a standard deviation of 0.2–0.3 °C on the verification data. The model identified by the subspace methods, enhanced by a Kalman filter, shows a standard deviation of 0.063 °C for output tracking. Such a model is ready to be used in modern multidimensional controllers, such as model-based predictive controllers (MPC).