Estimating time constants for underfloor heating control

Time constants are used for tuning PID control parameters and should be correctly estimated to achieve a well-performing controller. However, the estimation of time constants for a very slowly reacting system such as underfloor heating is not easy in practice. In this work, different methods were used to estimate the time constants for underfloor heating. Graphical estimation and transfer function fitting were the core approaches. Measurement data and simulations on a calibrated model were used for the estimations. The resulting time constant values for the graphical method depended clearly on the setback duration and the values differed up to a factor of 100. For the transfer function method, time constant values did not vary significantly. For light construction, the time constant was around 10 hours and for massive, around 30 hours for the otherwise identical room.