Dynamic behaviour modelling

For control purposes a linear model is often used to describe the behaviour of HVAC plants. This article from Switzerland describes a method for calculating the parameters of delay time, time lag and gain. A model step (or pulse response) is calculated analytically as a function of the parameters and is fitted to a measured step by a Fletcher‐Powell‐Davidon optimisation. One example shows the method used to evaluate the relation between the parameters and the operating point of a heater battery; the other describes how a PID controller is adjusted automatically using the identified parameters. Mr Wehrli is an engineer with Landis & Gyr and Dr Todtli is with the Federal Institute of Technology, Zurich.