## 3 Results and Discussion
### Monthly Energy Performance  
Figure 6 compares the monthly energy performance of the HVAC system based on the aerothermal heat pump and on the geothermal heat pump, by considering R-410A as the refrigerant fluid. Analyzing the obtained results, it is evident that, comparing the KPIs of the heat pump (\(COP_{n}\) and \(EER_{n}\)), the adoption of a GCHP guarantees a significant improvement in generator energy performance with respect to the aerothermal unit, for both heating and cooling modes. This is reasonable since the ground temperature is always more favorable for the heat pump than the air temperature; it is higher during the heating period and lower during the cooling season, thus enhancing the heat pump's efficiency [35]. Additionally, for both devices, the worst performance is reached in the middle of the conditioning seasons, when the building load is the highest, and the external source temperature is less favorable for the heat pump. In particular, compared to the first month of the conditioning seasons, the GCHP obtains the worst seasonal efficiency in February (\(-5.9\%\)) and August (\(-3.1\%\)), due to the high ground-exploitation rate, while the ASHP obtains the worst seasonal performance in January (\(-16.3\%\)) and August (\(-9.5\%\)), when the external air temperature reaches its minimum and maximum values, respectively. Another important aspect highlighted by Figure 6 is that the GCHP efficiency presents a smoother trend across the year (slight monthly performance variations) compared to the ASHP. Indeed, the exploitation of the ground source, characterized by a temperature almost constant over the year, neglects the influence of variable climatic conditions on the heat pump's performance. Comparing the energy performance of the entire system (KPIs \(COP\) and \(EER\)), it can be observed that the advantage linked to the adoption of a GCHP is strongly reduced, in particular, during the cooling season (Figure 6b). Indeed, the average summer performance of the GCHP is \(39\%\) higher than that of the ASHP, but this percentage reduces to only \(15\%\) when the whole HVAC system is considered (heat pump and circulators). From another point of view, the cooling performance of the entire system drops, with respect to that of the heat pump, by \(23\%\) with the GCHP and by \(7\%\) with the ASHP. In this case, the larger penalization of the overall energy performance of the GCHP system is caused by the energy consumption of the circulating pump installed within the BHE field, which is not present in the aerothermal configuration. This electric consumption has a higher influence on the seasonal performance factor during summer due to a lower cooling energy request from the building compared to that of the heating period. In other words, the energy need of auxiliaries assumes a more significant influence during the cooling season. In Figure 7, the energy performance of the HVAC system based on the aerothermal heat pump is compared to that achieved by the geothermal unit, considering R-454B as the refrigerant fluid. Figure 6: Monthly energy performance of the geothermal and aerothermal heat pumps with R-410A and of the whole HVAC system in the heating (**a**) and cooling (**b**) seasons. According to Figure 7, the performance obtained switching from R410A to R454B is similar to that analyzed previously. Indeed, the GCHP efficiency presents a flatter trend across the months compared to the ASHP, and a huge difference exists between the net energy performance of the heat pump (\(COP_{n}\), \(EER_{n}\)) and that of the whole HVAC system (\(COP\), \(EER\)). Due to the significant monthly variation of ASHP efficiency, the difference in terms of energy performance between ASHP and GCHP changes over the months; it reaches a peak in the middle of the conditioning seasons, when the external air temperature is unfavorable for the air-source unit and the building loads are more relevant, whereas, vice versa, it decreases in the midesasons.