*3.5. Event Threshold*

For the event "PLR significant change", 7% was selected as the PLR change threshold based on a previous study on the same AC system [11]. The threshold of SCOP deviation can be calculated based on the value of SCOPidl and an expected energy saving percentage (as shown in Appendix C Equation (A8)). For instance, an expected energy saving percentage can be specified by users (e.g., 10%), and the SCOPidl can be obtained from the developed ANN model. After the threshold is calculated, it should be checked that whether the calculated threshold is feasible or not based on the SCOP deviations in historical data. The threshold selection should also consider the uncertainties in the SCOPidl model and SCOP measurement in terms of the application concerns.

The thresholds of the SCOP deviation are set as 0.2057 (transient) and 2.057 (cumulative). The selection details are presented as follows: The targeted energy saving is set as 10%, based on handbook [16] and a previous study [10]. To help the threshold selection, the histogram of SCOPidl and SCOP deviation are plotted in Figure 10. The base case keeps all the four temperature set-points as constant. The SCOP deviation is the difference between SCOP of the base case and SCOPidl. From Figure 10, the mean of SCOPidl is 2.0544. Using a SCOPidl of 2.0544 and an expected energy saving of 10.0%, the threshold of SCOP deviation is 0.2057, based on Equation (A8) (Appendix C).

**Figure 10.** (**a**) Histogram of SCOPidl; (**b**) Histogram of SCOP deviation.

Since "0.2057" is within the range of SCOP deviation and the most frequent case (Figure 10b), it is a feasible threshold value.

For uncertainties, the value 0.01 was used for as the model uncertainty of SCOPidl, which was the averaged value over the training and validation Mean Squared Error (MSE) of the ANN model. The measurement uncertainty for the case study was calculated in Appendix B, where sensor uncertainties were added to the simulation-generated operation data. As a negative value is considered, "–0.0694" was used for measurement uncertainty. Thus, the combined uncertainty is "–0.0794" ("–0.01"+"–0.0694"), and *SCOP*1 can be set as "*SCOPidl* − 0.0794".

In comparison, the threshold 0.2057 is nearly three times greater the combined uncertainty, which can largely prevent the uncertainty-caused event triggering. Thus, 0.2057 is used as the threshold of transient SCOP deviation. The cumulative SCOP deviation depends on both the time duration and the SCOP deviation. The deviation for cumulative SCOP was considered as half of the transient SCOP deviation threshold (i.e., 0.2057/2), or a 5% energy saving equivalently. The time duration was selected as 20 minutes for a demonstration. Thus, the threshold of cumulative SCOP deviation is 2.057.

## **4. Results and Discussions**
