## 4 Conclusions  
In this study, the thermal and energy performance of an existing large-diameter earth-air heat exchanger (EAHX) was evaluated as a strategy for standalone cooling of a small existing office building. The study used monitored data gathered during the summer period at the EAHX location, in Alentejo, a region in the south of Portugal characterized by hot and dry summer conditions. Outdoor and EAHX outflow air temperatures were registered and the loads removed in the EAHX were determined for the nominal airflow rate (8000 m\({}^{3}\)/h). From the analysis of the experimental data and from the discussions presented, the paper's findings can be summarized as follows:  
* The large temperature difference between the undisturbed soil temperature (\(\sim\)17 \({}^{\circ}\)C) and the room upper setpoint (\(\sim\)30 \({}^{\circ}\)C, considering adaptive comfort principles [29]) confirmed the feasibility of EAHX standalone cooling. * Daily maximum EAHX outflow temperatures can be 9 K lower than the simultaneous outdoor air temperatures and results confirm that air exits the EAHX at temperatures that never exceed room upper setpoint for Category III, and that seldom exceed room upper setpoint for Category I comfort expectancy level [29]. * Median values of EAHX specific room load removal are larger than 20 W/m\({}^{2}\), the room _design_ cooling demand; however, smaller EAHX room load removal occurs during the afternoon, precisely when the room cooling demand is higher. * A detailed analysis of EAHX room load removal shows that the EAHX is capable of standalone cooling when outdoor temperatures do not exceed 33 \({}^{\circ}\)C. When this temperature is exceeded, standalone cooling would require changes in the EAHX design. Despite this limitation, the built EAHX is capable of delivering more than 50% of the required cooling (for Category III comfort expectancy) when outdoor temperatures are as high as 37 \({}^{\circ}\)C (the most demanding outdoor air temperature criterion used in \"traditional\" HVAC design [38]), and the combined use of the EAHX and passive cooling strategies (i.e., nighttime ventilation) should increase the cooling delivered, meeting the room _design_ cooling demand. Although this study has focused on monitoring data for a particular case, it showed that cooling with large-diameter EAHXs is feasible and that this technology fits the needs of buildings located in hot and dry climates. Used in standalone mode or in combination with building passive cooling techniques, large-diameter EAHXs extend the use of free cooling with outdoor air and can replace refrigeration machines for room cooling. These conclusions should remain valid for other projects with similar conditions; however, because construction costs vary significantly depending on the site and on the building design specifications, the decision to use a large-diameter EAHX for building cooling should be supported by a thorough investment analysis. Moreover, given the sharp difference to \"traditional\" (refrigeration machine) cooling, project promoters and key decision makers should be advised of the limitations associated with standalone EAHX cooling. Conceptualization, R.D., M.d.G.G. and A.M.R. ; methodology, R.D., M.d.G.G. and A.M.R. ; validation, R.D., A.M.R., M.d.G.G. and F.P. ; formal analysis, R.D., A.M.R. and M.d.G.G. ; investigation, R.D. ; resources, R.D. and F.P. ; data curation, R.D. and F.P. ; writing--original draft preparation, R.D. ; writing--review and editing, A.M.R., M.d.G.G. and F.P. ; visualization, R.D. ; project administration, M.d.G.G. and R.D. All authors have read and agreed to the published version of the manuscript. The CERNES research unit (UIDB/04625/2020) to which the second and third authors belong is funded by the Portuguese Foundation for Science and Technology (FCT). Not applicable. Data Availability Statement: Data are contained within the article.