**5. Conclusions**

In this paper, a combined GHE was proposed and its performance in five operational modes was analysed by using the validated models previously developed for horizontal and vertical arrangements of GHEs. The main conclusions, which followed from the calculations, are summarised as follows:


**Author Contributions:** Conceptualization, methodology, and results and were initiated and wrote by S.E.S., E.H. and A.K.; S.E.S. contributed to the experiment and writing—original draft preparation; Writing—review and editing, T.M.I.R., R.T.; Supervision by E.H. and A.K. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research received no external funding.

**Acknowledgments:** The authors graciously acknowledge the support provided by the School of Mechanical Engineering, the University of Adelaide.

**Conflicts of Interest:** The authors declare no conflict of interest.
