Transient suppression in non-parametric frequency response function estimates of heat diffusion phenomena

The modeling of heat diffusion phenomena is important to develop optimal control strategies for ground coupled heat pump systems. In order to find the best heat diffusion model, a good estimate of the non-parametric Frequency Response Function (FRF) is desired. Due to the large transients in the diffusion system, it is mandatory to take transient effects in the data into account. This paper compares two methods to suppress the transient effects. Both methods assume that the excitation signal is periodic. The first method uses time domain windowing to reduce the transient, while the second method uses the property that the influence of the transient can locally be approximated in the frequency domain by a low degree polynomial. It will be shown that the latter method reduces the variance of the transfer function estimate because it suppresses the transient more efficiently. The experimental verification is done using measurements on the heat diffusion problem in a thermally isolated bar.