## 4 Results and Discussion  
### Monitoring Data  
Monitoring data collected between June and September were used to analyze the performance of the built EAHX. During this period, EAHX airflow rate was kept in the 7000 to 9000 m\({}^{3}\)/h range--nominal 8000 m\({}^{3}\)/h airflow rate (4000 m\({}^{3}\)/h per pipe)--24 h a day, 7 days a week. The timeseries presented in this section serve two purposes. They allow the generic evaluation of the EAHX performance with hot and dry climate conditions. Additionally, they allow the assessment of the EAHX design, namely the assessment of the standalone capability of the large-diameter EAHX. Figure 9 compares timeseries of outdoor air temperature (equal to EAHX inlet temperature, \(T_{\text{a0}}\)) and EAHX outflow air temperature (\(T_{\text{aL}}\)). The amplitude damping promoted by the EAHX on the outdoor air thermal wave is highlighted with contour lines for daily maxima outdoor air and EAHX exit air temperatures. The EAHX airflow rate timeseries (\(\tilde{V}\)) is also depicted close to horizontal time axis. Figure 9 shows that EAHX exit temperatures lay below 30 \({}^{\circ}\)C despite frequent outdoor daily maxima above 35 \({}^{\circ}\)C.  
Figure 8: Photograph of the EAHX while the buried pipes were being installed at an average depth of 5.5 m below soil surface. Figure 9 includes lines for running mean and upper free-floating setpoint temperatures [28] (category III). Free-floating setpoints exceed 30 \({}^{\circ}\)C, showing little variability, with a mean value of 31 \({}^{\circ}\)C and maxima of approximately 32 \({}^{\circ}\)C during July and most of August. Using the design free-floating setpoint temperature \(T_{\rm ar}=32\)\({}^{\circ}\)C and monitoring data, Figure 10 presents timeseries of daily energy (heat) removed by the EAHX, namely total energy \(Q_{\rm t}^{\rm EAHX}(=Q_{\rm cm}^{\rm EAHX}+Q_{\rm oa}^{\rm EAHX})\) and energy removed from room air \(Q_{\rm cm}^{\rm EAHX}\). Time-series of daily fan electricity consumption (\(W^{\rm EAHX}\)) and EAHX coefficient of performance (\(\rm COP=Q_{t}/W\)) are also included in Figure 10.  
Figure 10 shows that total loads extracted in the EAHX reached 330 kWh/day. Room maximum and average load extraction were 240 and 112 kWh/day, respectively. Daily fan electricity consumption--50 kWh/day--remained (approximately) constant during the monitoring period. EAHX energy performance measured by the COP shows that with the exception of September, with lower outdoor air temperatures, heat removed in the EAHX exceeded between 2.5 and 5 times the fan electricity consumption. Figure 10: Timeseries plot (monitored data) for daily energy (heat) removed by the EAHX (\(Q_{\rm cm}^{\rm EAHX}\) and \(Q_{\rm t}^{\rm EAHX}\), considering \(T_{\rm ar}=32^{\circ}\)C) and daily fan electricity consumption (\(W^{\rm EAHX}\)). EAHX coefficient of performance (\(\rm COP\)) is also presented. Figure 9: Timeseries plot (monitored data) for outdoor air temperature \(T_{\rm a0}\), EAHX outflow air temperature \(T_{\rm aL}\), and EAHX airflow rate \(\dot{V}\) (kept at the nominal 8000 m\({}^{3}\)/h value). Outdoor running mean and upper free-floating setpoint (category III, [28]) depicted as dash and dash-dot-dot lines, respectively. Using the room design setpoint \(T_{\rm ar}=32\)\({}^{\circ}\)C and monitored data, Figure 11 presents outdoor air and room loads removed in the EAHX as a function of outdoor air temperature \(T_{\rm a0}\). These loads are identified as gray crosses (\(Q^{\rm meas}_{\rm ca}\)) and gray circles (\(Q^{\rm meas}_{\rm rm}\)), respectively. As regards the monitored room loads (gray circles), the depicted variability is attributed to changes in the temperatures of air and soil, and to the multiple combinations of these parameters that occurred in the four-month monitoring period.