Supply air temperature according to four indicators: variance, auto-correlation function, power spectrum and variational autoencoder. The moment of the failure (when the supply air temperature increases anomalously for the first time) is 9:30AM of the 27th of January 2019. Plot starts at 5:30 AM of the 25th of January, 64 hours prior to the failure. Variance is shown in logarithmic scale to make the increase prior to failure more visible. Window sizes used: 22 hours for variance and ACF1, 8 hours for PS and 4 hours for VAERE.