## 3 Results and Discussion
### EAHX Exit Air Temperature: Assessing EAHX Room Load Removal  
Figure 7 presents EAHX exit air temperature (\(T_{\text{AL}}\)) and EAHX airflow rate (\(\dot{V}_{\text{a}}\)) data for the summer period between 1 June and 30 September. To simplify the comparison to Figure 5, EAHX air exit temperatures are superimposed into a background of outdoor air temperature data and upper and lower room setpoint temperatures (categories III and I) are also depicted. Figure 7 confirms that the ventilation rate was kept (approximately) constant at the nominal 8000 m\({}^{3}\)/h rate. It also confirms a consistent reduction in air temperature amplitude between EAHX inflow (at outdoor temperature) and outflow (at EAHX exit temperature). Comparing time series of room upper setpoints with EAHX exit air temperatures shows that daily maximum exit temperatures seldom exceed Category I and never exceed Category III comfort expectancy levels. The built EAHX avoids, therefore, region D conditions for an acceptable comfort expectancy level (Category III) during the whole summer (June-September). For a higher comfort expectancy level (Category I), the built EAHX fails to deliver the required cooling with region D conditions in late June. Figure 6: Hourly violin- and box-plots for outdoor air temperature. Obtained from summer monitoring data between 1 June and 30 September. Grey shading highlights room occupied period. Table 6 presents monthly and summer (Jun-Sep) statistics of EAHX exit air temperature (\(T_{\text{AL}}\)). Comparing summer (June-September) statistics in Tables 4 and 6, the decrease in maximum temperature from 40 to 31\({}^{\circ}\)C and the increase in minimum temperature from 11 to 16 \({}^{\circ}\)C are observed; median outdoor air and EAHX exit air temperatures remain, however, equal (23.3 \({}^{\circ}\)C). Table 6 includes statistics for the absolute value of temperature gradient \(\Delta T_{\text{AL,a0}}\). Maximum and median summer (June-September) gradients are 11 and 4 K, respectively, and July is the month with the largest median gradient. Figure 8 presents a scatter plot of temperature gradients \(|\Delta T_{\text{AL,a0}}|\) used to obtain the statistics in Table 6 as a function of outdoor air temperature, \(T_{\text{a0}}\). From \(|\Delta T_{\text{AL,a0}}|\) values in Figure 8, it is concluded that the EAHX cooling mode starts when the outdoor air temperature is approximately 19 \({}^{\circ}\)C (point 1, Figure 8). Since cooling is only possible when the EAHX (inner pipes) surface temperature is lower than the outdoor air temperature, 19 \({}^{\circ}\)C is an estimate of the lowest EAHX surface temperature for the cooling operating mode. Since null temperature gradients \(|\Delta T_{\text{AL,a0}}|\) extend from 19 \({}^{\circ}\)C to 25 \({}^{\circ}\)C (from point 1 to point 2), this range is an estimate of the surface temperatures for which EAHX shifted between cooling and heating modes from 1 June and 30 September. \begin{table}
\begin{tabular}{c c c c c c c} \hline  & & **June** & **July** & **August** & **September** & **Summer (June–September)** \\ \hline \multirow{4}{*}{\(T_{\text{AL}}\) [\({}^{\circ}\)C]} & max. & 31.0 & 29.9 & 29.8 & 25.6 & 31.0 \\  & \(Q_{3}\) & 25.4 & 26.7 & 25.5 & 22.6 & 25.4 \\  & median & 23.0 & 24.4 & 23.7 & 21.1 & 23.3 \\  & \(Q_{1}\) & 20.5 & 22.7 & 22.0 & 20.1 & 21.4 \\  & min. & 16.0 & 20 & 19.3 & 17.6 & 16.0 \\ \hline \multirow{4}{*}{\(|\Delta T_{\text{AL,a0}}|\) [\({}^{\circ}\)K] a} & max. & 10.9 & 9.1 & 9.2 & 7.1 & 10.9 \\  & \(Q_{3}\) & 5.9 & 5.8 & 5.4 & 4.2 & 5.5 \\ \cline{1-1}  & median & 3.7 & 4.2 & 3.9 & 2.5 & 3.7 \\ \cline{1-1}  & \(Q_{1}\) & 1.6 & 2.2 & 1.8 & 1.1 & 1.7 \\ \cline{1-1}  & min. & \(\sim\)0 & \(\sim\)0 & \(\sim\)0 & \(\sim\)0 & \(\sim\)0 \\ \hline \end{tabular} \({}^{\text{a}}\) Cooling only. Instants with \(T_{\text{AL}}>T_{\text{a0}}\) excluded.  
\end{table} 
Table 6: Statistics for EAHX exit air temperature and for absolute value of EAHX exit air to outdoor air temperature gradient. Obtained from summer monitoring data between 1 June and 30 September.