## 3 Methodology
### Data Collection and Pre-Processing
In the test bed, the inlet/outlet temperature of the heat source and load side at one-minute intervals utilized an RTD (Resistance Temperature Detector) temperature sensor and was stored as a data logger (MV2000). The flow rate was measured through the load and heat source side thermostat system, and the flow meter (FMAG5000) was installed on the water pipeline. The power consumption was measured by installing a watt-hour meter (CW240) on the heat pump. The outside air temperature and humidity were measured, and data were collected through the HOBO U12. Figure 6 shows the measurement items and devices measured in the experiment and Table 7 shows the accuracy of the measurement devices. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Category** & **Building** & **Test-Bed** \\ \hline \multirow{2}{*}{Data collection period} & 1 January 2018–31 & 25 August 2019–27 \\  & December 2018 & August 2019 \\ \multirow{2}{*}{Data collection cycle} & 3 h & 1 min \\ \multirow{2}{*}{Data collection method} & BAS & Measurement \\ \multirow{2}{*}{Temperature range (cooling)} & 24–43 \({}^{\circ}\)C & 20–49 \({}^{\circ}\)C \\ \multirow{2}{*}{Temperature range (heating)} & 11–24 \({}^{\circ}\)C & 8.1–26.8 \({}^{\circ}\)C \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Overview of operation data collection. Figure 5: View of systems installed in the target building. Figure 6: Equipment for measuring coefficient of performance. For performance evaluation in a broader range of heat source inlet-temperature conditions considering actual operating conditions, each item was measured while changing the heat source inlet temperature in the range of 8.1-26.8 \({}^{\circ}\)C during the heating operation and 20-49 \({}^{\circ}\)C during the cooling operation. The experiment was carried out as the water in the water tank on the heat source, and the load side was circulated and heated or cooled to the initial set temperature. After opening various valves connecting the heat pump and the water tank on the heat source side to circulate water, the temperature and flow rate of water at the inlet side of the heat pump heat-source-side were set to suit the experimental conditions. Various valves connecting the heat pump and the water tank on the load side were opened to circulate water. The temperature and flow rate of water at the inlet of the load side of the heat pump was set according to the experimental conditions. When a steady state was reached, each measurement item required to derive the heat pump performance coefficient was measured and recorded according to the measurement cycle. Table 8 lists the operational data items collected for the two systems. As for the measurement uncertainty, as shown in Table 9, the uncertainty of the temperature measuring device is 0.2 and the uncertainty of the flow meter is 0.26-0.32. A large amount of data collected through the heat pump operation in the target building were analyzed to select the input variable by assessing the correlation between the coefficients of performance. An input variable was selected by quantitatively evaluating the relationship with a performance coefficient to be predicted using a Pearson correlation coefficient and a coefficient of determination. The Pearson correlation coefficient was calculated using Equation (1), and the coefficient of determination was calculated as the square of the Pearson correlation coefficient. \[\text{r}=\frac{\sum_{i=1}^{n}\left(\text{X}_{i}-\overline{\text{X}}\right) \left(\text{Y}_{i}-\overline{\text{Y}}\right)}{\sqrt{\sum_{i=1}^{n}\left( \text{X}_{i}-\overline{\text{X}}\right)^{2}}\sqrt{\sum_{i=1}^{n}\left(\text{ Y}_{i}-\overline{\text{Y}}\right)^{2}}} \tag{1}\]  
r: Pearson correlation coefficient