On-line Identification of a Load-Dependent Heat Exchanger in Closed Loop Using a Modified Instrumental Variable Method

Abstract In this paper a solution for the parameter estimation of industrial processes in closed loop operation is presented, using two modified versions of the instrumental variable method (IV-method), the direct and the indirect identification. Both modifications are applied under various conditions, initially for test purposes, to the identification of a 3rd order system in closed loop. In this way results can be obtained with nearly the same accuracy as those obtained by means of an estimation in the open loop. Dependent on the noise level, however, it is necessary to increase the measuring time to between 50 and 200% of that required for open loop identification. The direct method will, in addition, be applied to the identification of a heat exchanger in closed loop which, as a result of variations in the fluid flow rate, demonstrates a time dependent dynamic behaviour. Here too, the efficiency of the applied method can be fully confirmed.