## 3 Results and Discussion  
### Outdoor Conditions and Challenges Facing Standalone EAHX Cooling  
Figure 5 presents outdoor air temperature (\(T_{\text{a0}}\)) data for the summer period between 1 June and 30 September. Figure 5: Timeseries of outdoor air temperature (\(T_{\text{a0}}\), monitored data); upper and lower room setpoint temperatures (\(T_{\text{k}}^{\text{U}}\) and \(T_{\text{k}}^{\text{L}}\) with \(k\in\{\text{rsIII},\text{rsI}\}\) determined from Equations (10) and (11) using monitoring data); estimate of undisturbed soil temperature (\(T_{\text{soo}}\), determined from average annual outdoor air temperature data). \begin{table}
\begin{tabular}{l l} \hline
**EAHX** & \\ \hline Exit air temp. sensor, \(T_{\text{aL}}\) & Duration: From 1 June to 30 September. \\ (Onset datalogger [36]) & Log.frequency: 15 min. \\  & Sensor location: Arthur mixing chamber. \\  & Range: \(-20\) to \(+70\)\({}^{\circ}\)C. \\  & Accuracy: \(\pm 0.35\)\({}^{\circ}\)C (from 0 to 50 \({}^{\circ}\)C). \\ Airflow rate, \(\dot{V}_{\text{a}}\) & Duration: From 1 June to 30 September. \\ (Fan controller module [37] & Log.frequency: 15 min. \\ measuring airflow rate & Sensor location: AHU. \\ from fan diff.pressure) & Range: 0 to 1000 Pa. \\  & Accuracy: \(\pm 1.3\)\% (max). \\ \hline \end{tabular}
\end{table} 
Table 3: _Cont_. For the time period depicted in Figure 5, Table 4 presents monthly and summer (June-September) statistics of outdoor air temperature and of outdoor air relative humidity. Table 4 shows that monthly median air temperatures exceeded 20 \({}^{\circ}\)C, reaching 26 \({}^{\circ}\)C in July. The outdoor air temperature range is largest in June, with maximum and minimum temperatures of 40 \({}^{\circ}\)C and 12 \({}^{\circ}\)C, respectively. The temperature range decreases in subsequent months, but maximum temperatures remain higher than 35 \({}^{\circ}\)C in July and August. Table 4 also presents monthly and summer statistics of outdoor air relative humidity (\(\phi_{\text{a0}}\)). Confirming dry summer conditions, relative humidity interquartile range is defined between 32% and 65% with a median of 47% (June-September). An increase in monthly median relative humidity is observed from June (41%) to September (54%). Using summer outdoor air temperature and relative humidity data, median and 95% percentile dew point temperatures of 11 and 16 \({}^{\circ}\)C (respectively) were determined [38]. Since these values are significantly lower than EAHX (pipes inner) surface temperatures (see Section 3.2), condensation in the EAHX has low likelihood, supporting the assessment of the EAHX cooling performance based on sensible heat exchanges (based on Equations (1) and (2)). Figure 5 presents upper and lower room free-floating setpoint temperatures obtained from Equations (10) and (11) using monitoring data to derive the running mean outdoor temperature (Equation (12)). In spite of the large outdoor temperature variations (with daily ranges exceeding 15 K), the room setpoint variance is small. Statistics for these setpoints are presented in Table 5.  
Table 5 confirms small variance in setpoints along the summer period with differences between median and maximum setpoints of only 1 K and setpoint ranges not exceeding 3 K.  
It is obvious from Figure 5 that outdoor air temperatures exceed room upper setpoint temperatures throughout the whole summer. Furthermore, outdoor air temperatures lower than the room lower setpoint temperatures are also common. When discussing Figure 4, in Section 2.3, outdoor air temperatures above and below comfort limits were associated with daytime and nighttime, respectively. Since office rooms are unoccupied during nighttime, it